threading锁机制：守护共享数据

import threading lock = threading.Lock()counter = 0 def increment():    global counter    for _ in range(1000):        with lock:            counter += 1 threads = [threading.Thread(target=increment) for _ in range(10)]for t in threads:    t.start()for t in threads:    t.join()print(counter)  # 10000，永远正确

lock = threading.Lock()def recursive(n):    with lock:          # 第一次获取成功        if n == 0:            return        recursive(n-1)  # 第二次获取——死锁！

rlock = threading.RLock()def recursive(n):    with rlock:          # 第一次获取，计数=1        if n == 0:            return        recursive(n-1)  # 第二次获取，计数=2，不阻塞# 完全释放需要等所有嵌套的 with 退出

semaphore = threading.Semaphore(3)  # 最多3个线程同时进入 def worker():    with semaphore:      # 获取信号量，计数减1        # 访问有限资源        time.sleep(1)    # 释放信号量，计数加1

pool = threading.Semaphore(5)def query():    with pool:           # 最多5个线程同时进入        db.execute("SELECT ...")

condition = threading.Condition() def consumer():    with condition:        while not data_ready:            condition.wait()       # 释放锁，挂起等待        process(data)              # 被唤醒后处理数据 def producer():    with condition:        data = produce_data()        data_ready = True        condition.notify()         # 唤醒等待的消费者

def transfer(from_acct, to_acct, amount):    with from_acct.lock:       # 先锁自己的账户        with to_acct.lock:     # 再锁对方的账户            from_acct.balance -= amount            to_acct.balance += amount # 线程1: transfer(A, B, 100)# 线程2: transfer(B, A, 100)# A被线程1锁住，B被线程2锁住，双方都等对方锁的资源——死锁！

def transfer(from_acct, to_acct, amount):    acct1, acct2 = sorted([from_acct, to_acct], key=lambda a: a.id)    with acct1.lock:        with acct2.lock:            from_acct.balance -= amount            to_acct.balance += amount

import threadingimport time # 死锁复现def deadlock_demo():    lock1 = threading.Lock()    lock2 = threading.Lock()     def worker_a():        with lock1:            time.sleep(0.01)            with lock2:   # 等待锁2，而锁2可能在B手中                pass     def worker_b():        with lock2:            time.sleep(0.01)            with lock1:   # 等待锁1，而锁1在A手中                pass     t1 = threading.Thread(target=worker_a)    t2 = threading.Thread(target=worker_b)    t1.start(); t2.start()    t1.join(timeout=1); t2.join(timeout=1)    print("死锁发生：两个线程互相等待，卡死不动")

"""线程锁四件套演示：计数器保护 + 可重入 + 信号量限流 + 条件同步"""import threadingimport timeimport random class SharedCounter:    def __init__(self):        self.value = 0        self.lock = threading.RLock()     def increment(self):        with self.lock:            self.value += 1            # 嵌套调用Rlock仍然安全            self.check()     def check(self):        with self.lock:            if self.value % 1000 == 0:                print(f"计数到: {self.value}") def lock_demo():    counter = SharedCounter()    threads = [threading.Thread(target=counter.increment)               for _ in range(10)]    for t in threads:        t.start()    for t in threads:        t.join()    print(f"Lock/RLock保护结果: {counter.value}") def semaphore_demo():    pool = threading.Semaphore(2)    active = []     def worker(idx):        with pool:            active.append(idx)            print(f"线程{idx}进入, 活跃数={len(active)}")            time.sleep(random.uniform(0.1, 0.3))            active.remove(idx)     threads = [threading.Thread(target=worker, args=(i,))               for i in range(5)]    for t in threads:        t.start()    for t in threads:        t.join()    print("信号量限流完成") def condition_demo():    cv = threading.Condition()    items = []     def producer():        for i in range(3):            with cv:                items.append(i)                print(f"生产: {i}")                cv.notify_all()            time.sleep(0.1)     def consumer():        for _ in range(3):            with cv:                while not items:                    cv.wait()                item = items.pop(0)                print(f"消费: {item}")     p = threading.Thread(target=producer)    c = threading.Thread(target=consumer)    c.start()    p.start()    p.join()    c.join()    print("条件变量同步完成") if __name__ == "__main__":    lock_demo()    semaphore_demo()    condition_demo()