CODEWITHSUNDEEP
grpcgrpc-c++
Joe Schrag
Joe Schrag

Reputation: 865

How to get visibility into completion queue on C++ gRPC server

Note: Help with the immediate problem would be great, but mostly I'm looking for advice on troubleshooting gRPC timing issues in general (this isn't my first such issue).

I am adding a new server streaming service to a C++ module which has an existing server streaming service, and the two appear to be conflicting. Specifically, the completion queue Next() call on the server is crashing intermittently after the C# client calls Cancel() on the cancellation token for one of the services. This doesn't happen if I run each service independently.

On the client, I get this at the response stream MoveNext() call:

System.InvalidOperationException
  HResult=0x80131509
  Message=Shutdown has already been called
  Source=Grpc.Core
  StackTrace:
   at Grpc.Core.Internal.CompletionQueueSafeHandle.BeginOp()
   at Grpc.Core.Internal.CallSafeHandle.StartReceiveMessage(IReceivedMessageCallback callback)
   at Grpc.Core.Internal.AsyncCallBase`2.ReadMessageInternalAsync()
   at Grpc.Core.Internal.ClientResponseStream`2.<MoveNext>d__5.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at MyModule.Connection.<DoSubscriptionReceives>d__7.MoveNext() in C:\snip\Connection.cs:line 67

On the server, I get this at the completion queue next() call:

Exception thrown: read access violation.
core_cq_tag->**** was 0xDDDDDDDD.

The stack trace:

    MyModule.exe!grpc_impl::CompletionQueue::AsyncNextInternal(void * * tag, bool * ok, gpr_timespec deadline) Line 59  C++
>   MyModule.exe!grpc_impl::CompletionQueue::Next(void * * tag, bool * ok) Line 176 C++
...snip...

It appears something is being added to the queue after shutdown. The difficulty is I have little visibility into what is being added into the queue and in what order.

I'm trying to write a server-side interceptor to log all requests & responses, but there seems to be no documentation. So far, poking through the API hasn't gotten me very far. Is there any documentation available on wiring up an interceptor in C++? Or, are there other approaches for troubleshooting timing conflicts between services?

Windows 11, Grpc.Core 1.27

What I've tried: I first played with the GRPC_TRACE & GRPC_VERBOSITY environment variables. I was able to get some unhelpful output from the client, but nothing from the server. Of course, there's been lots of debugging, stripping the client & server down to barebones, disabling keep alives, ensuring we aren't using deadlines, having the services share a cancellation token, etc.

Update: I have found that the crash only happens when the client is run from an NUnit test. In that environment, the completion queue is getting more hits on Next(), but I'm still trying to figure out where they are coming from.

Upvotes: 0

Views: 972

Answers (1)

Yash Tibrewal
Yash Tibrewal

Reputation: 537

Is 1.27 the version you are using? That seems pretty old.. There might have been fixes since then.

For using the C++ server interception API, I think you would find this very useful - https://github.com/grpc/grpc/blob/0f2a0f5fc9b9e9b9c98d227d16575d106f1e8d43/test/cpp/end2end/server_interceptors_end2end_test.cc#L48

One suggestion I have is to run the code another sanitizers https://github.com/google/sanitizers to make sure that we don't have a heap-use-after-free type bug.

I would also check for API misuse issues. (If you had posted the code, I could've given a look to see if anything seems weird..)

Upvotes: 1

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