python - 正确锁定方法调用

Question

我正在与测量设备通话。我基本上发送命令并接收答案。但我提供了一个方法 ask 来发送命令并读回答案。如果我锁定此方法，则会由于调用的方法 read 和 write 锁定而陷入死锁。如果我不锁定另一个线程可能会在我阅读之前窃取答案或写。您将如何实现？

import threading

class Device(object):
    lock = threading.Lock()
    def ask(self, value):
        # can't use lock here would block
        self.write(value) # another thread could start reading the answer
        return self.read()

    def read(self):
        with self.lock:
            # read values from device

    def write(self, value):
        with self.lock:
            # send command to device

Answer 1

使用threading.RLock()避免单个线程内的争用:

A reentrant lock is a synchronization primitive that may be acquired multiple times by the same thread. Internally, it uses the concepts of “owning thread” and “recursion level” in addition to the locked/unlocked state used by primitive locks. In the locked state, some thread owns the lock; in the unlocked state, no thread owns it.