C is a popular programming language that is widely used in various types of applications, especially those that work more complexly or have high requirements on system resources. Therefore, asynchronous programming techniques have become more and more important in C development in recent years, and in this article, we will explore how to use C for asynchronous programming.

Asynchronous Programming Background

For some tedious and time-consuming tasks, the synchronous programming model cannot meet the needs. The operating system often sets these tasks to asynchronous mode in order to use system resources more efficiently. . With the asynchronous programming model, a program can perform multiple tasks in parallel without waiting for the previous task to complete. This helps improve the overall performance of the program.

Asynchronous Programming Tips

When doing asynchronous programming in C, we need to use an asynchronous library. Among them, the C 11 standard includes an asynchronous library, std::async, which can run functions in threads other than the main thread. The specific process of using std::async function is as follows:

1. Create an asynchronous task: std::future object.

2. To run a function in an asynchronous task, use the std::async function to specify the function and parameters.

3. Execute other tasks in the main thread and wait for the asynchronous task to complete before obtaining the results.

The following is a sample code:

//Include header file

include

include

//Asynchronous task
int foo(int x) {

return x * x; 

}

//Main function
int main() {

//创建异步任务 
std::future<int> result = std::async(foo,2);

//在此期间执行其他任务 
std::cout << "Main Task Finished" << std::endl;

//等待异步任务完成 
int r = result.get();

//输出异步任务结果 
std::cout << "Result is " << r << std::endl;

}

It is worth noting that when waiting for the asynchronous task to complete in the main thread, the main thread will be blocked. Therefore, we can use one of the std::future_status enumeration types, namely std::future_status::ready, to detect whether the asynchronous task has been completed, as follows:

//Detect whether the asynchronous task has been completed Complete
if (result.wait_for(std::chrono::seconds(0)) == std::future_status::ready) {

//异步任务已完成

}

In addition, we also You can use std::promise and std::future together to meet more fine-grained asynchronous programming needs. For example, in multi-threaded programming, we may need to wait for one thread to complete before performing other tasks. At this time, we can use std::promise and std::future to implement the semaphore mechanism:

//Include header files

include

include

include

include

//Asynchronous task
void foo(std::promise& p) {

std::this_thread::sleep_for(std::chrono::seconds(2)); //模拟长时间的任务
p.set_value(); //使用set_value()将结果返回给主线程 

}

//Main function
int main () {

//创建promise对象 
std::promise<void> p; 

//获取future对象 
std::future<void> f = p.get_future();

//在单独的线程中运行异步任务 
std::thread t(foo, std::ref(p));

//在此期间执行其他任务
std::cout << "Main Task Started" << std::endl;

//等待异步任务完成 
f.wait();

//输出结果 
std::cout << "Main Task Finished" << std::endl;

//等待异步线程完成 
t.join();

}

In this example, we use std::promise to transmit a semaphore value (void) to the asynchronous thread. After the asynchronous thread completes the task, Use the set_value() function to return the semaphore value to the main thread. The main thread needs to wait for the asynchronous thread to complete before it can continue execution.

Summary

Asynchronous programming is an important skill in C programming, which can improve the overall performance and concurrency of the program. In this article, we introduced the basic principles of asynchronous programming in C and showed several related example codes. If you want to improve the performance of your program or need to do multi-threaded programming, asynchronous programming skills are one of the core technologies you need to master.

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