python全局字典是什么_在python中使用带有线程的全局字典

假设cpython:yes和no,从共享字典中获取/存储值实际上是安全的,因为多个并发读/写请求不会损坏字典。这是由于实现维护的全局解释器锁(“gil”)。即:

A线运行:

a = global_dict["foo"]

B线运行:

global_dict["bar"] = "hello"

线程C运行:

global_dict["baz"] = "world"

不会损坏字典,即使所有三次访问尝试同时发生。解释器将以某种未定义的方式序列化它们。

但是,以下序列的结果未定义:

线程A:

if "foo" not in global_dict:

global_dict["foo"] = 1

线程B:

global_dict["foo"] = 2

因为线程A中的测试/设置不是原子的(“检查时间/使用时间”竞争条件)。所以,一般来说,最好是锁上东西:

from threading import RLock

lock = RLock()

def thread_A():

lock.acquire()

try:

if "foo" not in global_dict:

global_dict["foo"] = 1

finally:

lock.release()

def thread_B():

lock.acquire()

try:

global_dict["foo"] = 2

finally:

lock.release()