Add callback-based alarms

include/grpcpp/alarm.h

@@ -21,6 +21,8 @@
 #ifndef GRPCPP_ALARM_H
 #define GRPCPP_ALARM_H
 
+#include <functional>
+
 #include <grpc/grpc.h>
 #include <grpcpp/impl/codegen/completion_queue.h>
 #include <grpcpp/impl/codegen/completion_queue_tag.h>
@@ -76,8 +78,30 @@ class Alarm : private GrpcLibraryCodegen {
   /// has already fired has no effect.
   void Cancel();
 
+  /// NOTE: class experimental_type is not part of the public API of this class
+  /// TODO(vjpai): Move these contents to the public API of Alarm when
+  ///              they are no longer experimental
+  class experimental_type {
+   public:
+    explicit experimental_type(Alarm* alarm) : alarm_(alarm) {}
+
+    template <typename T>
+    void Set(const T& deadline, std::function<void(bool)> f) {
+      alarm_->SetInternal(TimePoint<T>(deadline).raw_time(), std::move(f));
+    }
+
+   private:
+    Alarm* alarm_;
+  };
+
+  /// NOTE: The function experimental() is not stable public API. It is a view
+  /// to the experimental components of this class. It may be changed or removed
+  /// at any time.
+  experimental_type experimental() { return experimental_type(this); }
+
  private:
   void SetInternal(CompletionQueue* cq, gpr_timespec deadline, void* tag);
+  void SetInternal(gpr_timespec deadline, std::function<void(bool)> f);
 
   internal::CompletionQueueTag* alarm_;
 };

src/cpp/common/alarm.cc

@@ -39,17 +39,6 @@ class AlarmImpl : public CompletionQueueTag {
   AlarmImpl() : cq_(nullptr), tag_(nullptr) {
     gpr_ref_init(&refs_, 1);
     grpc_timer_init_unset(&timer_);
-    GRPC_CLOSURE_INIT(&on_alarm_,
-                      [](void* arg, grpc_error* error) {
-                        // queue the op on the completion queue
-                        AlarmImpl* alarm = static_cast<AlarmImpl*>(arg);
-                        alarm->Ref();
-                        grpc_cq_end_op(
-                            alarm->cq_, alarm, error,
-                            [](void* arg, grpc_cq_completion* completion) {},
-                            arg, &alarm->completion_);
-                      },
-                      this, grpc_schedule_on_exec_ctx);
   }
   ~AlarmImpl() {
     grpc_core::ExecCtx exec_ctx;
@@ -68,6 +57,32 @@ class AlarmImpl : public CompletionQueueTag {
     cq_ = cq->cq();
     tag_ = tag;
     GPR_ASSERT(grpc_cq_begin_op(cq_, this));
+    GRPC_CLOSURE_INIT(&on_alarm_,
+                      [](void* arg, grpc_error* error) {
+                        // queue the op on the completion queue
+                        AlarmImpl* alarm = static_cast<AlarmImpl*>(arg);
+                        alarm->Ref();
+                        grpc_cq_end_op(
+                            alarm->cq_, alarm, error,
+                            [](void* arg, grpc_cq_completion* completion) {},
+                            arg, &alarm->completion_);
+                      },
+                      this, grpc_schedule_on_exec_ctx);
+    grpc_timer_init(&timer_, grpc_timespec_to_millis_round_up(deadline),
+                    &on_alarm_);
+  }
+  void Set(gpr_timespec deadline, std::function<void(bool)> f) {
+    grpc_core::ExecCtx exec_ctx;
+    // Don't use any CQ at all. Instead just use the timer to fire the function
+    callback_ = std::move(f);
+    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();
+                      },
+                      this, grpc_schedule_on_exec_ctx);
     grpc_timer_init(&timer_, grpc_timespec_to_millis_round_up(deadline),
                     &on_alarm_);
   }
@@ -95,6 +110,7 @@ class AlarmImpl : public CompletionQueueTag {
   // completion queue where events about this alarm will be posted
   grpc_completion_queue* cq_;
   void* tag_;
+  std::function<void(bool)> callback_;
 };
 }  // namespace internal
 
@@ -113,6 +129,15 @@ void Alarm::SetInternal(CompletionQueue* cq, gpr_timespec deadline, void* tag) {
   static_cast<internal::AlarmImpl*>(alarm_)->Set(cq, deadline, tag);
 }
 
+void Alarm::SetInternal(gpr_timespec deadline, std::function<void(bool)> f) {
+  // Note that we know that alarm_ is actually an internal::AlarmImpl
+  // but we declared it as the base pointer to avoid a forward declaration
+  // or exposing core data structures in the C++ public headers.
+  // Thus it is safe to use a static_cast to the subclass here, and the
+  // C++ style guide allows us to do so in this case
+  static_cast<internal::AlarmImpl*>(alarm_)->Set(deadline, std::move(f));
+}
+
 Alarm::~Alarm() {
   if (alarm_ != nullptr) {
     static_cast<internal::AlarmImpl*>(alarm_)->Destroy();

test/cpp/common/alarm_test.cc

@@ -16,9 +16,13 @@
  *
  */
 
+#include <condition_variable>
+#include <memory>
+#include <mutex>
+#include <thread>
+
 #include <grpcpp/alarm.h>
 #include <grpcpp/completion_queue.h>
-#include <thread>
 
 #include <gtest/gtest.h>
 
@@ -43,6 +47,66 @@ TEST(AlarmTest, RegularExpiry) {
   EXPECT_EQ(junk, output_tag);
 }
 
+struct Completion {
+  bool completed = false;
+  std::mutex mu;
+  std::condition_variable cv;
+};
+
+TEST(AlarmTest, CallbackRegularExpiry) {
+  Alarm alarm;
+
+  auto c = std::make_shared<Completion>();
+  alarm.experimental().Set(
+      std::chrono::system_clock::now() + std::chrono::seconds(1), [c](bool ok) {
+        EXPECT_TRUE(ok);
+        std::lock_guard<std::mutex> l(c->mu);
+        c->completed = true;
+        c->cv.notify_one();
+      });
+
+  std::unique_lock<std::mutex> l(c->mu);
+  EXPECT_TRUE(c->cv.wait_until(
+      l, std::chrono::system_clock::now() + std::chrono::seconds(10),
+      [c] { return c->completed; }));
+}
+
+TEST(AlarmTest, CallbackZeroExpiry) {
+  Alarm alarm;
+
+  auto c = std::make_shared<Completion>();
+  alarm.experimental().Set(grpc_timeout_seconds_to_deadline(0), [c](bool ok) {
+    EXPECT_TRUE(ok);
+    std::lock_guard<std::mutex> l(c->mu);
+    c->completed = true;
+    c->cv.notify_one();
+  });
+
+  std::unique_lock<std::mutex> l(c->mu);
+  EXPECT_TRUE(c->cv.wait_until(
+      l, std::chrono::system_clock::now() + std::chrono::seconds(10),
+      [c] { return c->completed; }));
+}
+
+TEST(AlarmTest, CallbackNegativeExpiry) {
+  Alarm alarm;
+
+  auto c = std::make_shared<Completion>();
+  alarm.experimental().Set(
+      std::chrono::system_clock::now() + std::chrono::seconds(-1),
+      [c](bool ok) {
+        EXPECT_TRUE(ok);
+        std::lock_guard<std::mutex> l(c->mu);
+        c->completed = true;
+        c->cv.notify_one();
+      });
+
+  std::unique_lock<std::mutex> l(c->mu);
+  EXPECT_TRUE(c->cv.wait_until(
+      l, std::chrono::system_clock::now() + std::chrono::seconds(10),
+      [c] { return c->completed; }));
+}
+
 TEST(AlarmTest, MultithreadedRegularExpiry) {
   CompletionQueue cq;
   void* junk = reinterpret_cast<void*>(1618033);
@@ -182,6 +246,26 @@ TEST(AlarmTest, Cancellation) {
   EXPECT_EQ(junk, output_tag);
 }
 
+TEST(AlarmTest, CallbackCancellation) {
+  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();
+      });
+  alarm.Cancel();
+
+  std::unique_lock<std::mutex> l(c->mu);
+  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);
@@ -200,6 +284,26 @@ TEST(AlarmTest, SetDestruction) {
   EXPECT_EQ(junk, output_tag);
 }
 
+TEST(AlarmTest, CallbackSetDestruction) {
+  auto c = std::make_shared<Completion>();
+  {
+    Alarm alarm;
+    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);
+  EXPECT_TRUE(c->cv.wait_until(
+      l, std::chrono::system_clock::now() + std::chrono::seconds(1),
+      [c] { return c->completed; }));
+}
+
 TEST(AlarmTest, UnsetDestruction) {
   CompletionQueue cq;
   Alarm alarm;