识别戈兰死锁。5 哲学家问题
我正在排队 大约30%的运行都会发生这种情况，其余的都完成了，没有错误。我想我使用WaitGroup的方式是错误的，但不确定我做错了什么。也许有人可以帮助我识别我的错误？谢谢！fatal error: all goroutines are asleep - deadlock!wg.Wait()
package main
import (
"fmt"
"math/rand"
"sync"
"time"
)
const (
numOfPhilosophers = 5
numOfMeals = 3
maxEaters = 2
)
var doOnce sync.Once
func main() {
chopsticks := make([]sync.Mutex, 5)
permissionChannel := make(chan bool)
finishEating := make(chan bool)
go permissionFromHost(permissionChannel,finishEating)
var wg sync.WaitGroup
wg.Add(numOfPhilosophers)
for i:=1 ; i<=numOfPhilosophers ; i++ {
go eat(i, chopsticks[i-1], chopsticks[i%numOfPhilosophers], &wg, permissionChannel, finishEating)
}
wg.Wait()
}
func eat(philosopherId int, left sync.Mutex, right sync.Mutex, wg *sync.WaitGroup, permissionChannel <-chan bool, finishEatingChannel chan<- bool) {
defer wg.Done()
for i:=1 ; i<=numOfMeals ; i++ {
//lock chopsticks in random order
if RandBool() {
left.Lock()
right.Lock()
} else {
right.Lock()
left.Lock()
}
fmt.Printf("waiting for permission from host %d\n",philosopherId)
<-permissionChannel
fmt.Printf("starting to eat %d (time %d)\n", philosopherId, i)
fmt.Printf("finish to eat %d (time %d)\n", philosopherId, i)
//release chopsticks
left.Unlock()
right.Unlock()
//let host know I am done eating
finishEatingChannel<-true
}
}
func permissionFromHost(permissionChannel chan<-bool, finishEating <-chan bool) {
ctr := 0
for {
select {
case <-finishEating:
ctr--
default:
if ctr<maxEaters {
ctr++
permissionChannel<-true
}
}
}
}
func RandBool() bool {
rand.Seed(time.Now().UnixNano())
return rand.Intn(2) == 1
}
编辑1：我修复了通过引用传递的互斥体。它没有解决问题。
编辑2：我试图使用缓冲通道，使其工作permissionChannel:=make(chan bool, numOfPhilosophers)
编辑3：也@Jaroslaw例子使它工作
跃然一笑2回答
-
蛊毒传说
最后一个 goroutine 不会退出，当它写入通道时，它将在最后一次迭代中被阻止，因为它没有消费者。没有消费者的原因是函数中的选择情况正在写入，但没有消费者，因为它正在等待它被读取，所以我们有一个死锁。finishEatingChannelfinishEatingChannelpermissionFromHostpermissionChannel<-truepermissionChannel您可以使权限从主机通道缓冲，它将解决此问题。您的代码中还有一个错误，您正在按值传递互斥体，这是不允许的 -
慕后森
该命令说go vet./main.go:26:13: call of eat copies lock value: sync.Mutex./main.go:26:30: call of eat copies lock value: sync.Mutex./main.go:31:34: eat passes lock by value: sync.Mutex./main.go:31:52: eat passes lock by value: sync.Mutex另一个问题是，有时 goroutines（哲学家）在尝试发送确认时会被阻止，因为负责从此无缓冲通道读取数据的 goroutine（主机）正忙于尝试发送权限。以下是代码的确切部分：finishEatingChannel if ctr<maxEaters { ctr++ // This goroutine stucks since the last philosopher is not reading from permissionChannel. // Philosopher is not reading from this channel at is busy trying to write finishEating channel which is not read by this goroutine. // Thus the deadlock happens. permissionChannel<-true }死锁是100%可重复的，当只剩下一个哲学家需要吃两次饭时。固定版本的代码：package mainimport ( "fmt" "math/rand" "sync" "time")const ( numOfPhilosophers = 5 numOfMeals = 3 maxEaters = 2)func main() { chopsticks := make([]sync.Mutex, 5) permissionChannel := make(chan bool) finishEating := make(chan bool) go permissionFromHost(permissionChannel, finishEating) var wg sync.WaitGroup wg.Add(numOfPhilosophers) for i := 1; i <= numOfPhilosophers; i++ { go eat(i, &chopsticks[i-1], &chopsticks[i%numOfPhilosophers], &wg, permissionChannel, finishEating) } wg.Wait()}func eat(philosopherId int, left *sync.Mutex, right *sync.Mutex, wg *sync.WaitGroup, permissionChannel <-chan bool, finishEatingChannel chan<- bool) { defer wg.Done() for i := 1; i <= numOfMeals; i++ { //lock chopsticks in random order if RandBool() { left.Lock() right.Lock() } else { right.Lock() left.Lock() } fmt.Printf("waiting for permission from host %d\n", philosopherId) <-permissionChannel fmt.Printf("starting to eat %d (time %d)\n", philosopherId, i) fmt.Printf("finish to eat %d (time %d)\n", philosopherId, i) //release chopsticks left.Unlock() right.Unlock() //let host know I am done eating finishEatingChannel <- true }}func permissionFromHost(permissionChannel chan<- bool, finishEating <-chan bool) { ctr := 0 for { if ctr < maxEaters { select { case <-finishEating: ctr-- case permissionChannel <- true: ctr++ } } else { <-finishEating ctr-- } }}func RandBool() bool { rand.Seed(time.Now().UnixNano()) return rand.Intn(2) == 1}
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