uWS::Loop::defer causes crashes (SIGSEGV)

[damirbarr]

uWS::Loop::defer causes crashes (SIGSEGV)

[ddevienne]

uWS is single-threaded, and uses thread_local variables. So while it can be used in a multi-threaded environment, you have to be careful when crossing thread boundaries. I don't recall whether defer() can be used safely across-threads. But given you crash, maybe not? FWIW.

[damirbarr]

I was using the defer() function so far for exactly this reason and it worked. For some reason now it sometimes crashes.
The defer function uses the loop's thread, and this is why I'm using it.
My software is multithreaded and I think there's maybe a bug here.

Reference from this repo:

    /* Defer this callback on Loop's thread of execution */
    void defer(MoveOnlyFunction<void()> &&cb) {
        LoopData *loopData = (LoopData *) us_loop_ext((us_loop_t *) this);

        //if (std::thread::get_id() == ) // todo: add fast path for same thread id
        loopData->deferMutex.lock();
        loopData->deferQueues[loopData->currentDeferQueue].emplace_back(std::move(cb));
        loopData->deferMutex.unlock();

        us_wakeup_loop((us_loop_t *) this);
    }

[uNetworkingAB]

defer is thread safe. But you need to check your composition with ThreadSanitizer or AddressSanitizer. The stacktrace is very weird and most likely not showing the real problem