Promise异步任务并发

function sleep (timeout: number, taskName: string) {
    return new Promise<void>(resolve => {
        console.log(`${taskName}开始啦`);
        setTimeout(() => {
            console.log(`${taskName}结束啦`);
            resolve();
        }, timeout)
    });
}

const tasks = [
    () => sleep(1000, '睡觉'),
    () => sleep(2000, '吃饭'),
    () => sleep(3000, '打游戏'),
    () => sleep(5000, '写代码'),
    () => sleep(7000, '做运动'),
];

async function doSomething(tasks:(()=>Promise<void>)[], limit=2) {
    // 正在执行中的任务的集合
    const taskPool = new Set();
    for (const task of tasks) {
        const promise = task();
        taskPool.add(promise);
        promise.then(() => taskPool.delete(promise));
        if (taskPool.size >= limit) {
            await Promise.race(taskPool);
        }
    }
    return Promise.all(taskPool);
}

/** 如果存在同步任务情况
async function doSomething(tasks:(()=>Promise<void>)[], limit=2) {
    // 正在执行中的任务的集合
    const taskPool = new Set();
    for (const task of tasks) {
        const promise = task();
        const p = Promise.resolve(promise)  // 包装Promise, 同步任务直接返回
        taskPool.add(p);
        promise.then(() => taskPool.delete(p));
        if (taskPool.size >= limit) {
            await Promise.race(taskPool);
        }
    }
    return Promise.all(taskPool);
}
 */

doSomethin(tasks).then(() => {
    console.log('任务全部执行完了');
})

// 加载图片
function getTasks(urls) {
    const tasks = [];
    urls.forEach(url => {
        tasks.push(() => {
            new Promise(resolve => {
                const img = new Image();
                img.onload = () => {
                    resolve();
                }
                img.src = url;
            })
        })
    })
    return tasks;
}

doSomething(getTasks(['xxxx.jpg', 'xxxx.png'])).then(() => {
    console.log('全部执行完了');
})
// 加载图片