Does libevent allow to run callback for timer/io in a different thread?

Question

Due to some application reasons I need to run callback for timer/io events in a different thread.

Example:

void EventLoop::createIOEvent(int fd, short kind, event_cb originalCallback, void* originalUserData) 
{
    ...
    const auto data{std::make_shared<UserData>(originalUserData, originalCallback, callbackExecutor)};
    event* event{event_new(_eventBase, fd, kind, EventLoop::asyncCall, data.get())};
    event_add(event, nullptr);
    ...
}

void EventLoop::asyncCall(int fd, short kind, void* data)
{
    const auto userData{*(reinterpret_cast<UserData*>(data))};
    ExecutorWrapper(userData._callbackExecutor)
        .addRunnable([=]() {
            userData._originalCallback(fd, kind, userData._originalUserData);
    })
    .exec();
 }

Is it legal for libevent to use such approach?

Note: it seems that all works fine on Macos and iOS but on Android my test application just closes without any reasons.

score 2 · Accepted Answer · answered Nov 06 '19 at 10:25

Is it legal for libevent to use such approach?

So access to event/event_base can be done from multiple threads, in this case you need to enable threading support for libevent:

evthread_use_pthreads(); // or similar

And later use BEV_OPT_THREADSAFE for bufferevent thread-safety.

For more details take a look in the book.

And even though your approach should work after this modifications, it is not a good design choice. It will be way more better to create event workers (separate event_base + thread) and schedule your event (event_add) in the event_base of the background thread.

Android my test application just closes without any reasons.

Need details.

Does libevent allow to run callback for timer/io in a different thread?

1 Answers1