Python线程协作threading.Condition实现过程解析

  • Z时代
  • 2024-01-10
  • 分类：综合

领会下面这个示例吧,其实跟java中wait/nofity是一样一样的道理

import threading
# 条件变量,用于复杂的线程间同步锁
"""
需求:
  男:小姐姐,你好呀!
  女:哼,想泡老娘不成?
  男:对呀,想泡你
  女:滚蛋,门都没有!
  男:切,长这么丑, 还这么吊...
  女:关你鸟事!
"""
class Boy(threading.Thread):
  def __init__(self, name, condition):
    super().__init__(name=name)
    self.condition = condition
  def run(self):
    with self.condition:
      print("{}:小姐姐,你好呀!".format(self.name))
      self.condition.wait()
      self.condition.notify()
      print("{}:对呀,想泡你".format(self.name))
      self.condition.wait()
      self.condition.notify()
      print("{}:切,长这么丑, 还这么吊...".format(self.name))
      self.condition.wait()
      self.condition.notify()
class Girl(threading.Thread):
  def __init__(self, name, condition):
    super().__init__(name=name)
    self.condition = condition
  def run(self):
    with self.condition:
      print("{}:哼,想泡老娘不成?".format(self.name))
      self.condition.notify()
      self.condition.wait()
      print("{}:滚蛋,门都没有!".format(self.name))
      self.condition.notify()
      self.condition.wait()
      print("{}:关你鸟事!".format(self.name))
      self.condition.notify()
      self.condition.wait()
if __name__ == '__main__':
  condition = threading.Condition()
  boy_thread = Boy('男', condition)
  girl_thread = Girl('女', condition)
  boy_thread.start()
  girl_thread.start()

Condition的底层实现了__enter__和 __exit__协议.所以可以使用with上下文管理器

由Condition的__init__方法可知,它的底层也是维护了一个RLock锁

 def __enter__(self):
    return self._lock.__enter__()

  def __exit__(self, *args):
    return self._lock.__exit__(*args)

 def __exit__(self, t, v, tb):
    self.release()

def release(self):
    """Release a lock, decrementing the recursion level.
    If after the decrement it is zero, reset the lock to unlocked (not owned
    by any thread), and if any other threads are blocked waiting for the
    lock to become unlocked, allow exactly one of them to proceed. If after
    the decrement the recursion level is still nonzero, the lock remains
    locked and owned by the calling thread.
    Only call this method when the calling thread owns the lock. A
    RuntimeError is raised if this method is called when the lock is
    unlocked.
    There is no return value.
    """
    if self._owner != get_ident():
      raise RuntimeError("cannot release un-acquired lock")
    self._count = count = self._count - 1
    if not count:
      self._owner = None
      self._block.release()

至于wait/notify是如何操作的,还是有点懵.....

wait()方法源码中这样三行代码

waiter = _allocate_lock() #从底层获取了一把锁,并非Lock锁

waiter.acquire()

self._waiters.append(waiter) # 然后将这个锁加入到_waiters(deque)中

saved_state = self._release_save() # 这是释放__enter__时的那把锁???

notify()方法源码

all_waiters = self._waiters  
waiters_to_notify = _deque(_islice(all_waiters, n))# 从_waiters中取出n个
if not waiters_to_notify:  # 如果是None,结束
   return
for waiter in waiters_to_notify: # 循环release
   waiter.release()
   try:
     all_waiters.remove(waiter) #从_waiters中移除
   except ValueError:
     pass

大体意思: wait先从底层创建锁,acquire, 放到一个deque中,然后释放掉with锁, notify时,从deque取拿出锁,release

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