110 lines
3.0 KiB
Go
110 lines
3.0 KiB
Go
//go:build windows
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package lockfile
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import (
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"os"
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"time"
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"golang.org/x/sys/windows"
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)
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const (
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reserved = 0
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allBytes = ^uint32(0)
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)
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type fileHandle windows.Handle
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// GetLastWrite returns a LastWrite value corresponding to current state of the lock.
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// This is typically called before (_not after_) loading the state when initializing a consumer
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// of the data protected by the lock.
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// During the lifetime of the consumer, the consumer should usually call ModifiedSince instead.
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//
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// The caller must hold the lock (for reading or writing) before this function is called.
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func (l *LockFile) GetLastWrite() (LastWrite, error) {
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l.AssertLocked()
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contents := make([]byte, lastWriterIDSize)
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ol := new(windows.Overlapped)
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var n uint32
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err := windows.ReadFile(windows.Handle(l.fd), contents, &n, ol)
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if err != nil && err != windows.ERROR_HANDLE_EOF {
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return LastWrite{}, err
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}
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// It is important to handle the partial read case, because
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// the initial size of the lock file is zero, which is a valid
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// state (no writes yet)
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contents = contents[:n]
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return newLastWriteFromData(contents), nil
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}
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// RecordWrite updates the lock with a new LastWrite value, and returns the new value.
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//
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// If this function fails, the LastWriter value of the lock is indeterminate;
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// the caller should keep using the previously-recorded LastWrite value,
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// and possibly detecting its own modification as an external one:
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//
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// lw, err := state.lock.RecordWrite()
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// if err != nil { /* fail */ }
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// state.lastWrite = lw
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//
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// The caller must hold the lock for writing.
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func (l *LockFile) RecordWrite() (LastWrite, error) {
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l.AssertLockedForWriting()
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lw := newLastWrite()
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lockContents := lw.serialize()
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ol := new(windows.Overlapped)
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var n uint32
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err := windows.WriteFile(windows.Handle(l.fd), lockContents, &n, ol)
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if err != nil {
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return LastWrite{}, err
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}
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if int(n) != len(lockContents) {
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return LastWrite{}, windows.ERROR_DISK_FULL
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}
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return lw, nil
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}
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// TouchedSince indicates if the lock file has been touched since the specified time
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func (l *LockFile) TouchedSince(when time.Time) bool {
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stat, err := os.Stat(l.file)
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if err != nil {
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return true
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}
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return when.Before(stat.ModTime())
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}
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func openHandle(path string, mode int) (fileHandle, error) {
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mode |= windows.O_CLOEXEC
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fd, err := windows.Open(path, mode, windows.S_IWRITE)
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return fileHandle(fd), err
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}
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func lockHandle(fd fileHandle, lType lockType, nonblocking bool) error {
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flags := 0
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if lType != readLock {
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flags = windows.LOCKFILE_EXCLUSIVE_LOCK
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}
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if nonblocking {
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flags |= windows.LOCKFILE_FAIL_IMMEDIATELY
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}
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ol := new(windows.Overlapped)
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if err := windows.LockFileEx(windows.Handle(fd), uint32(flags), reserved, allBytes, allBytes, ol); err != nil {
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if nonblocking {
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return err
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}
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panic(err)
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}
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return nil
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}
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func unlockAndCloseHandle(fd fileHandle) {
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ol := new(windows.Overlapped)
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windows.UnlockFileEx(windows.Handle(fd), reserved, allBytes, allBytes, ol)
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closeHandle(fd)
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}
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func closeHandle(fd fileHandle) {
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windows.Close(windows.Handle(fd))
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}
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