Detailed introduction to the usage of golang cond

Golang is an efficient, concise, and concurrent programming language. In Golang, cond is a tool used to control the concurrent execution of programs. This article will introduce the usage of cond in detail.

1. Basic introduction to cond

The full name of cond is condition variable, which is an important concurrency control mechanism in Golang. The main function of cond is to allow multiple goroutines to wait for the state of a shared variable to change at the same time, and to notify the waiting goroutine to perform subsequent operations when the state of the shared variable changes. Unlike mutex, cond cannot be used to protect concurrent access to shared variables, it needs to rely on mutex to complete. Its basic usage is very simple and is divided into three steps:

1. When goroutine needs to wait for changes in the status of shared variables, call the cond.Wait() function to enter the waiting state;
2. Other goroutines When the state of a shared variable changes, call the cond.Signal() or cond.Broadcast() function to wake up the waiting goroutine;
3. After waking up the waiting goroutine, you need to reacquire the mutex lock of the shared variable. Continue execution.

2. Usage of cond

In practical applications, cond is usually used in combination with mutex to achieve concurrent safe access to shared variables. The following is a simple sample program that demonstrates how to use cond to control the concurrent execution of multiple goroutines:

package main

import (
    "fmt"
    "sync"
)

var (
    count int
    mutex sync.Mutex
    cond  *sync.Cond = sync.NewCond(&mutex)
)

func worker() {
    for {
        mutex.Lock()
        for count < 10 {
            cond.Wait()
        }
        count--
        fmt.Printf("worker: %d\n", count)
        mutex.Unlock()
        cond.Signal()
    }
}

func main() {
    for i := 0; i < 10; i++ {
        go worker()
    }
    for {
        mutex.Lock()
        if count >= 10 {
            mutex.Unlock()
            break
        }
        count++
        fmt.Printf("main: %d\n", count)
        mutex.Unlock()
        cond.Signal()
    }
}

In this sample code, count represents a shared variable with an initial value of 0, indicating the number of tasks that can be executed. . When the value of the shared variable count is less than 10, all worker goroutines will wait until the value of the shared variable count is increased to more than 10 before being awakened.

In the main goroutine, increase the value of the shared variable count by calling the cond.Signal() function in a loop, and notify the waiting worker goroutines to continue execution. When the value of the shared variable count is increased to 10, the main goroutine stops calling the cond.Signal() function, and all worker goroutines exit execution.

It is worth noting that when goroutine waits for cond, it will automatically release the mutex lock so that other goroutines can access shared variables. Once awakened, the goroutine needs to reacquire the mutex lock to continue execution.

3. Precautions for cond

Although using cond is an efficient synchronization mechanism compared to the traditional condition variable mechanism, there are also matters that need to be paid attention to when using it:

1. The cond.Wait() function should always be used in a for loop to avoid false wake-ups. Specifically, the judgment of waiting conditions should be added when waking up;
2. When using Before cond, mutex should be initialized;
3. After using cond.Signal() or cond.Broadcast(), the awakened goroutine needs to reacquire the mutex lock;
4. cond also cannot guarantee thread safety , so when multiple goroutines access shared variables, mutex needs to be used for concurrency security control.

4. Conclusion

Golang’s concurrency control mechanism is very powerful. Through the two basic concurrency control mechanisms of mutex and cond, powerful concurrent programs can be realized. When using cond, you need to pay attention to its basic usage methods and precautions, and understand the operating principle of the cond mechanism in order to better play its role.

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