touchfile

touchfile is a Go package that provides a mechanism for creating, locking, and managing touch files to coordinate access between different processes and goroutines. It uses file locks (flock) to ensure only one process or thread has exclusive access to a critical section at a time.

This package is designed for scenarios where multiple processes or threads need to coordinate on a shared resource (e.g., a file). It leverages mutexes for goroutine safety and file-based locks for process-level coordination.

Features

• Mutex protection: Ensures safe access across multiple goroutines.
• Process-level locking: Uses advisory locking (flock) for file-level coordination between different processes.
• Support for both shared and exclusive locks: Choose between shared (read) locks and exclusive (write) locks.
• Timeout handling with context: Automatically handle lock acquisition with context-based timeouts and cancellation.
• Critical section helpers: Simplified WithLock function for running code within a lock-protected critical section.

Important notes

Non-reentrant

This package is not reentrant. It is up to the caller to avoid recursive calls that attempt to acquire the same lock, which would result in deadlocks.

File system compatibility

flock may not be compatible with all file systems (notably networked file systems like NFS). Please ensure your file system supports advisory file locks.

Installation

To install the package, run:

go get github.com/trufflesecurity/touchfile

In your Go module, import the package with:

import "github.com/trufflesecurity/touchfile"

Example usage

Basic usage

ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()

tf, err := touchfile.NewTouchFile("/tmp/mylockfile")
if err != nil {
    log.Fatalf("failed to create touch file: %v", err)
}

if err := tf.Lock(ctx, touchfile.Exclusive); err != nil {
    log.Fatalf("failed to acquire lock: %v", err)
}
defer func() {
    if err := tf.Unlock(); err != nil {
        log.Printf("failed to release lock: %v", err)
    }
}()

Global lock using the program binary

program, err := os.Executable()
if err != nil {
  log.Fatalf("failed to determine executable path: %v", err)
}

tf, err := touchfile.NewTouchFile(program)
...

Using WithLock for a critical section

tf, err := touchfile.NewTouchFile("/tmp/mylockfile")
if err != nil {
    log.Fatalf("failed to create touch file: %v", err)
}

err = tf.WithLock(ctx, touchfile.Exclusive, func() error {
    fmt.Println("Doing some work while holding the lock")
    return nil
})
if err != nil {
    log.Fatalf("operation failed: %v", err)
}

API

NewTouchFile(path string) (*TouchFile, error)

Creates a new TouchFile instance using the specified file path. If the path is empty, a temporary file will be used.

Lock(ctx context.Context, lockType LockType) error

Acquires the specified lock (Shared or Exclusive) on the touch file. The function will attempt to acquire the lock until the context times out or is canceled.

Unlock() error

Releases the lock on the touch file.

WithLock(ctx context.Context, lockType LockType, f func() error) error

A convenience function that locks the touch file, executes the provided function, and then releases the lock. It ensures the lock is always released, even if the function returns an error.