死锁示例

deadlock.py

#!/usr/bin/env python
# encoding: utf-8

import time


def multi_acquire_worker(mutex):
    ''' 同一线程多次请求同一资源，直接造成死锁

    为了解决在同一线程中多次请求同一资源，使用可重入锁 threading.RLock
    RLock 中维护着一个 Lock 和一个 counter，counter 记录了被 acquire 的
    总次数，直到该线程中所有的 acquire 都被 release，其它的线程才能够获
    得资源

    >>> import threading
    >>> mutex = threading.Lock()
    >>> # mutex = threading.RLock()
    >>> for i in range(10):
    ...   thread = threading.Thread(
    ...     target=multi_acquire_worker,
    ...     args=(mutex,)
    ...   )
    ...   thread.start()

    '''
    mutex.acquire()
    mutex.acquire()
    mutex.release()
    mutex.release()


def cross_acquire_worker(mutex_1, mutex_2):
    '''
    相互调用导致死锁

    >>> import threading
    >>> mutex_a = threading.Lock()
    >>> mutex_b = threading.Lock()
    >>> for args in [(mutex_a, mutex_b), (mutex_b, mutex_a)]:
    ...   thread = threading.Thread(target=cross_acquire_worker, args=args)
    ...   thread.start()

    '''
    mutex_1.acquire()
    time.sleep(1)
    mutex_2.acquire()
    mutex_2.release()
    mutex_1.release()