python wait方法_Python条件类| 带有示例的wait（）方法

python wait方法

Python Condition.wait()方法 (Python Condition.wait() Method)

wait() is an inbuilt method of the Condition class of the threading module in Python.

wait()是Python中线程模块的Condition类的内置方法。

Condition class implements condition variable objects. A condition variable allows one or more threads to wait until they are notified by another thread. wait() method is used to block the thread and wait until some other thread notifies it by calling the notify() or notify_all() method or if the timeout occurs. The method returns a True Boolean value if it is released by notify() or notify_all() method otherwise a timeout happens, in that case, it returns False. If you wait on an unacquired lock, a Runtime Error is raised.

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，直到被另一个线程通知为止。 wait()方法用于阻塞线程，并等待直到其他线程通过调用notify()或notify_all()方法通知该线程或发生超时。如果方法是通过notify()或notify_all()方法释放的，则该方法返回True布尔值，否则会发生超时，在这种情况下，它将返回False。如果等待未获得的锁定，则会引发“运行时错误”。

Read about Producer-Consumer here: Condition.acquire() Method

在这里阅读有关Producer-Consumer的信息： Condition.acquire()方法

Module:

模块：

    from threading import Condition

Syntax:

句法：

    wait(timeout=None)

Parameter(s):

参数：

timeout: It is an optional parameter, which specifies the time for which the thread will wait for a notify call. Its default value is None.
timeout ：这是一个可选参数，它指定线程等待通知调用的时间。其默认值为无。

Return value:

返回值：

The return type of this method is <class 'bool'>. It returns True if it gets notified by the notify() method within given time. In case of a timeout, it returns False.

此方法的返回类型为<class'bool'> 。如果在指定时间内通过notify()方法得到通知，则返回True。如果超时，则返回False。

Example:

例：

# Python program to explain the
# use of wait() 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")

Output:

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