How is the scheduler implemented in golang functions?

The Go language scheduler is a non-preemptive scheduler that can manage the execution of Goroutine. It maintains a queue of Goroutines organized by priority: when a Goroutine completes, it returns to the scheduler. The scheduler removes completed Goroutines from the queue. The scheduler selects the highest priority Goroutine in the queue. The scheduler schedules selected Goroutines to available processors.

Scheduler implementation in Go language

Introduction

The scheduler is A key component of the Go runtime environment (runtime), responsible for managing the execution of Goroutines (lightweight threads). It decides when and on which CPU to run a Goroutine to fully utilize computer resources and improve program performance.

Scheduler design

The Go language scheduler is a non-preemptive scheduler. This means that it will not interrupt a running Goroutine, even if a higher priority Goroutine is ready to run. Instead, the current Goroutine must exit on a specific event (for example, an IO operation) before the scheduler selects the next Goroutine to run.

The scheduler maintains a Goroutine queue, called a queue. This queue is organized according to the priority of Goroutines, with higher priority Goroutines being queued in front of lower priority Goroutines.

Workflow

When a Goroutine completes, it returns to the scheduler. The scheduler will then:

1. remove the Goroutine from the queue.
2. Select the highest priority Goroutine in the queue.
3. Scheduling the selected Goroutine to available processors.

Practical case

The following code example demonstrates how the scheduler in a Go program operates:

package main

import (
    "fmt"
    "runtime"
    "sync/atomic"
    "time"
)

var counter int64

var wg sync.WaitGroup

func main() {
    // 创建 50 个 Goroutine
    for i := 0; i < 50; i++ {
        wg.Add(1)
        go func() {
            defer wg.Done()
            for j := 0; j < 100000; j++ {
                atomic.AddInt64(&counter, 1)
            }
        }()
    }

    // 等待所有 Goroutine 完成
    wg.Wait()

    fmt.Println("Final counter value:", counter)
}

In this example:

• The main Goroutine creates 50 Goroutines.
• Each Goroutine increases the value of a local counter 100000 times.
• The main Goroutine waits for all Goroutines to complete.
• Once all Goroutines complete, the main Goroutine prints the value of the final global counter.

Running this program will output:

Final counter value: 5000000

This output shows that the scheduler can effectively manage the concurrent execution of all 50 Goroutines and ensure the correctness of the final result.

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