Golang high concurrency programming skills: in-depth understanding of the scheduling strategy of Goroutines

Golang high-concurrency programming skills: In-depth understanding of the scheduling strategy of Goroutines

Introduction: Golang is a high-concurrency language, and its built-in lightweight thread Goroutines is one of the core features of its concurrent programming. This article will delve into the scheduling strategy of Goroutines and how to optimize the performance of concurrent programs through reasonable use of scheduling strategies.

1. Scheduling strategy of Goroutines

Goroutines are lightweight threads of Golang. Compared with traditional operating system threads, the scheduling of Goroutines is more flexible and efficient. Golang uses a component called the scheduler to decide which Goroutine to execute and when. In Golang, we generally do not need to manually control the scheduling of Goroutines, but the scheduler does it automatically.

The scheduling strategy of Goroutines mainly includes three aspects: preemptive scheduling, collaborative scheduling and Work Stealing.

1. Preemptive scheduling

Golang's scheduler adopts a preemptive scheduling strategy, that is, the execution of any Goroutine may be interrupted by other Goroutines at any time. The advantage of this scheduling strategy is that it can reasonably allocate CPU resources and prevent a certain Goroutine from monopolizing the CPU for a long time, causing other Goroutines to be unable to execute. When a Goroutine is preempted, the scheduler saves its state and switches to other executable Goroutines.

2. Collaborative scheduling

In addition to preemptive scheduling, Golang's scheduler also adopts a collaborative scheduling strategy. In cooperative scheduling, Goroutine will automatically give up the execution rights of the CPU instead of occupying the CPU all the time. By actively giving up the CPU at the appropriate time and switching between Goroutines reasonably, the concurrency performance of the entire system can be improved.

3. Work Stealing

Work Stealing is a very important mechanism in the Golang scheduler. Its core idea is to allow idle threads to actively "steal" tasks from other threads for execution, thereby achieving load balancing between threads. This mechanism can avoid the situation where some threads work too much while other threads remain idle, further improving the performance of concurrent programs.

2. Scheduling strategy example demonstration

In order to better understand the scheduling strategy of Goroutines, let’s look at a simple example code to explore the impact of different scheduling strategies on concurrent programs.

package main

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

func main() {
    runtime.GOMAXPROCS(1) // 设置只使用一个CPU核心

    var wg sync.WaitGroup
    wg.Add(2)

    fmt.Println("Start Goroutines")

    // 第一个Goroutine
    go func() {
        defer wg.Done()

        for i := 0; i < 3; i++ {
            fmt.Println("Goroutine 1: ", i)
        }
    }()

    // 第二个Goroutine
    go func() {
        defer wg.Done()

        for i := 0; i < 3; i++ {
            fmt.Println("Goroutine 2: ", i)
        }
    }()

    fmt.Println("Waiting to finish")
    wg.Wait()
    fmt.Println("Terminating the program")
}

In the above code, we set up to use only one CPU core through runtime.GOMAXPROCS(1) in order to better observe the effects of different scheduling strategies.

When running the sample code, we can observe the effects of the following different scheduling strategies:

1. Only one Goroutine is executing. In this case, the Goroutine that finishes executing first will release the CPU and execute other Goroutines.
2. Two Goroutines are executed alternately. In this case, since there is only one CPU core, Goroutines will switch execution between each other.
3. After one Goroutine is completely executed, another Goroutine begins to execute.

By continuously adjusting the value of runtime.GOMAXPROCS and observing the output of the program, we can have a deeper understanding of the impact of different scheduling strategies on concurrent programs.

Conclusion:

By deeply understanding the scheduling strategy of Goroutines, we can better evaluate the performance of Golang programs and optimize the running effects of concurrent programs. By setting reasonable scheduling strategies and writing efficient concurrency code, we can give full play to the high concurrency features of the Golang language and improve the performance and stability of the program.

References:

1. https://golang.org/doc/effective_go.html#goroutines
2. https://blog.golang.org/scheduler

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