Python Event wait()用法及代码示例

Python Event.wait() 方法

wait() 是 Python 中线程模块的 Event 类的内置方法。

当我们想要一个线程等待一个事件时，我们可以在内部标志设置为 false 的事件上调用 wait() 方法，从而阻塞线程，直到该事件对象的内部标志被 set() 方法设置为 true。如果内部标志在进入时为真，则线程不会被阻塞。线程保持阻塞状态，直到内部标志保持为 false 或发生超时。我们可以在 timeout 参数的帮助下为函数提供可选的超时。

模块：

    from threading import Event

用法:

    wait(timeout=None)

参数：

• timeout: 可选参数，指定wait()方法的超时时间。一旦超过该值，等待该事件的线程就会解除阻塞。其默认值为无。

返回值：

这个方法的返回类型是<class 'Bool'>.如果线程在超时之前被释放，则返回，否则返回 false。

范例1：

# Python program to explain the
# use of wait() method in Event() class
import threading
import time

def helper_function(event_obj, timeout,i):
  # Thread has started, but it will wait 10 seconds for the event  
  print("Thread started, for the event to set")
 
  flag = event_obj.wait(timeout)
  if flag:
    print("Event was set to true() earlier, moving ahead with the thread")
  else:
    print("Time out occured, event internal flag still false. Executing thread without waiting for event")
    print("Value to be printed=", i)
    
if __name__ == '__main__':
  # Initialising an event object
  event_obj = threading.Event()
  
  # starting the thread who will wait for the event
  thread1 = threading.Thread(target=helper_function, args=(event_obj,10,27))
  thread1.start()
  # sleeping the current thread for 5 seconds
  time.sleep(5)
  
  # generating the event
  event_obj.set()
  print("Event is set to true. Now threads can be released.")
  print()

输出：

Thread started, for the event to set
Event is set to true. Now threads can be released.

Event was set to true() earlier, moving ahead with the thread

范例2：

# Python program to explain the
# use of wait() method in Event() class
import threading
import time

def helper_function(event_obj, timeout,i):
  # Thread has started, but it will wait 3 seconds for the event  
  print("Thread started, for the event to set")
 
  flag = event_obj.wait(timeout)
  if flag:
    print("Event was set to true() earlier, moving ahead with the thread")
  else:
    print("Time out occured, event internal flag still false. Executing thread without waiting for event")
    print("Value to be printed=", i)
    
if __name__ == '__main__':
  # Initialising an event object
  event_obj = threading.Event()
  
  # starting the thread who will wait for the event
  thread1 = threading.Thread(target=helper_function, args=(event_obj,3,27))
  thread1.start()
  # sleeping the current thread for 5 seconds
  time.sleep(5)
  
  # generating the event
  event_obj.set()
  print("Event is set to true. Now threads can be released.")
  print()

输出：

Thread started, for the event to set
Time out occured, event internal flag still false. Executing thread without waiting for event
Value to be printed= 27
Event is set to true. Now threads can be released.