In-depth analysis of Golang's GC mechanism

As we all know, Go language is an efficient and easy-to-develop programming language. As a language with relatively automated memory management, there is a very important function in its runtime system called garbage collection. Garbage Collection, also known as automatic memory management, is an automated memory management mechanism and is one of the choices for many current programming languages.

For Golang's garbage collection mechanism, scheduling is based on the memory currently used by the program. By default, GC speed is randomly assigned and based on very fine-grained configurable parameters. This makes garbage collection more flexible and adjustable. However, Golang's GC will seriously affect the performance of the program, so we must clearly know the execution time of GC.

Golang’s GC mechanism is generally based on three parameters: gcpercent, GOGC and maxprocs. They are all parameters related to GC.

The gcpercent parameter specifies how much memory the Golang program uses before starting to run GC. By default, gcpercent is 100, that is, when the used memory exceeds 1 times the maximum memory size of the program (-X), GC will be triggered. However, we can change this value through the command line parameter "-gcpercent". For example, "-gcpercent=50" means that half of the current maximum memory is used to start executing GC.

The GOGC parameter specifies the triggering frequency of GC by the program. When GOGC is equal to 100, it means that every time the memory size is doubled, the program will trigger a GC. Since the default value is 100, the Go program will live for a very limited time, that is, garbage collection will be very frequent. Therefore, in order to reduce the execution frequency of GC, we can appropriately reduce the value of the GOGC parameter, for example, set it to 20. That is to say, every time 1/5 of the current maximum memory is used, a GC will be triggered.

The maxprocs parameter can be used to control the concurrency of the program. If the machine has 8 CPUs, each CPU can execute one thread. This means that the default concurrency level of Golang programs is 8. When we set the maxprocs parameter to a smaller value, such as 2 or 4, the GC execution time of the program will be reduced. Because this parameter describes the "concurrency" of the Golang program, the burden on each CPU is reduced, and even when GC is required, CPU context switching can be reduced, thereby improving the performance and response speed of the program.

So, how long is the GC execution time of a Golang program? In fact, the answer to this question is uncertain because it depends on factors such as the GC mode, GC parameters, the size and complexity of the application, and so on. However, in actual operation, we can check how well the GC is performed by adding code to the program to measure the time required for each GC cycle. For example:

package main

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

func main() {
    for i := 0; i < 10; i++ {
        t := time.Now()
        m := new([1 << 20]byte) 
        fmt.Println(time.Since(t))

        _ = m
        runtime.GC() 
    }
}

This code will create a 1 MB memory block, and then in each loop, measure the time required for each GC cycle. By running the above code, we can get a result, for example:

10.537µs
12.006µs
13.350µs
14.306µs
9.764µs
13.955µs
15.262µs
14.515µs
15.621µs
15.714µs

As can be seen from the above output, the time required for each GC cycle is unstable, but its time itself is relatively short. Therefore, we can conclude that in Golang programs, the GC execution time depends on factors such as the size, complexity, and application load of the program, but for the overall performance of the program, the GC execution time is relatively short. . By optimizing the design of GC parameters and programs, we can better utilize Golang's efficient performance.

In short, Golang’s garbage collection mechanism is a very important automatic memory management tool. By appropriately adjusting the GC parameters of the Golang program, computer resources can be better utilized and the execution efficiency and response speed of the program can be improved.

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