Safe Cross Thread Signals/Slot C++

Question

It seem that the only implementation that provide Safe Cross-Thread Signals for both the Signal class and what's being called in the slot is QT. (Maybe I'm wrong?).

But I cannot use QT in the project I'm doing. So how could I provide safe Slots call from a different thread (Using Boost::signals2 for example)? Are mutex inside the slot the only way? I think signals2 protect themself but not what's being done inside the slot.

Thanks

Answer 1

It's not a signals-slots implementation, exactly, but there's a C++ implementation of Twisted's Deferred pattern that accomplishes a similar goal to a cross-thread signal-slot mechanism. If someone doesn't come along and post a better solution, it might be worth a look: http://sourceforge.net/projects/deferred/

Answer 2

You can combine boost::bind and boost ASIO to create Cross-Thread Calls.

# In Thread 2
boost::asio::io_service service;
boost::asio::io_service::work work (service); // so io service won't stop if there is no work 
service.run() # starting work thread

# In Thread 1
service.post (boost::bind (&YourClass::function, &yourClassInstance, parameter1, parameter2))

Thread 2 will go into a loop and will execute your bound function. I think you can also call Boost::Signals2 calls into this loop.

But keep care: If you do cross-thread-signaling, make sure that the destination object still exists when being called. You can garantuee that by dropping all connections in your targets destructor (not in their base class destructor, also see Signals-Trackable Class)

I do not like Boost::Signals2 oo much, because of its very long stack trace and compile times (blog post).