Merge pull request #18341 from vjpai/cancel_callback

Support callback on cancellation of server-side unary RPCs

include/grpcpp/impl/codegen/server_callback.h

@@ -69,6 +69,40 @@ class ServerCallbackRpcController {
   // Allow the method handler to push out the initial metadata before
   // the response and status are ready
   virtual void SendInitialMetadata(std::function<void(bool)>) = 0;
+
+  /// SetCancelCallback passes in a callback to be called when the RPC is
+  /// canceled for whatever reason (streaming calls have OnCancel instead). This
+  /// is an advanced and uncommon use with several important restrictions. This
+  /// function may not be called more than once on the same RPC.
+  ///
+  /// If code calls SetCancelCallback on an RPC, it must also call
+  /// ClearCancelCallback before calling Finish on the RPC controller. That
+  /// method makes sure that no cancellation callback is executed for this RPC
+  /// beyond the point of its return. ClearCancelCallback may be called even if
+  /// SetCancelCallback was not called for this RPC, and it may be called
+  /// multiple times. It _must_ be called if SetCancelCallback was called for
+  /// this RPC.
+  ///
+  /// The callback should generally be lightweight and nonblocking and primarily
+  /// concerned with clearing application state related to the RPC or causing
+  /// operations (such as cancellations) to happen on dependent RPCs.
+  ///
+  /// If the RPC is already canceled at the time that SetCancelCallback is
+  /// called, the callback is invoked immediately.
+  ///
+  /// The cancellation callback may be executed concurrently with the method
+  /// handler that invokes it but will certainly not issue or execute after the
+  /// return of ClearCancelCallback. If ClearCancelCallback is invoked while the
+  /// callback is already executing, the callback will complete its execution
+  /// before ClearCancelCallback takes effect.
+  ///
+  /// To preserve the orderings described above, the callback may be called
+  /// under a lock that is also used for ClearCancelCallback and
+  /// ServerContext::IsCancelled, so the callback CANNOT call either of those
+  /// operations on this RPC or any other function that causes those operations
+  /// to be called before the callback completes.
+  virtual void SetCancelCallback(std::function<void()> callback) = 0;
+  virtual void ClearCancelCallback() = 0;
 };
 
 // NOTE: The actual streaming object classes are provided
@@ -349,6 +383,15 @@ class CallbackUnaryHandler : public MethodHandler {
       call_.PerformOps(&meta_ops_);
     }
 
+    // Neither SetCancelCallback nor ClearCancelCallback should affect the
+    // callbacks_outstanding_ count since they are paired and both must precede
+    // the invocation of Finish (if they are used at all)
+    void SetCancelCallback(std::function<void()> callback) override {
+      ctx_->SetCancelCallback(std::move(callback));
+    }
+
+    void ClearCancelCallback() override { ctx_->ClearCancelCallback(); }
+
    private:
     friend class CallbackUnaryHandler<RequestType, ResponseType>;
 

include/grpcpp/impl/codegen/server_context.h

@@ -329,6 +329,9 @@ class ServerContext {
 
   uint32_t initial_metadata_flags() const { return 0; }
 
+  void SetCancelCallback(std::function<void()> callback);
+  void ClearCancelCallback();
+
   experimental::ServerRpcInfo* set_server_rpc_info(
       const char* method, internal::RpcMethod::RpcType type,
       const std::vector<

src/cpp/server/server_context.cc

@@ -95,6 +95,22 @@ class ServerContext::CompletionOp final : public internal::CallOpSetInterface {
     tag_ = tag;
   }
 
+  void SetCancelCallback(std::function<void()> callback) {
+    std::lock_guard<std::mutex> lock(mu_);
+
+    if (finalized_ && (cancelled_ != 0)) {
+      callback();
+      return;
+    }
+
+    cancel_callback_ = std::move(callback);
+  }
+
+  void ClearCancelCallback() {
+    std::lock_guard<std::mutex> g(mu_);
+    cancel_callback_ = nullptr;
+  }
+
   void set_core_cq_tag(void* core_cq_tag) { core_cq_tag_ = core_cq_tag; }
 
   void* core_cq_tag() override { return core_cq_tag_; }
@@ -141,6 +157,7 @@ class ServerContext::CompletionOp final : public internal::CallOpSetInterface {
   std::mutex mu_;
   bool finalized_;
   int cancelled_;  // This is an int (not bool) because it is passed to core
+  std::function<void()> cancel_callback_;
   bool done_intercepting_;
   internal::InterceptorBatchMethodsImpl interceptor_methods_;
 };
@@ -191,11 +208,17 @@ bool ServerContext::CompletionOp::FinalizeResult(void** tag, bool* status) {
   // Decide whether to call the cancel callback before releasing the lock
   bool call_cancel = (cancelled_ != 0);
 
+  // If it's a unary cancel callback, call it under the lock so that it doesn't
+  // race with ClearCancelCallback
+  if (cancel_callback_) {
+    cancel_callback_();
+  }
+
   // Release the lock since we are going to be calling a callback and
   // interceptors now
   lock.unlock();
 
-  if (call_cancel && (reactor_ != nullptr)) {
+  if (call_cancel && reactor_ != nullptr) {
     reactor_->OnCancel();
   }
 
@@ -315,6 +338,14 @@ void ServerContext::TryCancel() const {
   }
 }
 
+void ServerContext::SetCancelCallback(std::function<void()> callback) {
+  completion_op_->SetCancelCallback(std::move(callback));
+}
+
+void ServerContext::ClearCancelCallback() {
+  completion_op_->ClearCancelCallback();
+}
+
 bool ServerContext::IsCancelled() const {
   if (completion_tag_) {
     // When using callback API, this result is always valid.

test/cpp/end2end/BUILD

@@ -245,6 +245,9 @@ grpc_cc_test(
     size = "large",
     deps = [
         ":end2end_test_lib",
+        # DO NOT REMOVE THE grpc++ dependence below since the internal build
+        # system uses it to specialize targets
+        "//:grpc++",
     ],
 )
 

test/cpp/end2end/end2end_test.cc

@@ -1381,6 +1381,80 @@ TEST_P(End2endTest, ExpectErrorTest) {
   }
 }
 
+TEST_P(End2endTest, DelayedRpcEarlyCanceledUsingCancelCallback) {
+  MAYBE_SKIP_TEST;
+  // This test case is only relevant with callback server.
+  // Additionally, using interceptors makes this test subject to
+  // timing-dependent failures if the interceptors take too long to run.
+  if (!GetParam().callback_server || GetParam().use_interceptors) {
+    return;
+  }
+
+  ResetStub();
+  ClientContext context;
+  context.AddMetadata(kServerUseCancelCallback,
+                      grpc::to_string(MAYBE_USE_CALLBACK_EARLY_CANCEL));
+  EchoRequest request;
+  EchoResponse response;
+  request.set_message("Hello");
+  request.mutable_param()->set_skip_cancelled_check(true);
+  context.TryCancel();
+  Status s = stub_->Echo(&context, request, &response);
+  EXPECT_EQ(StatusCode::CANCELLED, s.error_code());
+}
+
+TEST_P(End2endTest, DelayedRpcLateCanceledUsingCancelCallback) {
+  MAYBE_SKIP_TEST;
+  // This test case is only relevant with callback server.
+  // Additionally, using interceptors makes this test subject to
+  // timing-dependent failures if the interceptors take too long to run.
+  if (!GetParam().callback_server || GetParam().use_interceptors) {
+    return;
+  }
+
+  ResetStub();
+  ClientContext context;
+  context.AddMetadata(kServerUseCancelCallback,
+                      grpc::to_string(MAYBE_USE_CALLBACK_LATE_CANCEL));
+  EchoRequest request;
+  EchoResponse response;
+  request.set_message("Hello");
+  request.mutable_param()->set_skip_cancelled_check(true);
+  // Let server sleep for 80 ms first to give the cancellation a chance.
+  // This is split into 40 ms to start the cancel and 40 ms extra time for
+  // it to make it to the server, to make it highly probable that the server
+  // RPC would have already started by the time the cancellation is sent
+  // and the server-side gets enough time to react to it.
+  request.mutable_param()->set_server_sleep_us(80 * 1000);
+
+  std::thread echo_thread{[this, &context, &request, &response] {
+    Status s = stub_->Echo(&context, request, &response);
+    EXPECT_EQ(StatusCode::CANCELLED, s.error_code());
+  }};
+  std::this_thread::sleep_for(std::chrono::microseconds(40000));
+  context.TryCancel();
+  echo_thread.join();
+}
+
+TEST_P(End2endTest, DelayedRpcNonCanceledUsingCancelCallback) {
+  MAYBE_SKIP_TEST;
+  if (!GetParam().callback_server) {
+    return;
+  }
+
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  request.set_message("Hello");
+
+  ClientContext context;
+  context.AddMetadata(kServerUseCancelCallback,
+                      grpc::to_string(MAYBE_USE_CALLBACK_NO_CANCEL));
+
+  Status s = stub_->Echo(&context, request, &response);
+  EXPECT_TRUE(s.ok());
+}
+
 //////////////////////////////////////////////////////////////////////////
 // Test with and without a proxy.
 class ProxyEnd2endTest : public End2endTest {
@@ -2015,7 +2089,7 @@ INSTANTIATE_TEST_CASE_P(
 
 INSTANTIATE_TEST_CASE_P(
     ProxyEnd2end, ProxyEnd2endTest,
-    ::testing::ValuesIn(CreateTestScenarios(true, true, true, true, false)));
+    ::testing::ValuesIn(CreateTestScenarios(true, true, true, true, true)));
 
 INSTANTIATE_TEST_CASE_P(
     SecureEnd2end, SecureEnd2endTest,
@@ -2023,7 +2097,7 @@ INSTANTIATE_TEST_CASE_P(
 
 INSTANTIATE_TEST_CASE_P(
     ResourceQuotaEnd2end, ResourceQuotaEnd2endTest,
-    ::testing::ValuesIn(CreateTestScenarios(false, true, true, true, false)));
+    ::testing::ValuesIn(CreateTestScenarios(false, true, true, true, true)));
 
 }  // namespace
 }  // namespace testing

test/cpp/end2end/test_service_impl.cc

@@ -126,13 +126,14 @@ void ServerTryCancelNonblocking(ServerContext* context) {
 }
 
 void LoopUntilCancelled(Alarm* alarm, ServerContext* context,
-                        experimental::ServerCallbackRpcController* controller) {
+                        experimental::ServerCallbackRpcController* controller,
+                        int loop_delay_us) {
   if (!context->IsCancelled()) {
     alarm->experimental().Set(
         gpr_time_add(gpr_now(GPR_CLOCK_REALTIME),
-                     gpr_time_from_micros(1000, GPR_TIMESPAN)),
-        [alarm, context, controller](bool) {
-          LoopUntilCancelled(alarm, context, controller);
+                     gpr_time_from_micros(loop_delay_us, GPR_TIMESPAN)),
+        [alarm, context, controller, loop_delay_us](bool) {
+          LoopUntilCancelled(alarm, context, controller, loop_delay_us);
         });
   } else {
     controller->Finish(Status::CANCELLED);
@@ -249,6 +250,25 @@ Status TestServiceImpl::CheckClientInitialMetadata(ServerContext* context,
 void CallbackTestServiceImpl::Echo(
     ServerContext* context, const EchoRequest* request, EchoResponse* response,
     experimental::ServerCallbackRpcController* controller) {
+  CancelState* cancel_state = new CancelState;
+  int server_use_cancel_callback =
+      GetIntValueFromMetadata(kServerUseCancelCallback,
+                              context->client_metadata(), DO_NOT_USE_CALLBACK);
+  if (server_use_cancel_callback != DO_NOT_USE_CALLBACK) {
+    controller->SetCancelCallback([cancel_state] {
+      EXPECT_FALSE(cancel_state->callback_invoked.exchange(
+          true, std::memory_order_relaxed));
+    });
+    if (server_use_cancel_callback == MAYBE_USE_CALLBACK_EARLY_CANCEL) {
+      EXPECT_TRUE(context->IsCancelled());
+      EXPECT_TRUE(
+          cancel_state->callback_invoked.load(std::memory_order_relaxed));
+    } else {
+      EXPECT_FALSE(context->IsCancelled());
+      EXPECT_FALSE(
+          cancel_state->callback_invoked.load(std::memory_order_relaxed));
+    }
+  }
   // A bit of sleep to make sure that short deadline tests fail
   if (request->has_param() && request->param().server_sleep_us() > 0) {
     // Set an alarm for that much time
@@ -256,11 +276,11 @@ void CallbackTestServiceImpl::Echo(
         gpr_time_add(gpr_now(GPR_CLOCK_MONOTONIC),
                      gpr_time_from_micros(request->param().server_sleep_us(),
                                           GPR_TIMESPAN)),
-        [this, context, request, response, controller](bool) {
-          EchoNonDelayed(context, request, response, controller);
+        [this, context, request, response, controller, cancel_state](bool) {
+          EchoNonDelayed(context, request, response, controller, cancel_state);
         });
   } else {
-    EchoNonDelayed(context, request, response, controller);
+    EchoNonDelayed(context, request, response, controller, cancel_state);
   }
 }
 
@@ -279,7 +299,26 @@ void CallbackTestServiceImpl::CheckClientInitialMetadata(
 
 void CallbackTestServiceImpl::EchoNonDelayed(
     ServerContext* context, const EchoRequest* request, EchoResponse* response,
-    experimental::ServerCallbackRpcController* controller) {
+    experimental::ServerCallbackRpcController* controller,
+    CancelState* cancel_state) {
+  int server_use_cancel_callback =
+      GetIntValueFromMetadata(kServerUseCancelCallback,
+                              context->client_metadata(), DO_NOT_USE_CALLBACK);
+
+  // Safe to clear cancel callback even if it wasn't set
+  controller->ClearCancelCallback();
+  if (server_use_cancel_callback == MAYBE_USE_CALLBACK_EARLY_CANCEL ||
+      server_use_cancel_callback == MAYBE_USE_CALLBACK_LATE_CANCEL) {
+    EXPECT_TRUE(context->IsCancelled());
+    EXPECT_TRUE(cancel_state->callback_invoked.load(std::memory_order_relaxed));
+    delete cancel_state;
+    controller->Finish(Status::CANCELLED);
+    return;
+  }
+
+  EXPECT_FALSE(cancel_state->callback_invoked.load(std::memory_order_relaxed));
+  delete cancel_state;
+
   if (request->has_param() && request->param().server_die()) {
     gpr_log(GPR_ERROR, "The request should not reach application handler.");
     GPR_ASSERT(0);
@@ -301,9 +340,11 @@ void CallbackTestServiceImpl::EchoNonDelayed(
     EXPECT_FALSE(context->IsCancelled());
     context->TryCancel();
     gpr_log(GPR_INFO, "Server called TryCancel() to cancel the request");
-    // Now wait until it's really canceled
 
-    LoopUntilCancelled(&alarm_, context, controller);
+    if (server_use_cancel_callback == DO_NOT_USE_CALLBACK) {
+      // Now wait until it's really canceled
+      LoopUntilCancelled(&alarm_, context, controller, 1000);
+    }
     return;
   }
 
@@ -318,20 +359,11 @@ void CallbackTestServiceImpl::EchoNonDelayed(
       std::unique_lock<std::mutex> lock(mu_);
       signal_client_ = true;
     }
-    std::function<void(bool)> recurrence = [this, context, request, controller,
-                                            &recurrence](bool) {
-      if (!context->IsCancelled()) {
-        alarm_.experimental().Set(
-            gpr_time_add(
-                gpr_now(GPR_CLOCK_REALTIME),
-                gpr_time_from_micros(request->param().client_cancel_after_us(),
-                                     GPR_TIMESPAN)),
-            recurrence);
-      } else {
-        controller->Finish(Status::CANCELLED);
+    if (server_use_cancel_callback == DO_NOT_USE_CALLBACK) {
+      // Now wait until it's really canceled
+      LoopUntilCancelled(&alarm_, context, controller,
+                         request->param().client_cancel_after_us());
     }
-    };
-    recurrence(true);
     return;
   } else if (request->has_param() &&
              request->param().server_cancel_after_us()) {

test/cpp/end2end/test_service_impl.h

@@ -33,6 +33,7 @@ namespace testing {
 const int kServerDefaultResponseStreamsToSend = 3;
 const char* const kServerResponseStreamsToSend = "server_responses_to_send";
 const char* const kServerTryCancelRequest = "server_try_cancel";
+const char* const kServerUseCancelCallback = "server_use_cancel_callback";
 const char* const kDebugInfoTrailerKey = "debug-info-bin";
 const char* const kServerFinishAfterNReads = "server_finish_after_n_reads";
 const char* const kServerUseCoalescingApi = "server_use_coalescing_api";
@@ -46,6 +47,13 @@ typedef enum {
   CANCEL_AFTER_PROCESSING
 } ServerTryCancelRequestPhase;
 
+typedef enum {
+  DO_NOT_USE_CALLBACK = 0,
+  MAYBE_USE_CALLBACK_EARLY_CANCEL,
+  MAYBE_USE_CALLBACK_LATE_CANCEL,
+  MAYBE_USE_CALLBACK_NO_CANCEL,
+} ServerUseCancelCallback;
+
 class TestServiceImpl : public ::grpc::testing::EchoTestService::Service {
  public:
   TestServiceImpl() : signal_client_(false), host_() {}
@@ -115,9 +123,13 @@ class CallbackTestServiceImpl
   }
 
  private:
+  struct CancelState {
+    std::atomic_bool callback_invoked{false};
+  };
   void EchoNonDelayed(ServerContext* context, const EchoRequest* request,
                       EchoResponse* response,
-                      experimental::ServerCallbackRpcController* controller);
+                      experimental::ServerCallbackRpcController* controller,
+                      CancelState* cancel_state);
 
   Alarm alarm_;
   bool signal_client_;