Library is not thread-safe: deadlock can happen

[sergey-shambir]

Here library calls foreign callbacks under mutex lock here:

template<typename R, typename... Args>
	R signal<R(Args...)>::operator() (Args... args)
	{
		std::lock_guard<std::mutex> locker(_mutex);
		// ...

Imagine that one thread connects to "signal1" own function "slot1" which fires "signal2". First, it locks "signal1" mutex, then attempts to lock "signal2" mutex.

Another thread connects to "signal2" own function "slot2" which fires "signal1". First, it locks "signal2" mutex, then attempts to lock "signal1" mutex.

In some cases, threads will enter into deadlock: thread1 always waits "signal2" mutex, while thread2 always waits "signal1" mutex.