shared lock support

files_test.go

@@ -11,12 +11,13 @@ func Test_FileLock(t *testing.T) {
 	filename := "./test.file"
 	lock := NewFileLock(filename)
 	lock2 := NewFileLock(filename)
-	fmt.Println("lock1", lock.LockNoBlocking())
+	fmt.Println("lock1", lock.LockNoBlocking(false))
 	time.Sleep(time.Second)
-	fmt.Println("lock2", lock2.LockWithTimeout(time.Second*5))
+	fmt.Println("lock2", lock2.LockWithTimeout(time.Second*5, false))
 	fmt.Println("unlock1", lock.Unlock())
 	time.Sleep(time.Second)
-	fmt.Println("lock2", lock2.LockNoBlocking())
+	fmt.Println("unlock2", lock2.Unlock())
+	fmt.Println("lock2", lock2.LockNoBlocking(true))
 	fmt.Println("unlock2", lock2.Unlock())
 	os.Remove(filename)
 }

files_unix.go

@@ -36,18 +36,30 @@ func (f *FileLock) openFileForLock() error {
 	return nil
 }
 
-func (f *FileLock) Lock() error {
+func (f *FileLock) Lock(Exclusive bool) error {
+	var lockType int
+	if Exclusive {
+		lockType = syscall.LOCK_EX
+	} else {
+		lockType = syscall.LOCK_SH
+	}
 	if err := f.openFileForLock(); err != nil {
 		return err
 	}
-	return syscall.Flock(f.fd, syscall.LOCK_EX)
+	return syscall.Flock(f.fd, lockType)
 }
 
-func (f *FileLock) LockNoBlocking() error {
+func (f *FileLock) LockNoBlocking(Exclusive bool) error {
+	var lockType int
+	if Exclusive {
+		lockType = syscall.LOCK_EX
+	} else {
+		lockType = syscall.LOCK_SH
+	}
 	if err := f.openFileForLock(); err != nil {
 		return err
 	}
-	err := syscall.Flock(f.fd, syscall.LOCK_EX|syscall.LOCK_NB)
+	err := syscall.Flock(f.fd, lockType|syscall.LOCK_NB)
 	if err != nil {
 		syscall.Close(f.fd)
 		if err == syscall.EWOULDBLOCK {
@@ -65,9 +77,9 @@ func (f *FileLock) Unlock() error {
 	return syscall.Close(f.fd)
 }
 
-func (f *FileLock) LockWithTimeout(tm time.Duration) error {
+func (f *FileLock) LockWithTimeout(tm time.Duration, Exclusive bool) error {
 	return stario.StopUntilTimeout(tm, func(tmout chan struct{}) error {
-		err := f.Lock()
+		err := f.Lock(Exclusive)
 		select {
 		case <-tmout:
 			f.Unlock()

files_windows.go

@@ -88,16 +88,34 @@ func (f *FileLock) lockForTimeout(timeout time.Duration, lockType win32api.DWORD
 	}
 }
 
-func (f *FileLock) Lock() error {
+func (f *FileLock) Lock(Exclusive bool) error {
-	return f.lockForTimeout(0, win32api.LOCKFILE_EXCLUSIVE_LOCK)
+	var lockType win32api.DWORD
+	if Exclusive {
+		lockType = win32api.LOCKFILE_EXCLUSIVE_LOCK
+	} else {
+		lockType = 0
+	}
+	return f.lockForTimeout(0, lockType)
 }
 
-func (f *FileLock) LockWithTimeout(tm time.Duration) error {
+func (f *FileLock) LockWithTimeout(tm time.Duration, Exclusive bool) error {
-	return f.lockForTimeout(tm, win32api.LOCKFILE_EXCLUSIVE_LOCK)
+	var lockType win32api.DWORD
+	if Exclusive {
+		lockType = win32api.LOCKFILE_EXCLUSIVE_LOCK
+	} else {
+		lockType = 0
+	}
+	return f.lockForTimeout(tm, lockType)
 }
 
-func (f *FileLock) LockNoBlocking() error {
+func (f *FileLock) LockNoBlocking(Exclusive bool) error {
-	return f.lockForTimeout(0, win32api.LOCKFILE_EXCLUSIVE_LOCK|win32api.LOCKFILE_FAIL_IMMEDIATELY)
+	var lockType win32api.DWORD
+	if Exclusive {
+		lockType = win32api.LOCKFILE_EXCLUSIVE_LOCK
+	} else {
+		lockType = 0
+	}
+	return f.lockForTimeout(0, lockType|win32api.LOCKFILE_FAIL_IMMEDIATELY)
 }
 
 func (f *FileLock) Unlock() error {