Merge branch 'slice_with_exec_ctx_and_new_closures' into metadata_filter_and_new_closures

34 files changed, 405 insertions, 372 deletions

diff --git a/src/core/lib/iomgr/closure.c b/src/core/lib/iomgr/closure.c
index c6ddc76732..da0ec878a3 100644
--- a/src/core/lib/iomgr/closure.c
+++ b/src/core/lib/iomgr/closure.c
@@ -37,10 +37,13 @@
 
 #include "src/core/lib/profiling/timers.h"
 
-void grpc_closure_init(grpc_closure *closure, grpc_iomgr_cb_func cb,
-                       void *cb_arg) {
+grpc_closure *grpc_closure_init(grpc_closure *closure, grpc_iomgr_cb_func cb,
+                                void *cb_arg,
+                                grpc_closure_scheduler *scheduler) {
   closure->cb = cb;
   closure->cb_arg = cb_arg;
+  closure->scheduler = scheduler;
+  return closure;
 }
 
 void grpc_closure_list_init(grpc_closure_list *closure_list) {
@@ -105,11 +108,12 @@ static void closure_wrapper(grpc_exec_ctx *exec_ctx, void *arg,
   cb(exec_ctx, cb_arg, error);
 }
 
-grpc_closure *grpc_closure_create(grpc_iomgr_cb_func cb, void *cb_arg) {
+grpc_closure *grpc_closure_create(grpc_iomgr_cb_func cb, void *cb_arg,
+                                  grpc_closure_scheduler *scheduler) {
   wrapped_closure *wc = gpr_malloc(sizeof(*wc));
   wc->cb = cb;
   wc->cb_arg = cb_arg;
-  grpc_closure_init(&wc->wrapper, closure_wrapper, wc);
+  grpc_closure_init(&wc->wrapper, closure_wrapper, wc, scheduler);
   return &wc->wrapper;
 }
 
@@ -117,8 +121,30 @@ void grpc_closure_run(grpc_exec_ctx *exec_ctx, grpc_closure *c,
                       grpc_error *error) {
   GPR_TIMER_BEGIN("grpc_closure_run", 0);
   if (c != NULL) {
-    c->cb(exec_ctx, c->cb_arg, error);
+    c->scheduler->vtable->run(exec_ctx, c, error);
+  } else {
+    GRPC_ERROR_UNREF(error);
   }
-  GRPC_ERROR_UNREF(error);
   GPR_TIMER_END("grpc_closure_run", 0);
 }
+
+void grpc_closure_sched(grpc_exec_ctx *exec_ctx, grpc_closure *c,
+                        grpc_error *error) {
+  GPR_TIMER_BEGIN("grpc_closure_sched", 0);
+  if (c != NULL) {
+    c->scheduler->vtable->sched(exec_ctx, c, error);
+  } else {
+    GRPC_ERROR_UNREF(error);
+  }
+  GPR_TIMER_END("grpc_closure_sched", 0);
+}
+
+void grpc_closure_list_sched(grpc_exec_ctx *exec_ctx, grpc_closure_list *list) {
+  grpc_closure *c = list->head;
+  while (c != NULL) {
+    grpc_closure *next = c->next_data.next;
+    c->scheduler->vtable->sched(exec_ctx, c, c->error_data.error);
+    c = next;
+  }
+  list->head = list->tail = NULL;
+}
diff --git a/src/core/lib/iomgr/closure.h b/src/core/lib/iomgr/closure.h
index ec0114a2a4..ee386fbc76 100644
--- a/src/core/lib/iomgr/closure.h
+++ b/src/core/lib/iomgr/closure.h
@@ -57,6 +57,22 @@ typedef struct grpc_closure_list {
 typedef void (*grpc_iomgr_cb_func)(grpc_exec_ctx *exec_ctx, void *arg,
                                    grpc_error *error);
 
+typedef struct grpc_closure_scheduler grpc_closure_scheduler;
+
+typedef struct grpc_closure_scheduler_vtable {
+  /* NOTE: for all these functions, closure->scheduler == the scheduler that was
+           used to find this vtable */
+  void (*run)(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+              grpc_error *error);
+  void (*sched)(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                grpc_error *error);
+} grpc_closure_scheduler_vtable;
+
+/** Abstract type that can schedule closures for execution */
+struct grpc_closure_scheduler {
+  const grpc_closure_scheduler_vtable *vtable;
+};
+
 /** A closure over a grpc_iomgr_cb_func. */
 struct grpc_closure {
   /** Once queued, next indicates the next queued closure; before then, scratch
@@ -73,6 +89,10 @@ struct grpc_closure {
   /** Arguments to be passed to "cb". */
   void *cb_arg;
 
+  /** Scheduler to schedule against: NULL to schedule against current execution
+      context */
+  grpc_closure_scheduler *scheduler;
+
   /** Once queued, the result of the closure. Before then: scratch space */
   union {
     grpc_error *error;
@@ -80,12 +100,14 @@ struct grpc_closure {
   } error_data;
 };
 
-/** Initializes \a closure with \a cb and \a cb_arg. */
-void grpc_closure_init(grpc_closure *closure, grpc_iomgr_cb_func cb,
-                       void *cb_arg);
+/** Initializes \a closure with \a cb and \a cb_arg. Returns \a closure. */
+grpc_closure *grpc_closure_init(grpc_closure *closure, grpc_iomgr_cb_func cb,
+                                void *cb_arg,
+                                grpc_closure_scheduler *scheduler);
 
 /* Create a heap allocated closure: try to avoid except for very rare events */
-grpc_closure *grpc_closure_create(grpc_iomgr_cb_func cb, void *cb_arg);
+grpc_closure *grpc_closure_create(grpc_iomgr_cb_func cb, void *cb_arg,
+                                  grpc_closure_scheduler *scheduler);
 
 #define GRPC_CLOSURE_LIST_INIT \
   { NULL, NULL }
@@ -113,4 +135,13 @@ bool grpc_closure_list_empty(grpc_closure_list list);
 void grpc_closure_run(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
                       grpc_error *error);
 
+/** Schedule a closure to be run. Does not need to be run from a safe point. */
+void grpc_closure_sched(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                        grpc_error *error);
+
+/** Schedule all closures in a list to be run. Does not need to be run from a
+ * safe point. */
+void grpc_closure_list_sched(grpc_exec_ctx *exec_ctx,
+                             grpc_closure_list *closure_list);
+
 #endif /* GRPC_CORE_LIB_IOMGR_CLOSURE_H */
diff --git a/src/core/lib/iomgr/combiner.c b/src/core/lib/iomgr/combiner.c
index cfc67020ae..c26a73b2b7 100644
--- a/src/core/lib/iomgr/combiner.c
+++ b/src/core/lib/iomgr/combiner.c
@@ -56,6 +56,10 @@ int grpc_combiner_trace = 0;
 struct grpc_combiner {
   grpc_combiner *next_combiner_on_this_exec_ctx;
   grpc_workqueue *optional_workqueue;
+  grpc_closure_scheduler uncovered_scheduler;
+  grpc_closure_scheduler covered_scheduler;
+  grpc_closure_scheduler uncovered_finally_scheduler;
+  grpc_closure_scheduler covered_finally_scheduler;
   gpr_mpscq queue;
   // state is:
   // lower bit - zero if orphaned (STATE_UNORPHANED)
@@ -70,6 +74,26 @@ struct grpc_combiner {
   grpc_closure offload;
 };
 
+static void combiner_exec_uncovered(grpc_exec_ctx *exec_ctx,
+                                    grpc_closure *closure, grpc_error *error);
+static void combiner_exec_covered(grpc_exec_ctx *exec_ctx,
+                                  grpc_closure *closure, grpc_error *error);
+static void combiner_finally_exec_uncovered(grpc_exec_ctx *exec_ctx,
+                                            grpc_closure *closure,
+                                            grpc_error *error);
+static void combiner_finally_exec_covered(grpc_exec_ctx *exec_ctx,
+                                          grpc_closure *closure,
+                                          grpc_error *error);
+
+static const grpc_closure_scheduler_vtable scheduler_uncovered = {
+    combiner_exec_uncovered, combiner_exec_uncovered};
+static const grpc_closure_scheduler_vtable scheduler_covered = {
+    combiner_exec_covered, combiner_exec_covered};
+static const grpc_closure_scheduler_vtable finally_scheduler_uncovered = {
+    combiner_finally_exec_uncovered, combiner_finally_exec_uncovered};
+static const grpc_closure_scheduler_vtable finally_scheduler_covered = {
+    combiner_finally_exec_covered, combiner_finally_exec_covered};
+
 static void offload(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error);
 
 typedef struct {
@@ -102,11 +126,16 @@ grpc_combiner *grpc_combiner_create(grpc_workqueue *optional_workqueue) {
   lock->time_to_execute_final_list = false;
   lock->optional_workqueue = optional_workqueue;
   lock->final_list_covered_by_poller = false;
+  lock->uncovered_scheduler.vtable = &scheduler_uncovered;
+  lock->covered_scheduler.vtable = &scheduler_covered;
+  lock->uncovered_finally_scheduler.vtable = &finally_scheduler_uncovered;
+  lock->covered_finally_scheduler.vtable = &finally_scheduler_covered;
   gpr_atm_no_barrier_store(&lock->state, STATE_UNORPHANED);
   gpr_atm_no_barrier_store(&lock->elements_covered_by_poller, 0);
   gpr_mpscq_init(&lock->queue);
   grpc_closure_list_init(&lock->final_list);
-  grpc_closure_init(&lock->offload, offload, lock);
+  grpc_closure_init(&lock->offload, offload, lock,
+                    grpc_workqueue_scheduler(lock->optional_workqueue));
   GRPC_COMBINER_TRACE(gpr_log(GPR_DEBUG, "C:%p create", lock));
   return lock;
 }
@@ -148,9 +177,9 @@ static void push_first_on_exec_ctx(grpc_exec_ctx *exec_ctx,
   }
 }
 
-void grpc_combiner_execute(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
-                           grpc_closure *cl, grpc_error *error,
-                           bool covered_by_poller) {
+static void combiner_exec(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
+                          grpc_closure *cl, grpc_error *error,
+                          bool covered_by_poller) {
   GPR_TIMER_BEGIN("combiner.execute", 0);
   gpr_atm last = gpr_atm_full_fetch_add(&lock->state, STATE_ELEM_COUNT_LOW_BIT);
   GRPC_COMBINER_TRACE(gpr_log(
@@ -171,6 +200,24 @@ void grpc_combiner_execute(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
   GPR_TIMER_END("combiner.execute", 0);
 }
 
+#define COMBINER_FROM_CLOSURE_SCHEDULER(closure, scheduler_name) \
+  ((grpc_combiner *)(((char *)((closure)->scheduler)) -          \
+                     offsetof(grpc_combiner, scheduler_name)))
+
+static void combiner_exec_uncovered(grpc_exec_ctx *exec_ctx, grpc_closure *cl,
+                                    grpc_error *error) {
+  combiner_exec(exec_ctx,
+                COMBINER_FROM_CLOSURE_SCHEDULER(cl, uncovered_scheduler), cl,
+                error, false);
+}
+
+static void combiner_exec_covered(grpc_exec_ctx *exec_ctx, grpc_closure *cl,
+                                  grpc_error *error) {
+  combiner_exec(exec_ctx,
+                COMBINER_FROM_CLOSURE_SCHEDULER(cl, covered_scheduler), cl,
+                error, true);
+}
+
 static void move_next(grpc_exec_ctx *exec_ctx) {
   exec_ctx->active_combiner =
       exec_ctx->active_combiner->next_combiner_on_this_exec_ctx;
@@ -188,8 +235,7 @@ static void queue_offload(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
   move_next(exec_ctx);
   GRPC_COMBINER_TRACE(gpr_log(GPR_DEBUG, "C:%p queue_offload --> %p", lock,
                               lock->optional_workqueue));
-  grpc_workqueue_enqueue(exec_ctx, lock->optional_workqueue, &lock->offload,
-                         GRPC_ERROR_NONE);
+  grpc_closure_sched(exec_ctx, &lock->offload, GRPC_ERROR_NONE);
 }
 
 bool grpc_combiner_continue_exec_ctx(grpc_exec_ctx *exec_ctx) {
@@ -312,23 +358,22 @@ bool grpc_combiner_continue_exec_ctx(grpc_exec_ctx *exec_ctx) {
 }
 
 static void enqueue_finally(grpc_exec_ctx *exec_ctx, void *closure,
-                            grpc_error *error) {
-  grpc_combiner_execute_finally(exec_ctx, exec_ctx->active_combiner, closure,
-                                GRPC_ERROR_REF(error), false);
-}
+                            grpc_error *error);
 
-void grpc_combiner_execute_finally(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
-                                   grpc_closure *closure, grpc_error *error,
-                                   bool covered_by_poller) {
+static void combiner_execute_finally(grpc_exec_ctx *exec_ctx,
+                                     grpc_combiner *lock, grpc_closure *closure,
+                                     grpc_error *error,
+                                     bool covered_by_poller) {
   GRPC_COMBINER_TRACE(gpr_log(
       GPR_DEBUG, "C:%p grpc_combiner_execute_finally c=%p; ac=%p; cov=%d", lock,
       closure, exec_ctx->active_combiner, covered_by_poller));
   GPR_TIMER_BEGIN("combiner.execute_finally", 0);
   if (exec_ctx->active_combiner != lock) {
     GPR_TIMER_MARK("slowpath", 0);
-    grpc_combiner_execute(exec_ctx, lock,
-                          grpc_closure_create(enqueue_finally, closure), error,
-                          false);
+    grpc_closure_sched(
+        exec_ctx, grpc_closure_create(enqueue_finally, closure,
+                                      grpc_combiner_scheduler(lock, false)),
+        error);
     GPR_TIMER_END("combiner.execute_finally", 0);
     return;
   }
@@ -342,3 +387,36 @@ void grpc_combiner_execute_finally(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
   grpc_closure_list_append(&lock->final_list, closure, error);
   GPR_TIMER_END("combiner.execute_finally", 0);
 }
+
+static void enqueue_finally(grpc_exec_ctx *exec_ctx, void *closure,
+                            grpc_error *error) {
+  combiner_execute_finally(exec_ctx, exec_ctx->active_combiner, closure,
+                           GRPC_ERROR_REF(error), false);
+}
+
+static void combiner_finally_exec_uncovered(grpc_exec_ctx *exec_ctx,
+                                            grpc_closure *cl,
+                                            grpc_error *error) {
+  combiner_execute_finally(exec_ctx, COMBINER_FROM_CLOSURE_SCHEDULER(
+                                         cl, uncovered_finally_scheduler),
+                           cl, error, false);
+}
+
+static void combiner_finally_exec_covered(grpc_exec_ctx *exec_ctx,
+                                          grpc_closure *cl, grpc_error *error) {
+  combiner_execute_finally(
+      exec_ctx, COMBINER_FROM_CLOSURE_SCHEDULER(cl, covered_finally_scheduler),
+      cl, error, true);
+}
+
+grpc_closure_scheduler *grpc_combiner_scheduler(grpc_combiner *combiner,
+                                                bool covered_by_poller) {
+  return covered_by_poller ? &combiner->covered_scheduler
+                           : &combiner->uncovered_scheduler;
+}
+
+grpc_closure_scheduler *grpc_combiner_finally_scheduler(
+    grpc_combiner *combiner, bool covered_by_poller) {
+  return covered_by_poller ? &combiner->covered_finally_scheduler
+                           : &combiner->uncovered_finally_scheduler;
+}
diff --git a/src/core/lib/iomgr/combiner.h b/src/core/lib/iomgr/combiner.h
index d04eeed83a..81dff85d40 100644
--- a/src/core/lib/iomgr/combiner.h
+++ b/src/core/lib/iomgr/combiner.h
@@ -50,14 +50,12 @@
 grpc_combiner *grpc_combiner_create(grpc_workqueue *optional_workqueue);
 // Destroy the lock
 void grpc_combiner_destroy(grpc_exec_ctx *exec_ctx, grpc_combiner *lock);
-// Execute \a action within the lock.
-void grpc_combiner_execute(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
-                           grpc_closure *closure, grpc_error *error,
-                           bool covered_by_poller);
-// Execute \a action within the lock just prior to unlocking.
-void grpc_combiner_execute_finally(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
-                                   grpc_closure *closure, grpc_error *error,
-                                   bool covered_by_poller);
+// Fetch a scheduler to schedule closures against
+grpc_closure_scheduler *grpc_combiner_scheduler(grpc_combiner *lock,
+                                                bool covered_by_poller);
+// Scheduler to execute \a action within the lock just prior to unlocking.
+grpc_closure_scheduler *grpc_combiner_finally_scheduler(grpc_combiner *lock,
+                                                        bool covered_by_poller);
 
 bool grpc_combiner_continue_exec_ctx(grpc_exec_ctx *exec_ctx);
 
diff --git a/src/core/lib/iomgr/ev_epoll_linux.c b/src/core/lib/iomgr/ev_epoll_linux.c
index 59b1fe896f..d6664aead2 100644
--- a/src/core/lib/iomgr/ev_epoll_linux.c
+++ b/src/core/lib/iomgr/ev_epoll_linux.c
@@ -201,6 +201,8 @@ static void fd_global_shutdown(void);
 
 /* This is also used as grpc_workqueue (by directly casing it) */
 typedef struct polling_island {
+  grpc_closure_scheduler workqueue_scheduler;
+
   gpr_mu mu;
   /* Ref count. Use PI_ADD_REF() and PI_UNREF() macros to increment/decrement
      the refcount.
@@ -304,6 +306,8 @@ static __thread polling_island *g_current_thread_polling_island;
 
 /* Forward declaration */
 static void polling_island_delete(grpc_exec_ctx *exec_ctx, polling_island *pi);
+static void workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                              grpc_error *error);
 
 #ifdef GRPC_TSAN
 /* Currently TSAN may incorrectly flag data races between epoll_ctl and
@@ -316,6 +320,9 @@ static void polling_island_delete(grpc_exec_ctx *exec_ctx, polling_island *pi);
 gpr_atm g_epoll_sync;
 #endif /* defined(GRPC_TSAN) */
 
+static const grpc_closure_scheduler_vtable workqueue_scheduler_vtable = {
+    workqueue_enqueue, workqueue_enqueue};
+
 static void pi_add_ref(polling_island *pi);
 static void pi_unref(grpc_exec_ctx *exec_ctx, polling_island *pi);
 
@@ -528,6 +535,7 @@ static polling_island *polling_island_create(grpc_exec_ctx *exec_ctx,
   *error = GRPC_ERROR_NONE;
 
   pi = gpr_malloc(sizeof(*pi));
+  pi->workqueue_scheduler.vtable = &workqueue_scheduler_vtable;
   gpr_mu_init(&pi->mu);
   pi->fd_cnt = 0;
   pi->fd_capacity = 0;
@@ -799,10 +807,10 @@ static polling_island *polling_island_merge(polling_island *p,
   return q;
 }
 
-static void workqueue_enqueue(grpc_exec_ctx *exec_ctx,
-                              grpc_workqueue *workqueue, grpc_closure *closure,
+static void workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
                               grpc_error *error) {
   GPR_TIMER_BEGIN("workqueue.enqueue", 0);
+  grpc_workqueue *workqueue = (grpc_workqueue *)closure->scheduler;
   /* take a ref to the workqueue: otherwise it can happen that whatever events
    * this kicks off ends up destroying the workqueue before this function
    * completes */
@@ -819,6 +827,12 @@ static void workqueue_enqueue(grpc_exec_ctx *exec_ctx,
   GPR_TIMER_END("workqueue.enqueue", 0);
 }
 
+static grpc_closure_scheduler *workqueue_scheduler(grpc_workqueue *workqueue) {
+  polling_island *pi = (polling_island *)workqueue;
+  return workqueue == NULL ? grpc_schedule_on_exec_ctx
+                           : &pi->workqueue_scheduler;
+}
+
 static grpc_error *polling_island_global_init() {
   grpc_error *error = GRPC_ERROR_NONE;
 
@@ -1029,8 +1043,7 @@ static void fd_orphan(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
     fd->po.pi = NULL;
   }
 
-  grpc_exec_ctx_sched(exec_ctx, fd->on_done_closure, GRPC_ERROR_REF(error),
-                      NULL);
+  grpc_closure_sched(exec_ctx, fd->on_done_closure, GRPC_ERROR_REF(error));
 
   gpr_mu_unlock(&fd->po.mu);
   UNREF_BY(fd, 2, reason); /* Drop the reference */
@@ -1056,16 +1069,14 @@ static grpc_error *fd_shutdown_error(bool shutdown) {
 static void notify_on_locked(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
                              grpc_closure **st, grpc_closure *closure) {
   if (fd->shutdown) {
-    grpc_exec_ctx_sched(exec_ctx, closure, GRPC_ERROR_CREATE("FD shutdown"),
-                        NULL);
+    grpc_closure_sched(exec_ctx, closure, GRPC_ERROR_CREATE("FD shutdown"));
   } else if (*st == CLOSURE_NOT_READY) {
     /* not ready ==> switch to a waiting state by setting the closure */
     *st = closure;
   } else if (*st == CLOSURE_READY) {
     /* already ready ==> queue the closure to run immediately */
     *st = CLOSURE_NOT_READY;
-    grpc_exec_ctx_sched(exec_ctx, closure, fd_shutdown_error(fd->shutdown),
-                        NULL);
+    grpc_closure_sched(exec_ctx, closure, fd_shutdown_error(fd->shutdown));
   } else {
     /* upcallptr was set to a different closure.  This is an error! */
     gpr_log(GPR_ERROR,
@@ -1087,7 +1098,7 @@ static int set_ready_locked(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
     return 0;
   } else {
     /* waiting ==> queue closure */
-    grpc_exec_ctx_sched(exec_ctx, *st, fd_shutdown_error(fd->shutdown), NULL);
+    grpc_closure_sched(exec_ctx, *st, fd_shutdown_error(fd->shutdown));
     *st = CLOSURE_NOT_READY;
     return 1;
   }
@@ -1358,7 +1369,7 @@ static void finish_shutdown_locked(grpc_exec_ctx *exec_ctx,
 
   /* Release the ref and set pollset->po.pi to NULL */
   pollset_release_polling_island(exec_ctx, pollset, "ps_shutdown");
-  grpc_exec_ctx_sched(exec_ctx, pollset->shutdown_done, GRPC_ERROR_NONE, NULL);
+  grpc_closure_sched(exec_ctx, pollset->shutdown_done, GRPC_ERROR_NONE);
 }
 
 /* pollset->po.mu lock must be held by the caller before calling this */
@@ -1409,7 +1420,9 @@ static bool maybe_do_workqueue_work(grpc_exec_ctx *exec_ctx,
         workqueue_maybe_wakeup(pi);
       }
       grpc_closure *c = (grpc_closure *)n;
-      grpc_closure_run(exec_ctx, c, c->error_data.error);
+      grpc_error *error = c->error_data.error;
+      c->cb(exec_ctx, c->cb_arg, error);
+      GRPC_ERROR_UNREF(error);
       return true;
     } else if (gpr_atm_no_barrier_load(&pi->workqueue_item_count) > 0) {
       /* n == NULL might mean there's work but it's not available to be popped
@@ -1958,7 +1971,7 @@ static const grpc_event_engine_vtable vtable = {
 
     .workqueue_ref = workqueue_ref,
     .workqueue_unref = workqueue_unref,
-    .workqueue_enqueue = workqueue_enqueue,
+    .workqueue_scheduler = workqueue_scheduler,
 
     .shutdown_engine = shutdown_engine,
 };
diff --git a/src/core/lib/iomgr/ev_poll_posix.c b/src/core/lib/iomgr/ev_poll_posix.c
index 21b28e5554..5bc5621443 100644
--- a/src/core/lib/iomgr/ev_poll_posix.c
+++ b/src/core/lib/iomgr/ev_poll_posix.c
@@ -397,7 +397,7 @@ static void close_fd_locked(grpc_exec_ctx *exec_ctx, grpc_fd *fd) {
   if (!fd->released) {
     close(fd->fd);
   }
-  grpc_exec_ctx_sched(exec_ctx, fd->on_done_closure, GRPC_ERROR_NONE, NULL);
+  grpc_closure_sched(exec_ctx, fd->on_done_closure, GRPC_ERROR_NONE);
 }
 
 static int fd_wrapped_fd(grpc_fd *fd) {
@@ -457,16 +457,14 @@ static grpc_error *fd_shutdown_error(bool shutdown) {
 static void notify_on_locked(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
                              grpc_closure **st, grpc_closure *closure) {
   if (fd->shutdown) {
-    grpc_exec_ctx_sched(exec_ctx, closure, GRPC_ERROR_CREATE("FD shutdown"),
-                        NULL);
+    grpc_closure_sched(exec_ctx, closure, GRPC_ERROR_CREATE("FD shutdown"));
   } else if (*st == CLOSURE_NOT_READY) {
     /* not ready ==> switch to a waiting state by setting the closure */
     *st = closure;
   } else if (*st == CLOSURE_READY) {
     /* already ready ==> queue the closure to run immediately */
     *st = CLOSURE_NOT_READY;
-    grpc_exec_ctx_sched(exec_ctx, closure, fd_shutdown_error(fd->shutdown),
-                        NULL);
+    grpc_closure_sched(exec_ctx, closure, fd_shutdown_error(fd->shutdown));
     maybe_wake_one_watcher_locked(fd);
   } else {
     /* upcallptr was set to a different closure.  This is an error! */
@@ -489,7 +487,7 @@ static int set_ready_locked(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
     return 0;
   } else {
     /* waiting ==> queue closure */
-    grpc_exec_ctx_sched(exec_ctx, *st, fd_shutdown_error(fd->shutdown), NULL);
+    grpc_closure_sched(exec_ctx, *st, fd_shutdown_error(fd->shutdown));
     *st = CLOSURE_NOT_READY;
     return 1;
   }
@@ -852,7 +850,7 @@ static void finish_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset) {
     GRPC_FD_UNREF(pollset->fds[i], "multipoller");
   }
   pollset->fd_count = 0;
-  grpc_exec_ctx_sched(exec_ctx, pollset->shutdown_done, GRPC_ERROR_NONE, NULL);
+  grpc_closure_sched(exec_ctx, pollset->shutdown_done, GRPC_ERROR_NONE);
 }
 
 static void work_combine_error(grpc_error **composite, grpc_error *error) {
@@ -901,7 +899,7 @@ static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
   if (!pollset_has_workers(pollset) &&
       !grpc_closure_list_empty(pollset->idle_jobs)) {
     GPR_TIMER_MARK("pollset_work.idle_jobs", 0);
-    grpc_exec_ctx_enqueue_list(exec_ctx, &pollset->idle_jobs, NULL);
+    grpc_closure_list_sched(exec_ctx, &pollset->idle_jobs);
     goto done;
   }
   /* If we're shutting down then we don't execute any extended work */
@@ -1081,7 +1079,7 @@ static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
        * TODO(dklempner): Can we refactor the shutdown logic to avoid this? */
       gpr_mu_lock(&pollset->mu);
     } else if (!grpc_closure_list_empty(pollset->idle_jobs)) {
-      grpc_exec_ctx_enqueue_list(exec_ctx, &pollset->idle_jobs, NULL);
+      grpc_closure_list_sched(exec_ctx, &pollset->idle_jobs);
       gpr_mu_unlock(&pollset->mu);
       grpc_exec_ctx_flush(exec_ctx);
       gpr_mu_lock(&pollset->mu);
@@ -1100,7 +1098,7 @@ static void pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
   pollset->shutdown_done = closure;
   pollset_kick(pollset, GRPC_POLLSET_KICK_BROADCAST);
   if (!pollset_has_workers(pollset)) {
-    grpc_exec_ctx_enqueue_list(exec_ctx, &pollset->idle_jobs, NULL);
+    grpc_closure_list_sched(exec_ctx, &pollset->idle_jobs);
   }
   if (!pollset->called_shutdown && !pollset_has_workers(pollset)) {
     pollset->called_shutdown = 1;
@@ -1288,10 +1286,8 @@ static void workqueue_unref(grpc_exec_ctx *exec_ctx,
                             grpc_workqueue *workqueue) {}
 #endif
 
-static void workqueue_enqueue(grpc_exec_ctx *exec_ctx,
-                              grpc_workqueue *workqueue, grpc_closure *closure,
-                              grpc_error *error) {
-  grpc_exec_ctx_sched(exec_ctx, closure, error, NULL);
+static grpc_closure_scheduler *workqueue_scheduler(grpc_workqueue *workqueue) {
+  return grpc_schedule_on_exec_ctx;
 }
 
 /*******************************************************************************
@@ -1534,7 +1530,7 @@ static const grpc_event_engine_vtable vtable = {
 
     .workqueue_ref = workqueue_ref,
     .workqueue_unref = workqueue_unref,
-    .workqueue_enqueue = workqueue_enqueue,
+    .workqueue_scheduler = workqueue_scheduler,
 
     .shutdown_engine = shutdown_engine,
 };
diff --git a/src/core/lib/iomgr/ev_posix.c b/src/core/lib/iomgr/ev_posix.c
index e148416760..c106ba5400 100644
--- a/src/core/lib/iomgr/ev_posix.c
+++ b/src/core/lib/iomgr/ev_posix.c
@@ -277,9 +277,8 @@ void grpc_workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {
 }
 #endif
 
-void grpc_workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
-                            grpc_closure *closure, grpc_error *error) {
-  g_event_engine->workqueue_enqueue(exec_ctx, workqueue, closure, error);
+grpc_closure_scheduler *grpc_workqueue_scheduler(grpc_workqueue *workqueue) {
+  return g_event_engine->workqueue_scheduler(workqueue);
 }
 
 #endif  // GRPC_POSIX_SOCKET
diff --git a/src/core/lib/iomgr/ev_posix.h b/src/core/lib/iomgr/ev_posix.h
index cb5832539d..1068a4bad5 100644
--- a/src/core/lib/iomgr/ev_posix.h
+++ b/src/core/lib/iomgr/ev_posix.h
@@ -106,8 +106,7 @@ typedef struct grpc_event_engine_vtable {
   grpc_workqueue *(*workqueue_ref)(grpc_workqueue *workqueue);
   void (*workqueue_unref)(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue);
 #endif
-  void (*workqueue_enqueue)(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
-                            grpc_closure *closure, grpc_error *error);
+  grpc_closure_scheduler *(*workqueue_scheduler)(grpc_workqueue *workqueue);
 } grpc_event_engine_vtable;
 
 void grpc_event_engine_init(void);
diff --git a/src/core/lib/iomgr/exec_ctx.c b/src/core/lib/iomgr/exec_ctx.c
index 604713e578..6aa788f8e5 100644
--- a/src/core/lib/iomgr/exec_ctx.c
+++ b/src/core/lib/iomgr/exec_ctx.c
@@ -57,7 +57,6 @@ bool grpc_always_ready_to_finish(grpc_exec_ctx *exec_ctx, void *arg_ignored) {
   return true;
 }
 
-#ifndef GRPC_EXECUTION_CONTEXT_SANITIZER
 bool grpc_exec_ctx_flush(grpc_exec_ctx *exec_ctx) {
   bool did_something = 0;
   GPR_TIMER_BEGIN("grpc_exec_ctx_flush", 0);
@@ -67,8 +66,10 @@ bool grpc_exec_ctx_flush(grpc_exec_ctx *exec_ctx) {
       exec_ctx->closure_list.head = exec_ctx->closure_list.tail = NULL;
       while (c != NULL) {
         grpc_closure *next = c->next_data.next;
+        grpc_error *error = c->error_data.error;
         did_something = true;
-        grpc_closure_run(exec_ctx, c, c->error_data.error);
+        c->cb(exec_ctx, c->cb_arg, error);
+        GRPC_ERROR_UNREF(error);
         c = next;
       }
     } else if (!grpc_combiner_continue_exec_ctx(exec_ctx)) {
@@ -76,30 +77,6 @@ bool grpc_exec_ctx_flush(grpc_exec_ctx *exec_ctx) {
     }
   }
   GPR_ASSERT(exec_ctx->active_combiner == NULL);
-  if (exec_ctx->stealing_from_workqueue != NULL) {
-    if (grpc_exec_ctx_ready_to_finish(exec_ctx)) {
-      grpc_workqueue_enqueue(exec_ctx, exec_ctx->stealing_from_workqueue,
-                             exec_ctx->stolen_closure,
-                             exec_ctx->stolen_closure->error_data.error);
-      GRPC_WORKQUEUE_UNREF(exec_ctx, exec_ctx->stealing_from_workqueue,
-                           "exec_ctx_sched");
-      exec_ctx->stealing_from_workqueue = NULL;
-      exec_ctx->stolen_closure = NULL;
-    } else {
-      grpc_closure *c = exec_ctx->stolen_closure;
-      GRPC_WORKQUEUE_UNREF(exec_ctx, exec_ctx->stealing_from_workqueue,
-                           "exec_ctx_sched");
-      exec_ctx->stealing_from_workqueue = NULL;
-      exec_ctx->stolen_closure = NULL;
-      grpc_error *error = c->error_data.error;
-      GPR_TIMER_BEGIN("grpc_exec_ctx_flush.stolen_cb", 0);
-      c->cb(exec_ctx, c->cb_arg, error);
-      GRPC_ERROR_UNREF(error);
-      GPR_TIMER_END("grpc_exec_ctx_flush.stolen_cb", 0);
-      grpc_exec_ctx_flush(exec_ctx);
-      did_something = true;
-    }
-  }
   GPR_TIMER_END("grpc_exec_ctx_flush", 0);
   return did_something;
 }
@@ -109,104 +86,21 @@ void grpc_exec_ctx_finish(grpc_exec_ctx *exec_ctx) {
   grpc_exec_ctx_flush(exec_ctx);
 }
 
-void grpc_exec_ctx_sched(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
-                         grpc_error *error,
-                         grpc_workqueue *offload_target_or_null) {
-  GPR_TIMER_BEGIN("grpc_exec_ctx_sched", 0);
-  if (offload_target_or_null == NULL) {
-    grpc_closure_list_append(&exec_ctx->closure_list, closure, error);
-  } else if (exec_ctx->stealing_from_workqueue == NULL) {
-    exec_ctx->stealing_from_workqueue = offload_target_or_null;
-    closure->error_data.error = error;
-    exec_ctx->stolen_closure = closure;
-  } else if (exec_ctx->stealing_from_workqueue != offload_target_or_null) {
-    grpc_workqueue_enqueue(exec_ctx, offload_target_or_null, closure, error);
-    GRPC_WORKQUEUE_UNREF(exec_ctx, offload_target_or_null, "exec_ctx_sched");
-  } else { /* stealing_from_workqueue == offload_target_or_null */
-    grpc_workqueue_enqueue(exec_ctx, offload_target_or_null,
-                           exec_ctx->stolen_closure,
-                           exec_ctx->stolen_closure->error_data.error);
-    closure->error_data.error = error;
-    exec_ctx->stolen_closure = closure;
-    GRPC_WORKQUEUE_UNREF(exec_ctx, offload_target_or_null, "exec_ctx_sched");
-  }
-  GPR_TIMER_END("grpc_exec_ctx_sched", 0);
+static void exec_ctx_run(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                         grpc_error *error) {
+  closure->cb(exec_ctx, closure->cb_arg, error);
+  GRPC_ERROR_UNREF(error);
 }
 
-void grpc_exec_ctx_enqueue_list(grpc_exec_ctx *exec_ctx,
-                                grpc_closure_list *list,
-                                grpc_workqueue *offload_target_or_null) {
-  grpc_closure_list_move(list, &exec_ctx->closure_list);
+static void exec_ctx_sched(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                           grpc_error *error) {
+  grpc_closure_list_append(&exec_ctx->closure_list, closure, error);
 }
 
 void grpc_exec_ctx_global_init(void) {}
 void grpc_exec_ctx_global_shutdown(void) {}
-#else
-static gpr_mu g_mu;
-static gpr_cv g_cv;
-static int g_threads = 0;
-
-static void run_closure(void *arg) {
-  grpc_closure *closure = arg;
-  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-  closure->cb(&exec_ctx, closure->cb_arg, (closure->final_data & 1) != 0);
-  grpc_exec_ctx_finish(&exec_ctx);
-  gpr_mu_lock(&g_mu);
-  if (--g_threads == 0) {
-    gpr_cv_signal(&g_cv);
-  }
-  gpr_mu_unlock(&g_mu);
-}
-
-static void start_closure(grpc_closure *closure) {
-  gpr_thd_id id;
-  gpr_mu_lock(&g_mu);
-  g_threads++;
-  gpr_mu_unlock(&g_mu);
-  gpr_thd_new(&id, run_closure, closure, NULL);
-}
-
-bool grpc_exec_ctx_flush(grpc_exec_ctx *exec_ctx) { return false; }
-
-void grpc_exec_ctx_finish(grpc_exec_ctx *exec_ctx) {}
 
-void grpc_exec_ctx_enqueue(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
-                           bool success,
-                           grpc_workqueue *offload_target_or_null) {
-  GPR_ASSERT(offload_target_or_null == NULL);
-  if (closure == NULL) return;
-  closure->final_data = success;
-  start_closure(closure);
-}
-
-void grpc_exec_ctx_enqueue_list(grpc_exec_ctx *exec_ctx,
-                                grpc_closure_list *list,
-                                grpc_workqueue *offload_target_or_null) {
-  GPR_ASSERT(offload_target_or_null == NULL);
-  if (list == NULL) return;
-  grpc_closure *p = list->head;
-  while (p) {
-    grpc_closure *start = p;
-    p = grpc_closure_next(start);
-    start_closure(start);
-  }
-  grpc_closure_list r = GRPC_CLOSURE_LIST_INIT;
-  *list = r;
-}
-
-void grpc_exec_ctx_global_init(void) {
-  gpr_mu_init(&g_mu);
-  gpr_cv_init(&g_cv);
-}
-
-void grpc_exec_ctx_global_shutdown(void) {
-  gpr_mu_lock(&g_mu);
-  while (g_threads != 0) {
-    gpr_cv_wait(&g_cv, &g_mu, gpr_inf_future(GPR_CLOCK_REALTIME));
-  }
-  gpr_mu_unlock(&g_mu);
-
-  gpr_mu_destroy(&g_mu);
-  gpr_cv_destroy(&g_cv);
-}
-#endif
+static const grpc_closure_scheduler_vtable exec_ctx_scheduler_vtable = {
+    exec_ctx_run, exec_ctx_sched};
+static grpc_closure_scheduler exec_ctx_scheduler = {&exec_ctx_scheduler_vtable};
+grpc_closure_scheduler *grpc_schedule_on_exec_ctx = &exec_ctx_scheduler;
diff --git a/src/core/lib/iomgr/exec_ctx.h b/src/core/lib/iomgr/exec_ctx.h
index 7e50cb9825..e566f1b3e8 100644
--- a/src/core/lib/iomgr/exec_ctx.h
+++ b/src/core/lib/iomgr/exec_ctx.h
@@ -66,17 +66,6 @@ typedef struct grpc_combiner grpc_combiner;
 #ifndef GRPC_EXECUTION_CONTEXT_SANITIZER
 struct grpc_exec_ctx {
   grpc_closure_list closure_list;
-  /** The workqueue we're stealing work from.
-      As items are queued to the execution context, we try to steal one
-      workqueue item and execute it inline (assuming the exec_ctx is not
-      finished) - doing so does not invalidate the workqueue's contract, and
-      provides a small latency win in cases where we get a hit */
-  grpc_workqueue *stealing_from_workqueue;
-  /** The workqueue item that was stolen from the workqueue above. When new
-      items are scheduled to be offloaded to that workqueue, we need to update
-      this like a 1-deep fifo to maintain the invariant that workqueue items
-      queued by one thread are started in order */
-  grpc_closure *stolen_closure;
   /** currently active combiner: updated only via combiner.c */
   grpc_combiner *active_combiner;
   /** last active combiner in the active combiner list */
@@ -89,10 +78,7 @@ struct grpc_exec_ctx {
 /* initializer for grpc_exec_ctx:
    prefer to use GRPC_EXEC_CTX_INIT whenever possible */
 #define GRPC_EXEC_CTX_INIT_WITH_FINISH_CHECK(finish_check, finish_check_arg) \
-  {                                                                          \
-    GRPC_CLOSURE_LIST_INIT, NULL, NULL, NULL, NULL, false, finish_check_arg, \
-        finish_check                                                         \
-  }
+  { GRPC_CLOSURE_LIST_INIT, NULL, NULL, false, finish_check_arg, finish_check }
 #else
 struct grpc_exec_ctx {
   bool cached_ready_to_finish;
@@ -108,6 +94,8 @@ struct grpc_exec_ctx {
 #define GRPC_EXEC_CTX_INIT \
   GRPC_EXEC_CTX_INIT_WITH_FINISH_CHECK(grpc_always_ready_to_finish, NULL)
 
+extern grpc_closure_scheduler *grpc_schedule_on_exec_ctx;
+
 /** Flush any work that has been enqueued onto this grpc_exec_ctx.
  *  Caller must guarantee that no interfering locks are held.
  *  Returns true if work was performed, false otherwise. */
@@ -115,14 +103,6 @@ bool grpc_exec_ctx_flush(grpc_exec_ctx *exec_ctx);
 /** Finish any pending work for a grpc_exec_ctx. Must be called before
  *  the instance is destroyed, or work may be lost. */
 void grpc_exec_ctx_finish(grpc_exec_ctx *exec_ctx);
-/** Add a closure to be executed in the future.
-    If \a offload_target_or_null is NULL, the closure will be executed at the
-    next exec_ctx.{finish,flush} point.
-    If \a offload_target_or_null is non-NULL, the closure will be scheduled
-    against the workqueue, and a reference to the workqueue will be consumed. */
-void grpc_exec_ctx_sched(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
-                         grpc_error *error,
-                         grpc_workqueue *offload_target_or_null);
 /** Returns true if we'd like to leave this execution context as soon as
     possible: useful for deciding whether to do something more or not depending
     on outside context */
@@ -131,11 +111,6 @@ bool grpc_exec_ctx_ready_to_finish(grpc_exec_ctx *exec_ctx);
 bool grpc_never_ready_to_finish(grpc_exec_ctx *exec_ctx, void *arg_ignored);
 /** A finish check that is always ready to finish */
 bool grpc_always_ready_to_finish(grpc_exec_ctx *exec_ctx, void *arg_ignored);
-/** Add a list of closures to be executed at the next flush/finish point.
- *  Leaves \a list empty. */
-void grpc_exec_ctx_enqueue_list(grpc_exec_ctx *exec_ctx,
-                                grpc_closure_list *list,
-                                grpc_workqueue *offload_target_or_null);
 
 void grpc_exec_ctx_global_init(void);
 
diff --git a/src/core/lib/iomgr/executor.c b/src/core/lib/iomgr/executor.c
index 4e78b619fb..852775564f 100644
--- a/src/core/lib/iomgr/executor.c
+++ b/src/core/lib/iomgr/executor.c
@@ -77,10 +77,18 @@ static void closure_exec_thread_func(void *ignored) {
       gpr_mu_unlock(&g_executor.mu);
       break;
     } else {
-      grpc_exec_ctx_enqueue_list(&exec_ctx, &g_executor.closures, NULL);
+      grpc_closure *c = g_executor.closures.head;
+      grpc_closure_list_init(&g_executor.closures);
+      gpr_mu_unlock(&g_executor.mu);
+      while (c != NULL) {
+        grpc_closure *next = c->next_data.next;
+        grpc_error *error = c->error_data.error;
+        c->cb(&exec_ctx, c->cb_arg, error);
+        GRPC_ERROR_UNREF(error);
+        c = next;
+      }
+      grpc_exec_ctx_flush(&exec_ctx);
     }
-    gpr_mu_unlock(&g_executor.mu);
-    grpc_exec_ctx_flush(&exec_ctx);
   }
   grpc_exec_ctx_finish(&exec_ctx);
 }
@@ -112,7 +120,8 @@ static void maybe_spawn_locked() {
   g_executor.pending_join = 1;
 }
 
-void grpc_executor_push(grpc_closure *closure, grpc_error *error) {
+static void executor_push(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
+                          grpc_error *error) {
   gpr_mu_lock(&g_executor.mu);
   if (g_executor.shutting_down == 0) {
     grpc_closure_list_append(&g_executor.closures, closure, error);
@@ -132,10 +141,24 @@ void grpc_executor_shutdown(grpc_exec_ctx *exec_ctx) {
    * list below because we aren't accepting new work */
 
   /* Execute pending callbacks, some may be performing cleanups */
-  grpc_exec_ctx_enqueue_list(exec_ctx, &g_executor.closures, NULL);
+  grpc_closure *c = g_executor.closures.head;
+  grpc_closure_list_init(&g_executor.closures);
+  while (c != NULL) {
+    grpc_closure *next = c->next_data.next;
+    grpc_error *error = c->error_data.error;
+    c->cb(exec_ctx, c->cb_arg, error);
+    GRPC_ERROR_UNREF(error);
+    c = next;
+  }
+  grpc_exec_ctx_flush(exec_ctx);
   GPR_ASSERT(grpc_closure_list_empty(g_executor.closures));
   if (pending_join) {
     gpr_thd_join(g_executor.tid);
   }
   gpr_mu_destroy(&g_executor.mu);
 }
+
+static const grpc_closure_scheduler_vtable executor_vtable = {executor_push,
+                                                              executor_push};
+static grpc_closure_scheduler executor_scheduler = {&executor_vtable};
+grpc_closure_scheduler *grpc_executor_scheduler = &executor_scheduler;
diff --git a/src/core/lib/iomgr/executor.h b/src/core/lib/iomgr/executor.h
index 7bf8f21940..1213016383 100644
--- a/src/core/lib/iomgr/executor.h
+++ b/src/core/lib/iomgr/executor.h
@@ -43,9 +43,7 @@
  * non-blocking solution available. */
 void grpc_executor_init();
 
-/** Enqueue \a closure for its eventual execution of \a f(arg) on a separate
- * thread */
-void grpc_executor_push(grpc_closure *closure, grpc_error *error);
+extern grpc_closure_scheduler *grpc_executor_scheduler;
 
 /** Shutdown the executor, running all pending work as part of the call */
 void grpc_executor_shutdown(grpc_exec_ctx *exec_ctx);
diff --git a/src/core/lib/iomgr/pollset_uv.c b/src/core/lib/iomgr/pollset_uv.c
index 3a74b842b6..ed3edeee94 100644
--- a/src/core/lib/iomgr/pollset_uv.c
+++ b/src/core/lib/iomgr/pollset_uv.c
@@ -83,7 +83,7 @@ void grpc_pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
     // Drain any pending UV callbacks without blocking
     uv_run(uv_default_loop(), UV_RUN_NOWAIT);
   }
-  grpc_exec_ctx_sched(exec_ctx, closure, GRPC_ERROR_NONE, NULL);
+  grpc_closure_sched(exec_ctx, closure, GRPC_ERROR_NONE);
 }
 
 void grpc_pollset_destroy(grpc_pollset *pollset) {
diff --git a/src/core/lib/iomgr/pollset_windows.c b/src/core/lib/iomgr/pollset_windows.c
index 5540303e49..2a45e708df 100644
--- a/src/core/lib/iomgr/pollset_windows.c
+++ b/src/core/lib/iomgr/pollset_windows.c
@@ -109,7 +109,7 @@ void grpc_pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
   pollset->shutting_down = 1;
   grpc_pollset_kick(pollset, GRPC_POLLSET_KICK_BROADCAST);
   if (!pollset->is_iocp_worker) {
-    grpc_exec_ctx_sched(exec_ctx, closure, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, closure, GRPC_ERROR_NONE);
   } else {
     pollset->on_shutdown = closure;
   }
@@ -167,8 +167,7 @@ grpc_error *grpc_pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
       }
 
       if (pollset->shutting_down && pollset->on_shutdown != NULL) {
-        grpc_exec_ctx_sched(exec_ctx, pollset->on_shutdown, GRPC_ERROR_NONE,
-                            NULL);
+        grpc_closure_sched(exec_ctx, pollset->on_shutdown, GRPC_ERROR_NONE);
         pollset->on_shutdown = NULL;
       }
       goto done;
diff --git a/src/core/lib/iomgr/resolve_address_posix.c b/src/core/lib/iomgr/resolve_address_posix.c
index 821932e562..50e470d149 100644
--- a/src/core/lib/iomgr/resolve_address_posix.c
+++ b/src/core/lib/iomgr/resolve_address_posix.c
@@ -163,10 +163,9 @@ typedef struct {
 static void do_request_thread(grpc_exec_ctx *exec_ctx, void *rp,
                               grpc_error *error) {
   request *r = rp;
-  grpc_exec_ctx_sched(
+  grpc_closure_sched(
       exec_ctx, r->on_done,
-      grpc_blocking_resolve_address(r->name, r->default_port, r->addrs_out),
-      NULL);
+      grpc_blocking_resolve_address(r->name, r->default_port, r->addrs_out));
   gpr_free(r->name);
   gpr_free(r->default_port);
   gpr_free(r);
@@ -185,12 +184,13 @@ static void resolve_address_impl(grpc_exec_ctx *exec_ctx, const char *name,
                                  grpc_closure *on_done,
                                  grpc_resolved_addresses **addrs) {
   request *r = gpr_malloc(sizeof(request));
-  grpc_closure_init(&r->request_closure, do_request_thread, r);
+  grpc_closure_init(&r->request_closure, do_request_thread, r,
+                    grpc_executor_scheduler);
   r->name = gpr_strdup(name);
   r->default_port = gpr_strdup(default_port);
   r->on_done = on_done;
   r->addrs_out = addrs;
-  grpc_executor_push(&r->request_closure, GRPC_ERROR_NONE);
+  grpc_closure_sched(exec_ctx, &r->request_closure, GRPC_ERROR_NONE);
 }
 
 void (*grpc_resolve_address)(
diff --git a/src/core/lib/iomgr/resolve_address_uv.c b/src/core/lib/iomgr/resolve_address_uv.c
index 3269c4f09f..9b5f3209f0 100644
--- a/src/core/lib/iomgr/resolve_address_uv.c
+++ b/src/core/lib/iomgr/resolve_address_uv.c
@@ -98,7 +98,7 @@ static void getaddrinfo_callback(uv_getaddrinfo_t *req, int status,
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   grpc_error *error;
   error = handle_addrinfo_result(status, res, r->addresses);
-  grpc_exec_ctx_sched(&exec_ctx, r->on_done, error, NULL);
+  grpc_closure_sched(&exec_ctx, r->on_done, error);
   grpc_exec_ctx_finish(&exec_ctx);
 
   gpr_free(r->hints);
@@ -193,7 +193,7 @@ static void resolve_address_impl(grpc_exec_ctx *exec_ctx, const char *name,
   int s;
   err = try_split_host_port(name, default_port, &host, &port);
   if (err != GRPC_ERROR_NONE) {
-    grpc_exec_ctx_sched(exec_ctx, on_done, err, NULL);
+    grpc_closure_sched(exec_ctx, on_done, err);
     return;
   }
   r = gpr_malloc(sizeof(request));
@@ -217,7 +217,7 @@ static void resolve_address_impl(grpc_exec_ctx *exec_ctx, const char *name,
     *addrs = NULL;
     err = GRPC_ERROR_CREATE("getaddrinfo failed");
     err = grpc_error_set_str(err, GRPC_ERROR_STR_OS_ERROR, uv_strerror(s));
-    grpc_exec_ctx_sched(exec_ctx, on_done, err, NULL);
+    grpc_closure_sched(exec_ctx, on_done, err);
     gpr_free(r);
     gpr_free(req);
     gpr_free(hints);
diff --git a/src/core/lib/iomgr/resolve_address_windows.c b/src/core/lib/iomgr/resolve_address_windows.c
index fada5ecbe8..2439ce3cb7 100644
--- a/src/core/lib/iomgr/resolve_address_windows.c
+++ b/src/core/lib/iomgr/resolve_address_windows.c
@@ -154,7 +154,7 @@ static void do_request_thread(grpc_exec_ctx *exec_ctx, void *rp,
   } else {
     GRPC_ERROR_REF(error);
   }
-  grpc_exec_ctx_sched(exec_ctx, r->on_done, error, NULL);
+  grpc_closure_sched(exec_ctx, r->on_done, error);
   gpr_free(r->name);
   gpr_free(r->default_port);
   gpr_free(r);
@@ -173,12 +173,13 @@ static void resolve_address_impl(grpc_exec_ctx *exec_ctx, const char *name,
                                  grpc_closure *on_done,
                                  grpc_resolved_addresses **addresses) {
   request *r = gpr_malloc(sizeof(request));
-  grpc_closure_init(&r->request_closure, do_request_thread, r);
+  grpc_closure_init(&r->request_closure, do_request_thread, r,
+                    grpc_executor_scheduler);
   r->name = gpr_strdup(name);
   r->default_port = gpr_strdup(default_port);
   r->on_done = on_done;
   r->addresses = addresses;
-  grpc_executor_push(&r->request_closure, GRPC_ERROR_NONE);
+  grpc_closure_sched(exec_ctx, &r->request_closure, GRPC_ERROR_NONE);
 }
 
 void (*grpc_resolve_address)(
diff --git a/src/core/lib/iomgr/resource_quota.c b/src/core/lib/iomgr/resource_quota.c
index 3dbc810102..21aa05e57a 100644
--- a/src/core/lib/iomgr/resource_quota.c
+++ b/src/core/lib/iomgr/resource_quota.c
@@ -265,9 +265,8 @@ static void rq_step_sched(grpc_exec_ctx *exec_ctx,
   if (resource_quota->step_scheduled) return;
   resource_quota->step_scheduled = true;
   grpc_resource_quota_ref_internal(resource_quota);
-  grpc_combiner_execute_finally(exec_ctx, resource_quota->combiner,
-                                &resource_quota->rq_step_closure,
-                                GRPC_ERROR_NONE, false);
+  grpc_closure_sched(exec_ctx, &resource_quota->rq_step_closure,
+                     GRPC_ERROR_NONE);
 }
 
 /* returns true if all allocations are completed */
@@ -294,7 +293,7 @@ static bool rq_alloc(grpc_exec_ctx *exec_ctx,
     }
     if (resource_user->free_pool >= 0) {
       resource_user->allocating = false;
-      grpc_exec_ctx_enqueue_list(exec_ctx, &resource_user->on_allocated, NULL);
+      grpc_closure_list_sched(exec_ctx, &resource_user->on_allocated);
       gpr_mu_unlock(&resource_user->mu);
     } else {
       rulist_add_head(resource_user, GRPC_RULIST_AWAITING_ALLOCATION);
@@ -432,7 +431,7 @@ static bool ru_post_reclaimer(grpc_exec_ctx *exec_ctx,
   resource_user->new_reclaimers[destructive] = NULL;
   GPR_ASSERT(resource_user->reclaimers[destructive] == NULL);
   if (gpr_atm_acq_load(&resource_user->shutdown) > 0) {
-    grpc_exec_ctx_sched(exec_ctx, closure, GRPC_ERROR_CANCELLED, NULL);
+    grpc_closure_sched(exec_ctx, closure, GRPC_ERROR_CANCELLED);
     return false;
   }
   resource_user->reclaimers[destructive] = closure;
@@ -473,10 +472,10 @@ static void ru_post_destructive_reclaimer(grpc_exec_ctx *exec_ctx, void *ru,
 
 static void ru_shutdown(grpc_exec_ctx *exec_ctx, void *ru, grpc_error *error) {
   grpc_resource_user *resource_user = ru;
-  grpc_exec_ctx_sched(exec_ctx, resource_user->reclaimers[0],
-                      GRPC_ERROR_CANCELLED, NULL);
-  grpc_exec_ctx_sched(exec_ctx, resource_user->reclaimers[1],
-                      GRPC_ERROR_CANCELLED, NULL);
+  grpc_closure_sched(exec_ctx, resource_user->reclaimers[0],
+                     GRPC_ERROR_CANCELLED);
+  grpc_closure_sched(exec_ctx, resource_user->reclaimers[1],
+                     GRPC_ERROR_CANCELLED);
   resource_user->reclaimers[0] = NULL;
   resource_user->reclaimers[1] = NULL;
   rulist_remove(resource_user, GRPC_RULIST_RECLAIMER_BENIGN);
@@ -489,10 +488,10 @@ static void ru_destroy(grpc_exec_ctx *exec_ctx, void *ru, grpc_error *error) {
   for (int i = 0; i < GRPC_RULIST_COUNT; i++) {
     rulist_remove(resource_user, (grpc_rulist)i);
   }
-  grpc_exec_ctx_sched(exec_ctx, resource_user->reclaimers[0],
-                      GRPC_ERROR_CANCELLED, NULL);
-  grpc_exec_ctx_sched(exec_ctx, resource_user->reclaimers[1],
-                      GRPC_ERROR_CANCELLED, NULL);
+  grpc_closure_sched(exec_ctx, resource_user->reclaimers[0],
+                     GRPC_ERROR_CANCELLED);
+  grpc_closure_sched(exec_ctx, resource_user->reclaimers[1],
+                     GRPC_ERROR_CANCELLED);
   if (resource_user->free_pool != 0) {
     resource_user->resource_quota->free_pool += resource_user->free_pool;
     rq_step_sched(exec_ctx, resource_user->resource_quota);
@@ -564,9 +563,12 @@ grpc_resource_quota *grpc_resource_quota_create(const char *name) {
     gpr_asprintf(&resource_quota->name, "anonymous_pool_%" PRIxPTR,
                  (intptr_t)resource_quota);
   }
-  grpc_closure_init(&resource_quota->rq_step_closure, rq_step, resource_quota);
+  grpc_closure_init(
+      &resource_quota->rq_step_closure, rq_step, resource_quota,
+      grpc_combiner_finally_scheduler(resource_quota->combiner, true));
   grpc_closure_init(&resource_quota->rq_reclamation_done_closure,
-                    rq_reclamation_done, resource_quota);
+                    rq_reclamation_done, resource_quota,
+                    grpc_combiner_scheduler(resource_quota->combiner, false));
   for (int i = 0; i < GRPC_RULIST_COUNT; i++) {
     resource_quota->roots[i] = NULL;
   }
@@ -607,9 +609,8 @@ void grpc_resource_quota_resize(grpc_resource_quota *resource_quota,
   rq_resize_args *a = gpr_malloc(sizeof(*a));
   a->resource_quota = grpc_resource_quota_ref_internal(resource_quota);
   a->size = (int64_t)size;
-  grpc_closure_init(&a->closure, rq_resize, a);
-  grpc_combiner_execute(&exec_ctx, resource_quota->combiner, &a->closure,
-                        GRPC_ERROR_NONE, false);
+  grpc_closure_init(&a->closure, rq_resize, a, grpc_schedule_on_exec_ctx);
+  grpc_closure_sched(&exec_ctx, &a->closure, GRPC_ERROR_NONE);
   grpc_exec_ctx_finish(&exec_ctx);
 }
 
@@ -658,15 +659,19 @@ grpc_resource_user *grpc_resource_user_create(
   resource_user->resource_quota =
       grpc_resource_quota_ref_internal(resource_quota);
   grpc_closure_init(&resource_user->allocate_closure, &ru_allocate,
-                    resource_user);
+                    resource_user,
+                    grpc_combiner_scheduler(resource_quota->combiner, false));
   grpc_closure_init(&resource_user->add_to_free_pool_closure,
-                    &ru_add_to_free_pool, resource_user);
+                    &ru_add_to_free_pool, resource_user,
+                    grpc_combiner_scheduler(resource_quota->combiner, false));
   grpc_closure_init(&resource_user->post_reclaimer_closure[0],
-                    &ru_post_benign_reclaimer, resource_user);
+                    &ru_post_benign_reclaimer, resource_user,
+                    grpc_combiner_scheduler(resource_quota->combiner, false));
   grpc_closure_init(&resource_user->post_reclaimer_closure[1],
-                    &ru_post_destructive_reclaimer, resource_user);
-  grpc_closure_init(&resource_user->destroy_closure, &ru_destroy,
-                    resource_user);
+                    &ru_post_destructive_reclaimer, resource_user,
+                    grpc_combiner_scheduler(resource_quota->combiner, false));
+  grpc_closure_init(&resource_user->destroy_closure, &ru_destroy, resource_user,
+                    grpc_combiner_scheduler(resource_quota->combiner, false));
   gpr_mu_init(&resource_user->mu);
   gpr_atm_rel_store(&resource_user->refs, 1);
   gpr_atm_rel_store(&resource_user->shutdown, 0);
@@ -701,9 +706,8 @@ static void ru_unref_by(grpc_exec_ctx *exec_ctx,
   gpr_atm old = gpr_atm_full_fetch_add(&resource_user->refs, -amount);
   GPR_ASSERT(old >= amount);
   if (old == amount) {
-    grpc_combiner_execute(exec_ctx, resource_user->resource_quota->combiner,
-                          &resource_user->destroy_closure, GRPC_ERROR_NONE,
-                          false);
+    grpc_closure_sched(exec_ctx, &resource_user->destroy_closure,
+                       GRPC_ERROR_NONE);
   }
 }
 
@@ -719,9 +723,12 @@ void grpc_resource_user_unref(grpc_exec_ctx *exec_ctx,
 void grpc_resource_user_shutdown(grpc_exec_ctx *exec_ctx,
                                  grpc_resource_user *resource_user) {
   if (gpr_atm_full_fetch_add(&resource_user->shutdown, 1) == 0) {
-    grpc_combiner_execute(exec_ctx, resource_user->resource_quota->combiner,
-                          grpc_closure_create(ru_shutdown, resource_user),
-                          GRPC_ERROR_NONE, false);
+    grpc_closure_sched(exec_ctx,
+                       grpc_closure_create(
+                           ru_shutdown, resource_user,
+                           grpc_combiner_scheduler(
+                               resource_user->resource_quota->combiner, false)),
+                       GRPC_ERROR_NONE);
   }
 }
 
@@ -741,12 +748,11 @@ void grpc_resource_user_alloc(grpc_exec_ctx *exec_ctx,
                              GRPC_ERROR_NONE);
     if (!resource_user->allocating) {
       resource_user->allocating = true;
-      grpc_combiner_execute(exec_ctx, resource_user->resource_quota->combiner,
-                            &resource_user->allocate_closure, GRPC_ERROR_NONE,
-                            false);
+      grpc_closure_sched(exec_ctx, &resource_user->allocate_closure,
+                         GRPC_ERROR_NONE);
     }
   } else {
-    grpc_exec_ctx_sched(exec_ctx, optional_on_done, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, optional_on_done, GRPC_ERROR_NONE);
   }
   gpr_mu_unlock(&resource_user->mu);
 }
@@ -765,9 +771,8 @@ void grpc_resource_user_free(grpc_exec_ctx *exec_ctx,
   if (is_bigger_than_zero && was_zero_or_negative &&
       !resource_user->added_to_free_pool) {
     resource_user->added_to_free_pool = true;
-    grpc_combiner_execute(exec_ctx, resource_user->resource_quota->combiner,
-                          &resource_user->add_to_free_pool_closure,
-                          GRPC_ERROR_NONE, false);
+    grpc_closure_sched(exec_ctx, &resource_user->add_to_free_pool_closure,
+                       GRPC_ERROR_NONE);
   }
   gpr_mu_unlock(&resource_user->mu);
   ru_unref_by(exec_ctx, resource_user, (gpr_atm)size);
@@ -779,9 +784,9 @@ void grpc_resource_user_post_reclaimer(grpc_exec_ctx *exec_ctx,
                                        grpc_closure *closure) {
   GPR_ASSERT(resource_user->new_reclaimers[destructive] == NULL);
   resource_user->new_reclaimers[destructive] = closure;
-  grpc_combiner_execute(exec_ctx, resource_user->resource_quota->combiner,
-                        &resource_user->post_reclaimer_closure[destructive],
-                        GRPC_ERROR_NONE, false);
+  grpc_closure_sched(exec_ctx,
+                     &resource_user->post_reclaimer_closure[destructive],
+                     GRPC_ERROR_NONE);
 }
 
 void grpc_resource_user_finish_reclamation(grpc_exec_ctx *exec_ctx,
@@ -790,18 +795,20 @@ void grpc_resource_user_finish_reclamation(grpc_exec_ctx *exec_ctx,
     gpr_log(GPR_DEBUG, "RQ %s %s: reclamation complete",
             resource_user->resource_quota->name, resource_user->name);
   }
-  grpc_combiner_execute(
-      exec_ctx, resource_user->resource_quota->combiner,
-      &resource_user->resource_quota->rq_reclamation_done_closure,
-      GRPC_ERROR_NONE, false);
+  grpc_closure_sched(
+      exec_ctx, &resource_user->resource_quota->rq_reclamation_done_closure,
+      GRPC_ERROR_NONE);
 }
 
 void grpc_resource_user_slice_allocator_init(
     grpc_resource_user_slice_allocator *slice_allocator,
     grpc_resource_user *resource_user, grpc_iomgr_cb_func cb, void *p) {
-  grpc_closure_init(&slice_allocator->on_allocated, ru_allocated_slices,
-                    slice_allocator);
-  grpc_closure_init(&slice_allocator->on_done, cb, p);
+  grpc_closure_init(
+      &slice_allocator->on_allocated, ru_allocated_slices, slice_allocator,
+      grpc_combiner_scheduler(resource_user->resource_quota->combiner, false));
+  grpc_closure_init(
+      &slice_allocator->on_done, cb, p,
+      grpc_combiner_scheduler(resource_user->resource_quota->combiner, false));
   slice_allocator->resource_user = resource_user;
 }
 
diff --git a/src/core/lib/iomgr/socket_windows.c b/src/core/lib/iomgr/socket_windows.c
index 54911e0e31..2f2e02f715 100644
--- a/src/core/lib/iomgr/socket_windows.c
+++ b/src/core/lib/iomgr/socket_windows.c
@@ -131,7 +131,7 @@ static void socket_notify_on_iocp(grpc_exec_ctx *exec_ctx,
   gpr_mu_lock(&socket->state_mu);
   if (info->has_pending_iocp) {
     info->has_pending_iocp = 0;
-    grpc_exec_ctx_sched(exec_ctx, closure, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, closure, GRPC_ERROR_NONE);
   } else {
     info->closure = closure;
   }
@@ -154,7 +154,7 @@ void grpc_socket_become_ready(grpc_exec_ctx *exec_ctx, grpc_winsocket *socket,
   GPR_ASSERT(!info->has_pending_iocp);
   gpr_mu_lock(&socket->state_mu);
   if (info->closure) {
-    grpc_exec_ctx_sched(exec_ctx, info->closure, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, info->closure, GRPC_ERROR_NONE);
     info->closure = NULL;
   } else {
     info->has_pending_iocp = 1;
diff --git a/src/core/lib/iomgr/tcp_client_posix.c b/src/core/lib/iomgr/tcp_client_posix.c
index 2db56b47ee..c8237dc38f 100644
--- a/src/core/lib/iomgr/tcp_client_posix.c
+++ b/src/core/lib/iomgr/tcp_client_posix.c
@@ -265,7 +265,7 @@ finish:
     grpc_channel_args_destroy(exec_ctx, ac->channel_args);
     gpr_free(ac);
   }
-  grpc_exec_ctx_sched(exec_ctx, closure, error, NULL);
+  grpc_closure_sched(exec_ctx, closure, error);
 }
 
 static void tcp_client_connect_impl(grpc_exec_ctx *exec_ctx,
@@ -294,7 +294,7 @@ static void tcp_client_connect_impl(grpc_exec_ctx *exec_ctx,
 
   error = grpc_create_dualstack_socket(addr, SOCK_STREAM, 0, &dsmode, &fd);
   if (error != GRPC_ERROR_NONE) {
-    grpc_exec_ctx_sched(exec_ctx, closure, error, NULL);
+    grpc_closure_sched(exec_ctx, closure, error);
     return;
   }
   if (dsmode == GRPC_DSMODE_IPV4) {
@@ -303,7 +303,7 @@ static void tcp_client_connect_impl(grpc_exec_ctx *exec_ctx,
     addr = &addr4_copy;
   }
   if ((error = prepare_socket(addr, fd, channel_args)) != GRPC_ERROR_NONE) {
-    grpc_exec_ctx_sched(exec_ctx, closure, error, NULL);
+    grpc_closure_sched(exec_ctx, closure, error);
     return;
   }
 
@@ -321,14 +321,13 @@ static void tcp_client_connect_impl(grpc_exec_ctx *exec_ctx,
   if (err >= 0) {
     *ep =
         grpc_tcp_client_create_from_fd(exec_ctx, fdobj, channel_args, addr_str);
-    grpc_exec_ctx_sched(exec_ctx, closure, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, closure, GRPC_ERROR_NONE);
     goto done;
   }
 
   if (errno != EWOULDBLOCK && errno != EINPROGRESS) {
     grpc_fd_orphan(exec_ctx, fdobj, NULL, NULL, "tcp_client_connect_error");
-    grpc_exec_ctx_sched(exec_ctx, closure, GRPC_OS_ERROR(errno, "connect"),
-                        NULL);
+    grpc_closure_sched(exec_ctx, closure, GRPC_OS_ERROR(errno, "connect"));
     goto done;
   }
 
@@ -343,8 +342,8 @@ static void tcp_client_connect_impl(grpc_exec_ctx *exec_ctx,
   addr_str = NULL;
   gpr_mu_init(&ac->mu);
   ac->refs = 2;
-  ac->write_closure.cb = on_writable;
-  ac->write_closure.cb_arg = ac;
+  grpc_closure_init(&ac->write_closure, on_writable, ac,
+                    grpc_schedule_on_exec_ctx);
   ac->channel_args = grpc_channel_args_copy(channel_args);
 
   if (grpc_tcp_trace) {
diff --git a/src/core/lib/iomgr/tcp_client_uv.c b/src/core/lib/iomgr/tcp_client_uv.c
index 5f2ccfee76..ed0de50fc1 100644
--- a/src/core/lib/iomgr/tcp_client_uv.c
+++ b/src/core/lib/iomgr/tcp_client_uv.c
@@ -110,7 +110,7 @@ static void uv_tc_on_connect(uv_connect_t *req, int status) {
   if (done) {
     uv_tcp_connect_cleanup(&exec_ctx, connect);
   }
-  grpc_exec_ctx_sched(&exec_ctx, closure, error, NULL);
+  grpc_closure_sched(&exec_ctx, closure, error);
   grpc_exec_ctx_finish(&exec_ctx);
 }
 
diff --git a/src/core/lib/iomgr/tcp_client_windows.c b/src/core/lib/iomgr/tcp_client_windows.c
index cc10060b9b..275258ebb5 100644
--- a/src/core/lib/iomgr/tcp_client_windows.c
+++ b/src/core/lib/iomgr/tcp_client_windows.c
@@ -129,7 +129,7 @@ static void on_connect(grpc_exec_ctx *exec_ctx, void *acp, grpc_error *error) {
   async_connect_unlock_and_cleanup(exec_ctx, ac, socket);
   /* If the connection was aborted, the callback was already called when
      the deadline was met. */
-  grpc_exec_ctx_sched(exec_ctx, on_done, error, NULL);
+  grpc_closure_sched(exec_ctx, on_done, error);
 }
 
 /* Tries to issue one async connection, then schedules both an IOCP
@@ -227,7 +227,7 @@ void grpc_tcp_client_connect(grpc_exec_ctx *exec_ctx, grpc_closure *on_done,
   ac->addr_name = grpc_sockaddr_to_uri(addr);
   ac->endpoint = endpoint;
   ac->resource_quota = resource_quota;
-  grpc_closure_init(&ac->on_connect, on_connect, ac);
+  grpc_closure_init(&ac->on_connect, on_connect, ac, grpc_schedule_on_exec_ctx);
 
   grpc_timer_init(exec_ctx, &ac->alarm, deadline, on_alarm, ac,
                   gpr_now(GPR_CLOCK_MONOTONIC));
@@ -247,7 +247,7 @@ failure:
     closesocket(sock);
   }
   grpc_resource_quota_unref_internal(exec_ctx, resource_quota);
-  grpc_exec_ctx_sched(exec_ctx, on_done, final_error, NULL);
+  grpc_closure_sched(exec_ctx, on_done, final_error);
 }
 
 #endif /* GRPC_WINSOCK_SOCKET */
diff --git a/src/core/lib/iomgr/tcp_posix.c b/src/core/lib/iomgr/tcp_posix.c
index 2b46544f82..ece44978b0 100644
--- a/src/core/lib/iomgr/tcp_posix.c
+++ b/src/core/lib/iomgr/tcp_posix.c
@@ -320,7 +320,7 @@ static void tcp_read(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
     tcp->finished_edge = false;
     grpc_fd_notify_on_read(exec_ctx, tcp->em_fd, &tcp->read_closure);
   } else {
-    grpc_exec_ctx_sched(exec_ctx, &tcp->read_closure, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, &tcp->read_closure, GRPC_ERROR_NONE);
   }
 }
 
@@ -464,11 +464,10 @@ static void tcp_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
 
   if (buf->length == 0) {
     GPR_TIMER_END("tcp_write", 0);
-    grpc_exec_ctx_sched(exec_ctx, cb,
-                        grpc_fd_is_shutdown(tcp->em_fd)
-                            ? tcp_annotate_error(GRPC_ERROR_CREATE("EOF"), tcp)
-                            : GRPC_ERROR_NONE,
-                        NULL);
+    grpc_closure_sched(exec_ctx, cb,
+                       grpc_fd_is_shutdown(tcp->em_fd)
+                           ? tcp_annotate_error(GRPC_ERROR_CREATE("EOF"), tcp)
+                           : GRPC_ERROR_NONE);
     return;
   }
   tcp->outgoing_buffer = buf;
@@ -488,7 +487,7 @@ static void tcp_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
       gpr_log(GPR_DEBUG, "write: %s", str);
       grpc_error_free_string(str);
     }
-    grpc_exec_ctx_sched(exec_ctx, cb, error, NULL);
+    grpc_closure_sched(exec_ctx, cb, error);
   }
 
   GPR_TIMER_END("tcp_write", 0);
@@ -556,10 +555,10 @@ grpc_endpoint *grpc_tcp_create(grpc_fd *em_fd,
   gpr_ref_init(&tcp->refcount, 1);
   gpr_atm_no_barrier_store(&tcp->shutdown_count, 0);
   tcp->em_fd = em_fd;
-  tcp->read_closure.cb = tcp_handle_read;
-  tcp->read_closure.cb_arg = tcp;
-  tcp->write_closure.cb = tcp_handle_write;
-  tcp->write_closure.cb_arg = tcp;
+  grpc_closure_init(&tcp->read_closure, tcp_handle_read, tcp,
+                    grpc_schedule_on_exec_ctx);
+  grpc_closure_init(&tcp->write_closure, tcp_handle_write, tcp,
+                    grpc_schedule_on_exec_ctx);
   grpc_slice_buffer_init(&tcp->last_read_buffer);
   tcp->resource_user = grpc_resource_user_create(resource_quota, peer_string);
   grpc_resource_user_slice_allocator_init(
diff --git a/src/core/lib/iomgr/tcp_server_posix.c b/src/core/lib/iomgr/tcp_server_posix.c
index 1e63142e0e..20efb678b2 100644
--- a/src/core/lib/iomgr/tcp_server_posix.c
+++ b/src/core/lib/iomgr/tcp_server_posix.c
@@ -208,7 +208,7 @@ static void finish_shutdown(grpc_exec_ctx *exec_ctx, grpc_tcp_server *s) {
   GPR_ASSERT(s->shutdown);
   gpr_mu_unlock(&s->mu);
   if (s->shutdown_complete != NULL) {
-    grpc_exec_ctx_sched(exec_ctx, s->shutdown_complete, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, s->shutdown_complete, GRPC_ERROR_NONE);
   }
 
   gpr_mu_destroy(&s->mu);
@@ -254,8 +254,8 @@ static void deactivated_all_ports(grpc_exec_ctx *exec_ctx, grpc_tcp_server *s) {
     grpc_tcp_listener *sp;
     for (sp = s->head; sp; sp = sp->next) {
       grpc_unlink_if_unix_domain_socket(&sp->addr);
-      sp->destroyed_closure.cb = destroyed_port;
-      sp->destroyed_closure.cb_arg = s;
+      grpc_closure_init(&sp->destroyed_closure, destroyed_port, s,
+                        grpc_schedule_on_exec_ctx);
       grpc_fd_orphan(exec_ctx, sp->emfd, &sp->destroyed_closure, NULL,
                      "tcp_listener_shutdown");
     }
@@ -723,8 +723,8 @@ void grpc_tcp_server_start(grpc_exec_ctx *exec_ctx, grpc_tcp_server *s,
           "clone_port", clone_port(sp, (unsigned)(pollset_count - 1))));
       for (i = 0; i < pollset_count; i++) {
         grpc_pollset_add_fd(exec_ctx, pollsets[i], sp->emfd);
-        sp->read_closure.cb = on_read;
-        sp->read_closure.cb_arg = sp;
+        grpc_closure_init(&sp->read_closure, on_read, sp,
+                          grpc_schedule_on_exec_ctx);
         grpc_fd_notify_on_read(exec_ctx, sp->emfd, &sp->read_closure);
         s->active_ports++;
         sp = sp->next;
@@ -733,8 +733,8 @@ void grpc_tcp_server_start(grpc_exec_ctx *exec_ctx, grpc_tcp_server *s,
       for (i = 0; i < pollset_count; i++) {
         grpc_pollset_add_fd(exec_ctx, pollsets[i], sp->emfd);
       }
-      sp->read_closure.cb = on_read;
-      sp->read_closure.cb_arg = sp;
+      grpc_closure_init(&sp->read_closure, on_read, sp,
+                        grpc_schedule_on_exec_ctx);
       grpc_fd_notify_on_read(exec_ctx, sp->emfd, &sp->read_closure);
       s->active_ports++;
       sp = sp->next;
@@ -760,7 +760,7 @@ void grpc_tcp_server_unref(grpc_exec_ctx *exec_ctx, grpc_tcp_server *s) {
   if (gpr_unref(&s->refs)) {
     grpc_tcp_server_shutdown_listeners(exec_ctx, s);
     gpr_mu_lock(&s->mu);
-    grpc_exec_ctx_enqueue_list(exec_ctx, &s->shutdown_starting, NULL);
+    grpc_closure_list_sched(exec_ctx, &s->shutdown_starting);
     gpr_mu_unlock(&s->mu);
     tcp_server_destroy(exec_ctx, s);
   }
diff --git a/src/core/lib/iomgr/tcp_server_uv.c b/src/core/lib/iomgr/tcp_server_uv.c
index 4ccc80c9f0..eed2773f8a 100644
--- a/src/core/lib/iomgr/tcp_server_uv.c
+++ b/src/core/lib/iomgr/tcp_server_uv.c
@@ -126,7 +126,7 @@ void grpc_tcp_server_shutdown_starting_add(grpc_tcp_server *s,
 
 static void finish_shutdown(grpc_exec_ctx *exec_ctx, grpc_tcp_server *s) {
   if (s->shutdown_complete != NULL) {
-    grpc_exec_ctx_sched(exec_ctx, s->shutdown_complete, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, s->shutdown_complete, GRPC_ERROR_NONE);
   }
 
   while (s->head) {
@@ -170,7 +170,7 @@ void grpc_tcp_server_unref(grpc_exec_ctx *exec_ctx, grpc_tcp_server *s) {
   if (gpr_unref(&s->refs)) {
     /* Complete shutdown_starting work before destroying. */
     grpc_exec_ctx local_exec_ctx = GRPC_EXEC_CTX_INIT;
-    grpc_exec_ctx_enqueue_list(&local_exec_ctx, &s->shutdown_starting, NULL);
+    grpc_closure_list_sched(&local_exec_ctx, &s->shutdown_starting);
     if (exec_ctx == NULL) {
       grpc_exec_ctx_flush(&local_exec_ctx);
       tcp_server_destroy(&local_exec_ctx, s);
diff --git a/src/core/lib/iomgr/tcp_server_windows.c b/src/core/lib/iomgr/tcp_server_windows.c
index 053bb35f6f..97d7827461 100644
--- a/src/core/lib/iomgr/tcp_server_windows.c
+++ b/src/core/lib/iomgr/tcp_server_windows.c
@@ -162,11 +162,12 @@ static void destroy_server(grpc_exec_ctx *exec_ctx, void *arg,
 static void finish_shutdown_locked(grpc_exec_ctx *exec_ctx,
                                    grpc_tcp_server *s) {
   if (s->shutdown_complete != NULL) {
-    grpc_exec_ctx_sched(exec_ctx, s->shutdown_complete, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, s->shutdown_complete, GRPC_ERROR_NONE);
   }
 
-  grpc_exec_ctx_sched(exec_ctx, grpc_closure_create(destroy_server, s),
-                      GRPC_ERROR_NONE, NULL);
+  grpc_closure_sched(exec_ctx, grpc_closure_create(destroy_server, s,
+                                                   grpc_schedule_on_exec_ctx),
+                     GRPC_ERROR_NONE);
 }
 
 grpc_tcp_server *grpc_tcp_server_ref(grpc_tcp_server *s) {
@@ -204,7 +205,7 @@ void grpc_tcp_server_unref(grpc_exec_ctx *exec_ctx, grpc_tcp_server *s) {
   if (gpr_unref(&s->refs)) {
     grpc_tcp_server_shutdown_listeners(exec_ctx, s);
     gpr_mu_lock(&s->mu);
-    grpc_exec_ctx_enqueue_list(exec_ctx, &s->shutdown_starting, NULL);
+    grpc_closure_list_sched(exec_ctx, &s->shutdown_starting);
     gpr_mu_unlock(&s->mu);
     tcp_server_destroy(exec_ctx, s);
   }
@@ -465,7 +466,7 @@ static grpc_error *add_socket_to_server(grpc_tcp_server *s, SOCKET sock,
   sp->new_socket = INVALID_SOCKET;
   sp->port = port;
   sp->port_index = port_index;
-  grpc_closure_init(&sp->on_accept, on_accept, sp);
+  grpc_closure_init(&sp->on_accept, on_accept, sp, grpc_schedule_on_exec_ctx);
   GPR_ASSERT(sp->socket);
   gpr_mu_unlock(&s->mu);
   *listener = sp;
diff --git a/src/core/lib/iomgr/tcp_uv.c b/src/core/lib/iomgr/tcp_uv.c
index 15c8b3cbee..a1ee597d09 100644
--- a/src/core/lib/iomgr/tcp_uv.c
+++ b/src/core/lib/iomgr/tcp_uv.c
@@ -170,7 +170,7 @@ static void read_callback(uv_stream_t *stream, ssize_t nread,
     // nread < 0: Error
     error = GRPC_ERROR_CREATE("TCP Read failed");
   }
-  grpc_exec_ctx_sched(&exec_ctx, cb, error, NULL);
+  grpc_closure_sched(&exec_ctx, cb, error);
   grpc_exec_ctx_finish(&exec_ctx);
 }
 
@@ -191,7 +191,7 @@ static void uv_endpoint_read(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
     error = GRPC_ERROR_CREATE("TCP Read failed at start");
     error =
         grpc_error_set_str(error, GRPC_ERROR_STR_OS_ERROR, uv_strerror(status));
-    grpc_exec_ctx_sched(exec_ctx, cb, error, NULL);
+    grpc_closure_sched(exec_ctx, cb, error);
   }
   if (grpc_tcp_trace) {
     const char *str = grpc_error_string(error);
@@ -218,7 +218,7 @@ static void write_callback(uv_write_t *req, int status) {
   gpr_free(tcp->write_buffers);
   grpc_resource_user_free(&exec_ctx, tcp->resource_user,
                           sizeof(uv_buf_t) * tcp->write_slices->count);
-  grpc_exec_ctx_sched(&exec_ctx, cb, error, NULL);
+  grpc_closure_sched(&exec_ctx, cb, error);
   grpc_exec_ctx_finish(&exec_ctx);
 }
 
@@ -244,8 +244,8 @@ static void uv_endpoint_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
   }
 
   if (tcp->shutting_down) {
-    grpc_exec_ctx_sched(exec_ctx, cb,
-                        GRPC_ERROR_CREATE("TCP socket is shutting down"), NULL);
+    grpc_closure_sched(exec_ctx, cb,
+                       GRPC_ERROR_CREATE("TCP socket is shutting down"));
     return;
   }
 
@@ -255,7 +255,7 @@ static void uv_endpoint_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
   if (tcp->write_slices->count == 0) {
     // No slices means we don't have to do anything,
     // and libuv doesn't like empty writes
-    grpc_exec_ctx_sched(exec_ctx, cb, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, cb, GRPC_ERROR_NONE);
     return;
   }
 
diff --git a/src/core/lib/iomgr/tcp_windows.c b/src/core/lib/iomgr/tcp_windows.c
index 8b3b44aaaa..84f791ba07 100644
--- a/src/core/lib/iomgr/tcp_windows.c
+++ b/src/core/lib/iomgr/tcp_windows.c
@@ -189,7 +189,7 @@ static void on_read(grpc_exec_ctx *exec_ctx, void *tcpp, grpc_error *error) {
 
   tcp->read_cb = NULL;
   TCP_UNREF(exec_ctx, tcp, "read");
-  grpc_exec_ctx_sched(exec_ctx, cb, error, NULL);
+  grpc_closure_sched(exec_ctx, cb, error);
 }
 
 static void win_read(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
@@ -203,8 +203,8 @@ static void win_read(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
   WSABUF buffer;
 
   if (tcp->shutting_down) {
-    grpc_exec_ctx_sched(exec_ctx, cb,
-                        GRPC_ERROR_CREATE("TCP socket is shutting down"), NULL);
+    grpc_closure_sched(exec_ctx, cb,
+                       GRPC_ERROR_CREATE("TCP socket is shutting down"));
     return;
   }
 
@@ -228,7 +228,7 @@ static void win_read(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
   /* Did we get data immediately ? Yay. */
   if (info->wsa_error != WSAEWOULDBLOCK) {
     info->bytes_transfered = bytes_read;
-    grpc_exec_ctx_sched(exec_ctx, &tcp->on_read, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, &tcp->on_read, GRPC_ERROR_NONE);
     return;
   }
 
@@ -241,8 +241,8 @@ static void win_read(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
     int wsa_error = WSAGetLastError();
     if (wsa_error != WSA_IO_PENDING) {
       info->wsa_error = wsa_error;
-      grpc_exec_ctx_sched(exec_ctx, &tcp->on_read,
-                          GRPC_WSA_ERROR(info->wsa_error, "WSARecv"), NULL);
+      grpc_closure_sched(exec_ctx, &tcp->on_read,
+                         GRPC_WSA_ERROR(info->wsa_error, "WSARecv"));
       return;
     }
   }
@@ -273,7 +273,7 @@ static void on_write(grpc_exec_ctx *exec_ctx, void *tcpp, grpc_error *error) {
   }
 
   TCP_UNREF(exec_ctx, tcp, "write");
-  grpc_exec_ctx_sched(exec_ctx, cb, error, NULL);
+  grpc_closure_sched(exec_ctx, cb, error);
 }
 
 /* Initiates a write. */
@@ -291,8 +291,8 @@ static void win_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
   size_t len;
 
   if (tcp->shutting_down) {
-    grpc_exec_ctx_sched(exec_ctx, cb,
-                        GRPC_ERROR_CREATE("TCP socket is shutting down"), NULL);
+    grpc_closure_sched(exec_ctx, cb,
+                       GRPC_ERROR_CREATE("TCP socket is shutting down"));
     return;
   }
 
@@ -323,7 +323,7 @@ static void win_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
     grpc_error *error = status == 0
                             ? GRPC_ERROR_NONE
                             : GRPC_WSA_ERROR(info->wsa_error, "WSASend");
-    grpc_exec_ctx_sched(exec_ctx, cb, error, NULL);
+    grpc_closure_sched(exec_ctx, cb, error);
     if (allocated) gpr_free(allocated);
     return;
   }
@@ -341,8 +341,7 @@ static void win_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
     int wsa_error = WSAGetLastError();
     if (wsa_error != WSA_IO_PENDING) {
       TCP_UNREF(exec_ctx, tcp, "write");
-      grpc_exec_ctx_sched(exec_ctx, cb, GRPC_WSA_ERROR(wsa_error, "WSASend"),
-                          NULL);
+      grpc_closure_sched(exec_ctx, cb, GRPC_WSA_ERROR(wsa_error, "WSASend"));
       return;
     }
   }
@@ -425,8 +424,8 @@ grpc_endpoint *grpc_tcp_create(grpc_winsocket *socket,
   tcp->socket = socket;
   gpr_mu_init(&tcp->mu);
   gpr_ref_init(&tcp->refcount, 1);
-  grpc_closure_init(&tcp->on_read, on_read, tcp);
-  grpc_closure_init(&tcp->on_write, on_write, tcp);
+  grpc_closure_init(&tcp->on_read, on_read, tcp, grpc_schedule_on_exec_ctx);
+  grpc_closure_init(&tcp->on_write, on_write, tcp, grpc_schedule_on_exec_ctx);
   tcp->peer_string = gpr_strdup(peer_string);
   tcp->resource_user = grpc_resource_user_create(resource_quota, peer_string);
   /* Tell network status tracking code about the new endpoint */
diff --git a/src/core/lib/iomgr/timer_generic.c b/src/core/lib/iomgr/timer_generic.c
index 00058f9d86..ecd3b284dc 100644
--- a/src/core/lib/iomgr/timer_generic.c
+++ b/src/core/lib/iomgr/timer_generic.c
@@ -184,22 +184,22 @@ void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
   shard_type *shard = &g_shards[shard_idx(timer)];
   GPR_ASSERT(deadline.clock_type == g_clock_type);
   GPR_ASSERT(now.clock_type == g_clock_type);
-  grpc_closure_init(&timer->closure, timer_cb, timer_cb_arg);
+  grpc_closure_init(&timer->closure, timer_cb, timer_cb_arg,
+                    grpc_schedule_on_exec_ctx);
   timer->deadline = deadline;
   timer->triggered = 0;
 
   if (!g_initialized) {
     timer->triggered = 1;
-    grpc_exec_ctx_sched(
+    grpc_closure_sched(
         exec_ctx, &timer->closure,
-        GRPC_ERROR_CREATE("Attempt to create timer before initialization"),
-        NULL);
+        GRPC_ERROR_CREATE("Attempt to create timer before initialization"));
     return;
   }
 
   if (gpr_time_cmp(deadline, now) <= 0) {
     timer->triggered = 1;
-    grpc_exec_ctx_sched(exec_ctx, &timer->closure, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, &timer->closure, GRPC_ERROR_NONE);
     return;
   }
 
@@ -251,7 +251,7 @@ void grpc_timer_cancel(grpc_exec_ctx *exec_ctx, grpc_timer *timer) {
   shard_type *shard = &g_shards[shard_idx(timer)];
   gpr_mu_lock(&shard->mu);
   if (!timer->triggered) {
-    grpc_exec_ctx_sched(exec_ctx, &timer->closure, GRPC_ERROR_CANCELLED, NULL);
+    grpc_closure_sched(exec_ctx, &timer->closure, GRPC_ERROR_CANCELLED);
     timer->triggered = 1;
     if (timer->heap_index == INVALID_HEAP_INDEX) {
       list_remove(timer);
@@ -317,7 +317,7 @@ static size_t pop_timers(grpc_exec_ctx *exec_ctx, shard_type *shard,
   grpc_timer *timer;
   gpr_mu_lock(&shard->mu);
   while ((timer = pop_one(shard, now))) {
-    grpc_exec_ctx_sched(exec_ctx, &timer->closure, GRPC_ERROR_REF(error), NULL);
+    grpc_closure_sched(exec_ctx, &timer->closure, GRPC_ERROR_REF(error));
     n++;
   }
   *new_min_deadline = compute_min_deadline(shard);
diff --git a/src/core/lib/iomgr/timer_uv.c b/src/core/lib/iomgr/timer_uv.c
index cfcb89268b..00b835ffb8 100644
--- a/src/core/lib/iomgr/timer_uv.c
+++ b/src/core/lib/iomgr/timer_uv.c
@@ -55,7 +55,7 @@ void run_expired_timer(uv_timer_t *handle) {
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   GPR_ASSERT(!timer->triggered);
   timer->triggered = 1;
-  grpc_exec_ctx_sched(&exec_ctx, &timer->closure, GRPC_ERROR_NONE, NULL);
+  grpc_closure_sched(&exec_ctx, &timer->closure, GRPC_ERROR_NONE);
   stop_uv_timer(handle);
   grpc_exec_ctx_finish(&exec_ctx);
 }
@@ -65,10 +65,11 @@ void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
                      void *timer_cb_arg, gpr_timespec now) {
   uint64_t timeout;
   uv_timer_t *uv_timer;
-  grpc_closure_init(&timer->closure, timer_cb, timer_cb_arg);
+  grpc_closure_init(&timer->closure, timer_cb, timer_cb_arg,
+                    grpc_schedule_on_exec_ctx);
   if (gpr_time_cmp(deadline, now) <= 0) {
     timer->triggered = 1;
-    grpc_exec_ctx_sched(exec_ctx, &timer->closure, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, &timer->closure, GRPC_ERROR_NONE);
     return;
   }
   timer->triggered = 0;
@@ -83,7 +84,7 @@ void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
 void grpc_timer_cancel(grpc_exec_ctx *exec_ctx, grpc_timer *timer) {
   if (!timer->triggered) {
     timer->triggered = 1;
-    grpc_exec_ctx_sched(exec_ctx, &timer->closure, GRPC_ERROR_CANCELLED, NULL);
+    grpc_closure_sched(exec_ctx, &timer->closure, GRPC_ERROR_CANCELLED);
     stop_uv_timer((uv_timer_t *)timer->uv_timer);
   }
 }
diff --git a/src/core/lib/iomgr/udp_server.c b/src/core/lib/iomgr/udp_server.c
index 3c24ea9afa..dfbd295c91 100644
--- a/src/core/lib/iomgr/udp_server.c
+++ b/src/core/lib/iomgr/udp_server.c
@@ -126,7 +126,7 @@ grpc_udp_server *grpc_udp_server_create(void) {
 
 static void finish_shutdown(grpc_exec_ctx *exec_ctx, grpc_udp_server *s) {
   if (s->shutdown_complete != NULL) {
-    grpc_exec_ctx_sched(exec_ctx, s->shutdown_complete, GRPC_ERROR_NONE, NULL);
+    grpc_closure_sched(exec_ctx, s->shutdown_complete, GRPC_ERROR_NONE);
   }
 
   gpr_mu_destroy(&s->mu);
@@ -170,8 +170,8 @@ static void deactivated_all_ports(grpc_exec_ctx *exec_ctx, grpc_udp_server *s) {
     for (sp = s->head; sp; sp = sp->next) {
       grpc_unlink_if_unix_domain_socket(&sp->addr);
 
-      sp->destroyed_closure.cb = destroyed_port;
-      sp->destroyed_closure.cb_arg = s;
+      grpc_closure_init(&sp->destroyed_closure, destroyed_port, s,
+                        grpc_schedule_on_exec_ctx);
 
       /* Call the orphan_cb to signal that the FD is about to be closed and
        * should no longer be used. */
@@ -446,8 +446,8 @@ void grpc_udp_server_start(grpc_exec_ctx *exec_ctx, grpc_udp_server *s,
     for (i = 0; i < pollset_count; i++) {
       grpc_pollset_add_fd(exec_ctx, pollsets[i], sp->emfd);
     }
-    sp->read_closure.cb = on_read;
-    sp->read_closure.cb_arg = sp;
+    grpc_closure_init(&sp->read_closure, on_read, sp,
+                      grpc_schedule_on_exec_ctx);
     grpc_fd_notify_on_read(exec_ctx, sp->emfd, &sp->read_closure);
 
     s->active_ports++;
diff --git a/src/core/lib/iomgr/workqueue.h b/src/core/lib/iomgr/workqueue.h
index 73d9849843..371b0f55dc 100644
--- a/src/core/lib/iomgr/workqueue.h
+++ b/src/core/lib/iomgr/workqueue.h
@@ -72,17 +72,16 @@ grpc_workqueue *grpc_workqueue_ref(grpc_workqueue *workqueue);
 void grpc_workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue);
 #endif
 
-/** Add a work item to a workqueue. Items added to a work queue will be started
-    in approximately the order they were enqueued, on some thread that may or
-    may not be the current thread. Successive closures enqueued onto a workqueue
-    MAY be executed concurrently.
+/** Fetch the workqueue closure scheduler. Items added to a work queue will be
+    started in approximately the order they were enqueued, on some thread that
+    may or may not be the current thread. Successive closures enqueued onto a
+    workqueue MAY be executed concurrently.
 
     It is generally more expensive to add a closure to a workqueue than to the
     execution context, both in terms of CPU work and in execution latency.
 
     Use work queues when it's important that other threads be given a chance to
     tackle some workload. */
-void grpc_workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
-                            grpc_closure *closure, grpc_error *error);
+grpc_closure_scheduler *grpc_workqueue_scheduler(grpc_workqueue *workqueue);
 
 #endif /* GRPC_CORE_LIB_IOMGR_WORKQUEUE_H */
diff --git a/src/core/lib/iomgr/workqueue_uv.c b/src/core/lib/iomgr/workqueue_uv.c
index e58ca476cc..4d61b40912 100644
--- a/src/core/lib/iomgr/workqueue_uv.c
+++ b/src/core/lib/iomgr/workqueue_uv.c
@@ -58,9 +58,8 @@ grpc_workqueue *grpc_workqueue_ref(grpc_workqueue *workqueue) {
 void grpc_workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {}
 #endif
 
-void grpc_workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
-                            grpc_closure *closure, grpc_error *error) {
-  grpc_exec_ctx_sched(exec_ctx, closure, error, NULL);
+grpc_closure_scheduler *grpc_workqueue_scheduler(grpc_workqueue *workqueue) {
+  return grpc_schedule_on_exec_ctx;
 }
 
 #endif /* GPR_UV */
diff --git a/src/core/lib/iomgr/workqueue_windows.c b/src/core/lib/iomgr/workqueue_windows.c
index 5c93d3c59e..234b47cdf5 100644
--- a/src/core/lib/iomgr/workqueue_windows.c
+++ b/src/core/lib/iomgr/workqueue_windows.c
@@ -56,9 +56,8 @@ grpc_workqueue *grpc_workqueue_ref(grpc_workqueue *workqueue) {
 void grpc_workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {}
 #endif
 
-void grpc_workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
-                            grpc_closure *closure, grpc_error *error) {
-  grpc_exec_ctx_sched(exec_ctx, closure, error, NULL);
+grpc_closure_scheduler *grpc_workqueue_scheduler(grpc_workqueue *workqueue) {
+  return grpc_schedule_on_exec_ctx;
 }
 
 #endif /* GPR_WINDOWS */