[GitHub] [incubator-brpc] zyearn commented on issue #1243: brpc::Join(CallId id) 支持带超时的等待

[GitBox <gi...@apache.org>]

zyearn commented on issue #1243:
URL: https://github.com/apache/incubator-brpc/issues/1243#issuecomment-693444506


   > 一个不太靠谱的基于future的实现
   > callback 里面设置 future
   > 
   > ```
   > void HandleEchoResponse(
   >         brpc::Controller* cntl,
   >         example::EchoResponse* response,
   >         std::shared_ptr<std::promise<bool>> waiter) {
   >     waiter->set_value(true);
   > }
   > ```
   > 
   > 等待的时候不join， 等future ，如果futre 不成功就 cancel 请求
   > 
   > ```
   >       std::shared_ptr<std::promise<bool>> waiter(std::make_shared<std::promise<bool>>());
   > 
   >         // Because `done'(last parameter) is NULL, this function waits until
   >         // the response comes back or error occurs(including timedout).
   >         google::protobuf::Closure* done = brpc::NewCallback(
   >             &HandleEchoResponse, &cntl, &response, waiter);
   > 
   >         auto call_id = cntl.call_id();
   >         stub.Echo(&cntl, &request, &response, done);
   >         LOG(INFO) << "waiting Join:" << errno << ", " << EINVAL;
   >         // brpc::Join(call_id);
   >         if (waiter->get_future().wait_for(std::chrono::microseconds(1)) != std::future_status::ready) {
   >           LOG(INFO) << "timeout";
   >           brpc::StartCancel(call_id);
   >         } else {
   >         .......
   >        }
   > ```
   
   这里用future来实现不太合适，future.wait会阻塞brpc的worker线程。
   
   Join的语义暗含的意思是当Join返回的时候，被Join的对象已经处于一个结束的状态，这里加个timeout会有点破坏语义。
   
    这个需求也可以通过bthread::CountdownEvent来实现，在原来future set_value的地方改成signal，在Join的地方改成timed_wait。
   


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