Extend ev_posix.* to prepare for the new background poller 'epollbg',

and get rid of the dependency loop on the grpc shutdown path. Make sure
all background closures are complete before shutting down the other grpc
modules.

Avoid using the backup poller in TCP endpoints if using the background
poller.

14 files changed, 73 insertions, 7 deletions

diff --git a/src/core/lib/iomgr/ev_epoll1_linux.cc b/src/core/lib/iomgr/ev_epoll1_linux.cc
index 38571b1957..4b8c891e9b 100644
--- a/src/core/lib/iomgr/ev_epoll1_linux.cc
+++ b/src/core/lib/iomgr/ev_epoll1_linux.cc
@@ -1242,6 +1242,8 @@ static void pollset_set_del_pollset_set(grpc_pollset_set* bag,
  * Event engine binding
  */
 
+static void shutdown_background_closure(void) {}
+
 static void shutdown_engine(void) {
   fd_global_shutdown();
   pollset_global_shutdown();
@@ -1255,6 +1257,7 @@ static void shutdown_engine(void) {
 static const grpc_event_engine_vtable vtable = {
     sizeof(grpc_pollset),
     true,
+    false,
 
     fd_create,
     fd_wrapped_fd,
@@ -1284,6 +1287,7 @@ static const grpc_event_engine_vtable vtable = {
     pollset_set_add_fd,
     pollset_set_del_fd,
 
+    shutdown_background_closure,
     shutdown_engine,
 };
 
diff --git a/src/core/lib/iomgr/ev_epollex_linux.cc b/src/core/lib/iomgr/ev_epollex_linux.cc
index 06a382c556..7a4870db78 100644
--- a/src/core/lib/iomgr/ev_epollex_linux.cc
+++ b/src/core/lib/iomgr/ev_epollex_linux.cc
@@ -1604,6 +1604,8 @@ static void pollset_set_del_pollset_set(grpc_pollset_set* bag,
  * Event engine binding
  */
 
+static void shutdown_background_closure(void) {}
+
 static void shutdown_engine(void) {
   fd_global_shutdown();
   pollset_global_shutdown();
@@ -1612,6 +1614,7 @@ static void shutdown_engine(void) {
 static const grpc_event_engine_vtable vtable = {
     sizeof(grpc_pollset),
     true,
+    false,
 
     fd_create,
     fd_wrapped_fd,
@@ -1641,6 +1644,7 @@ static const grpc_event_engine_vtable vtable = {
     pollset_set_add_fd,
     pollset_set_del_fd,
 
+    shutdown_background_closure,
     shutdown_engine,
 };
 
diff --git a/src/core/lib/iomgr/ev_poll_posix.cc b/src/core/lib/iomgr/ev_poll_posix.cc
index 16562538a6..67cbfbbd02 100644
--- a/src/core/lib/iomgr/ev_poll_posix.cc
+++ b/src/core/lib/iomgr/ev_poll_posix.cc
@@ -1782,6 +1782,8 @@ static void global_cv_fd_table_shutdown() {
  * event engine binding
  */
 
+static void shutdown_background_closure(void) {}
+
 static void shutdown_engine(void) {
   pollset_global_shutdown();
   if (grpc_cv_wakeup_fds_enabled()) {
@@ -1796,6 +1798,7 @@ static void shutdown_engine(void) {
 static const grpc_event_engine_vtable vtable = {
     sizeof(grpc_pollset),
     false,
+    false,
 
     fd_create,
     fd_wrapped_fd,
@@ -1825,6 +1828,7 @@ static const grpc_event_engine_vtable vtable = {
     pollset_set_add_fd,
     pollset_set_del_fd,
 
+    shutdown_background_closure,
     shutdown_engine,
 };
 
diff --git a/src/core/lib/iomgr/ev_posix.cc b/src/core/lib/iomgr/ev_posix.cc
index 8a7dc7b004..c876eb08c5 100644
--- a/src/core/lib/iomgr/ev_posix.cc
+++ b/src/core/lib/iomgr/ev_posix.cc
@@ -244,6 +244,10 @@ bool grpc_event_engine_can_track_errors(void) {
 #endif /* GRPC_LINUX_ERRQUEUE */
 }
 
+bool grpc_event_engine_run_in_background(void) {
+  return g_event_engine->run_in_background;
+}
+
 grpc_fd* grpc_fd_create(int fd, const char* name, bool track_err) {
   GRPC_POLLING_API_TRACE("fd_create(%d, %s, %d)", fd, name, track_err);
   GRPC_FD_TRACE("fd_create(%d, %s, %d)", fd, name, track_err);
@@ -395,4 +399,8 @@ void grpc_pollset_set_del_fd(grpc_pollset_set* pollset_set, grpc_fd* fd) {
   g_event_engine->pollset_set_del_fd(pollset_set, fd);
 }
 
+void grpc_shutdown_background_closure(void) {
+  g_event_engine->shutdown_background_closure();
+}
+
 #endif  // GRPC_POSIX_SOCKET_EV
diff --git a/src/core/lib/iomgr/ev_posix.h b/src/core/lib/iomgr/ev_posix.h
index b8fb8f534b..812c7a0f0f 100644
--- a/src/core/lib/iomgr/ev_posix.h
+++ b/src/core/lib/iomgr/ev_posix.h
@@ -42,6 +42,7 @@ typedef struct grpc_fd grpc_fd;
 typedef struct grpc_event_engine_vtable {
   size_t pollset_size;
   bool can_track_err;
+  bool run_in_background;
 
   grpc_fd* (*fd_create)(int fd, const char* name, bool track_err);
   int (*fd_wrapped_fd)(grpc_fd* fd);
@@ -79,6 +80,7 @@ typedef struct grpc_event_engine_vtable {
   void (*pollset_set_add_fd)(grpc_pollset_set* pollset_set, grpc_fd* fd);
   void (*pollset_set_del_fd)(grpc_pollset_set* pollset_set, grpc_fd* fd);
 
+  void (*shutdown_background_closure)(void);
   void (*shutdown_engine)(void);
 } grpc_event_engine_vtable;
 
@@ -101,6 +103,11 @@ const char* grpc_get_poll_strategy_name();
  */
 bool grpc_event_engine_can_track_errors();
 
+/* Returns true if polling engine runs in the background, false otherwise.
+ * Currently only 'epollbg' runs in the background.
+ */
+bool grpc_event_engine_run_in_background();
+
 /* Create a wrapped file descriptor.
    Requires fd is a non-blocking file descriptor.
    \a track_err if true means that error events would be tracked separately
@@ -174,6 +181,9 @@ void grpc_pollset_add_fd(grpc_pollset* pollset, struct grpc_fd* fd);
 void grpc_pollset_set_add_fd(grpc_pollset_set* pollset_set, grpc_fd* fd);
 void grpc_pollset_set_del_fd(grpc_pollset_set* pollset_set, grpc_fd* fd);
 
+/* Shut down all the closures registered in the background poller. */
+void grpc_shutdown_background_closure();
+
 /* override to allow tests to hook poll() usage */
 typedef int (*grpc_poll_function_type)(struct pollfd*, nfds_t, int);
 extern grpc_poll_function_type grpc_poll_function;
diff --git a/src/core/lib/iomgr/iomgr.cc b/src/core/lib/iomgr/iomgr.cc
index 46afda1774..7d2fa09d08 100644
--- a/src/core/lib/iomgr/iomgr.cc
+++ b/src/core/lib/iomgr/iomgr.cc
@@ -154,6 +154,10 @@ void grpc_iomgr_shutdown() {
   gpr_cv_destroy(&g_rcv);
 }
 
+void grpc_iomgr_shutdown_background_closure() {
+  grpc_iomgr_platform_shutdown_background_closure();
+}
+
 void grpc_iomgr_register_object(grpc_iomgr_object* obj, const char* name) {
   obj->name = gpr_strdup(name);
   gpr_mu_lock(&g_mu);
diff --git a/src/core/lib/iomgr/iomgr.h b/src/core/lib/iomgr/iomgr.h
index 537ef8a6ff..8ea9289e06 100644
--- a/src/core/lib/iomgr/iomgr.h
+++ b/src/core/lib/iomgr/iomgr.h
@@ -35,6 +35,10 @@ void grpc_iomgr_start();
  * exec_ctx. */
 void grpc_iomgr_shutdown();
 
+/** Signals the intention to shutdown all the closures registered in the
+ * background poller. */
+void grpc_iomgr_shutdown_background_closure();
+
 /* Exposed only for testing */
 size_t grpc_iomgr_count_objects_for_testing();
 
diff --git a/src/core/lib/iomgr/iomgr_custom.cc b/src/core/lib/iomgr/iomgr_custom.cc
index d34c8e7cd1..4b112c9097 100644
--- a/src/core/lib/iomgr/iomgr_custom.cc
+++ b/src/core/lib/iomgr/iomgr_custom.cc
@@ -40,9 +40,11 @@ static void iomgr_platform_init(void) {
 }
 static void iomgr_platform_flush(void) {}
 static void iomgr_platform_shutdown(void) { grpc_pollset_global_shutdown(); }
+static void iomgr_platform_shutdown_background_closure(void) {}
 
 static grpc_iomgr_platform_vtable vtable = {
-    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown};
+    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown,
+    iomgr_platform_shutdown_background_closure};
 
 void grpc_custom_iomgr_init(grpc_socket_vtable* socket,
                             grpc_custom_resolver_vtable* resolver,
diff --git a/src/core/lib/iomgr/iomgr_internal.cc b/src/core/lib/iomgr/iomgr_internal.cc
index 32dbabb79d..b6c9211865 100644
--- a/src/core/lib/iomgr/iomgr_internal.cc
+++ b/src/core/lib/iomgr/iomgr_internal.cc
@@ -41,3 +41,7 @@ void grpc_iomgr_platform_init() { iomgr_platform_vtable->init(); }
 void grpc_iomgr_platform_flush() { iomgr_platform_vtable->flush(); }
 
 void grpc_iomgr_platform_shutdown() { iomgr_platform_vtable->shutdown(); }
+
+void grpc_iomgr_platform_shutdown_background_closure() {
+  iomgr_platform_vtable->shutdown_background_closure();
+}
diff --git a/src/core/lib/iomgr/iomgr_internal.h b/src/core/lib/iomgr/iomgr_internal.h
index b011d9c7b1..bca7409907 100644
--- a/src/core/lib/iomgr/iomgr_internal.h
+++ b/src/core/lib/iomgr/iomgr_internal.h
@@ -35,6 +35,7 @@ typedef struct grpc_iomgr_platform_vtable {
   void (*init)(void);
   void (*flush)(void);
   void (*shutdown)(void);
+  void (*shutdown_background_closure)(void);
 } grpc_iomgr_platform_vtable;
 
 void grpc_iomgr_register_object(grpc_iomgr_object* obj, const char* name);
@@ -52,6 +53,9 @@ void grpc_iomgr_platform_flush(void);
 /** tear down all platform specific global iomgr structures */
 void grpc_iomgr_platform_shutdown(void);
 
+/** shut down all the closures registered in the background poller */
+void grpc_iomgr_platform_shutdown_background_closure(void);
+
 bool grpc_iomgr_abort_on_leaks(void);
 
 #endif /* GRPC_CORE_LIB_IOMGR_IOMGR_INTERNAL_H */
diff --git a/src/core/lib/iomgr/iomgr_posix.cc b/src/core/lib/iomgr/iomgr_posix.cc
index ca7334c9a4..9386adf060 100644
--- a/src/core/lib/iomgr/iomgr_posix.cc
+++ b/src/core/lib/iomgr/iomgr_posix.cc
@@ -51,8 +51,13 @@ static void iomgr_platform_shutdown(void) {
   grpc_wakeup_fd_global_destroy();
 }
 
+static void iomgr_platform_shutdown_background_closure(void) {
+  grpc_shutdown_background_closure();
+}
+
 static grpc_iomgr_platform_vtable vtable = {
-    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown};
+    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown,
+    iomgr_platform_shutdown_background_closure};
 
 void grpc_set_default_iomgr_platform() {
   grpc_set_tcp_client_impl(&grpc_posix_tcp_client_vtable);
diff --git a/src/core/lib/iomgr/iomgr_posix_cfstream.cc b/src/core/lib/iomgr/iomgr_posix_cfstream.cc
index 235a9e0712..552ef4309c 100644
--- a/src/core/lib/iomgr/iomgr_posix_cfstream.cc
+++ b/src/core/lib/iomgr/iomgr_posix_cfstream.cc
@@ -54,8 +54,13 @@ static void iomgr_platform_shutdown(void) {
   grpc_wakeup_fd_global_destroy();
 }
 
+static void iomgr_platform_shutdown_background_closure(void) {
+  grpc_shutdown_background_closure();
+}
+
 static grpc_iomgr_platform_vtable vtable = {
-    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown};
+    iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown,
+    iomgr_platform_shutdown_background_closure};
 
 void grpc_set_default_iomgr_platform() {
   char* enable_cfstream = getenv(grpc_cfstream_env_var);
diff --git a/src/core/lib/iomgr/tcp_posix.cc b/src/core/lib/iomgr/tcp_posix.cc
index aa2704ce26..c802fcca75 100644
--- a/src/core/lib/iomgr/tcp_posix.cc
+++ b/src/core/lib/iomgr/tcp_posix.cc
@@ -260,10 +260,17 @@ static void notify_on_write(grpc_tcp* tcp) {
   if (grpc_tcp_trace.enabled()) {
     gpr_log(GPR_INFO, "TCP:%p notify_on_write", tcp);
   }
-  cover_self(tcp);
-  GRPC_CLOSURE_INIT(&tcp->write_done_closure,
-                    tcp_drop_uncovered_then_handle_write, tcp,
-                    grpc_schedule_on_exec_ctx);
+  if (grpc_event_engine_run_in_background()) {
+    // If there is a polling engine always running in the background, there is
+    // no need to run the backup poller.
+    GRPC_CLOSURE_INIT(&tcp->write_done_closure, tcp_handle_write, tcp,
+                      grpc_schedule_on_exec_ctx);
+  } else {
+    cover_self(tcp);
+    GRPC_CLOSURE_INIT(&tcp->write_done_closure,
+                      tcp_drop_uncovered_then_handle_write, tcp,
+                      grpc_schedule_on_exec_ctx);
+  }
   grpc_fd_notify_on_write(tcp->em_fd, &tcp->write_done_closure);
 }
 
diff --git a/src/core/lib/surface/init.cc b/src/core/lib/surface/init.cc
index c6198b8ae7..67cf5d89bf 100644
--- a/src/core/lib/surface/init.cc
+++ b/src/core/lib/surface/init.cc
@@ -161,6 +161,7 @@ void grpc_shutdown(void) {
   if (--g_initializations == 0) {
     {
       grpc_core::ExecCtx exec_ctx(0);
+      grpc_iomgr_shutdown_background_closure();
       {
         grpc_timer_manager_set_threading(
             false);  // shutdown timer_manager thread