How to develop daemon process in Go language?

Go language is a fast and efficient programming language. It has good features in daemon process development, such as built-in concurrency support, lightweight threads, garbage collection mechanism, etc. A daemon is a program that can be executed in the background. It usually needs to run for a long time, constantly listening to external events, such as network connection requests, and processing the events that occur accordingly. This article will introduce how to develop daemon process in Go language.

1. Basic requirements of daemon process

In Linux and Unix operating systems, a daemon process needs to meet some basic requirements:

1. Must have a parent process, This parent process is preferably the init process, which ensures that the daemon can still run after the system is restarted.
2. The daemon needs to put itself in the background when it starts and release the controlling terminal.
3. The daemon needs to be able to handle signals such as SIGTERM and SIGINT in order to properly clean itself up when the system shuts down or terminates.

2. Steps to implement daemon process

To develop a daemon process in Go language, you need to complete the following steps:

1. Create a child process and exit the parent process Process;
2. Call the setsid() function to create a new session group and make the current process the leader of the session group and the only member of the new process group;
3. Close file descriptor 0, 1, 2 (standard input, standard output, standard error output);
4. Create a writable directory under the root directory (/) of the file system, open its file descriptor, and then use it as The working directory and root file system of the process;
5. Load the resources needed when the program starts, including configuration files, environment variables, etc.;
6. Process SIGTERM and SIGINT signals to clean up the program correctly resource.

Below, we will introduce the specific implementation of these steps one by one.

3. Implementation details

1. Create a child process and exit the parent process

The code snippet for creating a child process and exiting the parent process in Go language is as follows :

func startDaemon() {
    cmd := exec.Command(os.Args[0])
    cmd.Start()
    os.Exit(0)
}

This code will start a new process and exit the current process, making the new process a child process of the daemon process.

2. Create a new conversation group

The code snippet to create a new conversation group in Go language is as follows:

func startDaemon() {
    syscall.Umask(0)
    if syscall.Getppid() == 1 {
        return
    }
    cmd := exec.Command(os.Args[0])
    cmd.Start()
    os.Exit(0)
    ...
    sysret, syserr := syscall.Setsid()
    if syserr != nil || sysret < 0 {
        fmt.Fprintf(os.Stderr, "Error: syscall.Setsid errno:%d %v
", syserr, syserr)
        os.Exit(1)
    }
}

This code first sets up the file The permission mask is 0, and then checks whether the current process is already the leader process of a session group (that is, whether the parent process is the init process). If so, there is no need to create a new conversation group. Otherwise, call the setsid() function mentioned above to create a new session group and make the current process the leader of the session group.

3. Close the file descriptor

In the Go language, the code fragment for closing the file descriptor is as follows:

func startDaemon() {
    syscall.Umask(0)
    if syscall.Getppid() == 1 {
        return
    }
    cmd := exec.Command(os.Args[0])
    cmd.Start()
    os.Exit(0)
    ...
    syscall.Close(0)    // close stdin
    syscall.Close(1)    // close stdout
    syscall.Close(2)    // close stderr
}

This code uses the syscall package The Close() function closes file descriptors 0, 1, and 2.

4. Create a writable directory

The code snippet to create a writable directory in Go language is as follows:

func startDaemon() {
    syscall.Umask(0)
    if syscall.Getppid() == 1 {
        return
    }
    cmd := exec.Command(os.Args[0])
    cmd.Start()
    os.Exit(0)
    ...
    os.Chdir("/")
    dir, _ := ioutil.TempDir("", "")
    fd, _ := os.Open(dir)
    syscall.Dup2(int(fd.Fd()), 0)
    syscall.Dup2(int(fd.Fd()), 1)
    syscall.Dup2(int(fd.Fd()), 2)
}

This code first removes the process Change the current working directory to the root directory (/), and then use the TempDir() function in the ioutil package to create a new directory under the /tmp directory. Next, use the os.Open() function to open the directory and use the Dup2() function in the syscall package to copy its file descriptors to the file descriptors for standard input, standard output, and standard error.

5. Load the required resources

The code fragment for loading the required resources can be written in the entry function of the program.

6. Processing SIGTERM and SIGINT signals

The code for processing SIGTERM and SIGINT signals in Go language is as follows:

func main() {
    ...
    c := make(chan os.Signal, 1)
    signal.Notify(c, os.Interrupt, syscall.SIGTERM)
    go func() {
        <-c
        // 执行清理操作
        os.Exit(0)
    }()
    ...
}

This code uses the os package The Signal() function transfers the SIGTERM and SIGINT signals to a pipeline for processing. Then, by listening to this pipe in another goroutine, you can perform cleanup operations when these signals are received.

4. Summary

This article introduces how to develop a daemon process in the Go language. A daemon is a long-running program that needs to handle various external events. It needs to meet some basic requirements, such as having a parent process, putting itself in the background when starting, etc. Methods to implement these requirements in the Go language include creating a child process and exiting the parent process, creating a new session group, closing file descriptors, creating a writable directory, loading required resources, and handling SIGTERM and SIGINT signals. After mastering these methods, we can freely develop daemon processes in the Go language.

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