Initialize tcp_posix for CFStream when needed (#26530)

src/core/lib/iomgr/iomgr_posix_cfstream.cc

@@ -84,7 +84,43 @@ static grpc_iomgr_platform_vtable apple_vtable = {
     apple_iomgr_platform_is_any_background_poller_thread,
     apple_iomgr_platform_add_closure_to_background_poller};
 
+namespace {
+struct CFStreamEnv {
+  bool enable_cfstream;
+  bool enable_cfstream_run_loop;
+};
+
+// Parses environment variables for CFStream specific settings
+CFStreamEnv ParseEnvForCFStream() {
+  CFStreamEnv env;
+  char* enable_cfstream_str = getenv(grpc_cfstream_env_var);
+  env.enable_cfstream =
+      enable_cfstream_str == nullptr || enable_cfstream_str[0] != '0';
+  char* enable_cfstream_run_loop_str = getenv(grpc_cfstream_run_loop_env_var);
+  // CFStream run-loop is disabled by default. The user has to enable it
+  // explicitly with environment variable.
+  env.enable_cfstream_run_loop = enable_cfstream_run_loop_str != nullptr &&
+                                 enable_cfstream_run_loop_str[0] == '1';
+  return env;
+}
+
+void MaybeInitializeTcpPosix(void) {
+  CFStreamEnv env = ParseEnvForCFStream();
+  if (!env.enable_cfstream || !env.enable_cfstream_run_loop) {
+    grpc_tcp_posix_init();
+  }
+}
+
+void MaybeShutdownTcpPosix(void) {
+  CFStreamEnv env = ParseEnvForCFStream();
+  if (!env.enable_cfstream || !env.enable_cfstream_run_loop) {
+    grpc_tcp_posix_shutdown();
+  }
+}
+}  // namespace
+
 static void iomgr_platform_init(void) {
+  MaybeInitializeTcpPosix();
   grpc_wakeup_fd_global_init();
   grpc_event_engine_init();
 }
@@ -94,6 +130,7 @@ static void iomgr_platform_flush(void) {}
 static void iomgr_platform_shutdown(void) {
   grpc_event_engine_shutdown();
   grpc_wakeup_fd_global_destroy();
+  MaybeShutdownTcpPosix();
 }
 
 static void iomgr_platform_shutdown_background_closure(void) {
@@ -118,22 +155,15 @@ static grpc_iomgr_platform_vtable vtable = {
     iomgr_platform_add_closure_to_background_poller};
 
 void grpc_set_default_iomgr_platform() {
-  char* enable_cfstream_str = getenv(grpc_cfstream_env_var);
-  bool enable_cfstream =
-      enable_cfstream_str == nullptr || enable_cfstream_str[0] != '0';
-  char* enable_cfstream_run_loop_str = getenv(grpc_cfstream_run_loop_env_var);
-  // CFStream run-loop is disabled by default. The user has to enable it
-  // explicitly with environment variable.
-  bool enable_cfstream_run_loop = enable_cfstream_run_loop_str != nullptr &&
-                                  enable_cfstream_run_loop_str[0] == '1';
-  if (!enable_cfstream) {
+  CFStreamEnv env = ParseEnvForCFStream();
+  if (!env.enable_cfstream) {
     // Use POSIX sockets for both client and server
     grpc_set_tcp_client_impl(&grpc_posix_tcp_client_vtable);
     grpc_set_tcp_server_impl(&grpc_posix_tcp_server_vtable);
     grpc_set_pollset_vtable(&grpc_posix_pollset_vtable);
     grpc_set_pollset_set_vtable(&grpc_posix_pollset_set_vtable);
     grpc_set_iomgr_platform_vtable(&vtable);
-  } else if (enable_cfstream && !enable_cfstream_run_loop) {
+  } else if (env.enable_cfstream && !env.enable_cfstream_run_loop) {
     // Use CFStream with dispatch queue for client; use POSIX sockets for server
     grpc_set_tcp_client_impl(&grpc_cfstream_client_vtable);
     grpc_set_tcp_server_impl(&grpc_posix_tcp_server_vtable);