JS实现一个并发函数
实现并发控制的几种方法
在JavaScript中实现并发控制可以通过多种方式，以下是几种常见的方法：
Promise.all
使用Promise.all可以并行执行多个异步任务，等待所有任务完成后再继续执行后续代码。
const task1 = fetch('https://api.example.com/data1');
const task2 = fetch('https://api.example.com/data2');
const task3 = fetch('https://api.example.com/data3');
Promise.all([task1, task2, task3])
.then(responses => {
// 所有请求完成后的处理
console.log('All requests completed');
})
.catch(error => {
console.error('One of the requests failed', error);
});async/await结合Promise.all
使用async/await语法可以更清晰地处理并发任务。
async function runConcurrentTasks() {
try {
const [result1, result2, result3] = await Promise.all([
fetch('https://api.example.com/data1'),
fetch('https://api.example.com/data2'),
fetch('https://api.example.com/data3')
]);
console.log('All tasks completed');
} catch (error) {
console.error('Error in one of the tasks', error);
}
}限制并发数的实现
如果需要限制同时执行的并发数，可以使用以下方法：
async function concurrentLimit(tasks, limit) {
const results = [];
const executing = [];
for (const task of tasks) {
const p = Promise.resolve().then(() => task());
results.push(p);
const e = p.then(() => executing.splice(executing.indexOf(e), 1));
executing.push(e);
if (executing.length >= limit) {
await Promise.race(executing);
}
}
return Promise.all(results);
}
// 使用示例
const tasks = [
() => fetch('https://api.example.com/data1'),
() => fetch('https://api.example.com/data2'),
() => fetch('https://api.example.com/data3'),
// 更多任务...
];
concurrentLimit(tasks, 2)
.then(results => console.log('All tasks completed with limited concurrency'))
.catch(error => console.error('Error in limited concurrency', error));Worker Threads实现并发
在Node.js环境中，可以使用Worker Threads实现真正的并行执行。
const { Worker, isMainThread, parentPort } = require('worker_threads');
if (isMainThread) {
// 主线程代码
const worker1 = new Worker(__filename);
const worker2 = new Worker(__filename);
worker1.on('message', (msg) => console.log('Worker1:', msg));
worker2.on('message', (msg) => console.log('Worker2:', msg));
} else {
// 工作线程代码
parentPort.postMessage('Hello from worker');
}使用第三方库
对于更复杂的并发控制，可以考虑使用第三方库如p-limit或async库。
const pLimit = require('p-limit');
const limit = pLimit(2); // 限制并发数为2
const tasks = [
() => fetch('https://api.example.com/data1'),
() => fetch('https://api.example.com/data2'),
() => fetch('https://api.example.com/data3'),
];
(async () => {
const results = await Promise.all(tasks.map(task => limit(task)));
console.log('All tasks completed with p-limit');
})();这些方法可以根据具体需求选择使用，从简单的并行执行到复杂的并发控制都可以实现。
