From 825b5a9a29d80e1d006f7f4cc3e33ab928fe08bf Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?=E4=BD=99=E6=9E=97=E9=A2=96?= Date: Mon, 3 May 2021 01:34:34 +0800 Subject: [PATCH] docs: translated the async method invocation pattern into Chinese (#1741) --- zh/async-method-invocation/README.md | 161 +++++++++++++++++++++++++++ 1 file changed, 161 insertions(+) create mode 100644 zh/async-method-invocation/README.md diff --git a/zh/async-method-invocation/README.md b/zh/async-method-invocation/README.md new file mode 100644 index 000000000..e82d8fa19 --- /dev/null +++ b/zh/async-method-invocation/README.md @@ -0,0 +1,161 @@ +--- +layout: pattern +title: Async Method Invocation +folder: async-method-invocation +permalink: /patterns/async-method-invocation/ +categories: Concurrency +tags: + - Reactive +--- + +## 作用 + +异步方法是一种调用线程在等待任务结果时候不会被阻塞的模式。该模式提供了对多个任务的并行处理，并通过回调或等待，在所有任务完成后在提供结果读取。 + +## 解释 + +真实世界案例 + +> 发射太空火箭是一项令人兴奋的事业。在任务指挥部下达发射命令后， 经过一些未确定的时间，火箭要么成功发射，要么重演挑战者悲剧。 + +简而言之 + +> 异步方法调用开始任务处理并，在任务结果准备好之前立即返回。任务处理的结果会在稍后再返回给调用者。 + +维基百科的解释 + +> 在多线程计算机编程中，异步方法调用（AMI），也被称为异步方法调用或异步模式。这是一种设计模式，在这种模式下，调用点在等待被调用代码完成时不会被阻塞。相反，当返回点到达时，调用线程会得到通知。轮询结果是一种不受欢迎的选择。 + +**编程示例** + +在这个例子中，我们正在发射太空火箭和部署月球车。 + +该应用演示了异步方法调用模式。该模式的关键部分是 `AsyncResult`，它是一个异步计算值的中间容器，`AsyncCallback` 可以在任务完成时提供执行行动作，`AsyncExecutor` 负责管理异步任务的执行。 + +```java +public interface AsyncResult { + boolean isCompleted(); + T getValue() throws ExecutionException; + void await() throws InterruptedException; +} +``` + +```java +public interface AsyncCallback { + void onComplete(T value, Optional ex); +} +``` + +```java +public interface AsyncExecutor { + AsyncResult startProcess(Callable task); + AsyncResult startProcess(Callable task, AsyncCallback callback); + T endProcess(AsyncResult asyncResult) throws ExecutionException, InterruptedException; +} +``` + +`ThreadAsyncExecutor` 是 `AsyncExecutor` 的一个实现。接下来将着重说明它的一些关键部分。 + +```java +public class ThreadAsyncExecutor implements AsyncExecutor { + + @Override + public AsyncResult startProcess(Callable task) { + return startProcess(task, null); + } + + @Override + public AsyncResult startProcess(Callable task, AsyncCallback callback) { + var result = new CompletableResult<>(callback); + new Thread( + () -> { + try { + result.setValue(task.call()); + } catch (Exception ex) { + result.setException(ex); + } + }, + "executor-" + idx.incrementAndGet()) + .start(); + return result; + } + + @Override + public T endProcess(AsyncResult asyncResult) + throws ExecutionException, InterruptedException { + if (!asyncResult.isCompleted()) { + asyncResult.await(); + } + return asyncResult.getValue(); + } +} +``` + +然后我们准备发射一些火箭，看看所有东西是如何一起运作的。 + +```java +public static void main(String[] args) throws Exception { + // construct a new executor that will run async tasks + var executor = new ThreadAsyncExecutor(); + + // start few async tasks with varying processing times, two last with callback handlers + final var asyncResult1 = executor.startProcess(lazyval(10, 500)); + final var asyncResult2 = executor.startProcess(lazyval("test", 300)); + final var asyncResult3 = executor.startProcess(lazyval(50L, 700)); + final var asyncResult4 = executor.startProcess(lazyval(20, 400), callback("Deploying lunar rover")); + final var asyncResult5 = + executor.startProcess(lazyval("callback", 600), callback("Deploying lunar rover")); + + // emulate processing in the current thread while async tasks are running in their own threads + Thread.sleep(350); // Oh boy, we are working hard here + log("Mission command is sipping coffee"); + + // wait for completion of the tasks + final var result1 = executor.endProcess(asyncResult1); + final var result2 = executor.endProcess(asyncResult2); + final var result3 = executor.endProcess(asyncResult3); + asyncResult4.await(); + asyncResult5.await(); + + // log the results of the tasks, callbacks log immediately when complete + log("Space rocket <" + result1 + "> launch complete"); + log("Space rocket <" + result2 + "> launch complete"); + log("Space rocket <" + result3 + "> launch complete"); +} +``` + +以下是控制台输出。 + +```java +21:47:08.227 [executor-2] INFO com.iluwatar.async.method.invocation.App - Space rocket launched successfully +21:47:08.269 [main] INFO com.iluwatar.async.method.invocation.App - Mission command is sipping coffee +21:47:08.318 [executor-4] INFO com.iluwatar.async.method.invocation.App - Space rocket <20> launched successfully +21:47:08.335 [executor-4] INFO com.iluwatar.async.method.invocation.App - Deploying lunar rover <20> +21:47:08.414 [executor-1] INFO com.iluwatar.async.method.invocation.App - Space rocket <10> launched successfully +21:47:08.519 [executor-5] INFO com.iluwatar.async.method.invocation.App - Space rocket launched successfully +21:47:08.519 [executor-5] INFO com.iluwatar.async.method.invocation.App - Deploying lunar rover +21:47:08.616 [executor-3] INFO com.iluwatar.async.method.invocation.App - Space rocket <50> launched successfully +21:47:08.617 [main] INFO com.iluwatar.async.method.invocation.App - Space rocket <10> launch complete +21:47:08.617 [main] INFO com.iluwatar.async.method.invocation.App - Space rocket launch complete +21:47:08.618 [main] INFO com.iluwatar.async.method.invocation.App - Space rocket <50> launch complete +``` + +## 类图 + +![alt text](../../async-method-invocation/etc/async-method-invocation.png "Async Method Invocation") + +## 适用性 + +在以下场景可以使用异步调用模式 + +* 你有多有可以并行执行的独立任务 +* 你需要提高一组串行任务的性能 +* 你的处理能力有限、或者有长期运行的任务，调用者不应该等待任务所有任务运行结束 + +## 现实示例 + +* [FutureTask](http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/FutureTask.html) +* [CompletableFuture](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CompletableFuture.html) +* [ExecutorService](http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html) +* [Task-based Asynchronous Pattern](https://msdn.microsoft.com/en-us/library/hh873175.aspx) +