Python Condition notify()用法及代码示例

Python Condition.notify() 方法

notify() 是 Python 中线程模块的 Condition 类的内置方法。

条件类实现条件变量对象。条件变量允许一个或多个线程等待，直到它们被另一个线程通知。此方法用于唤醒任何等待条件变量的线程。只有当调用线程获得锁时，才必须调用该线程。这个方法最多可以唤醒n个正在等待条件变量的线程；如果没有线程在等待，则为 no-op。

在此处阅读有关 Producer-Consumer 的信息：Condition.acquire() 方法

模块：

    from threading import Condition

用法:

    notify(n=1)

参数：

• n:它是一个可选参数，它指定了等待条件变量的可以唤醒的线程数。其默认值为 1。

返回值：

这个方法的返回类型是<class 'NoneType'>.该方法不返回任何内容。它通知正在等待条件的线程。

例：

# Python program to explain the
# use of notify() method for Condition object

import threading
import time
import random

class subclass:
  # Initialising the shared resources
  def __init__(self):
    self.x = []
  
  # Add an item for the producer
  def produce_item(self, x_item):
    print("Producer adding an item to the list")
    self.x.append(x_item)
    
  # Consume an item for the consumer
  def consume_item(self):
    print("Consuming from the list")
    consumed_item = self.x[0]
    print("Consumed item:", consumed_item)
    self.x.remove(consumed_item)

def producer(subclass_obj, condition_obj):
    # Selecting a random number from the 1 to 3
    r = random.randint(1,3)
    print("Random number selected was:", r)
    
    # Creting r number of items by the producer
    for i in range(1, r):
      print("Producing an item, time it will take(seconds):" + str(i))
      time.sleep(i)
      
      print("Producer acquiring the lock")
      condition_obj.acquire()
      try:
        # Produce an item
        subclass_obj.produce_item(i)
        # Notify that an item  has been produced
        condition_obj.notify()
      finally:
        # Releasing the lock after producing
        condition_obj.release()
      
def consumer(subclass_obj, condition_obj):
    condition_obj.acquire()
    while True:
      try:
        # Consume the item 
        subclass_obj.consume_item()
      except:
        print("No item to consume, list empty")
        print("Waiting for 10 seconds")
        # wait with a maximum timeout of 10 sec
        value = condition_obj.wait(10)
        if value:
          print("Item produced notified")
          continue
        else:
          print("Waiting timeout")
          break
        
    # Releasig the lock after consuming
    condition_obj.release()
    
if __name__=='__main__':
    
  # Initialising a condition class object
  condition_obj = threading.Condition()
  # subclass object
  subclass_obj = subclass()
  
  # Producer thread
  pro = threading.Thread(target=producer, args=(subclass_obj,condition_obj,))
  pro.start()
  
  # consumer thread
  con = threading.Thread(target=consumer, args=(subclass_obj,condition_obj,))
  con.start()

  pro.join()
  con.join()
  print("Producer Consumer code executed")

输出：

Random number selected was:3
Producing an item, time it will take(seconds):1
Consuming from the list
No item to consume, list empty
Waiting for 10 seconds
Producer acquiring the lock
Producer adding an item to the list
Item produced notified
Consuming from the list
Consumed item: 1
Consuming from the list
No item to consume, list empty
Waiting for 10 seconds
Producing an item, time it will take(seconds):2
Producer acquiring the lock
Producer adding an item to the list
Item produced notified
Consuming from the list
Consumed item: 2
Consuming from the list
No item to consume, list empty
Waiting for 10 seconds
Waiting timeout
Producer Consumer code executed