A brief analysis of how golang achieves synchronization

With the continuous development of development languages, more and more companies are now beginning to adopt golang as their main development language. Due to its high efficiency and good concurrency, golang has played a very important role in many fields. However, when processing concurrently, we will inevitably encounter synchronization problems. If these problems are not handled well, it is likely to cause serious errors in the program. Therefore, let's introduce how golang achieves synchronization.

1. WaitGroup

WaitGroup waits for the end of a group of goroutines. It implements this function through a counter. The initial value of the counter can be arbitrary. When each goroutine completes The Done method will be called to decrement the counter by one. If the counter value is greater than 0, the Wait() method will block until the counter value becomes 0.

2. Mutex

The main function of Mutex (mutex lock) is to ensure that only one goroutine can access a shared resource at the same time. The definition of Mutex in golang is as follows:

type Mutex struct {
    state int32
    sema  uint32
}

state is used to indicate the status of the lock. If its value is 0, it means that no goroutine is accessing the shared resource. If its value is 1, it means that there is a goroutine. Access shared resources. When a goroutine tries to acquire the lock, if the state value is 0, it will directly modify the state value to 1, indicating that the goroutine successfully acquired the lock; if the state value is 1, it will call futex and wait for the state value to change until Acquire until the lock is reached.

3. Cond

Cond is one of the more important synchronization primitives in golang. It can realize event communication between goroutines. Cond can be used to suspend and resume the execution of goroutine, and can make goroutine wait for a certain condition to occur, or notify other goroutines when the condition is met. In golang, Cond is defined as follows:

type Cond struct {
    L Locker
    notify notifyList
    checker copyChecker
}

type notifyList struct {
    // 消息通知队列
    first *notifyListElement
    last  *notifyListElement
}

type notifyListElement struct {
    // 队列member
    // 每个member都持有一个goroutine的信息（Chan），它就是附加的消息通知
    // 在cond.AssociateWait即将信息放入通知队列时，会对通知消息进行复制
    // 在有新的消息到达时，cond.Broadcast会释放锁，并逐个将Chan中的消息进行阻塞的goroutine阻塞唤醒
    chan_ chan<- struct{}
    next  *notifyListElement
}

We can use the three methods of Wait(), Signal() and Broadcast() of the Cond variable to achieve synchronization between coroutines. The Wait() method will suspend the current goroutine and wait for other goroutines to send signals; the Signal() method will wake up a waiting goroutine. If there is no waiting goroutine, the Signal() method will return directly; Broadcast() ) method will wake up all waiting goroutines.

The above are the three ways to achieve synchronization in golang: WaitGroup, Mutex and Cond. They can be used to solve synchronization problems in concurrent processing in golang and improve the efficiency and stability of the program. Of course, in actual applications, we also need to choose the most appropriate synchronization method according to the specific situation.

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