Go-条件变量的那些事

Wait():

把当前的 goroutine 加入当前条件变量的通知队列.解锁当前条件变量基于的互斥锁. 所以 wait 前必须加锁.当前 goroutine 阻塞在 wait()通知到来并唤醒了当前 goroutine 后
解锁当前条件变量基于的互斥锁执行后面的代码

Signal()Broadcast

上代码, 自己品:

package main

import (
	"fmt"
	"sync"
	"time"
)

type MailBox struct {
	count    uint8
	locker   sync.RWMutex
	sendCond *sync.Cond
	recvCond *sync.Cond
}

func (self *MailBox) Init() {
	self.sendCond = sync.NewCond(&self.locker)
	self.recvCond = sync.NewCond(self.locker.RLocker())
}

func (self *MailBox) Send() {
	self.locker.Lock()
	defer self.locker.Unlock()
	for self.count == 1 {
		fmt.Println("Send wait...")
		self.sendCond.Wait()
	}
	fmt.Println("Send")
	self.count = 1
	self.recvCond.Signal()
}

func (self *MailBox) Recv() {
	self.locker.RLock()
	defer self.locker.RUnlock()
	for self.count == 0 {
		fmt.Println("Recv wait...")
		self.recvCond.Wait()
	}
	fmt.Println("Recv")
	self.count = 0
	self.sendCond.Signal()
}

func main() {
	var mailBox MailBox
	mailBox.Init()

	go func() {
		for i := 0; i < 5; i++ {
			mailBox.Send()
		}
	}()

	go func() {
		for i := 0; i < 5; i++ {
			mailBox.Recv()
		}
	}()

	time.Sleep(time.Second * 2)
}

package main

import (
	"fmt"
	"sync"
	"time"
)

type MailBox struct {
	count    uint8
	locker   sync.RWMutex
	sendCond *sync.Cond
	recvCond *sync.Cond
}

func (self *MailBox) Init() {
	self.sendCond = sync.NewCond(&self.locker)
	self.recvCond = sync.NewCond(self.locker.RLocker())
}

func (self *MailBox) Send(i int) {
	fmt.Println(i)
	self.locker.Lock()
	fmt.Println(i, "lock")
	defer self.locker.Unlock()
	for self.count == 1 {
		fmt.Println(i, " Send wait...")
		self.sendCond.Wait()
	}
	fmt.Println(i, " Send")
	self.count = 1
	self.recvCond.Signal()
}

func (self *MailBox) Recv() {
	self.locker.RLock()
	defer self.locker.RUnlock()
	for self.count == 0 {
		fmt.Println("Recv wait...")
		self.recvCond.Wait()
	}
	fmt.Println("Recv")
	self.count = 0
	self.sendCond.Signal()
}

func main() {
	var mailBox MailBox
	mailBox.Init()

	go func() {
		for i := 0; i < 5; i++ {
			mailBox.Send(i) // Send 里面的 for 循环会阻塞
		}
	}()

	time.Sleep(time.Second * 2)
}

package main

import (
	"fmt"
	"sync"
	"time"
)

type MailBox struct {
	count    uint8
	locker   sync.RWMutex
	sendCond *sync.Cond
	recvCond *sync.Cond
}

func (self *MailBox) Init() {
	self.sendCond = sync.NewCond(&self.locker)
	self.recvCond = sync.NewCond(self.locker.RLocker())
}

func (self *MailBox) Send(i int) {
	fmt.Println(i)
	self.locker.Lock()
	fmt.Println(i, "lock")
	defer self.locker.Unlock()
	for self.count == 1 {
		fmt.Println(i, " Send wait...")
		self.sendCond.Wait()
	}
	fmt.Println(i, " Send")
	self.count = 1
	self.recvCond.Signal()
}

func (self *MailBox) Recv() {
	self.locker.RLock()
	defer self.locker.RUnlock()
	for self.count == 0 {
		fmt.Println("Recv wait...")
		self.recvCond.Wait()
	}
	fmt.Println("Recv")
	self.count = 0
	self.sendCond.Signal()
}

func main() {
	var mailBox MailBox
	mailBox.Init()

	go func() {
		for i := 0; i < 5; i++ {
			go func(i int) {
				mailBox.Send(i) // wait 调用后, 其他的Send就可以获得锁了
			}(i)
		}
	}()

	time.Sleep(time.Second * 2)
}

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	var locker sync.Mutex

	var cond *sync.Cond = sync.NewCond(&locker)

	go func() {
		locker.Lock()
		defer locker.Unlock()
		time.Sleep(time.Second * 1)
		fmt.Println("1: wait...")
		cond.Wait()
	}()

	go func() {
		//cond2 := cond // 可以在 cond 使用前拷贝
		cond2 := *cond // 可以在 cond 使用前拷贝
		locker.Lock()
		defer locker.Unlock()
		time.Sleep(time.Second * 2)
		fmt.Println("2: wait...")
		cond2.Wait()
	}()

	time.Sleep(time.Second * 5)
}

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	var locker sync.Mutex

	var cond *sync.Cond = sync.NewCond(&locker)

	go func() {
		locker.Lock()
		defer locker.Unlock()
		time.Sleep(time.Second * 1)
		fmt.Println("1: wait...")
		cond.Wait()
	}()

	go func() {
		locker.Lock()
		defer locker.Unlock()
		time.Sleep(time.Second * 2)
		cond2 := cond // 在 cond 使用后拷贝指针的副本, 可以使用
		fmt.Println("2: wait...")
		cond2.Wait()
	}()

	time.Sleep(time.Second * 5)
}

package main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	var locker sync.Mutex

	var cond *sync.Cond = sync.NewCond(&locker)

	go func() {
		locker.Lock()
		defer locker.Unlock()
		time.Sleep(time.Second * 1)
		fmt.Println("1: wait...")
		cond.Wait()
	}()

	go func() {
		locker.Lock()
		defer locker.Unlock()
		time.Sleep(time.Second * 2)
		cond2 := *cond // 在 cond 使用后拷贝值的副本, 不可以使用
		fmt.Println("2: wait...")
		cond2.Wait() // panic: sync.Cond is copied
	}()

	time.Sleep(time.Second * 5)
}