【代码】缓存击穿保护器singleflight

fs = dict()
lock = Lock()
def singleflight(key, func):
    with lock:
        if key in fs:
            wait = True
            f = fs[key]
        else:
            wait = False
            f = [None, Event()]
            fs[key] = f
    if wait:
        f[1].wait()
        r = f[0]
    else:
        r = func()
        f[0] = r
        f[1].set()
    with lock:
        fs.pop(key, None)
    return r