Example Assignment: Counting Semaphores

class Semaphore:
    def __init__(self, value = 0):
        self.count = value
        self.queue = []
        self.mutex = thread.allocate_lock()

    def wait(self):
        self.mutex.acquire()
        self.count = self.count - 1
        if self.count < 0:
            wlock = thread.allocate_lock()
            wlock.acquire()
            self.queue.append(wlock)
            self.mutex.release()
            wlock.acquire()  # suspend on new lock
        else:
            self.mutex.release()

    def signal(self):
        self.mutex.acquire()
        self.count = self.count + 1
        if self.count <= 0:
            wlock = self.queue[0]
            del self.queue[0]
            wlock.release() # let the waiting thread go
        self.mutex.release()