本文介绍了Java中Executor服务的使用，它提供了一个间接层管理线程，简化并发编程。通过Executor，可以避免直接管理线程的生命周期，而是专注于任务的执行。文章通过代码示例展示了ExecutorService如何创建线程池，以及Executor如何执行任务，强调了其在Java并发编程中的重要性。
1.Executor为我们去管理Thread对象，从而简化了并发编程。Executor在客户端和任务执行之间提供了一个间接层；与客户端直接执行任务不同，这个中介是执行任务的，Executor允许你管理异步任务的执行，而无需去管理线程的生命周期，Executor是SE5以上的启动任务的优选方法。
代码如下所示；
1其根本原因是调度一个线程池，帮助我们去管理线程：
线程原始状态如下所示：
线程池大小为0,其次激活，也就是运行线程数目也是为0,其次队列的任务数也是为0，再其次，线程任务的完成数也是为0
去激活了一个线程，具体表现如下所示：
其中new liftOff的线程表现过程如下所示：
去调用线程的具体实现过程如下所示：
因为执行了exec这个对象对线程池去进行了摧毁，因此，线程整体就被销毁了
因此需要对代码进行修改：
不断的去线程的创建，这里是引用线程创建
运行结果如下所示：
"C:\Program Files\Java\jdk1.8.0_171\bin\java.exe" "-javaagent:D:\IDEA_JAVA\IntelliJ IDEA 2018.2.4\lib\idea_rt.jar=55437:D:\IDEA_JAVA\IntelliJ IDEA 2018.2.4\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_171\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_171\jre\lib\rt.jar;C:\Users\wu\Desktop\work\11\vue\并发\out\production\并发" CachedThreadPool
#0(9)
#0(8)
#1(9)
#2(9)
#0(7)
#1(8)
#2(8)
#3(9)
#0(6)
#4(9)
#2(7)
#3(8)
#1(7)
#2(6)
#4(8)
#1(6)
#4(7)
#0(5)
#4(6)
#1(5)
#2(5)
#3(7)
#0(4)
#4(5)
#2(4)
#4(4)
#1(4)
#4(3)
#2(3)
#0(3)
#3(6)
#4(2)
#1(3)
#2(2)
#3(5)
#0(2)
#3(4)
#2(1)
#1(2)
#4(1)
#2(liftOff!)
#3(3)
#0(1)
#4(liftOff!)
#1(1)
#3(2)
#0(liftOff!)
#1(liftOff!)
#3(1)
#3(liftOff!)
Process finished with exit code 0
其中executorservice基本代码如下所示:
/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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/*
*
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* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util.concurrent;
import java.util.List;
import java.util.Collection;
/**
* An {@link Executor} that provides methods to manage termination and
* methods that can produce a {@link Future} for tracking progress of
* one or more asynchronous tasks.
*
* <p>An {@code ExecutorService} can be shut down, which will cause
* it to reject new tasks. Two different methods are provided for
* shutting down an {@code ExecutorService}. The {@link #shutdown}
* method will allow previously submitted tasks to execute before
* terminating, while the {@link #shutdownNow} method prevents waiting
* tasks from starting and attempts to stop currently executing tasks.
* Upon termination, an executor has no tasks actively executing, no
* tasks awaiting execution, and no new tasks can be submitted. An
* unused {@code ExecutorService} should be shut down to allow
* reclamation of its resources.
*
* <p>Method {@code submit} extends base method {@link
* Executor#execute(Runnable)} by creating and returning a {@link Future}
* that can be used to cancel execution and/or wait for completion.
* Methods {@code invokeAny} and {@code invokeAll} perform the most
* commonly useful forms of bulk execution, executing a collection of
* tasks and then waiting for at least one, or all, to
* complete. (Class {@link ExecutorCompletionService} can be used to
* write customized variants of these methods.)
*
* <p>The {@link Executors} class provides factory methods for the
* executor services provided in this package.
*
* <h3>Usage Examples</h3>
*
* Here is a sketch of a network service in which threads in a thread
* pool service incoming requests. It uses the preconfigured {@link
* Executors#newFixedThreadPool} factory method:
*
* <pre> {@code
* class NetworkService implements Runnable {
* private final ServerSocket serverSocket;
* private final ExecutorService pool;
*
* public NetworkService(int port, int poolSize)
* throws IOException {
* serverSocket = new ServerSocket(port);
* pool = Executors.newFixedThreadPool(poolSize);
* }
*
* public void run() { // run the service
* try {
* for (;;) {
* pool.execute(new Handler(serverSocket.accept()));
* }
* } catch (IOException ex) {
* pool.shutdown();
* }
* }
* }
*
* class Handler implements Runnable {
* private final Socket socket;
* Handler(Socket socket) { this.socket = socket; }
* public void run() {
* // read and service request on socket
* }
* }}</pre>
*
* The following method shuts down an {@code ExecutorService} in two phases,
* first by calling {@code shutdown} to reject incoming tasks, and then
* calling {@code shutdownNow}, if necessary, to cancel any lingering tasks:
*
* <pre> {@code
* void shutdownAndAwaitTermination(ExecutorService pool) {
* pool.shutdown(); // Disable new tasks from being submitted
* try {
* // Wait a while for existing tasks to terminate
* if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
* pool.shutdownNow(); // Cancel currently executing tasks
* // Wait a while for tasks to respond to being cancelled
* if (!pool.awaitTermination(60, TimeUnit.SECONDS))
* System.err.println("Pool did not terminate");
* }
* } catch (InterruptedException ie) {
* // (Re-)Cancel if current thread also interrupted
* pool.shutdownNow();
* // Preserve interrupt status
* Thread.currentThread().interrupt();
* }
* }}</pre>
*
* <p>Memory consistency effects: Actions in a thread prior to the
* submission of a {@code Runnable} or {@code Callable} task to an
* {@code ExecutorService}
* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
* any actions taken by that task, which in turn <i>happen-before</i> the
* result is retrieved via {@code Future.get()}.
*
* @since 1.5
* @author Doug Lea
*/
public interface ExecutorService extends Executor {
/**
* Initiates an orderly shutdown in which previously submitted
* tasks are executed, but no new tasks will be accepted.
* Invocation has no additional effect if already shut down.
*
* <p>This method does not wait for previously submitted tasks to
* complete execution. Use {@link #awaitTermination awaitTermination}
* to do that.
*
* @throws SecurityException if a security manager exists and
* shutting down this ExecutorService may manipulate
* threads that the caller is not permitted to modify
* because it does not hold {@link
* java.lang.RuntimePermission}{@code ("modifyThread")},
* or the security manager's {@code checkAccess} method
* denies access.
*/
void shutdown();
/**
* Attempts to stop all actively executing tasks, halts the
* processing of waiting tasks, and returns a list of the tasks
* that were awaiting execution.
*
* <p>This method does not wait for actively executing tasks to
* terminate. Use {@link #awaitTermination awaitTermination} to
* do that.
*
* <p>There are no guarantees beyond best-effort attempts to stop
* processing actively executing tasks. For example, typical
* implementations will cancel via {@link Thread#interrupt}, so any
* task that fails to respond to interrupts may never terminate.
*
* @return list of tasks that never commenced execution
* @throws SecurityException if a security manager exists and
* shutting down this ExecutorService may manipulate
* threads that the caller is not permitted to modify
* because it does not hold {@link
* java.lang.RuntimePermission}{@code ("modifyThread")},
* or the security manager's {@code checkAccess} method
* denies access.
*/
List<Runnable> shutdownNow();
/**
* Returns {@code true} if this executor has been shut down.
*
* @return {@code true} if this executor has been shut down
*/
boolean isShutdown();
/**
* Returns {@code true} if all tasks have completed following shut down.
* Note that {@code isTerminated} is never {@code true} unless
* either {@code shutdown} or {@code shutdownNow} was called first.
*
* @return {@code true} if all tasks have completed following shut down
*/
boolean isTerminated();
/**
* Blocks until all tasks have completed execution after a shutdown
* request, or the timeout occurs, or the current thread is
* interrupted, whichever happens first.
*
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
* @return {@code true} if this executor terminated and
* {@code false} if the timeout elapsed before termination
* @throws InterruptedException if interrupted while waiting
*/
boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException;
/**
* Submits a value-returning task for execution and returns a
* Future representing the pending results of the task. The
* Future's {@code get} method will return the task's result upon
* successful completion.
*
* <p>
* If you would like to immediately block waiting
* for a task, you can use constructions of the form
* {@code result = exec.submit(aCallable).get();}
*
* <p>Note: The {@link Executors} class includes a set of methods
* that can convert some other common closure-like objects,
* for example, {@link java.security.PrivilegedAction} to
* {@link Callable} form so they can be submitted.
*
* @param task the task to submit
* @param <T> the type of the task's result
* @return a Future representing pending completion of the task
* @throws RejectedExecutionException if the task cannot be
* scheduled for execution
* @throws NullPointerException if the task is null
*/
<T> Future<T> submit(Callable<T> task);
/**
* Submits a Runnable task for execution and returns a Future
* representing that task. The Future's {@code get} method will
* return the given result upon successful completion.
*
* @param task the task to submit
* @param result the result to return
* @param <T> the type of the result
* @return a Future representing pending completion of the task
* @throws RejectedExecutionException if the task cannot be
* scheduled for execution
* @throws NullPointerException if the task is null
*/
<T> Future<T> submit(Runnable task, T result);
/**
* Submits a Runnable task for execution and returns a Future
* representing that task. The Future's {@code get} method will
* return {@code null} upon <em>successful</em> completion.
*
* @param task the task to submit
* @return a Future representing pending completion of the task
* @throws RejectedExecutionException if the task cannot be
* scheduled for execution
* @throws NullPointerException if the task is null
*/
Future<?> submit(Runnable task);
/**
* Executes the given tasks, returning a list of Futures holding
* their status and results when all complete.
* {@link Future#isDone} is {@code true} for each
* element of the returned list.
* Note that a <em>completed</em> task could have
* terminated either normally or by throwing an exception.
* The results of this method are undefined if the given
* collection is modified while this operation is in progress.
*
* @param tasks the collection of tasks
* @param <T> the type of the values returned from the tasks
* @return a list of Futures representing the tasks, in the same
* sequential order as produced by the iterator for the
* given task list, each of which has completed
* @throws InterruptedException if interrupted while waiting, in
* which case unfinished tasks are cancelled
* @throws NullPointerException if tasks or any of its elements are {@code null}
* @throws RejectedExecutionException if any task cannot be
* scheduled for execution
*/
<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
throws InterruptedException;
/**
* Executes the given tasks, returning a list of Futures holding
* their status and results
* when all complete or the timeout expires, whichever happens first.
* {@link Future#isDone} is {@code true} for each
* element of the returned list.
* Upon return, tasks that have not completed are cancelled.
* Note that a <em>completed</em> task could have
* terminated either normally or by throwing an exception.
* The results of this method are undefined if the given
* collection is modified while this operation is in progress.
*
* @param tasks the collection of tasks
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
* @param <T> the type of the values returned from the tasks
* @return a list of Futures representing the tasks, in the same
* sequential order as produced by the iterator for the
* given task list. If the operation did not time out,
* each task will have completed. If it did time out, some
* of these tasks will not have completed.
* @throws InterruptedException if interrupted while waiting, in
* which case unfinished tasks are cancelled
* @throws NullPointerException if tasks, any of its elements, or
* unit are {@code null}
* @throws RejectedExecutionException if any task cannot be scheduled
* for execution
*/
<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException;
/**
* Executes the given tasks, returning the result
* of one that has completed successfully (i.e., without throwing
* an exception), if any do. Upon normal or exceptional return,
* tasks that have not completed are cancelled.
* The results of this method are undefined if the given
* collection is modified while this operation is in progress.
*
* @param tasks the collection of tasks
* @param <T> the type of the values returned from the tasks
* @return the result returned by one of the tasks
* @throws InterruptedException if interrupted while waiting
* @throws NullPointerException if tasks or any element task
* subject to execution is {@code null}
* @throws IllegalArgumentException if tasks is empty
* @throws ExecutionException if no task successfully completes
* @throws RejectedExecutionException if tasks cannot be scheduled
* for execution
*/
<T> T invokeAny(Collection<? extends Callable<T>> tasks)
throws InterruptedException, ExecutionException;
/**
* Executes the given tasks, returning the result
* of one that has completed successfully (i.e., without throwing
* an exception), if any do before the given timeout elapses.
* Upon normal or exceptional return, tasks that have not
* completed are cancelled.
* The results of this method are undefined if the given
* collection is modified while this operation is in progress.
*
* @param tasks the collection of tasks
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
* @param <T> the type of the values returned from the tasks
* @return the result returned by one of the tasks
* @throws InterruptedException if interrupted while waiting
* @throws NullPointerException if tasks, or unit, or any element
* task subject to execution is {@code null}
* @throws TimeoutException if the given timeout elapses before
* any task successfully completes
* @throws ExecutionException if no task successfully completes
* @throws RejectedExecutionException if tasks cannot be scheduled
* for execution
*/
<T> T invokeAny(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException;
}
显示结果如下所示：
调用的是Executors这个类中的自带线程池的调度，具体实现代码如下所示：
以下这种是线程安全的线程池调度，具体过程如下所示：
还有众多的线程池实现方法，具体的实现可以自己去看，本文当中的显示如下所示：
调用exec对象去执行execute方法，执行结果如下所示：
再往下追踪其根本结果显示如下所示：
此时用new LiftOff进行代替，具体显示如下所示：
总结如下所示：
使用Exector来代替并创建Thread对象，
ExecutorService知道如何构建上下文去执行Runable对象，
cachedThreadPool为每一个任务创建一个线程，其中Executors是Executors静态方法创建的，这个方法可以确定其Executor的类型
再使用exec这个构建的对象去调用当前进程进行执行，具体结果显示如下所示：
实例源代码如下所示：
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class CachedThreadPool {
public static void main(String[] args){
ExecutorService exec= Executors.newCachedThreadPool();
for (int i=0;i<5;i++){
exec.execute(new LiftOff());
}
exec.shutdown();
}
}
public class LiftOff implements Runnable{
protected int CountDown =10;//3
private static int taskcount=0;//1
private final int id=taskcount++;//4
public LiftOff(){}//2
public LiftOff(int CountDown){
this.CountDown=CountDown;
}
public String status(){ //判断条件以及验证状态
return "#"+id+"("+(CountDown>0?CountDown:"liftOff!")+")";
}
public void run(){ //执行
while (CountDown-->0){//将CountDown进行自减操作：
System.out.println(status());
Thread.yield();
}
}
}
实现代码如上所示：请自己进行具体分解
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