Mark, Thanks for the information. This was very helpful.
On Wed, Oct 24, 2018 at 12:52 PM Mark D. Roth <r...@google.com> wrote: > I'm not sure exactly what is causing this crash, but I suspect it may be a > side-effect of the way you're monitoring the channel's connectivity state > via a timer. For example, it could be that the timer is firing after the > channel has already been destroyed (either because you're failing to cancel > the timer when you destroy the channel or due to some race condition in > your timer code). > > A much better approach would be to use either the NotifyOnStateChange() > <https://grpc.io/grpc/cpp/classgrpc_1_1_channel_interface.html#ac2e0a00712088ca461359a78eb0e2c69> > method > or the WaitForConnected() > <https://grpc.io/grpc/cpp/classgrpc_1_1_channel_interface.html#a31d360cd218614814d68e01e07ce55cc> > method > to get notified when the state changes, so that you don't have to mess with > timers to periodically check the state or worry about lifetime issues. The > difference between these two methods is that the former uses a completion > queue whereas the latter blocks a thread waiting for the state change. If > you're already using the C++ async API, then you probably want the former; > otherwise, you probably want the latter. > > If you use NotifyOnStateChange(), note that this API may miss state > transitions. For example, if the channel was in state IDLE when you first > got a result and is now in state READY, it's likely that the channel was in > state CONNECTING in between the two, but you might never have gotten a > notification for it. But that's probably what you want, since what you > really care about is when the channel goes into READY state, and if you > miss that transition, that means that the channel went into READY but then > immediately switched to another state, in which case you probably wouldn't > want to have started a new attempt anyway. > > If you use WaitForConnected(), you will probably want to call that > whenever an RPC fails with a status like UNAVAILABLE. Then it will block > until the channel is reconnected, at which point you can retry your RPC. > > I hope this information is helpful. > > On Fri, Oct 19, 2018 at 9:56 AM <mauricio.rami...@lacity.org> wrote: > >> I started with a simple synchronous unary call to a go based server from >> cpp. We decided to add a health check routine so that if we're >> disconnected when we re-established communication, I could sync data. I >> have a timer that every 5 seconds calls the GetState method to get the >> current state. That was working great. >> >> We then had to switch to the Async version of the rpc. I based my code >> off the example in the greeter_async_client_2 >> <https://github.com/grpc/grpc/blob/master/examples/cpp/helloworld/greeter_async_client2.cc> >> example >> and ever since the health check routine crashes everytime it calls >> GetState. >> >> Program terminated with signal 11, Segmentation fault. >> #0 0x00007f4b123c7920 in grpc::Channel::GetState(bool) () from >> /usr/local/lib/libgrpc++.so.1 >> (gdb) bt >> #0 0x00007f4b123c7920 in grpc::Channel::GetState(bool) () from >> /usr/local/lib/libgrpc++.so.1 >> #1 0x0000000000430289 in MobileFeedServer::OnHealthCheck (this=0x660f80 >> <mfeed>) at mobilefeed.cpp:865 >> #2 0x0000000000415723 in MobileFeedServer::TimerHealthCheck::onTimer >> (this=<optimized out>, timer=<optimized out>) at mobilefeed.cpp:858 >> #3 0x0000000000445014 in MiddlewareEvent_TimerCB (event=<optimized out>, >> msg=<optimized out>, closure=0x661068 <mfeed+232>) at >> /middleware/src/version/libmiddlewarecpp/event.cpp:357 >> #4 0x00007f4b126405c2 in _middlewareQueue_DispatchEx (q=0x1fb35b0, >> wait=wait@entry=0, >> ignoreListenerLimit=ignoreListenerLimit@entry=MIDDLEWARE_TRUE) >> at /middleware/src/version/libmiddleware/disp.c:471 >> #5 0x00007f4b1264082a in _middlewareQueue_Dispatch (q=<optimized out>, >> wait=wait@entry=0) at /middleware/src/version/libmiddleware/disp.c:538 >> #6 0x00007f4b12640cd0 in MiddlewareQueueGroup_TimedDispatch >> (qgroup=<optimized out>, wait=<optimized out>, wait@entry=0.5) at >> /middleware/src/version/libmiddleware/disp.c:733 >> #7 0x000000000044592c in MiddleWareQueueGroup::timedDispatch >> (this=this@entry=0x660ff0 <mfeed+112>, timeout=timeout@entry=0.5) at >> /middleware/src/version/libmiddlewarecpp/qgroup.cpp:58 >> #8 0x00007f4b12eb6591 in MyTask::MainLoop (this=0x660f80 <mfeed>, >> transport=<optimized out>) at mytask.cxx:317 >> #9 0x00007f4b12eb4529 in MyTask::MainLoop (this=this@entry=0x660f80 >> <mfeed>, Description=Description@entry=0x449e12 "MobileFeed", >> argc=argc@entry=7, argv=argv@entry=0x7fffa279e6e8) at mytask.cxx:272 >> #10 0x000000000040ff83 in main (argc=7, argv=0x7fffa279e6e8) at >> mobilefeed.cpp:958 >> (gdb) >> >> My code is fairly straightforward. When my timer goes off, I save my >> state as the previous state, get the current state, then if the current is >> ready and the previous wasn't, I synchronize. >> >> grpc_connectivity_state mystate; >> >> mystate = grpcClient->channelinterface->GetState(true); >> >> grpcClient->SetCurrentState(mystate); >> >> >> if ((mystate == GRPC_CHANNEL_READY) && (grpcClient->GetOldState() != >> GRPC_CHANNEL_READY)) >> >> { >> // synchronize data >> } >> else >> // log state >> >> Is there a better way to implement this health check? >> >> -- >> You received this message because you are subscribed to the Google Groups >> "grpc.io" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to grpc-io+unsubscr...@googlegroups.com. >> To post to this group, send email to grpc-io@googlegroups.com. >> Visit this group at https://groups.google.com/group/grpc-io. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/grpc-io/73677090-c564-4c09-be76-64b8dea35bdd%40googlegroups.com >> <https://groups.google.com/d/msgid/grpc-io/73677090-c564-4c09-be76-64b8dea35bdd%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> For more options, visit https://groups.google.com/d/optout. >> > > > -- > Mark D. Roth <r...@google.com> > Software Engineer > Google, Inc. > -- Mauricio Ramirez Programmer Analyst (213) 484 - 6773 -- You received this message because you are subscribed to the Google Groups "grpc.io" group. To unsubscribe from this group and stop receiving emails from it, send an email to grpc-io+unsubscr...@googlegroups.com. To post to this group, send email to grpc-io@googlegroups.com. Visit this group at https://groups.google.com/group/grpc-io. To view this discussion on the web visit https://groups.google.com/d/msgid/grpc-io/CAFDPuxL1oFoGgC9L%2BnGdxpnWzaVhNn4vViKhdspE7rJobbhb2g%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
