异常飞出去，锁还在不在

（每道题开头都有同一段：上面那几样。）

贯穿全条的几样东西：

Counter / SafeCounter   读-睡-写的计数器；Safe 版用 with self.lock 包住三步（conc_03 的写法）
hammer(counter, workers, times)   开几条线程各加 times 次，交回最终的 n（真线程，题里只比大小）
probe(lock)   这把锁现在能不能立刻拿到（acquire(blocking=False)，拿到就放回）——用它「看」锁的状态，不卡住
Guard(lock)   手写的 with 替身：__enter__ 拿、__exit__ 放

两种写法各让临界区里抛一次异常，看异常之后锁是不是放开了：

import threading
import time


class Counter:
    def __init__(self):
        self.n = 0

    def inc(self):
        tmp = self.n
        time.sleep(0.001)
        self.n = tmp + 1


class SafeCounter(Counter):
    def __init__(self):
        super().__init__()
        self.lock = threading.Lock()

    def inc(self):
        with self.lock:
            tmp = self.n
            time.sleep(0.001)
            self.n = tmp + 1


def hammer(counter, workers=2, times=30):
    def job():
        for _ in range(times):
            counter.inc()
    ts = [threading.Thread(target=job) for _ in range(workers)]
    for t in ts:
        t.start()
    for t in ts:
        t.join()
    return counter.n


def probe(lock):
    """这把锁现在能不能立刻拿到？能就拿了再放回去，交回 True；拿不到交回 False。"""
    if lock.acquire(blocking=False):
        lock.release()
        return True
    return False


class Guard:
    """手写的 with 替身：进就 acquire，出就 release——不管是正常出还是异常出。"""
    def __init__(self, lock):
        self.lock = lock

    def __enter__(self):
        self.lock.acquire()
        return self

    def __exit__(self, exc_type, exc, tb):
        self.lock.release()
        return False


def by_with(lock):
    with lock:
        raise ValueError("坏了")


def by_hand(lock):
    lock.acquire()
    raise ValueError("坏了")
    lock.release()


res = []
for fn in (by_with, by_hand):
    L = threading.Lock()
    try:
        fn(L)
    except ValueError:
        pass
    res.append(str(probe(L)))
print("/".join(res))