Understand the essential differences between concurrency and parallelism in Go language

When learning concurrent programming, you often hear two concepts: Concurrency and Parallelism. Although these two terms are sometimes used interchangeably, they actually represent two different concepts. In the Go language, understanding the essential differences between concurrency and parallelism is crucial to writing efficient and reliable concurrent programs.

First, let us understand the concept of concurrency. Concurrency refers to a way of programming that allows multiple tasks to be executed at the same time, but not necessarily at the same time. In the concurrency model, tasks may be executed alternately, and the effect of "simultaneous" execution is achieved by switching contexts. In the Go language, you can use goroutine to achieve concurrency. Each goroutine represents a concurrently executed task.

The following is a simple example that demonstrates how to use goroutine to achieve concurrency:

package main

import (
    "fmt"
    "time"
)

func printNumbers() {
    for i := 1; i <= 5; i++ {
        fmt.Println(i)
        time.Sleep(1 * time.Second)
    }
}

func main() {
    go printNumbers()
    go printNumbers()
    time.Sleep(6 * time.Second)
}

In the above example, we define a printNumbers function for printing Numbers from 1 to 5. In the main function, two printNumbers goroutines are started through the go keyword so that they can be executed concurrently. Use the time.Sleep function to wait for enough time to ensure that the goroutine has enough time to execute.

Next, let’s take a look at the concept of parallelism. Parallelism means that multiple tasks are truly executed simultaneously, and the characteristics of multi-core processors can be used to improve performance. In the Go language, you can use GOMAXPROCS in the runtime package to set the degree of parallelism and specify the number of goroutines that can be executed simultaneously.

The following is an example of using parallelism:

package main

import (
    "fmt"
    "runtime"
    "sync"
)

func printNumbers(wg *sync.WaitGroup) {
    defer wg.Done()
    for i := 1; i <= 5; i++ {
        fmt.Println(i)
    }
}

func main() {
    runtime.GOMAXPROCS(2) // 设置并行度为2
    var wg sync.WaitGroup
    wg.Add(2)

    go printNumbers(&wg)
    go printNumbers(&wg)

    wg.Wait()
}

In the above example, we use sync.WaitGroup to wait for all goroutines to complete execution. Set the parallelism to 2 through runtime.GOMAXPROCS so that two goroutines can be executed at the same time. In practical applications, the performance advantages brought by multi-core processors can be fully utilized by setting the parallelism reasonably according to the number of cores of the machine and the characteristics of the task.

Through the above examples, we can see the application of concurrency and parallelism in the Go language. Concurrency is a programming paradigm that allows multiple tasks to be executed alternately; parallelism uses multi-core processors to execute multiple tasks at the same time to improve program performance. For writing efficient and reliable concurrent programs, it is important to understand the essential differences between concurrency and parallelism. I hope the above examples can help you better understand the concepts of concurrency and parallelism in the Go language.

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