145 lines
3.9 KiB
Go
145 lines
3.9 KiB
Go
// Copyright 2015 Tim Heckman. All rights reserved.
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// Use of this source code is governed by the BSD 3-Clause
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// license that can be found in the LICENSE file.
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// Package flock implements a thread-safe interface for file locking.
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// It also includes a non-blocking TryLock() function to allow locking
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// without blocking execution.
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//
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// Package flock is released under the BSD 3-Clause License. See the LICENSE file
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// for more details.
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//
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// While using this library, remember that the locking behaviors are not
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// guaranteed to be the same on each platform. For example, some UNIX-like
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// operating systems will transparently convert a shared lock to an exclusive
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// lock. If you Unlock() the flock from a location where you believe that you
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// have the shared lock, you may accidentally drop the exclusive lock.
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package flock
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import (
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"context"
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"os"
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"runtime"
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"sync"
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"time"
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)
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// Flock is the struct type to handle file locking. All fields are unexported,
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// with access to some of the fields provided by getter methods (Path() and Locked()).
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type Flock struct {
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path string
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m sync.RWMutex
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fh *os.File
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l bool
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r bool
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}
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// New returns a new instance of *Flock. The only parameter
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// it takes is the path to the desired lockfile.
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func New(path string) *Flock {
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return &Flock{path: path}
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}
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// NewFlock returns a new instance of *Flock. The only parameter
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// it takes is the path to the desired lockfile.
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//
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// Deprecated: Use New instead.
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func NewFlock(path string) *Flock {
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return New(path)
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}
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// Close is equivalent to calling Unlock.
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//
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// This will release the lock and close the underlying file descriptor.
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// It will not remove the file from disk, that's up to your application.
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func (f *Flock) Close() error {
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return f.Unlock()
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}
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// Path returns the path as provided in NewFlock().
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func (f *Flock) Path() string {
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return f.path
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}
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// Locked returns the lock state (locked: true, unlocked: false).
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//
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// Warning: by the time you use the returned value, the state may have changed.
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func (f *Flock) Locked() bool {
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f.m.RLock()
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defer f.m.RUnlock()
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return f.l
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}
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// RLocked returns the read lock state (locked: true, unlocked: false).
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//
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// Warning: by the time you use the returned value, the state may have changed.
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func (f *Flock) RLocked() bool {
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f.m.RLock()
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defer f.m.RUnlock()
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return f.r
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}
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func (f *Flock) String() string {
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return f.path
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}
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// TryLockContext repeatedly tries to take an exclusive lock until one of the
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// conditions is met: TryLock succeeds, TryLock fails with error, or Context
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// Done channel is closed.
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func (f *Flock) TryLockContext(ctx context.Context, retryDelay time.Duration) (bool, error) {
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return tryCtx(ctx, f.TryLock, retryDelay)
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}
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// TryRLockContext repeatedly tries to take a shared lock until one of the
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// conditions is met: TryRLock succeeds, TryRLock fails with error, or Context
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// Done channel is closed.
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func (f *Flock) TryRLockContext(ctx context.Context, retryDelay time.Duration) (bool, error) {
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return tryCtx(ctx, f.TryRLock, retryDelay)
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}
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func tryCtx(ctx context.Context, fn func() (bool, error), retryDelay time.Duration) (bool, error) {
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if ctx.Err() != nil {
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return false, ctx.Err()
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}
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for {
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if ok, err := fn(); ok || err != nil {
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return ok, err
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}
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select {
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case <-ctx.Done():
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return false, ctx.Err()
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case <-time.After(retryDelay):
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// try again
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}
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}
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}
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func (f *Flock) setFh() error {
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// open a new os.File instance
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// create it if it doesn't exist, and open the file read-only.
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flags := os.O_CREATE
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if runtime.GOOS == "aix" {
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// AIX cannot preform write-lock (ie exclusive) on a
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// read-only file.
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flags |= os.O_RDWR
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} else {
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flags |= os.O_RDONLY
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}
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fh, err := os.OpenFile(f.path, flags, os.FileMode(0600))
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if err != nil {
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return err
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}
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// set the filehandle on the struct
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f.fh = fh
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return nil
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}
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// ensure the file handle is closed if no lock is held
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func (f *Flock) ensureFhState() {
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if !f.l && !f.r && f.fh != nil {
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f.fh.Close()
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f.fh = nil
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}
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}
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