How to use locks in Go?

In concurrent programming, lock is a mechanism used to protect shared resources. In the Go language, locks are one of the important tools for achieving concurrency. It ensures that when shared resources are accessed simultaneously by multiple coroutines, only one coroutine can read or modify these resources. This article will introduce the use of locks in Go language to help readers better understand concurrent programming.

1. Mutual Exclusion Lock

Mutual Exclusion Lock is the most commonly used locking mechanism in the Go language. It ensures that only one coroutine can access the critical section at the same time. In layman's terms, a mutex lock ensures that only one coroutine can access it at the same time by wrapping the shared resource in the lock critical section.

Using mutex locks in Go language is very simple. We can use the Mutex type in the sync package to create a mutex lock:

import "sync"

var mutex = &sync.Mutex{}

After that, in the location where the shared resource needs to be protected, we can use the following code to obtain the lock:

mutex.Lock()
defer mutex.Unlock()

Worth it Note that mutex locks do not support reentrancy. If a coroutine has already acquired the lock, trying to acquire the lock again will result in a deadlock. Therefore, we usually use the defer statement to automatically release the lock when the coroutine ends.

The following is an example of using a mutex lock:

import (
    "fmt"
    "sync"
)

var count = 0
var mutex = &sync.Mutex{}

func increment(wg *sync.WaitGroup) {
    mutex.Lock()
    defer mutex.Unlock()
    count++
    wg.Done()
}

func main() {
    var wg sync.WaitGroup
    for i := 0; i < 1000; i++ {
        wg.Add(1)
        go increment(&wg)
    }
    wg.Wait()
    fmt.Println("Count:", count)
}

In this example, we use a mutex lock to protect a counter. 1000 coroutines execute the increment function at the same time, adding 1 to the counter each time. Due to the use of mutex locks, the program can correctly output the final counter value.

2. Read-Write Lock

In a multi-coroutine environment, a read-write lock (Read-Write Lock) may be better than a mutex lock. In contrast, it can remain efficient when multiple coroutines read from a shared resource simultaneously, but still requires mutually exclusive access when there are write operations.

Read-write locks consist of two types of locks: read locks and write locks. Read locks allow multiple coroutines to access shared resources at the same time, but write locks ensure that only one coroutine can access them at the same time.

In Go language, you can use the RWMutex type in the sync package to create a read-write lock.

import "sync"

var rwlock = &sync.RWMutex{}

The acquisition methods of read locks and write locks are different. The following are some common usages:

• Acquire read lock: rwlock.RLock()
• Release read lock: rwlock.RUnlock()
• Acquire write lock: rwlock.Lock()
• Release the write lock: rwlock.Unlock()

The following is an example of using a read-write lock:

import (
    "fmt"
    "sync"
)

var count = 0
var rwlock = &sync.RWMutex{}

func increment(wg *sync.WaitGroup) {
    rwlock.Lock()
    defer rwlock.Unlock()
    count++
    wg.Done()
}

func read(wg *sync.WaitGroup) {
    rwlock.RLock()
    defer rwlock.RUnlock()
    fmt.Println("Count:", count)
    wg.Done()
}

func main() {
    var wg sync.WaitGroup
    for i := 0; i < 10; i++ {
        wg.Add(1)
        go increment(&wg)
    }
    wg.Wait()

    for i := 0; i < 5; i++ {
        wg.Add(1)
        go read(&wg)
    }
    wg.Wait()
}

In this example , we simultaneously opened 10 coroutines to write data to the counter, and 5 coroutines to read counter data. By using read-write locks, programs can read from shared resources in an efficient manner while ensuring the atomicity of write operations.

3. Atomic operations

In Go language, you can also use atomic operations to ensure that the operation of synchronization primitives is atomic. Atomic operations do not require locking and are therefore more efficient than locks in some situations.

Go language has multiple built-in atomic operation functions, you can refer to the official documentation. Here are two commonly used atomic operation functions: atomic.Add and atomic.Load.

• atomic.Add: performs an atomic addition operation on an integer.
• atomic.Load: Read the value of an integer atomically.

The following is an example:

import (
    "fmt"
    "sync/atomic"
    "time"
)

var count int32 = 0

func increment(wg *sync.WaitGroup) {
    defer wg.Done()
    atomic.AddInt32(&count, 1)
}

func printCount() {
    fmt.Println("Count: ", atomic.LoadInt32(&count))
}

func main() {
    var wg sync.WaitGroup

    for i := 0; i < 5; i++ {
        wg.Add(1)
        go increment(&wg)
    }
    wg.Wait()
    printCount()

    time.Sleep(time.Second)

    for i := 0; i < 3; i++ {
        wg.Add(1)
        go increment(&wg)
    }
    wg.Wait()
    printCount()
}

In this example, we use the atomic.Add function to perform an atomic addition operation on the counter, and the atomic.Load function to atomically read the counter. value. By using atomic operations, we can avoid the overhead of locks and achieve more efficient concurrent programming.

4. Summary

Go language provides a variety of synchronization mechanisms, including mutex locks, read-write locks and atomic operations. Using appropriate synchronization mechanisms in concurrent programming is key to ensuring that programs run correctly and efficiently. In order to avoid deadlock, we need to carefully think about which lock mechanism is most suitable for the current shared resources. In the Go language, the way to use locks is very simple. It should be noted that the lock holding time should be reduced as much as possible to avoid reducing the performance of the program.

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