go - 即使使用互斥锁和延迟运行 goroutines 也会感到恐慌

Question

**func (p *linkedList) showalldoctorsrecursive() error {
    defer wg.Done()
    mutex.Lock()
    {
        if p.head != nil {
            printRecursiveF(p.head)
        } else {
            fmt.Println("The list is empty.")
        }
    }
    mutex.Unlock()
    return nil
}
func (p *linkedList) showalldoctorsfront() error {
    defer wg.Done()
    mutex.Lock()
    {
        if p.head != nil {
            printfront(p.head)
        } else {
            fmt.Println("The list is empty.")
        }
    }
    mutex.Unlock()
    return nil
}
func printRecursiveF(n *Node2) {
    if n != nil {
        printRecursiveF(n.next)
        fmt.Println(n.item, n.next.time)
    }
}
func printfront(n *Node2) {
    if n != nil {
        fmt.Println(n.item)
        fmt.Println(n.item, n.next.time)
    }
}**

func (p *queue) displayallpatients() error {
    defer wg.Done()
    mutex.Lock()
    {
        currentNode := p.front
        if currentNode == nil {
            fmt.Println("There are no patients.")
            return nil
        }
        fmt.Println("Displaying all patients and their appointment times")
        fmt.Println(currentNode.item, currentNode.time)
        for currentNode.next != nil {
            currentNode = currentNode.next
            fmt.Println(currentNode.item, currentNode.time)
        }
    }
    mutex.Unlock()
    return nil
}

func main() {
    var num, num1, num2 int
    runtime.GOMAXPROCS(2)
    wg.Add(3)
    myList := &linkedList{nil, 0}
    myQueue := &queue{nil, nil, 0}
    for {
        fmt.Println("Please enter 1 to check for patient or 2 to check for doctor.Alternatively,enter 3 to exit menu")
        fmt.Scanln(&num)
        _, err := mainmenu(num)
        if err != nil {
            fmt.Println(err)
        } else if num == 3 {
            break
        } else {
            fmt.Printf("Please proceed to the main menu >")
        }

        if num == 1 {
            fmt.Println("Patient Main Menu")
            fmt.Println("1. Add Patient")
            fmt.Println("2. Remove Last Patient")
            fmt.Println("3. Update Patient Details")
            fmt.Println("4. Display All Patients")
            fmt.Println("--------------")
            fmt.Println("Please enter a number to access the menu")
            fmt.Scanln(&num1)
            _, err2 := patientmenu(num1)
            if err2 != nil {
                fmt.Println(err2)
            } else if num1 == 1 {
                myQueue.addPatient()
            } else if num1 == 2 {
                myQueue.removelastpatient()
            } else if num1 == 3 {
                myQueue.updatepatient()
            } else if num1 == 4 {
                go myQueue.displayallpatients()
            }
    }

        } else if num == 2 {
            fmt.Println("Doctor Main Menu")
            fmt.Println("1. Add Doctor")
            fmt.Println("2. Search For Doctor Thru Name")
            fmt.Println("3. Search For Doctors Thru Available Time")
            fmt.Println("4. Update Doctor Details")
            fmt.Println("5. Display All Doctors(Recursive)")
            fmt.Println("6. Display All Doctors")
            fmt.Println("--------------")
            fmt.Println("Please enter a number to access the menu")
            fmt.Scanln(&num2)
            _, err3 := doctormenu(num2)
            if err3 != nil {
                fmt.Println(err3)
            } else if num2 == 1 {
                myList.addDoctors()
            } else if num2 == 2 {
                myList.searchdoctor()
            } else if num2 == 3 {
                myList.searchdoctortiming()
            } else if num2 == 4 {
                myList.updatedoctor()
            } else if num2 == 5 {
                go myList.showalldoctorsrecursive()
            } else if num2 == 6 {
                go myList.showalldoctorsfront()
            }
        }
    }
    wg.Wait()
}

fatal error: all goroutines are asleep - deadlock!

goroutine 1 [semacquire]:
sync.runtime_Semacquire(0x89ec50)
        c:/go/src/runtime/sema.go:56 +0x49
sync.(*WaitGroup).Wait(0x89ec48)
        c:/go/src/sync/waitgroup.go:130 +0x6b
main.main()
        C:/Projects/Go/src/xxx/main.go:145 +0xd85
exit status 2

我尝试运行 goroutine 并应用互斥锁和延迟。但是，在运行 goroutine 时我会感到恐慌。有没有办法解决这个问题？我创建了一个队列和链表，其中包含一些要显示的函数，入队（添加）和出队（弹出），并对其应用一些并发性。我知道，wg.Add(n)n 是你运行的 goroutine 的数量，你想使用互斥锁来确保 goroutine 一次运行一个。

标签： gomutexgoroutine

Answer 1

代码执行时没有 mutex.Unlock() ：

if currentNode == nil {
    fmt.Println("There are no patients.")
    return nil
}

您正在锁定并且永远不会解锁：

func (p *queue) displayallpatients() error {
    defer wg.Done()
    mutex.Lock() // <- here we acquire a lock
    {
        currentNode := p.front
        if currentNode == nil {
            fmt.Println("There are no patients.")
            return nil // <- here we return without releasing the lock
        }
        // ...
    }
    mutex.Unlock() // <- never reach if currentNode == nil is true
    return nil
}

您可以使用 defer 或不提前返回来解决此问题：

func (p *queue) displayallpatients() error {
    defer wg.Done()
    defer mutex.Unlock() // <- defers the execution until the func returns (will release the lock)
    mutex.Lock()
    {
        currentNode := p.front
        if currentNode == nil {
            fmt.Println("There are no patients.")
            return nil
        }
        // ...
    }
    
    return nil
}

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