Python線程協(xié)作threading.Condition實現(xiàn)過程解析

更新時間：2020年03月12日 12:27:29 作者：我太難了008

這篇文章主要介紹了Python線程協(xié)作threading.Condition實現(xiàn)過程解析,文中通過示例代碼介紹的非常詳細，對大家的學習或者工作具有一定的參考學習價值,需要的朋友可以參考下

領會下面這個示例吧,其實跟java中wait/nofity是一樣一樣的道理

import threading


# 條件變量,用于復雜的線程間同步鎖
"""
需求:
  男:小姐姐,你好呀!
  女:哼,想泡老娘不成?
  男:對呀,想泡你
  女:滾蛋,門都沒有!
  男:切,長這么丑, 還這么吊...
  女:關(guān)你鳥事!

"""
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("{}:對呀,想泡你".format(self.name))
      self.condition.wait()
      self.condition.notify()

      print("{}:切,長這么丑, 還這么吊...".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("{}:滾蛋,門都沒有!".format(self.name))
      self.condition.notify()
      self.condition.wait()

      print("{}:關(guān)你鳥事!".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的底層實現(xiàn)了__enter__和 __exit__協(xié)議.所以可以使用with上下文管理器

由Condition的__init__方法可知,它的底層也是維護了一個RLock鎖

 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,還是有點懵.....

wait()方法源碼中這樣三行代碼

waiter = _allocate_lock() #從底層獲取了一把鎖,并非Lock鎖
waiter.acquire()
self._waiters.append(waiter) # 然后將這個鎖加入到_waiters(deque)中
saved_state = self._release_save() # 這是釋放__enter__時的那把鎖???

notify()方法源碼

all_waiters = self._waiters  
waiters_to_notify = _deque(_islice(all_waiters, n))# 從_waiters中取出n個
if not waiters_to_notify:  # 如果是None,結(jié)束
   return
for waiter in waiters_to_notify: # 循環(huán)release
   waiter.release()
   try:
     all_waiters.remove(waiter) #從_waiters中移除
   except ValueError:
     pass

大體意思: wait先從底層創(chuàng)建鎖,acquire, 放到一個deque中,然后釋放掉with鎖, notify時,從deque取拿出鎖,release

以上就是本文的全部內(nèi)容，希望對大家的學習有所幫助，也希望大家多多支持腳本之家。

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