Executor

An object that executes submitted Runnable tasks.

使用方式

1. Executor executor = anExecutor();
   executor.execute(new RunnableTask1());
   executor.execute(new RunnableTask1());
2. Execuor 在简单的任务可以立即执行提交的任务

// 直接调用 Runnable的run方法， 在调度线程线程执行; 不会启动一个线程
    class DirectExecutor implements Executor{

        public void execute(Runnable r){
             r.run();
        }

    }

3.大多数情况下 ，每个任务创建一个线程执行， 不是在调度者线程中执行

 class ThreadPerTaskExecutor implements Executor{
       
       public void execute(Runnable r){
             new Thread(r).start();
        }
   }

4.执行串行任务的实现方式

class SerialExecutor implements Executor{
     final Queue<Runnable> tasks = new ArrayDeque<>();
     final Executor executor;
     Runnable active;
     
     SerialExecutor(Executor executor){
         this.executor = executor;
     }
     
     public synchronized void execute(final Runnable r){
         
         tasks.add(new Runnable(){
             public void run(){
                
                try{
                    r.run();
                }finally{
                    scheduleNext();
                }
             }
         });
         
         if(active == null){
            scheduleNext();
         }
     }
     
     protected synchronized void scheduleNext(){
         
         if( active = (tasks.poll()) != null ){
            executor.execute(active); 
         }
         
     }
 }

5. ThreadPoolExecutor class provides an extensible thread pool implementation。

   The Executors class provides convenient factory methods for these Executors。

Executor源码

 public interface Executor{ 
    /**
     *The command
     * may execute in a new thread, in a pooled thread, or in the calling
     * thread, at the discretion of the {@code Executor} implementation
     */
     void execute(Runnable command)    
  }