JAVA并发工具包-线程控制

￡神魔★判官ぃ 2022-03-20 14:45 224阅读 0赞

## 闭锁CountDownLatch ##

java.util.concurrent.CountDownLatch 是一个并发控制器，协调一个或多个线程合作执行，使用CountDownLatch构造器实例对象时指定countDown的次数，如果线程A调用CountDownLatch.await方法，那么当countDown次数递减到零时，线程A方可继续向下执行。  
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package com.hk;
    
    import java.util.concurrent.CountDownLatch;
    
    public class TestCountDownLatch {
    	public static void main(String[] args) throws Exception
    	{
    		CountDownLatch latch = new CountDownLatch(3);
    		 
    		Thread1 th1 = new Thread1(latch);
    		Thread2 th2 = new Thread2(latch);
    		 
    		new Thread(th1).start();
    		new Thread(th2).start();
    		 
    		Thread.sleep(4000);
    	}
    }
    
    class Thread1 implements Runnable{
    	 
        CountDownLatch latch = null;
     
        public Thread1(CountDownLatch latch) {
            this.latch = latch;
        }
     
        public void run() {
            try {
                latch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
     
            System.out.println("线程一释放...");
        }
    }
     
    class Thread2 implements Runnable {
    	 
        CountDownLatch latch = null;
     
        public Thread2(CountDownLatch latch) {
            this.latch = latch;
        }
     
        public void run() {
     
            try {
                Thread.sleep(500);
                this.latch.countDown();
     
                Thread.sleep(500);
                this.latch.countDown();
     
                Thread.sleep(500);
                this.latch.countDown();
                System.out.println("线程二释放...");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

## 栅栏CyclicBarrier ##

java.util.concurrent.CyclicBarrier 类协调多线程同步执行，所有线程必须等待的一个栅栏对象，直到所有线程都到达此处，然后所有线程才可以继续做其他事情。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FpeGlhbmdfY2hlbg_size_16_color_FFFFFF_t_70 1]  
定义栅栏对象时需要指定多少个线程同时到达栅栏对象时释放线程，需要指定一个数量，栅栏释放线程时可以执行一个操作(此操作是一个线程对象)。如下代码：

package com.hk;
    
    import java.util.concurrent.BrokenBarrierException;
    import java.util.concurrent.CyclicBarrier;
    
    public class TestCyclicBarrier {
    	public static void main(String[] args)
    	{
    		Runnable action1 = new Runnable() {
    		    public void run() {
    		        System.out.println("栅栏动作一执行...");
    		    }
    		};
    		Runnable action2 = new Runnable() {
    		    public void run() {
    		    	System.out.println("栅栏动作啊执行...");
    		    }
    		};
    		 
    		CyclicBarrier barrier1 = new CyclicBarrier(2, action1);
    		CyclicBarrier barrier2 = new CyclicBarrier(2, action2);
    		 
    		MyThread barrierRunnable1 =
    		        new MyThread(barrier1, barrier2);
    		 
    		MyThread barrierRunnable2 =
    		        new MyThread(barrier1, barrier2);
    		 
    		new Thread(barrierRunnable1).start();
    		new Thread(barrierRunnable2).start();
    	}
    }
    
    class MyThread implements Runnable{
    	 
        CyclicBarrier barrier1 = null;
        CyclicBarrier barrier2 = null;
     
        public MyThread(
                CyclicBarrier barrier1,
                CyclicBarrier barrier2) {
     
            this.barrier1 = barrier1;
            this.barrier2 = barrier2;
        }
     
        public void run() {
            try {
                Thread.sleep(1000);
                System.out.println(Thread.currentThread().getName() +
                                    " 栅栏一 等待所有线程完成");
                this.barrier1.await();
     
                Thread.sleep(1000);
                System.out.println(Thread.currentThread().getName() +
                                    " 栅栏一 等待所有线程完成");
                this.barrier2.await();
     
                System.out.println(Thread.currentThread().getName() +
                                    " 完成...");
     
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }

## 交换机Exchanger ##

java.util.concurrent.Exchanger 类表示一种两个线程可以进行互相交换对象的会和点。两个线程可以通过Exchanger交换必须拥有的对象。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FpeGlhbmdfY2hlbg_size_16_color_FFFFFF_t_70 2]

package com.hk;
    
    import java.util.concurrent.Exchanger;
    
    public class TestExchanger {
    	public static void main(String[] args)
    	{
    		Exchanger exchanger = new Exchanger();
    		 
    		ExgThread exchangerRunnable1 =
    		        new ExgThread(exchanger, "A");
    		 
    		ExgThread exchangerRunnable2 =
    		        new ExgThread(exchanger, "B");
    		 
    		new Thread(exchangerRunnable1).start();
    		new Thread(exchangerRunnable2).start();
    	}
    }
    class ExgThread implements Runnable{
    	 
        Exchanger exchanger = null;
        Object    object    = null;
     
        public ExgThread(Exchanger exchanger, Object object) {
            this.exchanger = exchanger;
            this.object = object;
        }
     
        public void run() {
            try {
                Object previous = this.object;
     
                this.object = this.exchanger.exchange(this.object);
     
                System.out.println(
                        Thread.currentThread().getName() +
                        " 交换对象 " + previous + " 为 " + this.object
                );
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

## 信号量 Semaphore ##

java.util.concurrent.Semaphore 类是一个计数信号量。这就意味着它具备两个主要方法：  
acquire()  
release()  
计数信号量由一个指定数量的 “许可” 初始化。每调用一次 acquire()，一个许可会被调用线程取走。每调用一次 release()，一个许可会被返还给信号量。因此，在没有任何 release() 调用时，最多有 N 个线程能够通过 acquire() 方法，N 是该信号量初始化时的许可的指定数量。  
Semaphore内部主要通过AQS（AbstractQueuedSynchronizer）实现线程的管理。Semaphore有两个构造函数，参数permits表示许可数，它最后传递给了AQS的state值。线程在运行时首先获取许可，如果成功，许可数就减1，线程运行，当线程运行结束就释放许可，许可数就加1。如果许可数为0，则获取失败，线程位于AQS的等待队列中，它会被其它释放许可的线程唤醒。在创建Semaphore对象的时候还可以指定它的公平性。

package com.hk;
    
    import java.util.Random;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Semaphore;
    
    public class SemaphoreTest {
    	private Semaphore smp = new Semaphore(3); 
    	private Random rnd = new Random();
    	
    	//成员内部类
    	class TaskThread implements Runnable{
    		private String id;
    		
    		TaskThread(String id){
    			this.id = id;
    		}
    		
    		public void run(){
    			try {
    				smp.acquire();
    				System.out.println("线程 " + id + " 运行...");
    				Thread.sleep(rnd.nextInt(1000));
    				smp.release();
    				System.out.println("线程  " + id + " 终止...");
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    	
    	public static void main(String[] args){
    		SemaphoreTest semaphore = new SemaphoreTest();
    		//注意我创建的线程池类型，
    		ExecutorService se = Executors.newCachedThreadPool();
    		se.submit(semaphore.new TaskThread("a"));
    		se.submit(semaphore.new TaskThread("b"));
    		se.submit(semaphore.new TaskThread("c"));
    		se.submit(semaphore.new TaskThread("d"));
    		se.submit(semaphore.new TaskThread("e"));
    		se.submit(semaphore.new TaskThread("f"));
    		se.shutdown();
    	}
    }

## 执行器服务 ExecutorService ##

java.util.concurrent.ExecutorService 接口表示一个异步执行机制，其实现类可以使用多钟方式在后台执行任务。两个实现类有ThreadPoolExecutor和ScheduledThreadPoolExecutor。ExecutorService 接口提供的方法有：  
execute(Runnable)  
异步执行java.lang.Runnable 对象；

package com.hk;
    
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    
    public class ExecutorServiceTest {
    	public static void main(String[] args)
    	{
    		ExecutorService executorService = Executors.newSingleThreadExecutor();
    		 
    		executorService.execute(new Runnable() {
    		    public void run() {
    		        System.out.println("任务异步执行...");
    		    }
    		});
    		 
    		executorService.shutdown();
    	}
    	
    }

submit(Runnable)  
异步执行java.lang.Runnable， 它返回一个 Future 对象。这个 Future 对象可以用来检查 Runnable 是否已经执行完毕

package com.hk;
    
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    
    public class ExecutorServiceTest {
    	public static void main(String[] args) throws Exception
    	{
    		ExecutorService executorService = Executors.newSingleThreadExecutor();
    		 
    		Future future = executorService.submit(new Runnable() {
    		    public void run() {
    		        System.out.println("异步任务执行...");
    		    }
    		});
    		 
    		Object obj = future.get();//返回null,异步任务执行成功
    		System.out.println("Obj = "+obj);
    		executorService.shutdown();
    	}
    	
    }

submit(Callable)  
异步执行java.lang.Runnable，Callable 实例除了它的 call() 方法能够返回一个结果。

package com.hk;
    
    import java.util.concurrent.Callable;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    
    public class ExecutorServiceTest {
    	public static void main(String[] args) throws Exception
    	{
    		ExecutorService executorService = Executors.newSingleThreadExecutor();
    
    		Future future = executorService.submit(new Callable(){
    		    public Object call() throws Exception {
    		        System.out.println("异步任务执行...");
    		        return "Callable Success";
    		    }
    		});
    		 
    		System.out.println("future.get() = " + future.get());
    		executorService.shutdown();
    	}
    	
    }

invokeAny(…)  
方法要求一系列的 Callable 或者其子接口的实例对象。调用这个方法并不会返回一个 Future，但它返回其中一个 Callable 对象的结果。无法保证返回的是哪个 Callable 的结果 - 只能表明其中一个已执行结束。

package com.hk;
    
    import java.util.HashSet;
    import java.util.Set;
    import java.util.concurrent.Callable;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    
    public class ExecutorServiceTest {
    	public static void main(String[] args) throws Exception
    	{
    		ExecutorService executorService = Executors.newSingleThreadExecutor();
    
    		Set<Callable<String>> callables = new HashSet<Callable<String>>();
    		 
    		callables.add(new Callable<String>() {
    		    public String call() throws Exception {
    		        return "任务一";
    		    }
    		});
    		callables.add(new Callable<String>() {
    		    public String call() throws Exception {
    		        return "任务二";
    		    }
    		});
    		callables.add(new Callable<String>() {
    		    public String call() throws Exception {
    		        return "任务三";
    		    }
    		});
    		 
    		String result = executorService.invokeAny(callables);
    		 
    		System.out.println("执行的异步任务 = " + result);
    
    		executorService.shutdown();
    	}
    	
    }

invokeAll(…)  
方法将调用你在集合中传给 ExecutorService 的所有 Callable 对象。invokeAll() 返回一系列的 Future 对象，通过它们你可以获取每个 Callable 的执行结果。

package com.hk;
    
    import java.util.HashSet;
    import java.util.List;
    import java.util.Set;
    import java.util.concurrent.Callable;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    
    public class ExecutorServiceTest {
    	public static void main(String[] args) throws Exception
    	{
    		ExecutorService executorService = Executors.newSingleThreadExecutor();
    
    		Set<Callable<String>> callables = new HashSet<Callable<String>>();
    		 
    		callables.add(new Callable<String>() {
    		    public String call() throws Exception {
    		        return "任务一";
    		    }
    		});
    		callables.add(new Callable<String>() {
    		    public String call() throws Exception {
    		        return "任务二";
    		    }
    		});
    		callables.add(new Callable<String>() {
    		    public String call() throws Exception {
    		        return "任务三";
    		    }
    		});
    
    		List<Future<String>> futures = executorService.invokeAll(callables);
    		 
    		for(Future<String> future : futures){
    		    System.out.println("执行结果 = " + future.get());
    		}
    		executorService.shutdown();
    	}
    	
    }

## 线程池执行者 ThreadPoolExecutor ##

ThreadPoolExecutor作为java.util.concurrent包对外提供基础实现，以内部线程池的形式对外提供管理任务执行，线程调度，线程池管理等等服务；

ThreadPoolExecutor构造方法参数  
corePoolSize:  
核心线程池大小

maximumPoolSize:  
最大线程池大小

keepAliveTime:  
线程池中超过corePoolSize数目的空闲线程最大存活时间；可以 allowCoreThreadTimeOut(true)使得核心线程有效时间

TimeUnit:  
keepAliveTime时间单位

workQueue:  
阻塞任务队列

threadFactory:  
新建线程工厂

RejectedExecutionHandler：  
当提交任务数超过maxmumPoolSize+workQueue之和时，任务会交给RejectedExecutionHandler来处理

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FpeGlhbmdfY2hlbg_size_16_color_FFFFFF_t_70 3]

int  corePoolSize  =    5;
    int  maxPoolSize   =   10;
    long keepAliveTime = 5000;
     
    ExecutorService threadPoolExecutor =
            new ThreadPoolExecutor(
                    corePoolSize,
                    maxPoolSize,
                    keepAliveTime,
                    TimeUnit.MILLISECONDS,
                    new LinkedBlockingQueue<Runnable>()
                    );

## 定时执行者服务 ScheduledExecutorService ##

java.util.concurrent.ScheduledExecutorService 是一个 ExecutorService， 它能够将任务延后执行，或者间隔固定时间多次执行。 任务由一个工作者线程异步执行。ScheduledExecutorService,是基于线程池设计的定时任务类,每个调度任务都会分配到线程池中的一个线程去执行。

package com.hk;
    
    import java.util.HashSet;
    import java.util.List;
    import java.util.Set;
    import java.util.concurrent.Callable;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    import java.util.concurrent.ScheduledExecutorService;
    import java.util.concurrent.TimeUnit;
    
    public class ExecutorServiceTest {
    	public static void main(String[] args) throws Exception
    	{
            ScheduledExecutorService service = Executors.newScheduledThreadPool(10);
            
            long initialDelay = 1;
            long period = 1;
            long period2 = 2;
            // 从1秒钟之后，每隔1秒钟执行一次job1
            service.scheduleAtFixedRate(new MyJob("job1"), initialDelay, period, TimeUnit.SECONDS);
            // 从1秒钟之后，每隔2秒钟执行一次job2
            service.scheduleWithFixedDelay(new MyJob("job2"), initialDelay, period2, TimeUnit.SECONDS);
            //service.shutdown();
    	}
    }
    class MyJob implements Runnable {
        
        private String jobName;
        
        MyJob() {
            
        }
        
        MyJob(String jobName) {
            this.jobName = jobName;
        }
    
        public void run() {
            System.out.println(jobName + " is running");
        }
    }

ScheduledExecutorService的方法  
schedule (Callable task, long delay, TimeUnit timeunit)  
这个方法计划指定的 Callable 在给定的延迟之后执行。  
这个方法返回一个 ScheduledFuture，通过它你可以在它被执行之前对它进行取消，或者在它执行之后获取结果。

package com.hk;
    
    import java.util.HashSet;
    import java.util.List;
    import java.util.Set;
    import java.util.concurrent.Callable;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    import java.util.concurrent.ScheduledExecutorService;
    import java.util.concurrent.ScheduledFuture;
    import java.util.concurrent.TimeUnit;
    
    public class ExecutorServiceTest {
    	public static void main(String[] args) throws Exception
    	{
    		ScheduledExecutorService scheduledExecutorService =
    		        Executors.newScheduledThreadPool(5);
    		//延时5秒后执行,使用scheduledFuture取得返回结果
    		ScheduledFuture scheduledFuture =
    		    scheduledExecutorService.schedule(new Callable() {
    		        public Object call() throws Exception {
    		            System.out.println("Executed!");
    		            return "Called!";
    		        }
    		    },
    		    5,
    		    TimeUnit.SECONDS);
    		//取消任务执行
    		//scheduledFuture.cancel(true);
    		System.out.println("返回结果 = " + scheduledFuture.get());
    		 
    		scheduledExecutorService.shutdown();
    	}
    }

schedule (Runnable task, long delay, TimeUnit timeunit)  
延时执行任务，无法获取任务执行结果。

scheduleAtFixedRate (Runnable, long initialDelay, long period, TimeUnit timeunit)  
定时执行某一个任务，如果给定任务的执行抛出了异常，该任务将不再执行。如果没有任何异常的话，这个任务将会持续循环执行到 ScheduledExecutorService 被关闭。  
如果一个任务占用了比计划的时间间隔更长的时候，下一次执行将在当前执行结束执行才开始。计划任务在同一时间不会有多个线程同时执行。

scheduleWithFixedDelay (Runnable, long initialDelay, long period, TimeUnit timeunit)  
除了 period 有不同的解释之外这个方法和 scheduleAtFixedRate() 非常像。  
scheduleAtFixedRate() 方法中，period 被解释为前一个执行的开始和下一个执行的开始之间的间隔时间。  
而在本方法中，period 则被解释为前一个执行的结束和下一个执行的结束之间的间隔。因此这个延迟是执行结束之间的间隔，而不是执行开始之间的间隔。

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