What are differences between multithreading, multiprocessing and asyncio in Python?

cpu bound tasks
memory management

Well, that is, except if you are working with multiprocessing/multithreading. Concurrent.futures API provides an easier methodology to implement threads and processes. In other words, it aids in the asynchronous execution of processes.

  • Since the processes Process-1 and Process-2 are performing the task of asking their own CPU core to sit idle for a few seconds, we don’t find high Power Usage.
  • If the user does the action before the Timer expires, .cancel() can be called.
  • Conventional compiled programming languages, such as C/C++, do not have interpreter, not even mention GIL.

Threads have a lower overhead compared to processes; spawning processes take more time than threads. Using processes and process pools via the multiprocessing module in Python is probably the best path toward achieving this end. The multiprocessing module provides powerful and flexible concurrency, although is not suited for all situations where you need to run a background task.

The order in which threads are run is determined by the operating system and can be quite hard to predict. It may vary from run to run, so you need to be aware of that when you design algorithms that use threading. A daemon thread will shut down immediately when the program exits. One way to think about these definitions is to consider the daemon thread a thread that runs in the background without worrying about shutting it down.

The computation is just to add one to the value and then .sleep() for a little bit. Finally, it writes the value back by copying the local value back to .value. Fortunately, this race condition will happen every time, and you’ll walk through it in detail to explain what is happening.

Multitasking made easy with Python examples

Of course, this is not good for executions that require greater computation, as the GIL/lock upon the thread would remain. In this case, multiprocessing is beneficial, allowing you to split your workload across multiple CPU cores. A thread is an entity within a process that can be scheduled for execution (Also known as “leightweight process”).

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This has implications for the types of tasks best suited to each class. Async version of the download_link method we’ve been using in the other examples. RQ is easy to use and covers simple use cases extremely well, but if more advanced options are required, other Python 3 queue solutions can be used. Creation of a thread is economical in both sense time and resource.

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Many of the examples in the rest of this article will have WARNING and DEBUG level logging. We’ll generally only show the WARNING level output, as the DEBUG logs can be quite lengthy. Try out the programs with the logging turned up and see what they do. In this output you can see Thread 0 acquires the lock and is still holding it when it goes to sleep.

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When the first thread’s IO returned the lock would then be reacquired. Therefore, threading has provided us with some additional benefit without requiring the overhead needed in creating multiple processes. Since threads share the same memory location within a parent process, special precautions must be taken so that two threads don’t write to the same memory location. CPython interpreters use the Global Interpreter Lock mechanism to prevent multiple threads from executing Python bytecodes at the same time. This lock is very important as CPython’s memory management is not thread-safe. For the CPU bound task, multiple processes perform way better than multiple threads.

As such, the limit on these operations is the python multiprocessing vs threading of the CPU. A CPU-bound task is a type of task that involves performing a computation and does not involve IO where data needs to be shared between processes. Additionally, the GIL is a design decision that affects the reference implementation of Python. If you use a different implementation of the Python interpreter , then you may not be subject to the GIL and can use threads for CPU bound tasks directly.

What is Multiprocessing? How is it different from threading?

Also, keep in mind that you don’t have to use a single form of parallelism throughout your program. You should use one or the other for different parts of your program, whichever is suitable for that particular part. Threading should be used for programs involving IO or user interaction. Processes are heavyweight structures; each has at least a main thread. In this section, we’ll look at broad types of tasks and why they are or are not appropriate for the processes.

You’ll be passing in large numbers, so this will take a while. First off, it does not specify how many processes to create in the Pool, although that is an optional parameter. By default, multiprocessing.Pool() will determine the number of CPUs in your computer and match that. This is frequently the best answer, and it is in our case.

It does not have any IO bottleneck; on the contrary, it’s a very CPU intensive task. Because of the added programming overhead of object synchronization, multi-threaded programming is more bug-prone. On the other hand, multi-processes programming is easy to get right. Sharing objects between threads is easier, as they share the same memory space.


We ran the the blocks concurrently giving an impression of parallel execution. Call asyncio.run to start the asynchronous section of your program. Add await keyword when you call your async functions (without it they won’t run).

Fortunately, sklearn has already implemented multiprocessing into this algorithm and we won’t have to write it from scratch. As you can see in the code below, we just have to provide a parameter n_jobs—the number of processes it should use—to enable multiprocessing. Now we’ll look into how we can reduce the running time of this algorithm. We know that this algorithm can be parallelized to some extent, but what kind of parallelization would be suitable?

In multithreading, accessing memory addresses is easy because all of the threads share the same parent process. Now that we got a fair idea about multiprocessing helping us achieve parallelism, we shall try to use this technique for running our IO-bound tasks. We do observe that the results are extraordinary, just as in the case of multithreading.

  • As you can imagine, hitting this exact situation is fairly rare.
  • For this example, you’re going to imagine a program that needs to read messages from a network and write them to disk.
  • At a high level, it does this by creating a new instance of the Python interpreter to run on each CPU and then farming out part of your program to run on it.
  • One of the cool advantages of asyncio is that it scales far better than threading.

Since a https://forexhero.info/ doesn’t have to do anything until it receives a response, it doesn’t really matter that only one thread is executing at a given time. So processes and threads are both different operating system constructs. In brief, a thread is an execution stream, and a process is a container of threads that all share the same memory. Multithreading avoids pickling, whereas Multiprocessing relies on pickling objects in memory to send to other processes.

A threading.Barrier can be used to keep a fixed number of threads in sync. When creating a Barrier, the caller must specify how many threads will be synchronizing on it. They all will remain blocked until the specified number of threads are waiting, and then the are all released at the same time. As the program starts to wrap up, can you see the main thread generating the event which causes the producer to exit immediately. The consumer still has a bunch of work do to, so it keeps running until it has cleaned out the pipeline. If that happens, it’s possible for the consumer to wake up and exit with the queue still completely full.


Examples of things that are slower than your CPU are legion, but your program thankfully does not interact with most of them. The slow things your program will interact with most frequently are the file system and network connections. Concurrency can make a big difference for two types of problems. This website is using a security service to protect itself from online attacks. The action you just performed triggered the security solution.

threading library

Since there is only one thread in this example, this has no effect. In the usage above, index is passed as the first and only positional argument to database.update(). You’ll see later in this article where you can pass multiple arguments in a similar manner. When you create a Thread, you pass it a function and a list containing the arguments to that function. In this case, you’re telling the Thread to run thread_function() and to pass it 1 as an argument. I’ve written up a threading version of this code and placed it with the other example code in the GitHub repo so you can go test this yourself.

Once all of the tasks have been sorted into the right list again, the event loop picks the next task to run, and the process repeats. Your simplified event loop picks the task that has been waiting the longest and runs that. If the new code that is running modifies counter as well, then the first thread has a stale copy of the data and trouble will ensue.

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