In-depth understanding of the garbage collection mechanism in Go language

In-depth understanding of the garbage collection mechanism in Go language requires specific code examples

Introduction:
With the continuous development of software development and computer technology, garbage collection (Garbage Collection, GC), as an automatic memory management mechanism, has become one of the common features in modern programming languages. The garbage collection mechanism helps developers solve the complexity and difficulty of manual memory management, greatly improving the reliability and development efficiency of applications. As a language with high development efficiency and strong concurrency performance, Go language's garbage collection mechanism is an important part of its efficiency. This article will delve into the garbage collection mechanism in the Go language and deepen our understanding of this mechanism through specific code examples.

1. Garbage collection algorithm
Go language uses a garbage collection algorithm called Concurrent Mark and Sweep (CMS). This algorithm has the following characteristics:

1. Concurrent processing: During the garbage collection process, the program can continue to run without stopping the entire program, greatly reducing the pause time.
2. Incremental processing: The garbage collection process is divided into multiple stages, and only a part of the objects are processed each time, avoiding long delays.

2. Garbage collection process
The garbage collection process of Go language can be divided into three stages: marking stage, cleaning stage and compression stage.

1. Marking phase:
   The marking phase is the first phase of garbage collection. It traverses the object graph and marks reachable objects as "alive". Unmarked objects are considered "Rubbish". This is the most time-consuming stage of the entire garbage collection process, but because the Go language uses a concurrent marking algorithm, marking can be performed while the program is running.

The following is a simple sample code that shows how to manually trigger the garbage collection process:

package main

import (
    "fmt"
    "runtime"
    "time"
)

func main() {
    fmt.Println("程序开始时的内存占用：", getMemUsage())

    for i := 0; i < 10; i++ {
        createGarbage()
    }

    fmt.Println("初次创建垃圾后的内存占用：", getMemUsage())

    // 手动触发垃圾回收
    runtime.GC()

    fmt.Println("手动触发垃圾回收后的内存占用：", getMemUsage())
}

func createGarbage() {
    for i := 0; i < 10000; i++ {
        _ = make([]byte, 1024)
    }
}

func getMemUsage() uint64 {
    var m runtime.MemStats
    runtime.ReadMemStats(&m)
    return m.Alloc
}

In this sample code, we call the createGarbage function 10 times to create some garbage objects. In the initial state, we can check the memory usage of the program by calling the getMemUsage function. Then, we manually called runtime.GC() to trigger garbage collection. Calling the getMemUsage function again, we can see that the memory usage of the program has been reduced after garbage collection. This is because garbage collection cleans up unreferenced objects.

2. Cleaning phase:
   The cleaning phase is the second phase of garbage collection. It is mainly responsible for recycling objects marked as "garbage". During this phase, the garbage collector traverses all objects in the heap, releases unmarked objects, and reclaims the heap space.
3. Compression phase:
   The compression phase is the last phase of garbage collection. Its main function is to compress the heap. After some unmarked objects are released during the cleaning phase, a large number of memory holes will be generated, and these memory holes will affect the memory allocation efficiency of the program. The compression phase moves surviving objects to one end and frees up free space. After compression, programs can use memory more efficiently.

3. Garbage collection optimization parameters
In order to provide better performance and adjustability, the Go language provides some garbage collection optimization parameters, which can be adjusted according to the actual situation.

1. GOGC: By setting the environment variable GOGC, you can adjust the balance between the triggering and pause time of the garbage collector. The default value is 100, which means that garbage collection will be automatically triggered every time 100 objects are generated. Larger values ​​can trigger the garbage collector less frequently, but can also result in longer pause times.
2. GODEBUG: You can enable or disable some garbage collection related debugging information by setting the environment variable GODEBUG. For example, you can enable the garbage collection tracking function by setting GODEBUG=gctrace=1 to view the execution of each stage.

4. Summary
This article discusses the garbage collection mechanism in the Go language, and deepens the understanding of the mechanism through specific code examples. The garbage collection mechanism allows developers to focus more on the logic implementation of the program without paying too much attention to memory management. By properly adjusting the parameters of the garbage collector, the performance and adjustability of the program can be further improved. I believe that by in-depth understanding of the garbage collection mechanism, we can better take advantage of the Go language and develop efficient and reliable applications.

Reference:

• Go language official documentation (https://golang.org/doc/)
• "The Go Programming Language" by Alan A. A. Donovan and Brian W. Kernighan

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