Hello,
I would like to know what is the proper usage of grpc::ClientAsyncReader
with a server side stream. We use older version of grpc library - 1.16.0
on Debian Stretch.
After I create the reader, I use the grpc::ClientAsyncReader::StartCall()
method.
I am not quite sure when I should issue the
grpc::ClientAsyncReader::Finish() and if the returned status should be
checked in case we receive many replies using server side stream.
And, I would like to know, under which circumstances it makes sense to
use/shoudl be used ReadInitialMetadata() method.
I tried to issue it right after StartCall() and also before first Read(),
but in both cases I get some assertions :
After Start: 12160 channel_cc.cc:160] assertion failed:
GRPC_CALL_OK == grpc_call_start_batch(call->call(), cops, nops,
ops->cq_tag(), nullptr)
After Finish: 12327 async_stream.h:230] assertion failed:
!context_->initial_metadata_received_
Here a simplified version of the code I use:
grpc::CompletionQueue cq;
grpc::ClientContext context;
StartStreamingRequest request;
StreamingNotification reply;
std::unique_ptr< grpc::ClientAsyncReader<StreamingNotification> >
async_reader( stub_->PrepareAsyncStartStreaming(&context, request,
&cq) );
void *tag = (void*)1234;
async_reader->StartCall(tag);
// Do I need to perform Finish immediately or should I wait?
grpc::Status status;
async_reader->Finish(&status, tag);
void *recv_tag = nullptr;
bool ok = false;
while(cq.Next(&recv_tag, &ok))
{
if (!ok)
LOG_DEBUG("Completion queue returns nOK");
if (recv_tag != tag)
LOG_INFO("Tag does not match expected value" );
else
{
// Does it make sense to check the status.ok() here, is it necessary ?
if (status.ok())
{
async_reader->Read(&reply, tag);
ProcessNotification(reply);
}
}
}
Thanks for any explanation or suggestions.
Peter
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