补全：一把大锁拆成每键一把

👁️ 3 人浏览 💬 0 人评论 ❤️ 添加收藏

本节的东西：

model(tasks)   时间模型：每条线程 (算, 改) 两段耗时；粗锁全串行 = Σ(算+改)，细锁算并行改串行 = max(算) + Σ改；交回 (粗, 细)
timed(fn, workers, work)   开 workers 条线程各跑 fn(work)，交回耗时
coarse(work)   sleep(work) 关在锁里再改 total；fine(work)   sleep 在锁外，只把改关在锁里

一个计数字典，键之间互不相关。补全 Sharded：每个键一把锁（self.locks[key]），inc(key) 只拿那个键的锁做读-睡-写。四条线程各对自己的键加 10 次；和 Global（一把大锁）比：结果都对、Sharded 更快。

提交你的答案

请登录后提交答案。

去登录

← 补全：太细会超卖补全：给临界区计时 →

更多题目

代码编辑器

语言： Ctrl + Enter 运行

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 Global:
    def __init__(self, keys):
        self.d = {k: 0 for k in keys}
        self.lock = threading.Lock()

def inc(self, key):
        with self.lock:
            tmp = self.d[key]
            time.sleep(0.001)
            self.d[key] = tmp + 1

class Sharded:
    def __init__(self, keys):
        self.d = {k: 0 for k in keys}
        self.locks = {k: threading.Lock() for k in keys}

def inc(self, key):
        # TODO
        pass

def run(store):
    def job(k):
        for _ in range(10):
            store.inc(k)
    ts = [threading.Thread(target=job, args=(k,)) for k in "甲乙丙丁"]
    t0 = time.perf_counter()
    for t in ts:
        t.start()
    for t in ts:
        t.join()
    return time.perf_counter() - t0, sorted(store.d.values())

tg, vg = run(Global("甲乙丙丁"))
ts_, vs = run(Sharded("甲乙丙丁"))
print(str(vg).replace(" ", "") + "/" + str(vs).replace(" ", "") + "/" + str(ts_ < tg))

本次输入：

输出：

👩‍🏫

AI

💬 题目评论

补全：一把大锁拆成每键一把

更多题目

全部评论