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中線程模塊的Condition類的內置方法。

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.

條件類實現條件變量對象 。 條件變量允許一個或多個線程等待，直到被另一個線程通知為止。 wait()方法用于阻塞線程，并等待直到其他線程通過調用notify()或notify_all()方法通知該線程或發生超時。 如果方法是通過notify()或notify_all()方法釋放的，則該方法返回True布爾值，否則會發生超時，在這種情況下，它將返回False。 如果等待未獲得的鎖定，則會引發“運行時錯誤”。

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

在這里閱讀有關Producer-Consumer的信息： Condition.acquire()方法

Module:

模塊：

    from threading import Condition

Syntax:

句法：

    wait(timeout=None)

Parameter(s):

參數：

• 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 ：這是一個可選參數，它指定線程等待通知調用的時間。 其默認值為無。

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.

此方法的返回類型為<class'bool'> 。 如果在指定時間內通過notify()方法得到通知，則返回True。 如果超時，則返回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:

輸出：

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

翻譯自: https://www.includehelp.com/python/condition-wait-method-with-example.aspx

python wait方法