20 files changed, 361 insertions, 273 deletions

diff --git a/src/core/lib/iomgr/error.h b/src/core/lib/iomgr/error.h
index ffacdac393..2613512acb 100644
--- a/src/core/lib/iomgr/error.h
+++ b/src/core/lib/iomgr/error.h
@@ -137,8 +137,8 @@ typedef enum {
 } grpc_error_times;
 
 /// The following "special" errors can be propagated without allocating memory.
-/// They are always even so that other code (particularly combiner locks) can
-/// safely use the lower bit for themselves.
+/// They are always even so that other code (particularly combiner locks,
+/// polling engines) can safely use the lower bit for themselves.
 
 #define GRPC_ERROR_NONE ((grpc_error *)NULL)
 #define GRPC_ERROR_OOM ((grpc_error *)2)
diff --git a/src/core/lib/iomgr/ev_epoll_linux.c b/src/core/lib/iomgr/ev_epoll_linux.c
index 51842fc208..11208b9ad1 100644
--- a/src/core/lib/iomgr/ev_epoll_linux.c
+++ b/src/core/lib/iomgr/ev_epoll_linux.c
@@ -68,7 +68,7 @@ static int grpc_polling_trace = 0; /* Disabled by default */
     gpr_log(GPR_INFO, (fmt), __VA_ARGS__); \
   }
 
-/* Uncomment the following enable extra checks on poll_object operations */
+/* Uncomment the following to enable extra checks on poll_object operations */
 /* #define PO_DEBUG */
 
 static int grpc_wakeup_signal = -1;
@@ -140,24 +140,61 @@ struct grpc_fd {
      Ref/Unref by two to avoid altering the orphaned bit */
   gpr_atm refst;
 
-  /* Indicates that the fd is shutdown and that any pending read/write closures
-     should fail */
-  bool shutdown;
-  grpc_error *shutdown_error; /* reason for shutdown: set iff shutdown==true */
+  /* Internally stores data of type (grpc_error *). If the FD is shutdown, this
+     contains reason for shutdown (i.e a pointer to grpc_error) ORed with
+     FD_SHUTDOWN_BIT. Since address allocations are word-aligned, the lower bit
+     of (grpc_error *) addresses is guaranteed to be zero. Even if the
+     (grpc_error *), is of special types like GRPC_ERROR_NONE, GRPC_ERROR_OOM
+     etc, the lower bit is guaranteed to be zero.
 
-  /* The fd is either closed or we relinquished control of it. In either cases,
-     this indicates that the 'fd' on this structure is no longer valid */
+     Once an fd is shutdown, any pending or future read/write closures on the
+     fd should fail */
+  gpr_atm shutdown_error;
+
+  /* The fd is either closed or we relinquished control of it. In either
+     cases, this indicates that the 'fd' on this structure is no longer
+     valid */
   bool orphaned;
 
-  /* TODO: sreek - Move this to a lockfree implementation */
-  grpc_closure *read_closure;
-  grpc_closure *write_closure;
+  /* Closures to call when the fd is readable or writable respectively. These
+     fields contain one of the following values:
+       CLOSURE_READY     : The fd has an I/O event of interest but there is no
+                           closure yet to execute
+
+       CLOSURE_NOT_READY : The fd has no I/O event of interest
+
+       closure ptr       : The closure to be executed when the fd has an I/O
+                           event of interest
+
+       shutdown_error | FD_SHUTDOWN_BIT :
+                          'shutdown_error' field ORed with FD_SHUTDOWN_BIT.
+                           This indicates that the fd is shutdown. Since all
+                           memory allocations are word-aligned, the lower two
+                           bits of the shutdown_error pointer are always 0. So
+                           it is safe to OR these with FD_SHUTDOWN_BIT
+
+     Valid state transitions:
+
+       <closure ptr> <-----3------ CLOSURE_NOT_READY ----1---->  CLOSURE_READY
+         |  |                         ^   |    ^                         |  |
+         |  |                         |   |    |                         |  |
+         |  +--------------4----------+   6    +---------2---------------+  |
+         |                                |                                 |
+         |                                v                                 |
+         +-----5------->  [shutdown_error | FD_SHUTDOWN_BIT] <----7---------+
+
+      For 1, 4 : See set_ready() function
+      For 2, 3 : See notify_on() function
+      For 5,6,7: See set_shutdown() function */
+  gpr_atm read_closure;
+  gpr_atm write_closure;
 
   struct grpc_fd *freelist_next;
   grpc_closure *on_done_closure;
 
-  /* The pollset that last noticed that the fd is readable */
-  grpc_pollset *read_notifier_pollset;
+  /* The pollset that last noticed that the fd is readable. The actual type
+   * stored in this is (grpc_pollset *) */
+  gpr_atm read_notifier_pollset;
 
   grpc_iomgr_object iomgr_object;
 };
@@ -180,8 +217,10 @@ static void fd_unref(grpc_fd *fd);
 static void fd_global_init(void);
 static void fd_global_shutdown(void);
 
-#define CLOSURE_NOT_READY ((grpc_closure *)0)
-#define CLOSURE_READY ((grpc_closure *)1)
+#define CLOSURE_NOT_READY ((gpr_atm)0)
+#define CLOSURE_READY ((gpr_atm)2)
+
+#define FD_SHUTDOWN_BIT 1
 
 /*******************************************************************************
  * Polling island Declarations
@@ -908,7 +947,11 @@ static void unref_by(grpc_fd *fd, int n) {
     fd->freelist_next = fd_freelist;
     fd_freelist = fd;
     grpc_iomgr_unregister_object(&fd->iomgr_object);
-    if (fd->shutdown) GRPC_ERROR_UNREF(fd->shutdown_error);
+
+    grpc_error *err = (grpc_error *)gpr_atm_acq_load(&fd->shutdown_error);
+    /* Clear the least significant bit if it set (in case fd was shutdown) */
+    err = (grpc_error *)((intptr_t)err & ~FD_SHUTDOWN_BIT);
+    GRPC_ERROR_UNREF(err);
 
     gpr_mu_unlock(&fd_freelist_mu);
   } else {
@@ -972,13 +1015,14 @@ static grpc_fd *fd_create(int fd, const char *name) {
 
   gpr_atm_rel_store(&new_fd->refst, (gpr_atm)1);
   new_fd->fd = fd;
-  new_fd->shutdown = false;
+  gpr_atm_no_barrier_store(&new_fd->shutdown_error, (gpr_atm)GRPC_ERROR_NONE);
   new_fd->orphaned = false;
-  new_fd->read_closure = CLOSURE_NOT_READY;
-  new_fd->write_closure = CLOSURE_NOT_READY;
+  gpr_atm_no_barrier_store(&new_fd->read_closure, CLOSURE_NOT_READY);
+  gpr_atm_no_barrier_store(&new_fd->write_closure, CLOSURE_NOT_READY);
+  gpr_atm_no_barrier_store(&new_fd->read_notifier_pollset, (gpr_atm)NULL);
+
   new_fd->freelist_next = NULL;
   new_fd->on_done_closure = NULL;
-  new_fd->read_notifier_pollset = NULL;
 
   gpr_mu_unlock(&new_fd->po.mu);
 
@@ -1060,101 +1104,206 @@ static void fd_orphan(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
   GRPC_ERROR_UNREF(error);
 }
 
-static grpc_error *fd_shutdown_error(grpc_fd *fd) {
-  if (!fd->shutdown) {
-    return GRPC_ERROR_NONE;
-  } else {
-    return GRPC_ERROR_CREATE_REFERENCING("FD shutdown", &fd->shutdown_error, 1);
+static void notify_on(grpc_exec_ctx *exec_ctx, grpc_fd *fd, gpr_atm *state,
+                      grpc_closure *closure) {
+  while (true) {
+    /* Fast-path: CLOSURE_NOT_READY -> <closure>.
+       The 'release' cas here matches the 'acquire' load in set_ready and
+       set_shutdown ensuring that the closure (scheduled by set_ready or
+       set_shutdown) happens-after the I/O event on the fd */
+    if (gpr_atm_rel_cas(state, CLOSURE_NOT_READY, (gpr_atm)closure)) {
+      return; /* Fast-path successful. Return */
+    }
+
+    /* Slowpath. The 'acquire' load matches the 'release' cas in set_ready and
+       set_shutdown */
+    gpr_atm curr = gpr_atm_acq_load(state);
+    switch (curr) {
+      case CLOSURE_NOT_READY: {
+        break; /* retry */
+      }
+
+      case CLOSURE_READY: {
+        /* Change the state to CLOSURE_NOT_READY. Schedule the closure if
+           successful. If not, the state most likely transitioned to shutdown.
+           We should retry.
+
+           This can be a no-barrier cas since the state is being transitioned to
+           CLOSURE_NOT_READY; set_ready and set_shutdown do not schedule any
+           closure when transitioning out of CLOSURE_NO_READY state (i.e there
+           is no other code that needs to 'happen-after' this) */
+        if (gpr_atm_no_barrier_cas(state, CLOSURE_READY, CLOSURE_NOT_READY)) {
+          grpc_closure_sched(exec_ctx, closure, GRPC_ERROR_NONE);
+          return; /* Slow-path successful. Return */
+        }
+
+        break; /* retry */
+      }
+
+      default: {
+        /* 'curr' is either a closure or the fd is shutdown(in which case 'curr'
+           contains a pointer to the shutdown-error). If the fd is shutdown,
+           schedule the closure with the shutdown error */
+        if ((curr & FD_SHUTDOWN_BIT) > 0) {
+          grpc_error *shutdown_err = (grpc_error *)(curr & ~FD_SHUTDOWN_BIT);
+          grpc_closure_sched(
+              exec_ctx, closure,
+              GRPC_ERROR_CREATE_REFERENCING("FD Shutdown", &shutdown_err, 1));
+          return;
+        }
+
+        /* There is already a closure!. This indicates a bug in the code */
+        gpr_log(GPR_ERROR,
+                "notify_on called with a previous callback still pending");
+        abort();
+      }
+    }
   }
+
+  GPR_UNREACHABLE_CODE(return );
 }
 
-static void notify_on_locked(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
-                             grpc_closure **st, grpc_closure *closure) {
-  if (fd->shutdown) {
-    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_closure_sched(exec_ctx, closure, fd_shutdown_error(fd));
-  } else {
-    /* upcallptr was set to a different closure.  This is an error! */
-    gpr_log(GPR_ERROR,
-            "User called a notify_on function with a previous callback still "
-            "pending");
-    abort();
+static void set_shutdown(grpc_exec_ctx *exec_ctx, grpc_fd *fd, gpr_atm *state,
+                         grpc_error *shutdown_err) {
+  /* Try the fast-path first (i.e expect the current value to be
+     CLOSURE_NOT_READY */
+  gpr_atm curr = CLOSURE_NOT_READY;
+  gpr_atm new_state = (gpr_atm)shutdown_err | FD_SHUTDOWN_BIT;
+
+  while (true) {
+    /* The 'release' cas here matches the 'acquire' load in notify_on to ensure
+       that the closure it schedules 'happens-after' the set_shutdown is called
+       on the fd */
+    if (gpr_atm_rel_cas(state, curr, new_state)) {
+      return; /* Fast-path successful. Return */
+    }
+
+    /* Fallback to slowpath. This 'acquire' load matches the 'release' cas in
+       notify_on and set_ready */
+    curr = gpr_atm_acq_load(state);
+    switch (curr) {
+      case CLOSURE_READY: {
+        break; /* retry */
+      }
+
+      case CLOSURE_NOT_READY: {
+        break; /* retry */
+      }
+
+      default: {
+        /* 'curr' is either a closure or the fd is already shutdown */
+
+        /* If fd is already shutdown, we are done */
+        if ((curr & FD_SHUTDOWN_BIT) > 0) {
+          return;
+        }
+
+        /* Fd is not shutdown. Schedule the closure and move the state to
+           shutdown state. The 'release' cas here matches the 'acquire' load in
+           notify_on to ensure that the closure it schedules 'happens-after'
+           the set_shutdown is called on the fd */
+        if (gpr_atm_rel_cas(state, curr, new_state)) {
+          grpc_closure_sched(
+              exec_ctx, (grpc_closure *)curr,
+              GRPC_ERROR_CREATE_REFERENCING("FD Shutdown", &shutdown_err, 1));
+          return;
+        }
+
+        /* 'curr' was a closure but now changed to a different state. We will
+          have to retry */
+        break;
+      }
+    }
   }
+
+  GPR_UNREACHABLE_CODE(return );
 }
 
-/* returns 1 if state becomes not ready */
-static int set_ready_locked(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
-                            grpc_closure **st) {
-  if (*st == CLOSURE_READY) {
-    /* duplicate ready ==> ignore */
-    return 0;
-  } else if (*st == CLOSURE_NOT_READY) {
-    /* not ready, and not waiting ==> flag ready */
-    *st = CLOSURE_READY;
-    return 0;
-  } else {
-    /* waiting ==> queue closure */
-    grpc_closure_sched(exec_ctx, *st, fd_shutdown_error(fd));
-    *st = CLOSURE_NOT_READY;
-    return 1;
+static void set_ready(grpc_exec_ctx *exec_ctx, grpc_fd *fd, gpr_atm *state) {
+  /* Try an optimistic case first (i.e assume current state is
+     CLOSURE_NOT_READY).
+
+     This 'release' cas matches the 'acquire' load in notify_on ensuring that
+     any closure (scheduled by notify_on) 'happens-after' the return from
+     epoll_pwait */
+  if (gpr_atm_rel_cas(state, CLOSURE_NOT_READY, CLOSURE_READY)) {
+    return; /* early out */
+  }
+
+  /* The 'acquire' load here matches the 'release' cas in notify_on and
+     set_shutdown */
+  gpr_atm curr = gpr_atm_acq_load(state);
+  switch (curr) {
+    case CLOSURE_READY: {
+      /* Already ready. We are done here */
+      break;
+    }
+
+    case CLOSURE_NOT_READY: {
+      /* The state was not CLOSURE_NOT_READY when we checked initially at the
+         beginning of this function but now it is CLOSURE_NOT_READY again.
+         This is only possible if the state transitioned out of
+         CLOSURE_NOT_READY to either CLOSURE_READY or <some closure> and then
+         back to CLOSURE_NOT_READY again (i.e after we entered this function,
+         the fd became "ready" and the necessary actions were already done).
+         So there is no need to make the state CLOSURE_READY now */
+      break;
+    }
+
+    default: {
+      /* 'curr' is either a closure or the fd is shutdown */
+      if ((curr & FD_SHUTDOWN_BIT) > 0) {
+        /* The fd is shutdown. Do nothing */
+      } else if (gpr_atm_no_barrier_cas(state, curr, CLOSURE_NOT_READY)) {
+        /* The cas above was no-barrier since the state is being transitioned to
+           CLOSURE_NOT_READY; notify_on and set_shutdown do not schedule any
+           closures when transitioning out of CLOSURE_NO_READY state (i.e there
+           is no other code that needs to 'happen-after' this) */
+
+        grpc_closure_sched(exec_ctx, (grpc_closure *)curr, GRPC_ERROR_NONE);
+      }
+      /* else the state changed again (only possible by either a racing
+         set_ready or set_shutdown functions. In both these cases, the closure
+         would have been scheduled for execution. So we are done here */
+      break;
+    }
   }
 }
 
 static grpc_pollset *fd_get_read_notifier_pollset(grpc_exec_ctx *exec_ctx,
                                                   grpc_fd *fd) {
-  grpc_pollset *notifier = NULL;
-
-  gpr_mu_lock(&fd->po.mu);
-  notifier = fd->read_notifier_pollset;
-  gpr_mu_unlock(&fd->po.mu);
-
-  return notifier;
+  gpr_atm notifier = gpr_atm_acq_load(&fd->read_notifier_pollset);
+  return (grpc_pollset *)notifier;
 }
 
 static bool fd_is_shutdown(grpc_fd *fd) {
-  gpr_mu_lock(&fd->po.mu);
-  const bool r = fd->shutdown;
-  gpr_mu_unlock(&fd->po.mu);
-  return r;
+  grpc_error *err = (grpc_error *)gpr_atm_acq_load(&fd->shutdown_error);
+  return (((intptr_t)err & FD_SHUTDOWN_BIT) > 0);
 }
 
 /* Might be called multiple times */
 static void fd_shutdown(grpc_exec_ctx *exec_ctx, grpc_fd *fd, grpc_error *why) {
-  gpr_mu_lock(&fd->po.mu);
-  /* Do the actual shutdown only once */
-  if (!fd->shutdown) {
-    fd->shutdown = true;
-    fd->shutdown_error = why;
-
+  /* Store the shutdown error ORed with FD_SHUTDOWN_BIT in fd->shutdown_error */
+  if (gpr_atm_rel_cas(&fd->shutdown_error, (gpr_atm)GRPC_ERROR_NONE,
+                      (gpr_atm)why | FD_SHUTDOWN_BIT)) {
     shutdown(fd->fd, SHUT_RDWR);
-    /* Flush any pending read and write closures. Since fd->shutdown is 'true'
-       at this point, the closures would be called with 'success = false' */
-    set_ready_locked(exec_ctx, fd, &fd->read_closure);
-    set_ready_locked(exec_ctx, fd, &fd->write_closure);
+
+    set_shutdown(exec_ctx, fd, &fd->read_closure, why);
+    set_shutdown(exec_ctx, fd, &fd->write_closure, why);
   } else {
+    /* Shutdown already called */
     GRPC_ERROR_UNREF(why);
   }
-  gpr_mu_unlock(&fd->po.mu);
 }
 
 static void fd_notify_on_read(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
                               grpc_closure *closure) {
-  gpr_mu_lock(&fd->po.mu);
-  notify_on_locked(exec_ctx, fd, &fd->read_closure, closure);
-  gpr_mu_unlock(&fd->po.mu);
+  notify_on(exec_ctx, fd, &fd->read_closure, closure);
 }
 
 static void fd_notify_on_write(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
                                grpc_closure *closure) {
-  gpr_mu_lock(&fd->po.mu);
-  notify_on_locked(exec_ctx, fd, &fd->write_closure, closure);
-  gpr_mu_unlock(&fd->po.mu);
+  notify_on(exec_ctx, fd, &fd->write_closure, closure);
 }
 
 static grpc_workqueue *fd_get_workqueue(grpc_fd *fd) {
@@ -1343,18 +1492,19 @@ static int poll_deadline_to_millis_timeout(gpr_timespec deadline,
 
 static void fd_become_readable(grpc_exec_ctx *exec_ctx, grpc_fd *fd,
                                grpc_pollset *notifier) {
-  /* Need the fd->po.mu since we might be racing with fd_notify_on_read */
-  gpr_mu_lock(&fd->po.mu);
-  set_ready_locked(exec_ctx, fd, &fd->read_closure);
-  fd->read_notifier_pollset = notifier;
-  gpr_mu_unlock(&fd->po.mu);
+  set_ready(exec_ctx, fd, &fd->read_closure);
+
+  /* Note, it is possible that fd_become_readable might be called twice with
+     different 'notifier's when an fd becomes readable and it is in two epoll
+     sets (This can happen briefly during polling island merges). In such cases
+     it does not really matter which notifer is set as the read_notifier_pollset
+     (They would both point to the same polling island anyway) */
+  /* Use release store to match with acquire load in fd_get_read_notifier */
+  gpr_atm_rel_store(&fd->read_notifier_pollset, (gpr_atm)notifier);
 }
 
 static void fd_become_writable(grpc_exec_ctx *exec_ctx, grpc_fd *fd) {
-  /* Need the fd->po.mu since we might be racing with fd_notify_on_write */
-  gpr_mu_lock(&fd->po.mu);
-  set_ready_locked(exec_ctx, fd, &fd->write_closure);
-  gpr_mu_unlock(&fd->po.mu);
+  set_ready(exec_ctx, fd, &fd->write_closure);
 }
 
 static void pollset_release_polling_island(grpc_exec_ctx *exec_ctx,
@@ -1405,16 +1555,6 @@ static void pollset_destroy(grpc_pollset *pollset) {
   gpr_mu_destroy(&pollset->po.mu);
 }
 
-static void pollset_reset(grpc_pollset *pollset) {
-  GPR_ASSERT(pollset->shutting_down);
-  GPR_ASSERT(!pollset_has_workers(pollset));
-  pollset->shutting_down = false;
-  pollset->finish_shutdown_called = false;
-  pollset->kicked_without_pollers = false;
-  pollset->shutdown_done = NULL;
-  GPR_ASSERT(pollset->po.pi == NULL);
-}
-
 static bool maybe_do_workqueue_work(grpc_exec_ctx *exec_ctx,
                                     polling_island *pi) {
   if (gpr_mu_trylock(&pi->workqueue_read_mu)) {
@@ -1747,7 +1887,7 @@ retry:
               (void *)pi_new, FD_FROM_PO(item)->fd, poll_obj_string(bag_type),
               (void *)bag);
           /* No need to lock 'pi_new' here since this is a new polling island
-            * and no one has a reference to it yet */
+             and no one has a reference to it yet */
           polling_island_remove_all_fds_locked(pi_new, true, &error);
 
           /* Ref and unref so that the polling island gets deleted during unref
@@ -1852,13 +1992,12 @@ static grpc_pollset_set *pollset_set_create(void) {
   return pss;
 }
 
-static void pollset_set_destroy(grpc_pollset_set *pss) {
+static void pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                                grpc_pollset_set *pss) {
   gpr_mu_destroy(&pss->po.mu);
 
   if (pss->po.pi != NULL) {
-    grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-    PI_UNREF(&exec_ctx, pss->po.pi, "pss_destroy");
-    grpc_exec_ctx_finish(&exec_ctx);
+    PI_UNREF(exec_ctx, pss->po.pi, "pss_destroy");
   }
 
   gpr_free(pss);
@@ -1958,7 +2097,6 @@ static const grpc_event_engine_vtable vtable = {
 
     .pollset_init = pollset_init,
     .pollset_shutdown = pollset_shutdown,
-    .pollset_reset = pollset_reset,
     .pollset_destroy = pollset_destroy,
     .pollset_work = pollset_work,
     .pollset_kick = pollset_kick,
diff --git a/src/core/lib/iomgr/ev_poll_posix.c b/src/core/lib/iomgr/ev_poll_posix.c
index ca12932219..c03fadaebb 100644
--- a/src/core/lib/iomgr/ev_poll_posix.c
+++ b/src/core/lib/iomgr/ev_poll_posix.c
@@ -149,7 +149,7 @@ static void fd_end_poll(grpc_exec_ctx *exec_ctx, grpc_fd_watcher *rec,
 static bool fd_is_orphaned(grpc_fd *fd);
 
 /* Reference counting for fds */
-/*#define GRPC_FD_REF_COUNT_DEBUG*/
+//#define GRPC_FD_REF_COUNT_DEBUG
 #ifdef GRPC_FD_REF_COUNT_DEBUG
 static void fd_ref(grpc_fd *fd, const char *reason, const char *file, int line);
 static void fd_unref(grpc_fd *fd, const char *reason, const char *file,
@@ -191,6 +191,7 @@ struct grpc_pollset {
   int kicked_without_pollers;
   grpc_closure *shutdown_done;
   grpc_closure_list idle_jobs;
+  int pollset_set_count;
   /* all polled fds */
   size_t fd_count;
   size_t fd_capacity;
@@ -228,7 +229,7 @@ static grpc_error *pollset_kick_ext(grpc_pollset *p,
 
 /* Return 1 if the pollset has active threads in pollset_work (pollset must
  * be locked) */
-static int pollset_has_workers(grpc_pollset *pollset);
+static bool pollset_has_workers(grpc_pollset *pollset);
 
 /*******************************************************************************
  * pollset_set definitions
@@ -282,8 +283,8 @@ cv_fd_table g_cvfds;
 static void ref_by(grpc_fd *fd, int n, const char *reason, const char *file,
                    int line) {
   gpr_log(GPR_DEBUG, "FD %d %p   ref %d %d -> %d [%s; %s:%d]", fd->fd, fd, n,
-          gpr_atm_no_barrier_load(&fd->refst),
-          gpr_atm_no_barrier_load(&fd->refst) + n, reason, file, line);
+          (int)gpr_atm_no_barrier_load(&fd->refst),
+          (int)gpr_atm_no_barrier_load(&fd->refst) + n, reason, file, line);
 #else
 #define REF_BY(fd, n, reason) ref_by(fd, n)
 #define UNREF_BY(fd, n, reason) unref_by(fd, n)
@@ -297,8 +298,8 @@ static void unref_by(grpc_fd *fd, int n, const char *reason, const char *file,
                      int line) {
   gpr_atm old;
   gpr_log(GPR_DEBUG, "FD %d %p unref %d %d -> %d [%s; %s:%d]", fd->fd, fd, n,
-          gpr_atm_no_barrier_load(&fd->refst),
-          gpr_atm_no_barrier_load(&fd->refst) - n, reason, file, line);
+          (int)gpr_atm_no_barrier_load(&fd->refst),
+          (int)gpr_atm_no_barrier_load(&fd->refst) - n, reason, file, line);
 #else
 static void unref_by(grpc_fd *fd, int n) {
   gpr_atm old;
@@ -658,10 +659,18 @@ static void remove_worker(grpc_pollset *p, grpc_pollset_worker *worker) {
   worker->next->prev = worker->prev;
 }
 
-static int pollset_has_workers(grpc_pollset *p) {
+static bool pollset_has_workers(grpc_pollset *p) {
   return p->root_worker.next != &p->root_worker;
 }
 
+static bool pollset_in_pollset_sets(grpc_pollset *p) {
+  return p->pollset_set_count;
+}
+
+static bool pollset_has_observers(grpc_pollset *p) {
+  return pollset_has_workers(p) || pollset_in_pollset_sets(p);
+}
+
 static grpc_pollset_worker *pop_front_worker(grpc_pollset *p) {
   if (pollset_has_workers(p)) {
     grpc_pollset_worker *w = p->root_worker.next;
@@ -800,6 +809,7 @@ static void pollset_init(grpc_pollset *pollset, gpr_mu **mu) {
   pollset->fd_count = 0;
   pollset->fd_capacity = 0;
   pollset->fds = NULL;
+  pollset->pollset_set_count = 0;
 }
 
 static void pollset_destroy(grpc_pollset *pollset) {
@@ -815,16 +825,6 @@ static void pollset_destroy(grpc_pollset *pollset) {
   gpr_mu_destroy(&pollset->mu);
 }
 
-static void pollset_reset(grpc_pollset *pollset) {
-  GPR_ASSERT(pollset->shutting_down);
-  GPR_ASSERT(!pollset_has_workers(pollset));
-  GPR_ASSERT(pollset->idle_jobs.head == pollset->idle_jobs.tail);
-  GPR_ASSERT(pollset->fd_count == 0);
-  pollset->shutting_down = 0;
-  pollset->called_shutdown = 0;
-  pollset->kicked_without_pollers = 0;
-}
-
 static void pollset_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                            grpc_fd *fd) {
   gpr_mu_lock(&pollset->mu);
@@ -1071,7 +1071,7 @@ static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
   if (pollset->shutting_down) {
     if (pollset_has_workers(pollset)) {
       pollset_kick(pollset, NULL);
-    } else if (!pollset->called_shutdown) {
+    } else if (!pollset->called_shutdown && !pollset_has_observers(pollset)) {
       pollset->called_shutdown = 1;
       gpr_mu_unlock(&pollset->mu);
       finish_shutdown(exec_ctx, pollset);
@@ -1103,7 +1103,7 @@ static void pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
   if (!pollset_has_workers(pollset)) {
     grpc_closure_list_sched(exec_ctx, &pollset->idle_jobs);
   }
-  if (!pollset->called_shutdown && !pollset_has_workers(pollset)) {
+  if (!pollset->called_shutdown && !pollset_has_observers(pollset)) {
     pollset->called_shutdown = 1;
     finish_shutdown(exec_ctx, pollset);
   }
@@ -1137,12 +1137,27 @@ static grpc_pollset_set *pollset_set_create(void) {
   return pollset_set;
 }
 
-static void pollset_set_destroy(grpc_pollset_set *pollset_set) {
+static void pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                                grpc_pollset_set *pollset_set) {
   size_t i;
   gpr_mu_destroy(&pollset_set->mu);
   for (i = 0; i < pollset_set->fd_count; i++) {
     GRPC_FD_UNREF(pollset_set->fds[i], "pollset_set");
   }
+  for (i = 0; i < pollset_set->pollset_count; i++) {
+    grpc_pollset *pollset = pollset_set->pollsets[i];
+    gpr_mu_lock(&pollset->mu);
+    pollset->pollset_set_count--;
+    /* check shutdown */
+    if (pollset->shutting_down && !pollset->called_shutdown &&
+        !pollset_has_observers(pollset)) {
+      pollset->called_shutdown = 1;
+      gpr_mu_unlock(&pollset->mu);
+      finish_shutdown(exec_ctx, pollset);
+    } else {
+      gpr_mu_unlock(&pollset->mu);
+    }
+  }
   gpr_free(pollset_set->pollsets);
   gpr_free(pollset_set->pollset_sets);
   gpr_free(pollset_set->fds);
@@ -1153,6 +1168,9 @@ static void pollset_set_add_pollset(grpc_exec_ctx *exec_ctx,
                                     grpc_pollset_set *pollset_set,
                                     grpc_pollset *pollset) {
   size_t i, j;
+  gpr_mu_lock(&pollset->mu);
+  pollset->pollset_set_count++;
+  gpr_mu_unlock(&pollset->mu);
   gpr_mu_lock(&pollset_set->mu);
   if (pollset_set->pollset_count == pollset_set->pollset_capacity) {
     pollset_set->pollset_capacity =
@@ -1188,6 +1206,17 @@ static void pollset_set_del_pollset(grpc_exec_ctx *exec_ctx,
     }
   }
   gpr_mu_unlock(&pollset_set->mu);
+  gpr_mu_lock(&pollset->mu);
+  pollset->pollset_set_count--;
+  /* check shutdown */
+  if (pollset->shutting_down && !pollset->called_shutdown &&
+      !pollset_has_observers(pollset)) {
+    pollset->called_shutdown = 1;
+    gpr_mu_unlock(&pollset->mu);
+    finish_shutdown(exec_ctx, pollset);
+  } else {
+    gpr_mu_unlock(&pollset->mu);
+  }
 }
 
 static void pollset_set_add_pollset_set(grpc_exec_ctx *exec_ctx,
@@ -1514,7 +1543,6 @@ static const grpc_event_engine_vtable vtable = {
 
     .pollset_init = pollset_init,
     .pollset_shutdown = pollset_shutdown,
-    .pollset_reset = pollset_reset,
     .pollset_destroy = pollset_destroy,
     .pollset_work = pollset_work,
     .pollset_kick = pollset_kick,
diff --git a/src/core/lib/iomgr/ev_posix.c b/src/core/lib/iomgr/ev_posix.c
index 5bb55631d6..b5be5504b9 100644
--- a/src/core/lib/iomgr/ev_posix.c
+++ b/src/core/lib/iomgr/ev_posix.c
@@ -191,10 +191,6 @@ void grpc_pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
   g_event_engine->pollset_shutdown(exec_ctx, pollset, closure);
 }
 
-void grpc_pollset_reset(grpc_pollset *pollset) {
-  g_event_engine->pollset_reset(pollset);
-}
-
 void grpc_pollset_destroy(grpc_pollset *pollset) {
   g_event_engine->pollset_destroy(pollset);
 }
@@ -219,8 +215,9 @@ grpc_pollset_set *grpc_pollset_set_create(void) {
   return g_event_engine->pollset_set_create();
 }
 
-void grpc_pollset_set_destroy(grpc_pollset_set *pollset_set) {
-  g_event_engine->pollset_set_destroy(pollset_set);
+void grpc_pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                              grpc_pollset_set *pollset_set) {
+  g_event_engine->pollset_set_destroy(exec_ctx, pollset_set);
 }
 
 void grpc_pollset_set_add_pollset(grpc_exec_ctx *exec_ctx,
diff --git a/src/core/lib/iomgr/ev_posix.h b/src/core/lib/iomgr/ev_posix.h
index a589efdeec..1a9e5c115a 100644
--- a/src/core/lib/iomgr/ev_posix.h
+++ b/src/core/lib/iomgr/ev_posix.h
@@ -64,7 +64,6 @@ typedef struct grpc_event_engine_vtable {
   void (*pollset_init)(grpc_pollset *pollset, gpr_mu **mu);
   void (*pollset_shutdown)(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                            grpc_closure *closure);
-  void (*pollset_reset)(grpc_pollset *pollset);
   void (*pollset_destroy)(grpc_pollset *pollset);
   grpc_error *(*pollset_work)(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                               grpc_pollset_worker **worker, gpr_timespec now,
@@ -75,7 +74,8 @@ typedef struct grpc_event_engine_vtable {
                          struct grpc_fd *fd);
 
   grpc_pollset_set *(*pollset_set_create)(void);
-  void (*pollset_set_destroy)(grpc_pollset_set *pollset_set);
+  void (*pollset_set_destroy)(grpc_exec_ctx *exec_ctx,
+                              grpc_pollset_set *pollset_set);
   void (*pollset_set_add_pollset)(grpc_exec_ctx *exec_ctx,
                                   grpc_pollset_set *pollset_set,
                                   grpc_pollset *pollset);
diff --git a/src/core/lib/iomgr/network_status_tracker.c b/src/core/lib/iomgr/network_status_tracker.c
index 1601a39002..4104bf927a 100644
--- a/src/core/lib/iomgr/network_status_tracker.c
+++ b/src/core/lib/iomgr/network_status_tracker.c
@@ -31,95 +31,18 @@
  *
  */
 
-#include <grpc/support/alloc.h>
-#include <grpc/support/log.h>
 #include "src/core/lib/iomgr/endpoint.h"
 
-typedef struct endpoint_ll_node {
-  grpc_endpoint *ep;
-  struct endpoint_ll_node *next;
-} endpoint_ll_node;
-
-static endpoint_ll_node *head = NULL;
-static gpr_mu g_endpoint_mutex;
-
-void grpc_network_status_shutdown(void) {
-  if (head != NULL) {
-    gpr_log(GPR_ERROR,
-            "Memory leaked as not all network endpoints were shut down");
-  }
-  gpr_mu_destroy(&g_endpoint_mutex);
-}
+void grpc_network_status_shutdown(void) {}
 
 void grpc_network_status_init(void) {
-  gpr_mu_init(&g_endpoint_mutex);
   // TODO(makarandd): Install callback with OS to monitor network status.
 }
 
-void grpc_destroy_network_status_monitor() {
-  for (endpoint_ll_node *curr = head; curr != NULL;) {
-    endpoint_ll_node *next = curr->next;
-    gpr_free(curr);
-    curr = next;
-  }
-  gpr_mu_destroy(&g_endpoint_mutex);
-}
-
-void grpc_network_status_register_endpoint(grpc_endpoint *ep) {
-  gpr_mu_lock(&g_endpoint_mutex);
-  if (head == NULL) {
-    head = (endpoint_ll_node *)gpr_malloc(sizeof(endpoint_ll_node));
-    head->ep = ep;
-    head->next = NULL;
-  } else {
-    endpoint_ll_node *prev_head = head;
-    head = (endpoint_ll_node *)gpr_malloc(sizeof(endpoint_ll_node));
-    head->ep = ep;
-    head->next = prev_head;
-  }
-  gpr_mu_unlock(&g_endpoint_mutex);
-}
+void grpc_destroy_network_status_monitor() {}
 
-void grpc_network_status_unregister_endpoint(grpc_endpoint *ep) {
-  gpr_mu_lock(&g_endpoint_mutex);
-  GPR_ASSERT(head);
-  bool found = false;
-  endpoint_ll_node *prev = head;
-  // if we're unregistering the head, just move head to the next
-  if (ep == head->ep) {
-    head = head->next;
-    gpr_free(prev);
-    found = true;
-  } else {
-    for (endpoint_ll_node *curr = head->next; curr != NULL; curr = curr->next) {
-      if (ep == curr->ep) {
-        prev->next = curr->next;
-        gpr_free(curr);
-        found = true;
-        break;
-      }
-      prev = curr;
-    }
-  }
-  gpr_mu_unlock(&g_endpoint_mutex);
-  GPR_ASSERT(found);
-}
+void grpc_network_status_register_endpoint(grpc_endpoint *ep) { (void)ep; }
 
-// Walk the linked-list from head and execute shutdown. It is possible that
-// other threads might be in the process of shutdown as well, but that has
-// no side effect since endpoint shutdown is idempotent.
-void grpc_network_status_shutdown_all_endpoints() {
-  gpr_mu_lock(&g_endpoint_mutex);
-  if (head == NULL) {
-    gpr_mu_unlock(&g_endpoint_mutex);
-    return;
-  }
-  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+void grpc_network_status_unregister_endpoint(grpc_endpoint *ep) { (void)ep; }
 
-  for (endpoint_ll_node *curr = head; curr != NULL; curr = curr->next) {
-    curr->ep->vtable->shutdown(&exec_ctx, curr->ep,
-                               GRPC_ERROR_CREATE("Network unavailable"));
-  }
-  gpr_mu_unlock(&g_endpoint_mutex);
-  grpc_exec_ctx_finish(&exec_ctx);
-}
+void grpc_network_status_shutdown_all_endpoints() {}
diff --git a/src/core/lib/iomgr/pollset.h b/src/core/lib/iomgr/pollset.h
index 8d9edc8406..c4b62a2790 100644
--- a/src/core/lib/iomgr/pollset.h
+++ b/src/core/lib/iomgr/pollset.h
@@ -58,9 +58,6 @@ void grpc_pollset_init(grpc_pollset *pollset, gpr_mu **mu);
  * pollset's mutex must be held */
 void grpc_pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                            grpc_closure *closure);
-/** Reset the pollset to its initial state (perhaps with some cached objects);
- *  must have been previously shutdown */
-void grpc_pollset_reset(grpc_pollset *pollset);
 void grpc_pollset_destroy(grpc_pollset *pollset);
 
 /* Do some work on a pollset.
diff --git a/src/core/lib/iomgr/pollset_set.h b/src/core/lib/iomgr/pollset_set.h
index 34bb728c41..d11801d63b 100644
--- a/src/core/lib/iomgr/pollset_set.h
+++ b/src/core/lib/iomgr/pollset_set.h
@@ -44,7 +44,8 @@
 typedef struct grpc_pollset_set grpc_pollset_set;
 
 grpc_pollset_set *grpc_pollset_set_create(void);
-void grpc_pollset_set_destroy(grpc_pollset_set *pollset_set);
+void grpc_pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                              grpc_pollset_set *pollset_set);
 void grpc_pollset_set_add_pollset(grpc_exec_ctx *exec_ctx,
                                   grpc_pollset_set *pollset_set,
                                   grpc_pollset *pollset);
diff --git a/src/core/lib/iomgr/pollset_set_uv.c b/src/core/lib/iomgr/pollset_set_uv.c
index e5ef8b29e0..836cfee4ef 100644
--- a/src/core/lib/iomgr/pollset_set_uv.c
+++ b/src/core/lib/iomgr/pollset_set_uv.c
@@ -41,7 +41,8 @@ grpc_pollset_set* grpc_pollset_set_create(void) {
   return (grpc_pollset_set*)((intptr_t)0xdeafbeef);
 }
 
-void grpc_pollset_set_destroy(grpc_pollset_set* pollset_set) {}
+void grpc_pollset_set_destroy(grpc_exec_ctx* exec_ctx,
+                              grpc_pollset_set* pollset_set) {}
 
 void grpc_pollset_set_add_pollset(grpc_exec_ctx* exec_ctx,
                                   grpc_pollset_set* pollset_set,
diff --git a/src/core/lib/iomgr/pollset_set_windows.c b/src/core/lib/iomgr/pollset_set_windows.c
index 645650db9b..ae18c8a3ce 100644
--- a/src/core/lib/iomgr/pollset_set_windows.c
+++ b/src/core/lib/iomgr/pollset_set_windows.c
@@ -42,7 +42,8 @@ grpc_pollset_set* grpc_pollset_set_create(void) {
   return (grpc_pollset_set*)((intptr_t)0xdeafbeef);
 }
 
-void grpc_pollset_set_destroy(grpc_pollset_set* pollset_set) {}
+void grpc_pollset_set_destroy(grpc_exec_ctx* exec_ctx,
+                              grpc_pollset_set* pollset_set) {}
 
 void grpc_pollset_set_add_pollset(grpc_exec_ctx* exec_ctx,
                                   grpc_pollset_set* pollset_set,
diff --git a/src/core/lib/iomgr/pollset_uv.c b/src/core/lib/iomgr/pollset_uv.c
index ed3edeee94..5847771108 100644
--- a/src/core/lib/iomgr/pollset_uv.c
+++ b/src/core/lib/iomgr/pollset_uv.c
@@ -97,11 +97,6 @@ void grpc_pollset_destroy(grpc_pollset *pollset) {
   }
 }
 
-void grpc_pollset_reset(grpc_pollset *pollset) {
-  GPR_ASSERT(pollset->shutting_down);
-  pollset->shutting_down = 0;
-}
-
 static void timer_run_cb(uv_timer_t *timer) {}
 
 grpc_error *grpc_pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
diff --git a/src/core/lib/iomgr/pollset_windows.c b/src/core/lib/iomgr/pollset_windows.c
index 2a45e708df..9be73a7ce8 100644
--- a/src/core/lib/iomgr/pollset_windows.c
+++ b/src/core/lib/iomgr/pollset_windows.c
@@ -117,16 +117,6 @@ void grpc_pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
 
 void grpc_pollset_destroy(grpc_pollset *pollset) {}
 
-void grpc_pollset_reset(grpc_pollset *pollset) {
-  GPR_ASSERT(pollset->shutting_down);
-  GPR_ASSERT(
-      !has_workers(&pollset->root_worker, GRPC_POLLSET_WORKER_LINK_POLLSET));
-  pollset->shutting_down = 0;
-  pollset->is_iocp_worker = 0;
-  pollset->kicked_without_pollers = 0;
-  pollset->on_shutdown = NULL;
-}
-
 grpc_error *grpc_pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                               grpc_pollset_worker **worker_hdl,
                               gpr_timespec now, gpr_timespec deadline) {
diff --git a/src/core/lib/iomgr/resolve_address_uv.c b/src/core/lib/iomgr/resolve_address_uv.c
index 9b5f3209f0..79ff910738 100644
--- a/src/core/lib/iomgr/resolve_address_uv.c
+++ b/src/core/lib/iomgr/resolve_address_uv.c
@@ -113,14 +113,15 @@ static grpc_error *try_split_host_port(const char *name,
   /* parse name, splitting it into host and port parts */
   grpc_error *error;
   gpr_split_host_port(name, host, port);
-  if (host == NULL) {
+  if (*host == NULL) {
     char *msg;
     gpr_asprintf(&msg, "unparseable host:port: '%s'", name);
     error = GRPC_ERROR_CREATE(msg);
     gpr_free(msg);
     return error;
   }
-  if (port == NULL) {
+  if (*port == NULL) {
+    // TODO(murgatroid99): add tests for this case
     if (default_port == NULL) {
       char *msg;
       gpr_asprintf(&msg, "no port in name '%s'", name);
diff --git a/src/core/lib/iomgr/socket_utils_windows.c b/src/core/lib/iomgr/socket_utils_windows.c
index 628ad4a45b..5bbe8fa34c 100644
--- a/src/core/lib/iomgr/socket_utils_windows.c
+++ b/src/core/lib/iomgr/socket_utils_windows.c
@@ -41,8 +41,12 @@
 #include <grpc/support/log.h>
 
 const char *grpc_inet_ntop(int af, const void *src, char *dst, size_t size) {
+#ifdef GPR_WIN_INET_NTOP
+  return inet_ntop(af, src, dst, size);
+#else
   /* Windows InetNtopA wants a mutable ip pointer */
   return InetNtopA(af, (void *)src, dst, size);
+#endif /* GPR_WIN_INET_NTOP */
 }
 
 #endif /* GRPC_WINDOWS_SOCKETUTILS */
diff --git a/src/core/lib/iomgr/tcp_client_uv.c b/src/core/lib/iomgr/tcp_client_uv.c
index 5225a5402b..3de0795187 100644
--- a/src/core/lib/iomgr/tcp_client_uv.c
+++ b/src/core/lib/iomgr/tcp_client_uv.c
@@ -46,6 +46,8 @@
 #include "src/core/lib/iomgr/tcp_uv.h"
 #include "src/core/lib/iomgr/timer.h"
 
+extern int grpc_tcp_trace;
+
 typedef struct grpc_uv_tcp_connect {
   uv_connect_t connect_req;
   grpc_timer alarm;
@@ -70,6 +72,12 @@ static void uv_tc_on_alarm(grpc_exec_ctx *exec_ctx, void *acp,
                            grpc_error *error) {
   int done;
   grpc_uv_tcp_connect *connect = acp;
+  if (grpc_tcp_trace) {
+    const char *str = grpc_error_string(error);
+    gpr_log(GPR_DEBUG, "CLIENT_CONNECT: %s: on_alarm: error=%s",
+            connect->addr_name, str);
+    grpc_error_free_string(str);
+  }
   if (error == GRPC_ERROR_NONE) {
     /* error == NONE implies that the timer ran out, and wasn't cancelled. If
        it was cancelled, then the handler that cancelled it also should close
@@ -145,6 +153,12 @@ static void tcp_client_connect_impl(grpc_exec_ctx *exec_ctx,
   connect->resource_quota = resource_quota;
   uv_tcp_init(uv_default_loop(), connect->tcp_handle);
   connect->connect_req.data = connect;
+
+  if (grpc_tcp_trace) {
+    gpr_log(GPR_DEBUG, "CLIENT_CONNECT: %s: asynchronously connecting",
+            connect->addr_name);
+  }
+
   // TODO(murgatroid99): figure out what the return value here means
   uv_tcp_connect(&connect->connect_req, connect->tcp_handle,
                  (const struct sockaddr *)resolved_addr->addr,
diff --git a/src/core/lib/iomgr/tcp_uv.c b/src/core/lib/iomgr/tcp_uv.c
index 5fb398c50b..5541c62068 100644
--- a/src/core/lib/iomgr/tcp_uv.c
+++ b/src/core/lib/iomgr/tcp_uv.c
@@ -79,8 +79,6 @@ typedef struct {
   grpc_pollset *pollset;
 } grpc_tcp;
 
-static void uv_close_callback(uv_handle_t *handle) { gpr_free(handle); }
-
 static void tcp_free(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
   grpc_resource_user_unref(exec_ctx, tcp->resource_user);
   gpr_free(tcp);
@@ -119,6 +117,13 @@ static void tcp_unref(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
 static void tcp_ref(grpc_tcp *tcp) { gpr_ref(&tcp->refcount); }
 #endif
 
+static void uv_close_callback(uv_handle_t *handle) {
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_tcp *tcp = handle->data;
+  TCP_UNREF(&exec_ctx, tcp, "destroy");
+  grpc_exec_ctx_finish(&exec_ctx);
+}
+
 static void alloc_uv_buf(uv_handle_t *handle, size_t suggested_size,
                          uv_buf_t *buf) {
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
@@ -313,7 +318,6 @@ static void uv_destroy(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep) {
   grpc_network_status_unregister_endpoint(ep);
   grpc_tcp *tcp = (grpc_tcp *)ep;
   uv_close((uv_handle_t *)tcp->handle, uv_close_callback);
-  TCP_UNREF(exec_ctx, tcp, "destroy");
 }
 
 static char *uv_get_peer(grpc_endpoint *ep) {
diff --git a/src/core/lib/iomgr/timer_generic.c b/src/core/lib/iomgr/timer_generic.c
index 40c8351472..6d638bcbaa 100644
--- a/src/core/lib/iomgr/timer_generic.c
+++ b/src/core/lib/iomgr/timer_generic.c
@@ -121,12 +121,6 @@ void grpc_timer_list_shutdown(grpc_exec_ctx *exec_ctx) {
   g_initialized = false;
 }
 
-/* This is a cheap, but good enough, pointer hash for sharding the tasks: */
-static size_t shard_idx(const grpc_timer *info) {
-  size_t x = (size_t)info;
-  return ((x >> 4) ^ (x >> 9) ^ (x >> 14)) & (NUM_SHARDS - 1);
-}
-
 static double ts_to_dbl(gpr_timespec ts) {
   return (double)ts.tv_sec + 1e-9 * ts.tv_nsec;
 }
@@ -181,30 +175,30 @@ void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
                      gpr_timespec deadline, grpc_closure *closure,
                      gpr_timespec now) {
   int is_first_timer = 0;
-  shard_type *shard = &g_shards[shard_idx(timer)];
+  shard_type *shard = &g_shards[GPR_HASH_POINTER(timer, NUM_SHARDS)];
   GPR_ASSERT(deadline.clock_type == g_clock_type);
   GPR_ASSERT(now.clock_type == g_clock_type);
   timer->closure = closure;
   timer->deadline = deadline;
-  timer->triggered = 0;
 
   if (!g_initialized) {
-    timer->triggered = 1;
+    timer->pending = false;
     grpc_closure_sched(
         exec_ctx, timer->closure,
         GRPC_ERROR_CREATE("Attempt to create timer before initialization"));
     return;
   }
 
+  gpr_mu_lock(&shard->mu);
+  timer->pending = true;
   if (gpr_time_cmp(deadline, now) <= 0) {
-    timer->triggered = 1;
+    timer->pending = false;
     grpc_closure_sched(exec_ctx, timer->closure, GRPC_ERROR_NONE);
+    gpr_mu_unlock(&shard->mu);
+    /* early out */
     return;
   }
 
-  /* TODO(ctiller): check deadline expired */
-
-  gpr_mu_lock(&shard->mu);
   grpc_time_averaged_stats_add_sample(&shard->stats,
                                       ts_to_dbl(gpr_time_sub(deadline, now)));
   if (gpr_time_cmp(deadline, shard->queue_deadline_cap) < 0) {
@@ -247,11 +241,11 @@ void grpc_timer_cancel(grpc_exec_ctx *exec_ctx, grpc_timer *timer) {
     return;
   }
 
-  shard_type *shard = &g_shards[shard_idx(timer)];
+  shard_type *shard = &g_shards[GPR_HASH_POINTER(timer, NUM_SHARDS)];
   gpr_mu_lock(&shard->mu);
-  if (!timer->triggered) {
+  if (timer->pending) {
     grpc_closure_sched(exec_ctx, timer->closure, GRPC_ERROR_CANCELLED);
-    timer->triggered = 1;
+    timer->pending = false;
     if (timer->heap_index == INVALID_HEAP_INDEX) {
       list_remove(timer);
     } else {
@@ -302,7 +296,7 @@ static grpc_timer *pop_one(shard_type *shard, gpr_timespec now) {
     }
     timer = grpc_timer_heap_top(&shard->heap);
     if (gpr_time_cmp(timer->deadline, now) > 0) return NULL;
-    timer->triggered = 1;
+    timer->pending = false;
     grpc_timer_heap_pop(&shard->heap);
     return timer;
   }
diff --git a/src/core/lib/iomgr/timer_generic.h b/src/core/lib/iomgr/timer_generic.h
index 9d901c7e68..1608dce9fb 100644
--- a/src/core/lib/iomgr/timer_generic.h
+++ b/src/core/lib/iomgr/timer_generic.h
@@ -40,7 +40,7 @@
 struct grpc_timer {
   gpr_timespec deadline;
   uint32_t heap_index; /* INVALID_HEAP_INDEX if not in heap */
-  int triggered;
+  bool pending;
   struct grpc_timer *next;
   struct grpc_timer *prev;
   grpc_closure *closure;
diff --git a/src/core/lib/iomgr/timer_uv.c b/src/core/lib/iomgr/timer_uv.c
index fa2cdee964..f28a14405d 100644
--- a/src/core/lib/iomgr/timer_uv.c
+++ b/src/core/lib/iomgr/timer_uv.c
@@ -53,8 +53,8 @@ static void stop_uv_timer(uv_timer_t *handle) {
 void run_expired_timer(uv_timer_t *handle) {
   grpc_timer *timer = (grpc_timer *)handle->data;
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-  GPR_ASSERT(!timer->triggered);
-  timer->triggered = 1;
+  GPR_ASSERT(timer->pending);
+  timer->pending = 0;
   grpc_closure_sched(&exec_ctx, timer->closure, GRPC_ERROR_NONE);
   stop_uv_timer(handle);
   grpc_exec_ctx_finish(&exec_ctx);
@@ -67,11 +67,11 @@ void grpc_timer_init(grpc_exec_ctx *exec_ctx, grpc_timer *timer,
   uv_timer_t *uv_timer;
   timer->closure = closure;
   if (gpr_time_cmp(deadline, now) <= 0) {
-    timer->triggered = 1;
+    timer->pending = 0;
     grpc_closure_sched(exec_ctx, timer->closure, GRPC_ERROR_NONE);
     return;
   }
-  timer->triggered = 0;
+  timer->pending = 1;
   timeout = (uint64_t)gpr_time_to_millis(gpr_time_sub(deadline, now));
   uv_timer = gpr_malloc(sizeof(uv_timer_t));
   uv_timer_init(uv_default_loop(), uv_timer);
@@ -81,8 +81,8 @@ 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;
+  if (timer->pending) {
+    timer->pending = 0;
     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/timer_uv.h b/src/core/lib/iomgr/timer_uv.h
index 13cf8bd4fa..9870cd4a5c 100644
--- a/src/core/lib/iomgr/timer_uv.h
+++ b/src/core/lib/iomgr/timer_uv.h
@@ -41,7 +41,7 @@ struct grpc_timer {
   /* This is actually a uv_timer_t*, but we want to keep platform-specific
      types out of headers */
   void *uv_timer;
-  int triggered;
+  int pending;
 };
 
 #endif /* GRPC_CORE_LIB_IOMGR_TIMER_UV_H */