Alarm callback should run on executor

src/cpp/common/alarm.cc

@@ -25,6 +25,7 @@
 #include <grpcpp/impl/grpc_library.h>
 #include <grpcpp/support/time.h>
 #include "src/core/lib/iomgr/exec_ctx.h"
+#include "src/core/lib/iomgr/executor.h"
 #include "src/core/lib/iomgr/timer.h"
 #include "src/core/lib/surface/completion_queue.h"
 
@@ -81,9 +82,16 @@ class AlarmImpl : public ::grpc::internal::CompletionQueueTag {
     Ref();
     GRPC_CLOSURE_INIT(&on_alarm_,
                       [](void* arg, grpc_error* error) {
-                        AlarmImpl* alarm = static_cast<AlarmImpl*>(arg);
-                        alarm->callback_(error == GRPC_ERROR_NONE);
-                        alarm->Unref();
+                        grpc_core::Executor::Run(
+                            GRPC_CLOSURE_CREATE(
+                                [](void* arg, grpc_error* error) {
+                                  AlarmImpl* alarm =
+                                      static_cast<AlarmImpl*>(arg);
+                                  alarm->callback_(error == GRPC_ERROR_NONE);
+                                  alarm->Unref();
+                                },
+                                arg, nullptr),
+                            error);
                       },
                       this, grpc_schedule_on_exec_ctx);
     grpc_timer_init(&timer_, grpc_timespec_to_millis_round_up(deadline),

test/cpp/common/alarm_test.cc

@@ -304,6 +304,26 @@ TEST(AlarmTest, CallbackCancellation) {
       [c] { return c->completed; }));
 }
 
+TEST(AlarmTest, CallbackCancellationLocked) {
+  Alarm alarm;
+
+  auto c = std::make_shared<Completion>();
+  alarm.experimental().Set(
+      std::chrono::system_clock::now() + std::chrono::seconds(10),
+      [c](bool ok) {
+        EXPECT_FALSE(ok);
+        std::lock_guard<std::mutex> l(c->mu);
+        c->completed = true;
+        c->cv.notify_one();
+      });
+  std::unique_lock<std::mutex> l(c->mu);
+  alarm.Cancel();
+
+  EXPECT_TRUE(c->cv.wait_until(
+      l, std::chrono::system_clock::now() + std::chrono::seconds(1),
+      [c] { return c->completed; }));
+}
+
 TEST(AlarmTest, SetDestruction) {
   CompletionQueue cq;
   void* junk = reinterpret_cast<void*>(1618033);