""" Author: Allen B. Downey This file contains an example program from The Little Book of Semaphores, available from Green Tea Press, greenteapress.com This code is in the public domain. """ import threading, time, os, signal, sys class Thread(threading.Thread): """Wrapper for the Thread class in the threading module.""" def __init__(self, target, *args): """Create and start a thread. target: callable args: passed along to target """ threading.Thread.__init__(self, target=target, args=args) self.start() class Semaphore(threading._Semaphore): """Wrapper for the Semaphore class in the threading module.""" wait = threading._Semaphore.acquire def signal(self, n=1): """Signal the semaphore. n: how many times to signal """ for i in range(n): self.release() def value(self): """Returns the current value of the semaphore. Note: asking for the value of a semaphore is almost always a bad idea. If you do anything based on the result, it is likely to be a mistake. """ return self._Semaphore__value def watcher(): """Forks a process, and the child process returns. The parent process waits for a KeyBoard interrupt, kills the child, and exits. This is a workaround for a problem with Python threads: when there is more than one thread, a KeyBoard interrupt might be delivered to any of them (or occasionally, it seems, none of them). """ child = os.fork() if child == 0: return try: os.wait() except KeyboardInterrupt: print 'KeyBoardInterrupt' try: os.kill(child, signal.SIGKILL) except OSError: pass sys.exit()