// +build !plan9 package sftp import "sync" // stringLock locks for string IDs passed intype stringLock struct {	mu    sync.Mutex               // mutex to protect below	locks map[string]chan struct{} // map of locks} // newStringLock creates a stringLockfunc newStringLock() *stringLock {	return &stringLock{		locks: make(map[string]chan struct{}),	}} // Lock locks on the id passed infunc (l *stringLock) Lock(ID string) {	l.mu.Lock()	for {		ch, ok := l.locks[ID]		if !ok {			break		}		// Wait for the channel to be closed		l.mu.Unlock()		// fs.Logf(nil, "Waiting for stringLock on %q", ID)		<-ch		l.mu.Lock()	}	l.locks[ID] = make(chan struct{})	l.mu.Unlock()} // Unlock unlocks on the id passed in.  Will panic if Lock with the// given id wasn't called first.func (l *stringLock) Unlock(ID string) {	l.mu.Lock()	ch, ok := l.locks[ID]	if !ok {		panic("stringLock: Unlock before Lock")	}	close(ch)	delete(l.locks, ID)	l.mu.Unlock()}