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