补全：等 N 个人到齐

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本节的东西：

Box(cap)   Condition 保护的有界队列：put 满了等、get 空了等；等 = cond.wait_for(条件)，等的时候把锁交出去、醒来再拿回；改完 notify_all
run_pc(cap, n)   一个生产者放 0..n-1、一个消费者取 n 个，交回消费者拿到的顺序

补全 Meet(n)：arrive(name) 记下到的人，然后等到齐（人数 == n）才返回，返回时交回按名字排序的全体名单。三条线程各 arrive 一次，看三条都拿到同一份名单。

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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

class Meet:
    def __init__(self, n):
        self.n = n
        self.names = []
        self.cond = threading.Condition()

def arrive(self, name):
        # TODO: 记下、notify_all、wait_for 到齐、交回 sorted(self.names)
        return []

m = Meet(3)
results = []

def go(name):
    results.append(m.arrive(name))

ts = [threading.Thread(target=go, args=(x,)) for x in ("3", "1", "2")]
for t in ts:
    t.start()
for t in ts:
    t.join()
print(str(len(results)) + "/" + "".join(results[0]) + "/" + str(all(r == results[0] for r in results)))

本次输入：

输出：

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