Lock 和 RLock 各拿两次

（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

同一条线程对 Lock 和 RLock 各拿两次（第二次用不阻塞的 acquire，免得卡住），再放两次，看每一步：

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

res = []
for L in (threading.Lock(), threading.RLock()):
    L.acquire()
    second = L.acquire(blocking=False)
    L.release()
    if second:
        L.release()
    res.append(str(second) + ":" + str(probe(L)))
print("/".join(res))