feng-y commented on issue #1243:
URL: https://github.com/apache/incubator-brpc/issues/1243#issuecomment-693767387
> > 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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