package sync

import (
	"sync"
)

/*
ChannelRWMutexV1
	使用四把锁
*/

type ChannelRWMutexV1 struct {
	mu  sync.Mutex // 互斥锁
	rm  sync.Mutex // 读等待锁
	wm  sync.Mutex // 写等待锁
	cmu sync.Mutex // 计数锁
	rn  int        // 读等待
	wn  int        // 写等待
}

func NewRWMutexV1() RWLocker {
	return &ChannelRWMutexV1{}
}

func (rw *ChannelRWMutexV1) RLock() {
	rw.cmu.Lock()
	if rw.wn > 0 {
		rw.cmu.Unlock()
		rw.wm.Lock()
		rw.wm.Unlock()
	} else {
		defer rw.cmu.Unlock()
	}

	rw.rn++
	if rw.rn == 1 {
		rw.wm.Lock()
	}
}

func (rw *ChannelRWMutexV1) RUnlock() {
	rw.cmu.Lock()
	defer rw.cmu.Unlock()
	rw.rn--

	if rw.rn == 0 {
		rw.wm.Unlock()
	}
}

func (rw *ChannelRWMutexV1) Lock() {
	rw.cmu.Lock()
	if rw.rn > 0 {
		rw.cmu.Unlock()
		rw.wm.Lock()
		rw.wm.Unlock()
	} else {
		defer rw.cmu.Unlock()
	}

	rw.wn++

	if rw.wn == 1 {
		rw.rm.Lock()
	}
	rw.mu.Lock()
}

func (rw *ChannelRWMutexV1) Unlock() {
	rw.cmu.Lock()
	defer rw.cmu.Unlock()
	rw.wn--

	if rw.wn == 0 {
		rw.rm.Unlock()
	}
	rw.mu.Unlock()
}