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Python Condition Class | notify_all() Method with Example

Python Condition.notify_all() Method: Here, we are going to learn about the notify_all() method of Condition Class in Python with its definition, syntax, and examples.
Submitted by Hritika Rajput, on May 24, 2020

Python Condition.notify_all() Method

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

Condition class implements condition variable objects. A condition variable allows one or more threads to wait until they are notified by another thread. This method is used to wake all the threads which are waiting on a condition variable.

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

Module:

    from threading import Condition

Syntax:

    notify_all()

Parameter(s):

  • None

Return value:

The return type of this method is <class 'NoneType'>. The method does not return anything. It notifies all the threads that are waiting on the condition.

Example:

# Python program to explain the
# use of acquire() 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)
    print("Consumed by:", str(threading.current_thread().getName()))
    self.x.remove(consumed_item)

def producer(subclass_obj, condition_obj):
    # Selecting a random number from the 1 to 4
    r = random.randint(1,4)
    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 all consumers that an item  has been produced
        condition_obj.notify_all()
      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()
  
  # Consumer1 thread
  con1 = threading.Thread(target=consumer, args=(subclass_obj,condition_obj,))
  con1.start()

  # Consumer2 thread
  con2 = threading.Thread(target=consumer, args=(subclass_obj,condition_obj,))
  con2.start()

  pro.join()
  con1.join()
  con2.join()
  print("Producer Consumer code executed")

Output:

Random number selected was: 4
Producing an item, time it will take(seconds): 1
Consuming from the list
No item to consume, list empty
Waiting for 10 seconds
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
Consumed by: Thread-2
Consuming from the list
No item to consume, list empty
Waiting for 10 seconds
Item produced notified
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
Consumed by: Thread-3
Consuming from the list
No item to consume, list empty
Waiting for 10 seconds
Producing an item, time it will take(seconds): 3Item produced notified

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:  3
Consumed by: Thread-3
Consuming from the list
No item to consume, list empty
Waiting for 10 seconds
Item produced notified
Consuming from the list
No item to consume, list empty
Waiting for 10 seconds
Waiting timeout
Waiting timeout
Producer Consumer code executed
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