What is multiprocessing.Queue?
The multiprocessing.Queue is a class provided by the multiprocessing module in Python that allows for the creation of a queue that can be used by multiple processes to pass messages to each other. The queue is implemented using shared memory, which allows for fast and efficient communication between processes. The Queue class provides a number of useful methods for adding and retrieving items from the queue, such as put() and get(). It also provides a way to set a maximum size for the queue, so that it can only hold a certain number of items at a time. This can be useful for controlling the amount of memory used by the queue, or for ensuring that the queue does not become overwhelmed with too many items.
Need and use of multiprocessing.Queue:
The main use of Queue is to pass messages between multiple processes. For example, a producer process can put items into the queue, and a consumer process can retrieve items from the queue. This allows the two processes to run concurrently and communicate with each other. This can be useful in a variety of situations, such as when you want to run a task in parallel using multiple processes, or when you want to pass data between different parts of a program running in separate processes.
Example of multiprocessing.Queue()
This code demonstrates the use of the Queue class from the multiprocessing module to communicate between two separate processes. The Queue class is used to create a queue that can be used by multiple processes to pass messages to each other. The code defines two functions, process1 and process2, that will be run in separate processes. The process1 function takes a single argument, q, which is an instance of the Queue class. It puts a string “hello” into the queue using the put() method.
The process2 function also takes a single argument, q, which is the same instance of the Queue class that was passed to process1. It gets the message from the queue using the get() method and prints it to the console.
In the if __name__ == ‘__main__’: block, an instance of the Queue class is created and assigned to the variable q. Then, two instances of the Process class are created and assigned to the variables p1 and p2. The Process class takes two arguments, target and args. The target argument is the function that the process will run, and args is a tuple of arguments to pass to the function. In this case, p1 is set to run the process1 function and p2 is set to run the process2 function. Both processes are passed the same q variable as an argument.
The start() method is called on both p1 and p2 to start the processes. The join() method is called on both p1 and p2 to wait for the processes to complete. This ensures that the main program does not exit before the processes have finished running.
In summary, the code creates two separate processes using the Process class from the multiprocessing module and uses the Queue class to pass data between the processes. The process1 function puts a string into the queue, and the process2 function gets the string from the queue and prints it to the console. The start() method is used to start the processes, and the join() method is used to wait for the processes to complete.
Python3
from multiprocessing import Process, Queue # Define a function that will run in a separate process def process1(q): # Put a string into the queue q.put('hello') # Define a function that will run in a separate process def process2(q): # Get a message from the queue and print it to the console print(q.get()) # The following code will only run if the script is run directly if __name__ == '__main__': # Create an instance of the Queue class q = Queue() # Create two instances of the Process class, one for each function p1 = Process(target=process1, args=(q,)) p2 = Process(target=process2, args=(q,)) # Start both processes p1.start() p2.start() # Wait for both processes to finish p1.join() p2.join() |
Output:
Python multiprocessing.Queue vs multiprocessing.manager().Queue()
In Python, the multiprocessing module allows for the creation of separate processes that can run concurrently on different cores of a computer. One of the ways to communicate between these processes is by using queues. The multiprocessing module provides two types of queues:
- The Queue class is a simple way to create a queue that can be used by multiple processes. It can be used to pass messages between processes and has a number of useful methods for adding and retrieving items from the queue.
- The manager().Queue() class creates a queue that is managed by a separate process called a manager. The manager is responsible for maintaining the queue and ensuring that it is accessible to all processes that need to use it.