Java并发编程核心方法与框架-TheadPoolExecutor的使用

类ThreadPoolExecutor最常使用的构造方法是

ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, unit, BlockingDeque<Runnable> workQueue)

• corePoolSize 线程池中所保存的线程数，包括空闲线程，也就是核心池的大小。当提交一个任务到线程池时，线程池会创建一个线程来执行任务，即使其他空闲的基本线程能够执行新任务也会创建线程，等到需要执行的任务数大于线程池基本大小时就不再创建。如果调用了线程池的prestartAllCoreThreads方法，线程池会提前创建并启动所有基本线程。
• maximumPoolSize 池中允许的最大线程数。如果队列满了，并且已创建的线程数小于最大线程数，则线程池会再创建新的线程执行任务。值得注意的是如果使用了无界的任务队列这个参数就没什么效果。
• keepAliveTime 当线程数量大于corePoolSize值时，在没有超过指定的时间内是不从线程池中将空闲线程删除的。如果超过此时间，则删除。所以如果任务很多，并且每个任务执行的时间比较短，可以调大这个时间，提高线程的利用率。
• unit keepAliveTime的时间单位
• workQueue 执行前用于保持任务的队列，此队列仅保持由execute方法提交的Runnable任务

ArrayBlockingQueue：是一个基于数组结构的有界阻塞队列，此队列按FIFO（先进先出）原则对元素进行排序。

LinkedBlockingQueue：一个基于链表结构的阻塞队列，此队列按FIFO（先进先出）排序元素，吞吐量通常要高于ArrayBlockingQueue。静态工厂方法Executors.newFixedThreadPool()使用了这个队列。

SynchronousQueue：一个不存储元素的阻塞队列。每个插入操作必须等到另一个线程调用移除操作，否则插入操作一直处于阻塞状态，吞吐量通常要高于LinkedBlockingQueue，静态工厂方法Executors.newCachedThreadPool使用了这个队列。

PriorityBlockingQueue：一个具有优先级的无限阻塞队列。

其他常用的构造方法参数：

• ThreadFactory：用于设置创建线程的工厂，可以通过线程工厂给每个创建出来的线程设置更有意义的名字。
• RejectedExecutionHandler（饱和策略）：当队列和线程池都满了，说明线程池处于饱和状态，那么必须采取一种策略处理提交的新任务。这个策略默认情况下是AbortPolicy，表示无法处理新任务时抛出异常。以下是JDK1.5提供的四种策略。

1. AbortPolicy：直接抛出异常。
2. CallerRunsPolicy：只用调用者所在线程来运行任务。
3. DiscardOldestPolicy：丢弃队列里最近的一个任务，并执行当前任务。
4. DiscardPolicy：不处理，丢弃掉。
   当然也可以根据应用场景需要来实现RejectedExecutionHandler接口自定义策略。如记录日志或持久化不能处理的任务。

---

当提交一个新任务到线程池时，线程池的处理流程如下：

1. 线程池判断基本线程池是否已满？没满，创建一个工作线程来执行任务。满了，则进入下个流程。
2. 线程池判断工作队列是否已满？没满，则将新提交的任务存储在工作队列里。满了，则进入下个流程。
3. 线程池判断整个线程池是否已满？没满，则创建一个新的工作线程来执行任务，满了，则交给饱和策略来处理这个任务。

---

/*
* 获取基本属性corePoolSize和maximumPoolSize
*/
public class Run {
	public static void main(String[] args) {
		int corePoolSize = 7;
		int maximumPoolSize = 8;
		int keepAliveTime = 5;
		TimeUnit unit = TimeUnit.SECONDS;
		LinkedBlockingDeque<Runnable> workQueue = new LinkedBlockingDeque<>();
		ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
		System.out.println(executor.getCorePoolSize());//7
		System.out.println(executor.getMaximumPoolSize());//8
		System.out.println("---------------------------");
		SynchronousQueue<Runnable> synchronousQueue = new SynchronousQueue<>();
		executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, synchronousQueue);
		System.out.println(executor.getCorePoolSize());//7
		System.out.println(executor.getMaximumPoolSize());//8
	}
}

---

如果欲执行的runnable的数量<=corePoolSize，则马上创建线程运行这个任务，并且不放入扩展队列Queue中。

/**
 * 队列使用LinkedBlockingDeque类，并且线程数量<=corePoolSize
 * 所以keepAliveTime>5时也不清除空闲线程
 */
public class Run2_1 {
	public static void main(String[] args) throws InterruptedException {
		Runnable runnable = new Runnable() {
			
			@Override
			public void run() {
				try {
					System.out.println(Thread.currentThread().getName() + " run!" + System.currentTimeMillis());
					Thread.sleep(1000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		};
		int corePoolSize = 7;
		int maximumPoolSize = 8;
		int keepAliveTime = 5;
		TimeUnit unit = TimeUnit.SECONDS;
		LinkedBlockingDeque<Runnable> workQueue = new LinkedBlockingDeque<Runnable>();
		ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
		executor.execute(runnable);//1
		executor.execute(runnable);//2
		executor.execute(runnable);//3
		executor.execute(runnable);//4
		executor.execute(runnable);//5
		executor.execute(runnable);//6
		executor.execute(runnable);//7
		Thread.sleep(300);
		System.out.println("A:" + executor.getCorePoolSize());//7
		System.out.println("A:" + executor.getPoolSize());//7
		System.out.println("A:" + executor.getQueue().size());//0
		Thread.sleep(10000);
		System.out.println("B:" + executor.getCorePoolSize());//7
		System.out.println("B:" + executor.getPoolSize());//7
		System.out.println("B:" + executor.getQueue().size());//0
	}
}

---

//如果欲执行的runnable的数量<=corePoolSize，则马上创建线程运行这个任务，并且不放入扩展队列Queue中。
/**
 * 队列使用SynchronousQueue类，并且线程数量<=corePoolSize
 * 所以keepAliveTime>5时也不清除空闲线程
 */
public class Run2_2 {
	public static void main(String[] args) throws InterruptedException {
		Runnable runnable = new Runnable() {
			
			@Override
			public void run() {
				try {
					System.out.println(Thread.currentThread().getName() + " begin " + System.currentTimeMillis());
					TimeUnit.SECONDS.sleep(1);
					System.out.println(Thread.currentThread().getName() + " end " + System.currentTimeMillis());
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		};
		int corePoolSize = 7;
		int maximumPoolSize = 8;
		int keepAliveTime = 5;
		TimeUnit unit = TimeUnit.SECONDS;
		SynchronousQueue<Runnable> workQueue = new SynchronousQueue<>();
//		LinkedBlockingDeque<Runnable> workQueue = new LinkedBlockingDeque<>();
		ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
		executor.execute(runnable);//1
		executor.execute(runnable);//2
		executor.execute(runnable);//3
		executor.execute(runnable);//4
		executor.execute(runnable);//5
		executor.execute(runnable);//6
		executor.execute(runnable);//7
//		TimeUnit.SECONDS.sleep(10);
		Thread.sleep(300);
		System.out.println("A:" + executor.getCorePoolSize());//7
		System.out.println("A:" + executor.getPoolSize());//7
		System.out.println("A:" + executor.getQueue().size());//0
		TimeUnit.SECONDS.sleep(10);
		System.out.println("B:" + executor.getCorePoolSize());//7
		System.out.println("B:" + executor.getPoolSize());//7
		System.out.println("B:" + executor.getQueue().size());//0
	}
}

---

数量>corePoolSize&&数量<=maxmimumPoolSize的情况

/*
 * BlockingQueue是一个接口，常用的实现类有LinkedBlockingQueue和ArrayBlockingQueue.
 * LinkedBlockingQueue的好处在于没有大小限制，队列容量非常大，所以执行execute()不会抛出异常
 * 线程池中运行的线程的数量永远也不会超过corePoolSize的值，
 * 因为多余的线程被放入LinkedBlockingQueue队列中，keepAliveTime参数也就没有意义了。
 */
public class Run3_1 {
	public static void main(String[] args) throws InterruptedException {
		Runnable runnable = new Runnable() {
			
			@Override
			public void run() {
				try {
					System.out.println(Thread.currentThread().getName() + " run!" + System.currentTimeMillis());
					Thread.sleep(1000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		};
		int corePoolSize = 7;
		int maximumPoolSize = 8;
		int keepAliveTime = 5;
		TimeUnit unit = TimeUnit.SECONDS;
		//队列使用LinkedBlockingDeque类，如果线程数量>corePoolSize时将其余的任务放入队列中。
		//同一时间最多只能有7个线程执行。
		//使用LinkedBlockingDeque类时，maximumPoolSize参数被忽略
		LinkedBlockingDeque<Runnable> workQueue = new LinkedBlockingDeque<Runnable>();
		ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
		executor.execute(runnable);//1
		executor.execute(runnable);//2
		executor.execute(runnable);//3
		executor.execute(runnable);//4
		executor.execute(runnable);//5
		executor.execute(runnable);//6
		executor.execute(runnable);//7
		executor.execute(runnable);//8
		//executor.execute(runnable);//8
		Thread.sleep(300);
		System.out.println("A:" + executor.getCorePoolSize());//7
		System.out.println("A:" + executor.getPoolSize());//7
		System.out.println("A:" + executor.getQueue().size());//1
		Thread.sleep(10000);
		System.out.println("B:" + executor.getCorePoolSize());//7
		System.out.println("B:" + executor.getPoolSize());//7
		System.out.println("B:" + executor.getQueue().size());//0
		
	}
}

以上代码运行结果如下：

pool-1-thread-1 run!1470813110727
pool-1-thread-5 run!1470813110728
pool-1-thread-4 run!1470813110728
pool-1-thread-7 run!1470813110728
pool-1-thread-2 run!1470813110727
pool-1-thread-3 run!1470813110727
pool-1-thread-6 run!1470813110728
A:7
A:7
A:1
pool-1-thread-1 run!1470813111731
B:7
B:7
B:0

可见，线程pool-1-thread-1执行了两个任务。

---

public class Run3_2 {
	public static void main(String[] args) throws InterruptedException {
		Runnable runnable = new Runnable() {
			
			@Override
			public void run() {
				try {
					System.out.println(Thread.currentThread().getName() + " run!" + System.currentTimeMillis());
					Thread.sleep(1000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		};
		int corePoolSize = 7;
		int maximumPoolSize = 8;
		int keepAliveTime = 5;
		TimeUnit unit = TimeUnit.SECONDS;
		/*
		 *队列使用SynchronousQueue类并且线程数量>corePoolSize时，将其余的线程放入池中，总数量为8
		 *并且线程总数量没有超过maximumPoolSize值8
		 *由于运行线程数为8，数量上>corePoolSize的值7
		 *所以keepAliveTime>5时清除空闲线程
		 *如果使用SynchronousQueue类则maximumPoolSize参数的作用将有效
		 */
		SynchronousQueue<Runnable> workQueue = new SynchronousQueue<Runnable>();
		ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
		executor.execute(runnable);//1
		executor.execute(runnable);//2
		executor.execute(runnable);//3
		executor.execute(runnable);//4
		executor.execute(runnable);//5
		executor.execute(runnable);//6
		executor.execute(runnable);//7
		executor.execute(runnable);//8
		//executor.execute(runnable);//8
		Thread.sleep(300);
		System.out.println("A:" + executor.getCorePoolSize());//7
		System.out.println("A:" + executor.getPoolSize());//8
		System.out.println("A:" + executor.getQueue().size());//0
		Thread.sleep(10000);
		System.out.println("B:" + executor.getCorePoolSize());//7
		System.out.println("B:" + executor.getPoolSize());//7
		System.out.println("B:" + executor.getQueue().size());//0
		//删除的是>corePoolSize的多余线程
	}
}

以上代码运行结果如下：

pool-1-thread-3 run!1470832826522
pool-1-thread-6 run!1470832826522
pool-1-thread-7 run!1470832826523
pool-1-thread-5 run!1470832826522
pool-1-thread-4 run!1470832826522
pool-1-thread-1 run!1470832826522
pool-1-thread-2 run!1470832826522
pool-1-thread-8 run!1470832826523
A:7
A:8
A:0
B:7
B:7
B:0

---

数量>maximumPoolSize的情况

public class Run4_1 {
	public static void main(String[] args) throws InterruptedException {
		Runnable runnable = new Runnable() {
			
			@Override
			public void run() {
				try {
					System.out.println(Thread.currentThread().getName() + " run!" + System.currentTimeMillis());
					Thread.sleep(1000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		};
		int corePoolSize = 7;
		int maximumPoolSize = 8;
		int keepAliveTime = 5;
		TimeUnit unit = TimeUnit.SECONDS;
		/*
		 *队列使用LinkedBlockingDeque类并且线程数量>corePoolSize时，将其余的线程放入池中
		 *同一时间内只有corePoolSize个线程在运行
		 *所以keepAliveTime>5时不清除空闲线程
		 */
		LinkedBlockingDeque<Runnable> workQueue = new LinkedBlockingDeque<Runnable>();
		ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
		executor.execute(runnable);//1
		executor.execute(runnable);//2
		executor.execute(runnable);//3
		executor.execute(runnable);//4
		executor.execute(runnable);//5
		executor.execute(runnable);//6
		executor.execute(runnable);//7
		executor.execute(runnable);//8
		executor.execute(runnable);//9
		Thread.sleep(300);
		System.out.println("A:" + executor.getCorePoolSize());//7
		System.out.println("A:" + executor.getPoolSize());//7
		System.out.println("A:" + executor.getQueue().size());//2
		Thread.sleep(10000);
		System.out.println("B:" + executor.getCorePoolSize());//7
		System.out.println("B:" + executor.getPoolSize());//7
		System.out.println("B:" + executor.getQueue().size());//0
	}
}

运行结果如下：

pool-1-thread-1 run!1470833462484
pool-1-thread-4 run!1470833462484
pool-1-thread-3 run!1470833462484
pool-1-thread-2 run!1470833462484
pool-1-thread-6 run!1470833462484
pool-1-thread-5 run!1470833462484
pool-1-thread-7 run!1470833462485
A:7
A:7
A:2
pool-1-thread-5 run!1470833463489
pool-1-thread-4 run!1470833463489
B:7
B:7
B:0

public class Run4_2 {
	public static void main(String[] args) throws InterruptedException {
		Runnable runnable = new Runnable() {
			
			@Override
			public void run() {
				try {
					System.out.println(Thread.currentThread().getName() + " run!" + System.currentTimeMillis());
					Thread.sleep(1000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		};
		int corePoolSize = 7;
		int maximumPoolSize = 10;
		int keepAliveTime = 5;
		TimeUnit unit = TimeUnit.SECONDS;
		/*
		 *队列使用SynchronousQueue类并且线程数量>=corePoolSize
		 *并且线程数量<=maximumPoolSize
		 *所以keepAliveTime>5时清除空闲线程
		 */
		SynchronousQueue<Runnable> workQueue = new SynchronousQueue<Runnable>();
		ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
		executor.execute(runnable);//1
		executor.execute(runnable);//2
		executor.execute(runnable);//3
		executor.execute(runnable);//4
		executor.execute(runnable);//5
		executor.execute(runnable);//6
		executor.execute(runnable);//7
		executor.execute(runnable);//8
		executor.execute(runnable);//9
		Thread.sleep(300);
		System.out.println("A:" + executor.getCorePoolSize());//7
		System.out.println("A:" + executor.getPoolSize());//9
		System.out.println("A:" + executor.getQueue().size());//0
		Thread.sleep(10000);
		System.out.println("B:" + executor.getCorePoolSize());//7
		System.out.println("B:" + executor.getPoolSize());//7
		System.out.println("B:" + executor.getQueue().size());//0
	}
}

以上代码运行结果如下：

pool-1-thread-2 run!1470833720785
pool-1-thread-5 run!1470833720786
pool-1-thread-4 run!1470833720785
pool-1-thread-3 run!1470833720785
pool-1-thread-1 run!1470833720785
pool-1-thread-6 run!1470833720786
pool-1-thread-7 run!1470833720786
pool-1-thread-8 run!1470833720786
pool-1-thread-9 run!1470833720786
A:7
A:9
A:0
B:7
B:7
B:0

public class Run4_3 {
	public static void main(String[] args) throws InterruptedException {
		Runnable runnable = new Runnable() {
			
			@Override
			public void run() {
				try {
					System.out.println(Thread.currentThread().getName() + " run!" + System.currentTimeMillis());
					Thread.sleep(1000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		};
		int corePoolSize = 7;
		int maximumPoolSize = 8;
		int keepAliveTime = 5;
		TimeUnit unit = TimeUnit.SECONDS;
		/*
		 *队列使用SynchronousQueue类并且线程数量>corePoolSize
		 *并且线程数量>maximumPoolSize
		 *所以出现异常
		 */
		SynchronousQueue<Runnable> workQueue = new SynchronousQueue<Runnable>();
		ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
		executor.execute(runnable);//1
		executor.execute(runnable);//2
		executor.execute(runnable);//3
		executor.execute(runnable);//4
		executor.execute(runnable);//5
		executor.execute(runnable);//6
		executor.execute(runnable);//7
		executor.execute(runnable);//8
		executor.execute(runnable);//9
		Thread.sleep(300);
		System.out.println("A:" + executor.getCorePoolSize());//
		System.out.println("A:" + executor.getPoolSize());//
		System.out.println("A:" + executor.getQueue().size());//
		Thread.sleep(10000);
		System.out.println("B:" + executor.getCorePoolSize());//
		System.out.println("B:" + executor.getPoolSize());//
		System.out.println("B:" + executor.getQueue().size());//
	}
}

运行结果如下：

pool-1-thread-2 run!1470833900655
pool-1-thread-6 run!1470833900655
pool-1-thread-5 run!1470833900655
pool-1-thread-4 run!1470833900655
pool-1-thread-1 run!1470833900655
pool-1-thread-7 run!1470833900656
pool-1-thread-3 run!1470833900655
pool-1-thread-8 run!1470833900656
Exception in thread "main" java.util.concurrent.RejectedExecutionException: Task com.concurrent.chapter4.concurrent07.Run4_3$1@c33f45e rejected from java.util.concurrent.ThreadPoolExecutor@6a754384[Running, pool size = 8, active threads = 8, queued tasks = 0, completed tasks = 0]
	at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048)
	at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821)
	at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1372)
	at com.concurrent.chapter4.concurrent07.Run4_3.main(Run4_3.java:42)

---

参数keepAliveTime为0时的实验

public class Run5 {
	public static void main(String[] args) throws InterruptedException {
		Runnable runnable = new Runnable() {
			
			@Override
			public void run() {
				try {
					System.out.println(Thread.currentThread().getName() + " run!" + System.currentTimeMillis());
					Thread.sleep(1000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		};
		int corePoolSize = 7;
		int maximumPoolSize = 10;
		int keepAliveTime = 0;
		TimeUnit unit = TimeUnit.SECONDS;
		/*
		 *队列使用SynchronousQueue类并且线程数量<corePoolSize
		 *并且线程数量<=maximumPoolSize
		 *并且keepAliveTime值为0时 线程执行完毕后立即清除
		 */
		SynchronousQueue<Runnable> workQueue = new SynchronousQueue<Runnable>();
		ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
		executor.execute(runnable);//1
		executor.execute(runnable);//2
		executor.execute(runnable);//3
		executor.execute(runnable);//4
		executor.execute(runnable);//5
		executor.execute(runnable);//6
		executor.execute(runnable);//7
		executor.execute(runnable);//8
		executor.execute(runnable);//9
		Thread.sleep(300);
		System.out.println("A:" + executor.getCorePoolSize());//7
		System.out.println("A:" + executor.getPoolSize());//9
		System.out.println("A:" + executor.getQueue().size());//0
		Thread.sleep(10000);
		System.out.println("B:" + executor.getCorePoolSize());//7
		System.out.println("B:" + executor.getPoolSize());//7
		System.out.println("B:" + executor.getQueue().size());//0
	}
}

运行结果如下：

pool-1-thread-3 run!1470834464969
pool-1-thread-5 run!1470834464969
pool-1-thread-4 run!1470834464969
pool-1-thread-6 run!1470834464969
pool-1-thread-1 run!1470834464969
pool-1-thread-2 run!1470834464969
pool-1-thread-7 run!1470834464970
pool-1-thread-8 run!1470834464970
pool-1-thread-9 run!1470834464970
A:7
A:9
A:0
B:7
B:7
B:0

---