Examples showing how to implement file locking in Go language

In the operating system, a file lock is a locking mechanism that allows file integrity and consistency to be maintained when multiple processes or threads access the same file. In Go language, file locking is also required. This article will introduce how to implement file locking in Go language.

File lock types provided by the operating system

In the Linux operating system, there are two types of file locks, namely file-based locks (also called flock locks) and record-based locks. Lock. Commonly used lock types are as follows:

• F_RDLCK: Shared lock for reading files;
• F_WRLCK: Exclusive lock for writing files;
• F_UNLCK: Do not use locks.

The Go language provides access to read-write locks, but flock and record-based locks are not supported.

File lock provided by Go language

The Go standard library provides synchronization primitives for files, including sync.Mutex and sync.RWMutex, They are used to solve access problems between multiple coroutines. These primitives do not work at the file system level, so they cannot be used to implement file locks. So how to implement file locking?

In the Go language, file locking can be implemented using the "golang.org/x/sys/unix" package using the POSIX API.

golang.org/x/sys/unix package

golang.org/x/sys/unix The package is a low-level underlying package provided by the Go language, which encapsulates the system Calls and POSIX API. Although there are some related packages and functions in the standard library, they do not work properly on many Unix systems. Therefore, the package is widely used and is officially maintained by Go.

Implementing file locks in Go

In the Go language, implementing file locks is very simple and requires only three steps: open the file, lock the file and release the lock.

The following is a code example that implements locking and releasing the lock:

package main

import (
    "fmt"
    "golang.org/x/sys/unix"
    "os"
)

func lockFile(f *os.File) error {
    err := unix.Flock(int(f.Fd()), unix.LOCK_EX|unix.LOCK_NB)
    if err != nil {
        return fmt.Errorf("cannot lock file: %s", err.Error())
    }
    return nil
}

func unlockFile(f *os.File) error {
    err := unix.Flock(int(f.Fd()), unix.LOCK_UN)
    if err != nil {
        return fmt.Errorf("cannot unlock file: %s", err.Error())
    }
    return nil
}

func main() {
    f, err := os.OpenFile("/tmp/file.lock", os.O_RDWR|os.O_CREATE, 0666)
    if err != nil {
        fmt.Println("error:", err)
        return
    }

    err = lockFile(f)
    if err != nil {
        fmt.Println("error:", err)
        return
    }

    // do something

    err = unlockFile(f)
    if err != nil {
        fmt.Println("error:", err)
        return
    }
}

After locking the code block, you can perform your operations. Only release the lock when you are finished with the operation or when you need to release the lock. Also, you cannot lock a file if another process or thread is using it. At this point, you can use the unix.LOCK_NB flag to make it fail quickly and prevent deadlocks.

Summary

In this article, we introduced the concept of file locking in the Go language and showed how to use the golang.org/x/sys/unix package and POSIX API implements the basic principles of file locking. When multiple coroutines need to read and write the same file, implementing file locks can help us ensure the integrity and consistency of the file.

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