Python timeout context manager with threads

I have timeout context manager that works perfectly with signals but it raises error in multithread mode because signals work only in main thread.

def timeout_handler(signum, frame):
    raise TimeoutException()

@contextmanager
def timeout(seconds):
    old_handler = signal.signal(signal.SIGALRM, timeout_handler)
    signal.alarm(seconds)
    try:
        yield
    finally:
        signal.alarm(0)
        signal.signal(signal.SIGALRM, old_handler)

I've seen decorator implementation of timeout but I don't know how to pass yield inside class derived from threading.Thread. My variant won't work.

@contextmanager
def timelimit(seconds):
    class FuncThread(threading.Thread):
        def run(self):
            yield

    it = FuncThread()        
    it.start()
    it.join(seconds)

    if it.isAlive():
        raise TimeoutException()