70 lines
1.5 KiB
Go
70 lines
1.5 KiB
Go
// The flock package provides a file-system mediated locking mechanism on linux
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// using the `flock` system call.
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package flock
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import (
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"errors"
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"os"
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"syscall"
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)
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// Lock gets an exclusive lock on the file at the given path. If the file
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// doesn't exist, it's created.
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func Lock(path string) (*os.File, error) {
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return lock(path, syscall.LOCK_EX)
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}
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// TryLock will return a nil file if the file is already locked.
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func TryLock(path string) (*os.File, error) {
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return lock(path, syscall.LOCK_EX|syscall.LOCK_NB)
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}
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func LockFile(f *os.File) error {
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_, err := lockFile(f, syscall.LOCK_EX)
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return err
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}
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// Returns true if the lock was successfully acquired.
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func TryLockFile(f *os.File) (bool, error) {
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return lockFile(f, syscall.LOCK_EX|syscall.LOCK_NB)
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}
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func lockFile(f *os.File, flags int) (bool, error) {
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if err := flock(int(f.Fd()), flags); err != nil {
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if flags&syscall.LOCK_NB != 0 && errors.Is(err, syscall.EAGAIN) {
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return false, nil
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}
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return false, err
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}
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return true, nil
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}
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func flock(fd int, how int) error {
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_, _, e1 := syscall.Syscall(syscall.SYS_FLOCK, uintptr(fd), uintptr(how), 0)
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if e1 != 0 {
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return syscall.Errno(e1)
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}
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return nil
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}
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func lock(path string, flags int) (*os.File, error) {
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perm := os.O_CREATE | os.O_RDWR
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f, err := os.OpenFile(path, perm, 0600)
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if err != nil {
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return nil, err
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}
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ok, err := lockFile(f, flags)
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if err != nil || !ok {
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f.Close()
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f = nil
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}
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return f, err
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}
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// Unlock releases the lock acquired via the Lock function.
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func Unlock(f *os.File) error {
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return f.Close()
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}
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