条件锁

condition_lock.go

package versionlock

import (
	"errors"
	"sync/atomic"
	"time"
)

var ErrOldVersion = errors.New("old version")
var ErrUnlockFailed = errors.New("unlock failed")

type VLock struct {
	version uint64
	lock    uint64
}

func (l *VLock) Lock(v uint64) error {
	for {
		version := atomic.LoadUint64(&l.version)
		if v < version {
			return ErrOldVersion
		}
		// new version try write to it
		if !atomic.CompareAndSwapUint64(&l.version, version, v) {
			// fail to write try again
			continue
		}
		break
	}

	for {
		lockV := atomic.LoadUint64(&l.lock)
		version := atomic.LoadUint64(&l.version)
		if v < version {
			return ErrOldVersion
		}
		if lockV&1 == 1 {
			time.Sleep(0)
			continue
		}
		if atomic.CompareAndSwapUint64(&l.lock, lockV, lockV+3) {
			return nil
		}
	}
}

func (l *VLock) UnLock() error {
	lockV := atomic.LoadUint64(&l.lock)
	if !atomic.CompareAndSwapUint64(&l.lock, lockV, lockV-1) {
		return ErrUnlockFailed
	}
	return nil
}