java 如何顺序执行ExecutorService中的任务？
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How to execute tasks in ExecutorService sequentially?
提问by Raees Sharif-Aamir
I have three threads that are joined, i.e. the second thread executes after the first dies.
我有三个加入的线程，即第二个线程在第一个死后执行。
This is the code I have:
这是我的代码：
public class Main {
public static void main(String args[]) throws Exception {
final Thread thrdA = new Thread(() -> System.out.println("Message 1"));
final Thread thrdB = new Thread(() -> System.out.println("Message 2"));
final Thread thrdC = new Thread(() -> System.out.println("Message 3"));
thrdA.start();
thrdA.join();
thrdB.start();
thrdB.join();
thrdC.start();
thrdC.join();
}
}
How would I implement this functionality using ExecutorServiceinstead of three thread objects?
我将如何使用ExecutorService而不是三个线程对象来实现此功能？
回答by Luiggi Mendoza
If what you want/need is to execute a group of jobs one after another but in a single thread different that the main app thread, then use Executors#newSingleThreadExecutor.
如果您想要/需要的是在与主应用程序线程不同的单个线程中一个接一个地执行一组作业，则使用Executors#newSingleThreadExecutor.
ExecutorService es = Executors.newSingleThreadExecutor();
es.submit(() -> System.out.println("Message 1"));
es.submit(() -> System.out.println("Message 2"));
es.submit(() -> System.out.println("Message 3"));
es.shutdown();
回答by Amit Tamrakar
You can control sequential execution of threads using SingleThread ExecutorService with future.get() method.
您可以使用带有 future.get() 方法的 SingleThread ExecutorService 来控制线程的顺序执行。
DummyTask Class
DummyTask 类
import java.util.concurrent.Callable;
public class DummyTask implements Callable<Integer>
{
int taskId;
public DummyTask(int taskId) {
this.taskId = taskId;
}
@Override
public Integer call() throws Exception
{
System.out.println("excuting task... Task Id: " + taskId);
return taskId;
}
}
SequentialExecution Class
顺序执行类
package com.amit.executorservice;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class SequentialExecution
{
public static void main(String[] args) throws InterruptedException, ExecutionException {
DummyTask task1 = new DummyTask(1);
DummyTask task2 = new DummyTask(2);
DummyTask task3 = new DummyTask(3);
Future<Integer> result = null;
ExecutorService executor = Executors.newSingleThreadExecutor();
result = executor.submit( task1 );
// future.get() Waits for the task to complete, and then retrieves its result.
result.get();
result = executor.submit( task2 );
// future.get() Waits for the task to complete, and then retrieves its result.
result.get();
result = executor.submit( task3 );
// future.get() Waits for the task to complete, and then retrieves its result.
result.get();
executor.shutdown();
}
}
Output
输出
excuting task... Task Id: 1
excuting task... Task Id: 2
excuting task... Task Id: 3
Output will always be same and all task will get executed in sequence.
输出将始终相同，所有任务将按顺序执行。
回答by Alexei Kaigorodov
If you already use a thread pool in your application, you can reuse it by means of zero-threaded proxy serial executor, without creating special single threaded thread pool. One implementation is described in the javadoc section of Executor interface, another, optimized implementation, at my Github repository CodeSamples.
如果您的应用程序中已经使用了线程池，您可以通过零线程代理串行执行器来重用它，而无需创建特殊的单线程线程池。一个实现在Executor interface的javadoc 部分进行了描述，另一个优化的实现在我的 Github 存储库CodeSamples 中。
