JDK1.5 Excutor 与ThreadFactory

Posted 2021-01-08 iscys

Excutor 源码解读：

/**
 * An object that executes submitted {@link Runnable} tasks. This
 * interface provides a way of decoupling task submission from the
 * mechanics of how each task will be run, including details of thread
 * use, scheduling, etc.  An {@code Executor} is normally used
 * instead of explicitly creating threads. For example, rather than
 * invoking {@code new Thread(new(RunnableTask())).start()} for each
 * of a set of tasks, you might use:
 *
　Excutor 是一个可以执行提交过来实现Runnable 接口的对象，这个接口提供了一种将任务的提交以及
　这个任务如何去执行进行了解耦；　包含了线程线程的使用细节，调度等；
　我们通常使用Excutor 而不是显式的创建线程，比如说，我们不会调用对每一个任务进行new Thread (Runnabe ()).start()
　方法；而是使用如下：

 * <pre>
 * Executor executor = <em>anExecutor</em>;
 * executor.execute(new RunnableTask1());
 * executor.execute(new RunnableTask2());
 * ...
 * </pre>
 创建一个执行器Excutor 
 调用执行器的execte方法

 * However, the {@code Executor} interface does not strictly
 * require that execution be asynchronous. In the simplest case, an
 * executor can run the submitted task immediately in the caller‘s
 * thread:
 然而，Excutor执行器并不是严格的要求执行是异步的，一个简单的情况，
一个执行器在调用者线程中会立刻运行提交的任务，不理解看下面例子：
 *  <pre> {@code
 * class DirectExecutor implements Executor {
 *   public void execute(Runnable r) {
 *     r.run();
 *   }
 * }}</pre>
 运行了.run 方法，并不会启用一个新的线程，.start 才会启动一个新的线程，就是这个意思
 * More typically, tasks are executed in some thread other
 * than the caller‘s thread.  The executor below spawns a new thread
 * for each task.
 *
 *  <pre> {@code
 * class ThreadPerTaskExecutor implements Executor {
 *   public void execute(Runnable r) {
 *     new Thread(r).start();
 *   }
 * }}</pre>
 *
 * Many {@code Executor} implementations impose some sort of
 * limitation on how and when tasks are scheduled.  The executor below
 * serializes the submission of tasks to a second executor,
 * illustrating a composite executor.
 *
 *  <pre> {@code
 * class SerialExecutor implements Executor {
 *   final Queue<Runnable> tasks = new ArrayDeque<Runnable>();
 *   final Executor executor;
 *   Runnable active;
 *
 *   SerialExecutor(Executor executor) {
 *     this.executor = executor;
 *   }
 *
 *   public synchronized void execute(final Runnable r) {
 *     tasks.offer(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);
 *     }
 *   }
 * }}</pre>
 *
 * The {@code Executor} implementations provided in this package
 * implement {@link ExecutorService}, which is a more extensive
 * interface.  The {@link ThreadPoolExecutor} class provides an
 * extensible thread pool implementation. The {@link Executors} class
 * provides convenient factory methods for these Executors.
 ************很重要了***************
在这个package 中Excutor 的实现提供了 关于Excutor 接口的扩展ExcutorService
ThreadPoolExcutor 类提供了可扩展的线程池的实现， Excutors 提供了 方便的工厂方法（常用） 

 * <p>Memory consistency effects: Actions in a thread prior to
 * submitting a {@code Runnable} object to an {@code Executor}
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * its execution begins, perhaps in another thread.
 *

 

 

ThreadFactory 源码解读“”
/**
 * An object that creates new threads on demand.  Using thread factories
 * removes hardwiring of calls to {@link Thread#Thread(Runnable) new Thread},
 * enabling applications to use special thread subclasses, priorities, etc.
 
ThreadFactory 是一个按需要创建线程的对象，使用线程工厂消除了使用

Thread(Runnable) new Thread 创建线程的硬连接 能够使应用程序使用使用特殊的线程子类，优先级等；下面是一个简单的例子：

* <p> * The simplest implementation of this interface is just: * <pre> 
{@code * class SimpleThreadFactory implements ThreadFactory 
{ * public Thread newThread(Runnable r) {
 * return new Thread(r); * } * }}
</pre>