Using mutex can ensure that only one goroutine can access shared resources at any time, thereby avoiding race conditions; locking and unlocking is achieved through the Lock() and Unlock() methods of sync.Mutex in Go, which must be used in pairs and it is recommended to use defer Unlock() to ensure release; for example, when multiple goroutines are concurrently incremented counters, locking is required before operating the shared variables, and unlocking is automatically unlocked after the operation is completed; scenarios where mutex should be used include multiple goroutines reading and writing shared data, building concurrent and secure data structures, or avoiding channel overhead; common errors include forgetting to unlock, not protecting all shared data access paths, and copying structures containing mutex, go run -race can be used to detect problems.
A mutex in Go is a synchronization primitive used to protect shared data from being accessed or modified by multiple goroutines at the same time, which could lead to race conditions.
The term mutex stands for mutual exclusion — meaning only one goroutine can access a shared resource at any given time. In Go, mutexes are part of the sync package and are represented by the sync.Mutex type.
How Does a Mutex Work?
A mutex has two main operations:
-
Lock()— acquires the lock. If another goroutine already holds the lock, the calling goroutine blocks (waits) until the lock is released. -
Unlock()— releases the lock so another goroutine can acquire it.
It's cruel to always pair a Lock() with a corresponding Unlock() , typically using defer to ensure the unlock happens even if a panic occurs.
Example: Using a Mutex to Protect a Counter
package main
import (
"fmt"
"sync"
"time"
)
var (
counter = 0
mutex = sync.Mutex{}
)
func increment(wg *sync.WaitGroup) {
defer wg.Done()
mutex.Lock()
defer mutex.Unlock()
counter
fmt.Println("Counter:", counter)
}
func main() {
var wg sync.WaitGroup
for i := 0; i < 5; i {
wg.Add(1)
go increment(&wg)
}
time.Sleep(time.Second) // Give goroutines time to finish
wg.Wait()
}In this example:
- Multiple goroutines call
increment(). - The
mutex.Lock()ensures only one goroutine can modifycounterat a time. -
defer mutex.Unlock()guarantees the lock is released after the function exits.
When Should You Use a Mutex?
You should use a mutex when:
- Multiple goroutines need to read and write shared data.
- You want to avoid race conditions without using channels.
- You're building a concurrent-safe data structure (like a concurrent map).
? Tip : Go encourages communication via channels (
chan), but mutexes are often simpler and more efficient for protecting small critical sections.
Common Mistakes
- Forgetting to unlock (always use
defer mutex.Unlock()). - Locking but not covering all access points to shared data.
- Copying a struct that contains a mutex (this breaks the protection).
Go's go run -race flag can help detect race conditions during testing.
Basically, a mutex is a simple but powerful tool for safe concurrency in Go — just lock before accessing shared state, and unlock when done.
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