[grpc-io] Re: grpc c++: how to create async callback client

['AJ Heller' via grpc.io]

 

You should not need to manage your own threads for basic callback usage, 
that’s one of the callback API’s design goals (
https://github.com/grpc/proposal/blob/master/L67-cpp-callback-api.md#proposal
).

Take a look at the route_guide example here: 
https://github.com/grpc/grpc/blob/v1.41.x/examples/cpp/route_guide/route_guide_callback_client.cc.
 
It has a server-streaming client for ListFeatures, a client-streaming 
client for RecordRoute, a bidi client for RouteChat, and the recommended 
“shortcut” method of making a client unary call via 
`stub->async()->GetFeature(…)`, where the lambda stands in for a 
ClientUnaryReactor’s OnDone method (
https://github.com/grpc/grpc/blob/v1.41.x/examples/cpp/route_guide/route_guide_callback_client.cc#L304).
 
For streaming operations, gRPC manages threads to call the reactor 
callbacks asynchronously. If the application needs to wait for some 
streaming operation to finish, it *can* block the main thread using 
something like the custom Await method of the ListFeatures Reader, but 
that's entirely optional and up to the application developer.

Hope that helps!
On Tuesday, September 7, 2021 at 2:22:47 PM UTC-7 oleg@idt.net wrote:

> Hello, could you possibly help me with creating async callback client? 
> Should I create UnaryClientReactor per rpc or I should run every rpc in 
> separate thread?
> There cq-based async client example but callback client example looks like 
> sync rpc with thread blocking.
>
> Thank you.
>

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[grpc-io] Re: grpc c++: how to create async callback client

['yas...@google.com' via grpc.io]

Hi,

If using the callback API, you wouldn't need to create a separate thread 
for each RPC. The callbacks in the reactor would be automatically invoked 
by the threads managed by the gRPC library. That being said, if the reactor 
is going to be blocking for a substantial amount of time, you would want to 
perform that in a separate application thread, so that the library threads 
can focus on polling connections and executing callbacks.

Creating a different reactor object per RPC would be a very common way of 
doing things and should work fine.

On Tuesday, September 7, 2021 at 2:22:47 PM UTC-7 oleg@idt.net wrote:

> Hello, could you possibly help me with creating async callback client? 
> Should I create UnaryClientReactor per rpc or I should run every rpc in 
> separate thread?
> There cq-based async client example but callback client example looks like 
> sync rpc with thread blocking.
>
> Thank you.
>

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