Why do I encounter the error 'fatal error: sync: unlock of unlocked mutex' when using mutex in Golang?

Deeply explore the "fatal error: unlock of unlocked mutex" of Golang mutex

In Go concurrent programming, mutexes are the key tool to ensure data consistency. However, incorrect mutex use often leads to "fatal error: sync: unlock of unlocked mutex" error, especially in high concurrency scenarios, such as frequent clicks or page refreshes. This article will analyze the causes of this error and provide effective solutions.

The problem reappears

The following code snippet demonstrates the error:

 package category

import (
    "sync"
)

type Sync struct {
    Name string
    age int
    Mu sync.Mutex
}

var (
    Cache *Sync
    CacheContainer Sync
)

// GetTree query list, there is an error func (s *Sync) GetTree() *Sync {
    s.Mu.Lock()
    defer s.Mu.Unlock()
    Cache = &Sync{
        Name: "abc",
        age: 18,
    }
    // Error here: Unlocking the unlocked mutex CacheContainer = *Cache 
    return &CacheContainer
}

// GetTree2 query list, correct example func (s *Sync) GetTree2() *Sync {
    s.Mu.Lock()
    defer s.Mu.Unlock()
    Cache = &Sync{
        Name: "abc",
        age: 18,
    }
    Return Cache
}

In the GetTree function, the line of CacheContainer = *Cache is the source of the error. It creates a new copy of the Sync structure that points to a different memory address than Cache . When defer s.Mu.Unlock() is executed, it tries to unlock the mutex pointed to by Cache , but in high concurrency, another goroutine may have modified Cache , causing s.Mu to no longer point to a valid lock, thus causing the "unlock of unlocked mutex" error.

Error analysis and solutions

The root cause lies in the wrong understanding and inappropriate operation of mutex locks. GetTree function attempts to copy a structure containing a mutex, which breaks the management mechanism of the mutex.

Solution:

1. Avoid copying structures containing mutexes: return the Cache pointer directly, avoid creating a copy, and ensure that defer s.Mu.Unlock() always unlocks the correct mutex. The GetTree2 function is the correct example.

2. Use global variables with caution: Global variables are prone to trigger race conditions in concurrent environments. If you have to use global variables, you need to control access to it more strictly, ensuring that only one goroutine can modify it at the same time.

3. Check the scope of the locks carefully: Make sure each Lock() has a corresponding Unlock() and that they operate on the same mutex.

4. Use more advanced concurrency control mechanisms: For complex concurrency scenarios, consider using more advanced concurrency control mechanisms such as channels or synchronization groups (sync.WaitGroup), which provide clearer and safer concurrency control.

Through the above analysis and improvements, the "fatal error: sync: unlock of unlocked mutex" error can be effectively avoided, ensuring the concurrency security and stability of the Go program. Remember that correct use of mutex is the key to writing efficient and reliable concurrent Go programs.

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