(juc系列)executors类的工厂方法
简介
提供一些工厂方法和工具类方法. 给Executor,ExecutorService,ScheduledExecutorService和ThreadFacotry使用. Callable类在这里定义.
这个类提供以下几种方法:
- 用一些常用的参数设置，创建一个新的
ExecutorService返回. 约等于ExecutorService的几个工厂方法. ScheduledExecutorSerivce的工厂方法，用一些常用的参数创建.- 创建并返回一些
ExecutorService的包装类, 关闭掉了重新设置参数的功能。 - 创建
ThreadFactory的一些方法. - 创建并返回
Callable的一些方法.
源码
ExecutorService的工厂方法
- newFixedThreadPool 创建一个固定大小的
ThreadPoolExecutor. - newSingleThreadExecutor 创建一个单个线程的
FinalizableDelegatedExecutorService. - newCachedThreadPool newCachedThreadPool创建一个无界的
ThreadPoolExecutor.没有核心线程，也没有最大线程数量的限制. - newWorkStealingPool 创建一个
ForkJoinPool. - newSingleThreadScheduledExecutor 创建一个具有单个线程的，周期定时执行的线程池.
DelegatedScheduledExecutorService - newScheduledThreadPool 创建多个线程的线程池，可以周期性的执行任务.
- unconfigurableExecutorService 将给定的
ExecutorService进行封装，不再允许修改相关的配置. - unconfigurableScheduledExecutorService 将给定的周期性线程池进行封装，不再允许修改配置.
ThreadFactory 线程工厂
- defaultThreadFactory 返回
DefaultThreadFactory类的一个实例，是默认的线程工厂，简单的创建一个非守护线程. - privilegedThreadFactory 返回
PrivilegedThreadFactory的一个实例，使得创建的线程拥有高级的访问权限和相同的类加载器. 代码如下.
private static class PrivilegedThreadFactory extends DefaultThreadFactory {
final AccessControlContext acc;
final ClassLoader ccl;
PrivilegedThreadFactory() {
super();
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
// Calls to getContextClassLoader from this class
// never trigger a security check, but we check
// whether our callers have this permission anyways.
sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
// Fail fast
sm.checkPermission(new RuntimePermission("setContextClassLoader"));
}
this.acc = AccessController.getContext();
this.ccl = Thread.currentThread().getContextClassLoader();
}
public Thread newThread(final Runnable r) {
return super.newThread(new Runnable() {
public void run() {
AccessController.doPrivileged(new PrivilegedAction<>() {
public Void run() {
Thread.currentThread().setContextClassLoader(ccl);
r.run();
return null;
}
}, acc);
}
});
}
}封装Callable
- callable(Runnable task, T result) 将给定的任务封装成Callable.但是不需要返回结果.
- callable(Runnable task) 给定的任务封装成Callable. 结束就返回null.
以上两个方法,通过RunnableAdapter实现.
// 一个run任务的装饰器
private static final class RunnableAdapter<T> implements Callable<T> {
private final Runnable task;
private final T result;
RunnableAdapter(Runnable task, T result) {
this.task = task;
this.result = result;
}
// 调用call时返回给定的结果
public T call() {
task.run();
return result;
}
public String toString() {
return super.toString() + "[Wrapped task = " + task + "]";
}
}- callable(final PrivilegedAction<?> action) 封装Callable.调用时执行action.
- callable(final PrivilegedExceptionAction<?> action) 同上
- privilegedCallable 具有特权的callable.
简单的ExecutorService实现
DelegatedExecutorService
一个ExecutorService的简单实现，同时对另外一个ExecutorService进行包装,使得传入的ExecutorService， 对外只能暴露ExecutorService接口的相关方法，所有的动态修改配置方法不可用. 可以起到强制不允许修改线程池参数的作用。
private static class DelegatedExecutorService
implements ExecutorService {
private final ExecutorService e;
DelegatedExecutorService(ExecutorService executor) { e = executor; }
public void execute(Runnable command) {
try {
e.execute(command);
} finally { reachabilityFence(this); }
}
public void shutdown() { e.shutdown(); }
public List<Runnable> shutdownNow() {
try {
return e.shutdownNow();
} finally { reachabilityFence(this); }
}
public boolean isShutdown() {
try {
return e.isShutdown();
} finally { reachabilityFence(this); }
}
public boolean isTerminated() {
try {
return e.isTerminated();
} finally { reachabilityFence(this); }
}
public boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException {
try {
return e.awaitTermination(timeout, unit);
} finally { reachabilityFence(this); }
}
public Future<?> submit(Runnable task) {
try {
return e.submit(task);
} finally { reachabilityFence(this); }
}
public <T> Future<T> submit(Callable<T> task) {
try {
return e.submit(task);
} finally { reachabilityFence(this); }
}
public <T> Future<T> submit(Runnable task, T result) {
try {
return e.submit(task, result);
} finally { reachabilityFence(this); }
}
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
throws InterruptedException {
try {
return e.invokeAll(tasks);
} finally { reachabilityFence(this); }
}
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException {
try {
return e.invokeAll(tasks, timeout, unit);
} finally { reachabilityFence(this); }
}
public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
throws InterruptedException, ExecutionException {
try {
return e.invokeAny(tasks);
} finally { reachabilityFence(this); }
}
public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
try {
return e.invokeAny(tasks, timeout, unit);
} finally { reachabilityFence(this); }
}
}可以看到，所有实现自ExecutorService的方法，都只是简单的做了委托，交给传入的ExecutorService去执行。
DelegatedScheduledExecutorService 周期性调度的线程池的委托者
private static class DelegatedScheduledExecutorService
extends DelegatedExecutorService
implements ScheduledExecutorService {
private final ScheduledExecutorService e;
DelegatedScheduledExecutorService(ScheduledExecutorService executor) {
super(executor);
e = executor;
}
public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
return e.schedule(command, delay, unit);
}
public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) {
return e.schedule(callable, delay, unit);
}
public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) {
return e.scheduleAtFixedRate(command, initialDelay, period, unit);
}
public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) {
return e.scheduleWithFixedDelay(command, initialDelay, delay, unit);
}
}类似与DelegatedExecutorService,对所有ScheduledExecutorService定义的方法进行实现，只做简单的委托，转发请求而已.
完。
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