Properly init TLS for callback exec context

src/core/lib/iomgr/exec_ctx.h

@@ -271,6 +271,12 @@ class ApplicationCallbackExecCtx {
     ctx->tail_ = functor;
   }
 
+  /** Global initialization for ApplicationCallbackExecCtx. Called by init. */
+  static void GlobalInit(void) { gpr_tls_init(&callback_exec_ctx_); }
+
+  /** Global shutdown for ApplicationCallbackExecCtx. Called by init. */
+  static void GlobalShutdown(void) { gpr_tls_destroy(&callback_exec_ctx_); }
+
  private:
   grpc_experimental_completion_queue_functor* head_{nullptr};
   grpc_experimental_completion_queue_functor* tail_{nullptr};

src/core/lib/surface/init.cc

@@ -130,6 +130,7 @@ void grpc_init(void) {
     grpc_channel_init_init();
     grpc_core::channelz::ChannelzRegistry::Init();
     grpc_security_pre_init();
+    grpc_core::ApplicationCallbackExecCtx::GlobalInit();
     grpc_core::ExecCtx::GlobalInit();
     grpc_iomgr_init();
     gpr_timers_global_init();
@@ -183,6 +184,7 @@ void grpc_shutdown(void) {
       grpc_core::Fork::GlobalShutdown();
     }
     grpc_core::ExecCtx::GlobalShutdown();
+    grpc_core::ApplicationCallbackExecCtx::GlobalShutdown();
   }
   gpr_mu_unlock(&g_init_mu);
 }