13.ThreadPoolExecutor线程池之submit⽅法
jdk1.7.0_79
在上⼀篇中提到了线程池ThreadPoolExecutor的原理以及它的execute⽅法。本⽂解析ThreadPoolExecutor#submit。
own 对于⼀个任务的执⾏有时我们不需要它返回结果，但是有我们需要它的返回执⾏结果。对于线程来讲，如果不需要它返回结果则实现Runnable，⽽如果需要执⾏结果的话则可以实现Callable。在线程池同样execute提供⼀个不需要返回结果的任务执⾏，⽽对于需要结果返回的则可调⽤其submit⽅法。
回顾ThreadPoolExecutor的继承关系。
在Executor接⼝中只定义了execute⽅法，⽽submit⽅法则是在ExecutorService接⼝中定义的。
//ExecutorService
public interface ExecutorService extends Executor {
...
<T> Future<T> submit(Callable<T> task);
<T> Future<T> submit(Runnable task, T result);
<T> Future<T> submit(Runnable task);
...
}
⽽在其⼦类AbstractExecutorService实现了submit⽅法。
//AbstractExecutorService
考研考试时间
public abstract class AbstractExecutorService implements ExecutorService {
...
public <T> Future<T> submit(Callable<T> task) {
if (task == null) throw new NullPointerException();
RunnableFuture<T> ftask = newTaskFor(task);
execute(ftask);
return ftask;
cha }
public <T> Future<T> submit(Runnable task, T result) {
if (task == null) throw new NullPointerException();
三年级英语上册教学计划 RunnableFuture<T> ftask = newTaskFor(task);
execute(ftask);
return ftask;
}
public Future<?> submit(Runnable task) {
if (task == null) throw new NullPointerExeption();
RunnableFuture<Void> ftask = newTaskFor(task, null);
execute(ftask);
return ftask;
}
...
}
在AbstractExecutorService实现的submit⽅法实际上是⼀个模板⽅法，定义了submit⽅法的算法⾻架，其execute交给了⼦类。（可以看到在很多源码中，模板⽅法模式被⼤量运⽤，有关模板⽅法模式可参考）
尽管submit⽅法能提供线程执⾏的返回值，但只有实现了Callable才会有返回值，⽽实现Runnable的线程则是没有返回值的，也就是说在上⾯的3个⽅法中，submit(Callable<T> task)能获取到它的返回值，submit(Runnable task, T result)能通过传⼊的载体result间接获得线程的返回值或者准确来说交给线程处理⼀下，⽽最后⼀个⽅法submit(Runnable task)则是没有返回值的，就算获取它的返回值也是null。
下⾯给出3个例⼦，来感受下submit⽅法。
submit(Callable<T> task)
package com.threadpoolexecutor;
import urrent.*;
/**
* ThreadPoolExecutor#sumit(Callable<T> task)
* Created by yulinfeng on 6/17/17.
*/
public class Sumit1 {
public static void main(String[] args) throws ExecutionException, InterruptedException {
Callable<String> callable = new Callable<String>() {
public String call() throws Exception {
System.out.println("This is ThreadPoolExetor#submit(Callable<T> task) method.");
return "result";
}
};
ExecutorService executor = wSingleThreadExecutor();
Future<String> future = executor.submit(callable);
System.out.());
}
}
submit(Runnable task, T result)
package com.threadpoolexecutor;
lloyds tsb
import urrent.ExecutionException;
import urrent.ExecutorService;
import urrent.Executors;
import urrent.Future;
/**
* ThreadPoolExecutor#submit(Runnable task, T result)
* Created by yulinfeng on 6/17/17.
*/
public class Submit2 {
public static void main(String[] args) throws ExecutionException, InterruptedException {
ExecutorService executor = wSingleThreadExecutor();
Data data = new Data();
Future<Data> future = executor.submit(new Task(data), data);
System.out.().getName());
}
}
class Data {
String name;
public String getName() {
return name;
}
public void tName(String name) {
this.name = name;
}
}
class Task implements Runnable {
Data data;
public Task(Data data) {
this.data = data;
}
public void run() {
System.out.println("This is ThreadPoolExetor#submit(Runnable task, T result) method."); data.tName("kevin");
}
}java软件培训
submit(Runnable task)
少儿口语package com.threadpoolexecutor;
import urrent.ExecutionException;
import urrent.ExecutorService;
import urrent.Executors;
import urrent.Future;
/**
* ThreadPoolExecutor#sumit(Runnable runnables)
* Created by yulinfeng on 6/17/17.
*/
public class Submit {
public static void main(String[] args) throws ExecutionException, InterruptedException {
Runnable runnable = new Runnable() {
public void run() {
System.out.println("This is ThreadPoolExetor#submit(Runnable runnable) method.");
}
};
ExecutorService executor = wSingleThreadExecutor();
Future future = executor.submit(runnable);
System.out.());
}
}
美好的回忆英文 通过上⾯的实例可以看到在调⽤submit(Runnable runnable)的时候是不需要其定义类型的，也就是说虽然在ExecutorService中对其定义的是泛型⽅法，⽽在AbstractExecutorService中则不是泛型⽅法，因为它没有返回值。（有关Object、T、?这三者的区别，可参考）。
spoiler 从上⾯的源码可以看到，这三者⽅法⼏乎是⼀样的，关键就在于：
RunnableFuture<T> ftask = newTaskFor(task);
execute(ftask);
它是如何将⼀个任务作为参数传递给了newTaskFor，然后调⽤execute⽅法，最后进⽽返回ftask的呢？高级翻译张璐
//AbstractExecutorService#newTaskFor
protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
return new FutureTask<T>(callable);
}
protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
return new FutureTask<T>(runnable, value);
}
看来是返回了⼀个FutureTask实例，FutureTask实现了Future和Runnable接⼝。Future接⼝是Java线程Future模式的实现，可⽤⽤来异步计算，实现Runnable接⼝表⽰可以作为⼀个线程执⾏。Future
Task实现了这两个接⼝意味着它代表异步计算的结果，同时可以作为⼀个线程交给Executor来执⾏。有关FutureTask放到下章来单独解析。所以本⽂对于线程池ThreadPoolExecutor线程池的submit⽅法解析并不完整，必须得了解Java线程的Future模式——。
