C++ server async read write multiplexing

[Arpit Baldeva]

Hi,

For bi-directional streaming, can I have both pending read and write operations at the same time (1 of each)?

All the examples I found so far seem to do ping-pong behavior (1 read followed by 1 write) but I don't recall reading any documentation that mentions this constraint on protocol level. In other words, can I do multiple reads followed by a single write (and vice versa)? And if that is true, I'd like to be able to request both async read and write at the same time.

Thanks. 

[Vijay Pai]

You can have a simultaneous pending read and write operation on a stream in the C++ async API, no problem. Ping-pong is not required for any gRPC streaming operations.

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[Arpit Baldeva]

Thanks for the info.

The documentation for  grpc::ServerAsyncReaderWriter< W, R >::Read says (http://www.grpc.io/grpc/cpp/classgrpc_1_1_server_async_reader_writer.html#a2adbae40645434ad5f55823967998acc ) -

" It should not be called concurrently with other streaming APIs on the same stream. "

So if a streaming write operation is allowed concurrently, this doc should be updated? 

And then on the same topic, if I have a read operation queued but meanwhile the server decides to finish up (say an error/whatever), can I queue up a Finish/FinishWithError call? Or is the correct usage there is to call TryCancel on the server context with an AsyncNotifyWhenDone call?

Thanks. 

On Wed, Feb 22, 2017 at 7:59 PM, Vijay Pai <vp...@google.com> wrote:

You can have a simultaneous pending read and write operation on a stream in the C++ async API, no problem. Ping-pong is not required for any gRPC streaming operations.

On Wed, Feb 22, 2017 at 4:45 PM Arpit Baldeva <abal...@gmail.com> wrote:

Hi,

For bi-directional streaming, can I have both pending read and write operations at the same time (1 of each)?

All the examples I found so far seem to do ping-pong behavior (1 read followed by 1 write) but I don't recall reading any documentation that mentions this constraint on protocol level. In other words, can I do multiple reads followed by a single write (and vice versa)? And if that is true, I'd like to be able to request both async read and write at the same time.

Thanks. 

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[Vijay Pai]

Please note the sentence before the one you quoted: "This is thread-safe with respect to Write or WritesDone methods. It should not be called concurrently with other streaming APIs on the same stream." By "other streaming APIs," I meant "other than Write or Writes Done," but I understand that it can be confusing so we can move to rewrite that comment.

If you need to finish up with an error while there is a read outstanding, you should do cancel/AsyncNotify as you mentioned. Finish isn't meant to be done concurrently with either Read or Write operations.

Regards,

Vijay

On Wed, Feb 22, 2017 at 8:24 PM Arpit Baldeva <abal...@gmail.com> wrote:

Thanks for the info.

The documentation for  grpc::ServerAsyncReaderWriter< W, R >::Read says (http://www.grpc.io/grpc/cpp/classgrpc_1_1_server_async_reader_writer.html#a2adbae40645434ad5f55823967998acc ) -

" It should not be called concurrently with other streaming APIs on the same stream. "

So if a streaming write operation is allowed concurrently, this doc should be updated? 

And then on the same topic, if I have a read operation queued but meanwhile the server decides to finish up (say an error/whatever), can I queue up a Finish/FinishWithError call? Or is the correct usage there is to call TryCancel on the server context with an AsyncNotifyWhenDone call?

Thanks. 

On Wed, Feb 22, 2017 at 7:59 PM, Vijay Pai <vp...@google.com> wrote:

You can have a simultaneous pending read and write operation on a stream in the C++ async API, no problem. Ping-pong is not required for any gRPC streaming operations.

On Wed, Feb 22, 2017 at 4:45 PM Arpit Baldeva <abal...@gmail.com> wrote:

Hi,

For bi-directional streaming, can I have both pending read and write operations at the same time (1 of each)?

All the examples I found so far seem to do ping-pong behavior (1 read followed by 1 write) but I don't recall reading any documentation that mentions this constraint on protocol level. In other words, can I do multiple reads followed by a single write (and vice versa)? And if that is true, I'd like to be able to request both async read and write at the same time.

Thanks. 

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