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How do I use the Lock() and Unlock() methods to protect a critical section of code in Go?
How do I use the Lock() and Unlock() methods to protect a critical section of code in Go?
Jun 23, 2025 pm 08:37 PM
The standard way to protect critical sections in Go is to use the Lock() and Unlock() methods of sync.Mutex. 1. Declare a mutex and use it with the data to be protected; 2. Call Lock() before entering the critical area to ensure that only one goroutine can access the shared resources; 3. Use defer Unlock() to ensure that the lock is always released to avoid deadlocks; 4. Shorten the operations in the critical area as much as possible to improve performance; 5. For scenarios where more reads and less writes, sync.RWMutex should be used to read operations through RLock()/RUnlock() and write operations through Lock()/Unlock() to improve concurrency efficiency.
When you need to protect a critical section of code in Go, using the Lock() and Unlock() methods from the sync.Mutex type is the standard approach. These methods help ensure that only one goroutine can access the protected section at any given time, preventing race conditions.
What is a Mutex in Go?
Go's sync.Mutex is a mutual exclusion lock used to synchronize access to shared resources across multiple goroutines. When a goroutine calls Lock() , it blocks until the mutex becomes available if it's already locked by another goroutine. Once done with the critical section, calling Unlock() releases the lock so others can proceed.
Here's how to declare and use a mutex:
var mu sync.Mutex
You typically embed this mutex alongside the data it protects. It's common to see this pattern when working with structs or global variables shared between goroutines.
How to Use Lock() and Unlock() Correctly
The most important thing is to always call Unlock() after finishing work in the critical section — even if an error occurs. A common practice is to use defer mu.Unlock() right after calling mu.Lock() .
Here's a basic example:
package main
import (
"fmt"
"sync"
)
var (
counter = 0
mu sync.Mutex
)
func increment(wg *sync.WaitGroup) {
defer wg.Done()
mu.Lock()
defer mu.Unlock()
counter
}
func main() {
var wg sync.WaitGroup
for i := 0; i < 1000; i {
wg.Add(1)
go increment(&wg)
}
wg.Wait()
fmt.Println("Final counter:", counter)
}In this example:
- Multiple goroutines try to increment a shared counter.
- The
mu.Lock()ensures only one goroutine can enter the critical section at a time. -
defer mu.Unlock()guarantees the lock is released even if something goes wrong inside the block.
Some key points:
- Always pair
Lock()andUnlock()together. - Preferring
Unlock()immediately after locking. - Avoid long-running operations inside a locked section — keep critical sections as short as possible.
Common Mistakes to Avoid
Even experienced developers sometimes make mistakes when managing locks. Here are a few pitfalls to watch out for:
- Forgetting to unlock : This leads to deadlocks. If one goroutine locks but never unlocks, other goroutines waiting on the same lock will be stuck forever.
- Double locking the same mutex : Calling
Lock()again on the same mutex without unlocking first causes a deadlock. - Copying a locked mutex : Go discourages copying values ??of types that contain mutexes. Doing so can break the synchronization logic silently.
To prevent these issues:
- Use
defer mu.Unlock()whenever possible. - Be careful when passing structs containing mutexes — pass by pointer instead of by value.
- Consider using tools like
-raceflag (go run -race) to detect race conditions during testing.
When to Use RWMutex instead
If your application has more read operations than writes, consider using sync.RWMutex . It allows multiple readers but gives exclusive access to a single writer.
- Use
RLock()/RUnlock()for reading. - Use
Lock()/Unlock()when writing.
This can significantly improve performance in read-heavy scenarios. But remember: a write lock blocks all reads, and a read lock blocks writes.
So in cases where:
- You have many concurrent readers,
- Writes are infrequent,
...using RWMutex might be a better fit than a regular Mutex .
Basically that's it.
The above is the detailed content of How do I use the Lock() and Unlock() methods to protect a critical section of code in Go?. For more information, please follow other related articles on the PHP Chinese website!
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