Certain scenerio and custom log dispatch causes deadlock at dispatch because of global lock

[abumq]

Consider following program (also added to samples)

#include <chrono>
#include <thread>
#include <future>
#include "easylogging++.h"

INITIALIZE_EASYLOGGINGPP

void f() {
    std::async(std::launch::async, [&]() {
        std::cout << "[internal] inside async()" << std::endl;
        std::this_thread::sleep_for(std::chrono::seconds(1));
        LOG(INFO) << "This is from async";
    });
}

class MyHandler : public el::LogDispatchCallback {
public:
    void handle(const el::LogDispatchData* d) {
        std::cout << "Message: " << d->logMessage()->message() << " [logger: " << d->logMessage()->logger()->id() << "]" << std::endl;
        if (d->logMessage()->logger()->id() != "default") {
            std::cout << "[internal] calling f()" << std::endl;
            f();
        }
    }
};



int main(int,char**){
    el::Loggers::addFlag(el::LoggingFlag::CreateLoggerAutomatically);
    // el::Helpers::uninstallLogDispatchCallback<el::base::DefaultLogDispatchCallback>("DefaultLogDispatchCallback");
    el::Helpers::installLogDispatchCallback<MyHandler>("MyHandler");

    LOG(INFO)<<"The program has started!";
    CLOG(INFO, "frommain") << "THis is another";

    std::thread t1([](){
        LOG(INFO) << "This is from thread";
    });

    t1.join();

    LOG(INFO) << "Shutting down.";
    return 0;
}

we should be able to use LOG(...) (i.e, default logger) in above case as we have custom handler. But because of global lock ELPP->lock() in LogDispatch this scenerio is not possible. We need to allow this scenerio

The expected output is

2017-10-12 13:55:48,712 INFO [default] The program has started!
Message: The program has started! [logger: default]
2017-10-12 13:55:48,713 INFO [frommain] THis is another
Message: THis is another [logger: frommain]
[internal] calling f()
[internal] inside async()
2017-10-12 13:55:49,716 INFO [default] This is from async
Message: This is from async [logger: default]
2017-10-12 13:55:49,717 INFO [default] This is from thread
Message: This is from thread [logger: default]
2017-10-12 13:55:49,717 INFO [default] Shutting down.
Message: Shutting down. [logger: default]

but we are getting a deadlock

2017-10-12 14:00:00,587 INFO [default] The program has started!
Message: The program has started! [logger: default]
2017-10-12 14:00:00,588 INFO [frommain] THis is another
Message: THis is another [logger: frommain]
[internal] calling f()
[internal] inside async()
... {no output after this}

Documentation

In documentation it says

DO NOT LOG ANYTHING IN THIS HANDLER OR YOU WILL END UP IN INFINITE-LOOP

that is still true but above if (d->logMessage()->logger()->id() != "default") { should allow logging with default logger inside the dispatch handler