What is the difference between concurrency and parallelism in Go

The difference between concurrency and parallelism: 1. Concurrency means assigning tasks to processors for processing at different points in time, while parallelism means assigning each task to each processor for independent completion; 2. Concurrency At the same point in time, tasks will not run at the same time, but in parallel, at the same point in time, the tasks must run at the same time.

The operating environment of this tutorial: Windows 7 system, GO version 1.18, Dell G3 computer.

When understanding the concept of concurrency, there is always another concept of parallelism involved. Let us understand the difference between concurrency and parallelism.

Concurrency: Handle tasks to the processor for processing at different points in time. At the same point in time, tasks do not run at the same time.

Parallelism: Assign each task to each processor to complete independently. At the same point in time, the tasks must be running at the same time.

Concurrency is not parallelism. Parallelism is having different pieces of code execute on different physical processors at the same time. The key to parallelism is to do many things at the same time, and concurrency refers to managing many things at the same time. These things may only be done halfway before being paused to do other things.

In many cases, concurrency is better than parallelism, because the total resources of the operating system and hardware are generally very small, but they can support the system to do many things at the same time. This philosophy of "doing more with less resources" is also the philosophy that guides the design of the Go language.

If you want to make goroutines parallel, you must use more than one logical processor. When there are multiple logical processors, the scheduler will distribute goroutines equally to each logical processor. This will cause the goroutine to run on a different thread. However, to truly achieve parallelism, users need to run their programs on machines with multiple physical processors. Otherwise, even if the Go language uses multiple threads when running, goroutines will still run concurrently on the same physical processor, and the parallel effect will not be achieved.

The following figure shows the difference between running goroutines concurrently on one logical processor and running two concurrent goroutines in parallel on two logical processors. The scheduler contains some clever algorithms that will be updated and improved with the release of the Go language, so it is not recommended to blindly modify the default settings for logical processors during the language runtime. If you really think that modifying the number of logical processors will improve performance, you can also make slight adjustments to the language runtime parameters.

Figure: The difference between concurrency and parallelism

Go language can achieve parallel execution when the number of GOMAXPROCS is equal to the number of tasks, but under normal circumstances it is executed concurrently .

【Related recommendations: Go video tutorial, Programming teaching】

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