java线程池

摘要: java线程池

相关类Executor，Executors，AbstractExecutorService，ExecutorService

Executor整个线程池执行者框架的顶层接口

public interface Executor {
void execute(Runnable command);
}
ExecutorService 定义了很多的方法:
public interface ExecutorService extends Executor {
void shutdown();
List<Runnable> shutdownNow();
boolean isShutdown();
boolean isTerminated();
boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException;
<T> Future<T> submit(Callable<T> task);
<T> Future<T> submit(Runnable task, T result);
Future<?> submit(Runnable task);
<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)

throws InterruptedException;

<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,long timeout, TimeUnit unit)

throws InterruptedException;

<T> T invokeAny(Collection<? extends Callable<T>> tasks)

throws InterruptedException, ExecutionException;

<T> T invokeAny(Collection<? extends Callable<T>> tasks,

long timeout, TimeUnit unit)

throws InterruptedException, ExecutionException, TimeoutException;

}

AbstractExecutorService是一个抽象类，它实现了ExecutorService接口的submit，invokeAll的方法

public Future<?> submit(Runnable task) {
if (task == null) throw new NullPointerException();
RunnableFuture<Void> ftask = newTaskFor(task, null);
execute(ftask);
return ftask;
}
public <T> Future<T> submit(Runnable task, T result) {
if (task == null) throw new NullPointerException();
RunnableFuture<T> ftask = newTaskFor(task, result);
execute(ftask);
return ftask;
}

public <T> Future<T> submit(Callable<T> task) {
if (task == null) throw new NullPointerException();
RunnableFuture<T> ftask = newTaskFor(task);
execute(ftask);
return ftask;
}
在这里，所有submit方法提交的任务最终还是调用了execute方法，execute是接口Executor中定义的方法，AbstractExecutorService没有实现它，
需要子类去实现这个方法，ThreadPoolExecutor继承了AbstractExecutorService，它实现了execute方法。ScheduledThreadPoolExecutor继承自ThreadPoolExecutor，并覆盖了ThreadPoolExecutor的execute方法。这个方法是线程执行框者架的核心逻辑，不同的线程池执行者有不同的实现逻辑。

ThreadPoolExecutor线程池执行者：它有一个核心的成员变量：
private final HashSet<Worker> workers = new HashSet<Worker>();
workers可以看做是ThreadPoolExecutor中用于运行任务的线程池。
worker是一个封装了一个Thread对象并实现了Runnable接口的类。封装Thread很容易理解，因为它要利用Thread去运行execute方法提交过来的runnable任务