How to correctly use grpc asynchronously (ClientAsyncReaderWriter) - c++

Question

I can't find a grpc example showing how to use the ClientAsyncReaderWriter (is there one?). I tried something on my own, but am having trouble with the reference counts. My question comes from tracing through the code.
struct grpc_call has a member of type gpr_refcount called ext_ref. The ClientContext C++ object wraps the grpc_call, and holds onto it in a member grpc_call *call_;. Only when ext_ref is 0, can this grpc_call pointer be deleted.
When I use grpc synchronously with ClientReader:
In its implementation it uses CreateCall() and PerformOps() to add to ext_ref (ext_ref == 2).
Then I use Pluck() which subtracts from ext_ref so that (ext_ref == 1).
The last use ~ClientContext() subtracts from ext_ref, so that ext_ref == 0 and deletes the call
But when I use grpc asynchronously with ClientAsyncReaderWriter:
First use asyncXXX(), this API use CreateCall() and register Write() (ext_ref == 2).
Then it uses AsyncNext() to get tag...which must use a write or read operator.
So ext_ref > 1 forever, unless got_event you don't handle.
I'm calling it like this:
struct Notice
{
std::unique_ptr<
grpc::ClientAsyncReaderWriter<ObserveNoticRequest, EventNotice>
> _rw;
ClientContext _context;
EventNotice _rsp;
}
Register Thread
CompletionQueue *cq = new CompletionQueue;
Notice *notice = new Notice;
notice->rw = stub->AsyncobserverNotice(&context, cq, notice);
// here context.call_.ext_ref is 2
Get CompletionQueue Event Thread
void *tag = NULL;
bool ok = false;
CompletionQueue::NextStatus got = CompletionQueue::NextStatus::TIMEOUT;
gpr_timespec deadline;
deadline.clock_type = GPR_TIMESPAN;
deadline.tv_sec = 0;
deadline.tv_nsec = 10000000;
got = cq->AsyncNext<gpr_timespec>(&tag, &ok, deadline);
if (GOT_EVENT == got) {
if (tag != NULL) {
Notice *notice = (Notice *)tag;
notice->_rw->Read(&_rsp, notice);
// here context.call_.ext_ref is 2.
// now I want to stop this CompletionQueue.
delete notice;
// use ~ClientContext(), ext_ref change to 1
// but only ext_ref == 0, call_ be deleted
}
}

Answer 1

Take a look at this file, client_async.cc, for good use of the ClientAsyncReaderWriter. If you still have confusion, please create a very clean reproduction of the issue, and we will look into it further.