function calcFileMD5(file) {
  return new Promise((resolve, reject) => {
    let chunkSize = 2097152, // 2M
      chunks = Math.ceil(file.size / chunkSize),
      currentChunk = 0,
      spark = new SparkMD5.ArrayBuffer(),
      fileReader = new FileReader();

      fileReader.onload = (e) => {
        spark.append(e.target.result);
        currentChunk++;
        if (currentChunk < chunks) {
          loadNext();
        } else {
          resolve(spark.end());
        }
      };

      fileReader.onerror = (e) => {
        reject(fileReader.error);
        reader.abort();
      };

      function loadNext() {
        let start = currentChunk * chunkSize,
          end = start + chunkSize >= file.size ? file.size : start + chunkSize;
        fileReader.readAsArrayBuffer(file.slice(start, end));
      }
      loadNext();
  });
}
async function asyncPool(poolLimit, array, iteratorFn) {
  const ret = []; // 存储所有的异步任务
  const executing = []; // 存储正在执行的异步任务
  for (const item of array) {
    // 调用iteratorFn函数创建异步任务
    const p = Promise.resolve().then(() => iteratorFn(item, array));
    ret.push(p); // 保存新的异步任务

    // 当poolLimit值小于或等于总任务个数时，进行并发控制
    if (poolLimit <= array.length) {
      // 当任务完成后，从正在执行的任务数组中移除已完成的任务
      const e = p.then(() => executing.splice(executing.indexOf(e), 1));
      executing.push(e); // 保存正在执行的异步任务
      if (executing.length >= poolLimit) {
        await Promise.race(executing); // 等待较快的任务执行完成
      }
    }
  }
  return Promise.all(ret);
}