python之多线程 threading.Lock() 和 threading.RLock()

2. threading.Lock() 的必要性
3.观察block
4.threading.RLock() 的应用场景

1.参考

Thread Synchronization Mechanisms in Python

count += 1 不是原子操作，三步操作可能被中断，通过lock将三步操作“封装”为一步操作，要么执行，要么不执行。

counter = 0

def process_item(item):
    global counter
    ... do something with item ...
    counter += 1

# The reason for this is that the increment operation is actually executed in three steps; 
#first, the interpreter fetches the current value of the counter,
# then it calculates the new value,
# and finally, it writes the new value back to the variable.

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