Python多线程死锁问题如何解决？

死锁在多线程里挺常见的，主要就是几个线程互相等对方手里的锁，结果全卡住了。解决思路就一个核心：让所有线程都按同一个固定的顺序去申请锁。

比如，你有锁A和锁B，线程1先拿A再拿B，线程2也必须是先拿A再拿B。这样就不会出现一个拿着A等B，另一个拿着B等A的死循环了。

看个具体例子。下面这段代码模拟了一个经典死锁场景，然后我们用固定顺序加锁的方式修复它：

import threading
import time

# 这是会死锁的错误写法
def bad_example():
    lock_a = threading.Lock()
    lock_b = threading.Lock()

    def thread_1():
        with lock_a:
            print("Thread 1 acquired lock A")
            time.sleep(0.1)  # 稍微等一下，让另一个线程有机会拿到B
            with lock_b:
                print("Thread 1 acquired lock B")

    def thread_2():
        with lock_b:
            print("Thread 2 acquired lock B")
            time.sleep(0.1)
            with lock_a:
                print("Thread 2 acquired lock A")

    t1 = threading.Thread(target=thread_1)
    t2 = threading.Thread(target=thread_2)
    t1.start()
    t2.start()
    t1.join()
    t2.join()

# 修复后的正确写法
def fixed_example():
    lock_a = threading.Lock()
    lock_b = threading.Lock()

    # 关键：两个线程都按照先A后B的顺序加锁
    def thread_1():
        with lock_a:
            print("Thread 1 acquired lock A")
            time.sleep(0.1)
            with lock_b:
                print("Thread 1 acquired lock B")

    def thread_2():
        with lock_a:  # 注意这里也先申请A
            print("Thread 2 acquired lock A")
            time.sleep(0.1)
            with lock_b:
                print("Thread 2 acquired lock B")

    t1 = threading.Thread(target=thread_1)
    t2 = threading.Thread(target=thread_2)
    t1.start()
    t2.start()
    t1.join()
    t2.join()

if __name__ == "__main__":
    print("=== 错误示例（可能会卡住）===")
    # bad_example()  # 运行这个可能会死锁
    print("\n=== 修复后的示例 ===")
    fixed_example()

另外，Python的threading模块里有个RLock（可重入锁），同一个线程可以多次acquire而不会阻塞自己，这在某些嵌套调用场景下也能避免死锁。但最根本的还是设计好锁的获取顺序。

简单说就是：定个规矩，大家都按顺序拿锁。