promise并发控制

[heyLiup]

function sleep (timer) {
    if (timer === 1) {
        return new Promise((res, rej) => rej(1));
    }
    return fetch('XXXX', {method: 'post'})
}



function asyncPool(poolLimit, array, iteratorFn) {
    let i = 0;
    const ret = [];
    const executing = [];

    return new Promise(resolve => {
        const enqueue = function () {
            // 所有请求结束
            if (i === array.length) {
                Promise.all(ret).then(data => {
                    return resolve(data);
                });
            } else {
                const item = array[i++];
                const p = iteratorFn(item);
                ret.push(p);

                // promise执行完毕，从executing数组中删除
                const e = p.then(() => {
                    executing.splice(executing.indexOf(e), 1);
                }, () => {

                    //可兼容reject的情况，将resolve的接口返回
                    ret.splice(ret.indexOf(p), 1);
                });

                // 插入executing数字，表示正在执行的promise
                executing.push(e);

                // 使用Promise.rece，每当executing数组中promise数量低于poolLimit，就实例化新的promise并执行
                let r = Promise.resolve();
                if (executing.length >= poolLimit) {
               
                    r = Promise.race(executing);
                }
                r.then(() => enqueue());
            }
        };

        enqueue();
    })
}

asyncPool(3, arr, sleep).then(res => {
    console.log(res);
});