common/task.js

function runTasks(taskParamsLists, createTask, concurrency) {
  concurrency = Math.min(taskParamsLists.length, concurrency);
  return new Promise((resolve, reject) => {
    let runningTaskCount = 0;
    let cursor = 0;
    let rets = [];

    function finishTask(res, idx) {
      rets[idx] = res;
      processNext();
    }

    function failTask(e) {
      console.error(e);
      processNext();
    }

    function processNext() {
      runningTaskCount--;
      addTask();

      if (runningTaskCount === 0) {
        resolve(rets);
      }
    }

    function addTask() {
      const param = taskParamsLists[cursor];
      if (param) {
        const currentTaskIdx = cursor;
        runningTaskCount++;
        createTask(param)
          .then((res) => finishTask(res, currentTaskIdx))
          .catch(failTask);
        cursor++;
      }
    }

    for (let i = 0; i < concurrency; i++) {
      addTask();
    }

    if (!runningTaskCount) {
      resolve(rets);
    }
  });
}

module.exports.runTasks = runTasks;