如何在不等待的情况下获得活动的结果？以事件驱动的方式

问题描述

团队，我对并行调用活动有疑问。

我知道可以使用 const request = require('request'); async function download(url,location) { try { const fileStream = fs.createWriteStream(location); await new Promise((resolve,reject) => { const res = request(url); res.on('data',function(chunk) { // instead of loading the file into memory // after the download,we can just pipe // the data as it's being downloaded fileStream.write(chunk); }); res.on('end',function() { resolve(); }); }); return } catch (e) { console.log("Err on download files ",e) } } 并行调用活动。

对于我的用例，我想在收到所有活动的结果后并行调用 n 个活动，我想转到下一个状态，可以是另一个活动，也可以是决策任务。

但是这里它给了我一个类似于 Java 中的 Future 的 Promise 对象。如果我们编写 promise.get() 来获取结果，但它阻塞了线程。

我需要类似于事件驱动方式的东西，而不阻塞线程。

希望你明白我的问题！！

解决方法

您不必使用 .get()。

在Promise中，可以注册一个回调函数，当结果可用或返回错误时调用。

您可以根据需要使用以下其中一种：

• 然后申请
• 处理
• 然后撰写
• 异常

这种风格类似于 Java 的 CompletableFuture。

  /**
   * Returns Promise that contains a result of a function. The function is called with the value of
   * this Promise when it is ready. #completeExceptionally is propagated directly to the returned
   * Promise skipping the function.
   *
   * <p>Note that no blocking calls are allowed inside of the function.
   */
  <U> Promise<U> thenApply(Functions.Func1<? super V,? extends U> fn);

  /**
   * Returns Promise that contains a result of a function. The function is called with the value of
   * this Promise or with an exception when it is completed. If the function throws a {@link
   * RuntimeException} it fails the resulting promise.
   *
   * <p>Note that no blocking calls are allowed inside of the function.
   */
  <U> Promise<U> handle(Functions.Func2<? super V,RuntimeException,? extends U> fn);

  /**
   * Returns a new Promise that,when this promise completes normally,is executed with this promise
   * as the argument to the supplied function.
   *
   * @param fn the function returning a new Promise
   * @param <U> the type of the returned CompletionStage's result
   * @return the Promise that completes when fn returned Promise completes.
   */
  <U> Promise<U> thenCompose(Functions.Func1<? super V,? extends Promise<U>> fn);

  /**
   * Returns a new Promise that,when this promise completes exceptionally,is executed with this
   * promise's exception as the argument to the supplied function. Otherwise,if this promise
   * completes normally,then the returned promise also completes normally with the same value.
   *
   * @param fn the function to use to compute the value of the returned CompletionPromise if this
   *     CompletionPromise completed exceptionally
   * @return the new Promise
   */
  Promise<V> exceptionally(Functions.Func1<Throwable,? extends V> fn);

,

添加到伟大的 Long 的答案中。

您可以使用 Promise.anyOf 以阻塞方式等待集合中的单个 Promise 完成。