Java線程同步 2

CyclicBarrier用於設置一個Barrier，達到Barrier的線程將等待，當所有線程都達到Barrier時，所有線程繼續執行。

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1. 創建CyclicBarrier時通過構造函數指定線程的數量n。

2. 每個線程調用await方法等待其他線程。

3. 當有n個await方法被調用時，所有處於await的線程都將繼續執行。

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
public class CyclicBarrierTest
{
    private static CyclicBarrier barrier = null;
    
    public static void main(String[] args)
    {
        // 初始化 
        barrier = new CyclicBarrier(10);
        
        // 啓動10個線程 
        System.out.println("main: starting 10 threads.");
        for (int i = 0; i < 10; i++)
        {
            Thread th = new Thread(new TestRunnable(), "thread " + i);
            th.start();
        }
    }
    
    private static class TestRunnable implements Runnable
    {
        @Override
        public void run()
        {
            String thName = Thread.currentThread().getName();
            try
            {
                // 隨機等待5-14秒 
                int n = (int)(Math.random() * 10 + 5);
                System.out.printf("%s: sleep for %d seconds. /n", thName, n);
                Thread.sleep(n * 1000);
                
                // 等待其他線程 
                System.out.printf("%s: waiting for other threads. /n", thName);
                barrier.await();
                
                // 結束 
                System.out.printf("%s: end. /n", thName);
            }
            catch (InterruptedException e)
            {
                System.out.printf("%s: interrupted. /n", thName);
                return;
            }
            catch (BrokenBarrierException e)
            {
                System.out.printf("%s: broken barrier. /n", thName);
                return;
            }
        }
    }
}

1. 在調用await方法時設置超時時間。

2. 當有一個await方法超時，所有處於await等待的線程將收到BrokenBarrierException，超時的線程自身將收到TimeoutException。

3. BrokenBarrier之後的所有await調用將直接拋出BrokenBarrierException。

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
public class CyclicBarrierBrokenTest
{
    private static CyclicBarrier barrier = null;
    
    public static void main(String[] args)
    {
        // 初始化 
        barrier = new CyclicBarrier(10);
        
        // 啓動10個線程 
        System.out.println("main: starting 10 threads.");
        for (int i = 0; i < 10; i++)
        {
            Thread th = new Thread(new TestRunnable(), "thread " + i);
            th.start();
        }
    }
    
    private static class TestRunnable implements Runnable
    {
        @Override
        public void run()
        {
            String thName = Thread.currentThread().getName();
            try
            {
                // 隨機等待5-14秒 
                int n = (int)(Math.random() * 10 + 5);
                System.out.printf("%s: sleep for %d seconds. /n", thName, n);
                Thread.sleep(n * 1000);
                
                // 等待其他線程 
                System.out.printf("%s: waiting for other threads. /n", thName);
                barrier.await(5, TimeUnit.SECONDS);
                
                // 結束 
                System.out.printf("%s: end. /n", thName);
            }
            catch (InterruptedException e)
            {
                System.out.printf("%s: interrupted. /n", thName);
                return;
            }
            catch (BrokenBarrierException e)
            {
                System.out.printf("%s: broken barrier. /n", thName);
                return;
            }
            catch (TimeoutException e)
            {
                System.out.printf("%s: timeout. /n", thName);
                return;
            }
        }
    }
}

當調用await線程達到CyclicBarrier的設置之後，CyclicBarrier將被重置，重新等待n個await調用。

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
public class CyclicBarrierResetTest
{
    private static CyclicBarrier barrier = null;
    
    public static void main(String[] args) throws Exception
    {
        barrier = new CyclicBarrier(2);
        
        Thread th1 = new Thread(new TestRunnable(), "thread 1");
        Thread th2 = new Thread(new TestRunnable(), "thread 2");
        
        th1.start();
        th2.start();
        
        Thread.sleep(60 * 1000);
        
        th1.interrupt();
        th2.interrupt();
        
        th1.join();
        th2.join();
    }
    
    private static class TestRunnable implements Runnable
    {
        @Override
        public void run()
        {
            String thName = Thread.currentThread().getName();
            System.out.printf("%s: start. /n", thName);
            
            try
            {
                while (true)
                {
                    // 隨機產生1-100的整數。 
                    int c = (int)(Math.random() * 100) + 1;
                    
                    // 隨機等待0-4秒。 
                    int t = (int)(Math.random() * 5);
                    System.out.printf("%s: sleep for %d seconds./n", thName, t);
                    Thread.sleep(t * 1000);
                    
                    // 等待另1線程。 
                    barrier.await();
                    
                    // 輸出產生的整數。 
                    System.out.printf("%s: %d /n", thName, c);
                    
                    // 等待其他線程輸出。 
                    Thread.sleep(100);
                }
            }
            catch (InterruptedException e)
            {
                System.out.printf("%s: interrupted. /n", thName);
            }
            catch (BrokenBarrierException e)
            {
                e.printStackTrace();
            }
            
            System.out.printf("%s: end. /n", thName);
        }
    }
}

1. 在創建CyclicBarrier的時候指定通過Barrier時需要執行的語句。

2. 通過構造方法的Runnable參數指定。

3. Runnable中的語句將由最後達到Barrier的線程執行。

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
public class CyclicBarrierActionTest
{
    private static CyclicBarrier barrier = null;
    
    public static void main(String[] args) throws Exception
    {
        barrier = new CyclicBarrier(10, new BarrierAction());
        
        for (int i = 0; i < 10; i++)
        {
            Thread th = new Thread(new TestRunnable(), "thread " + i);
            th.start();
        }
    }
    
    private static class TestRunnable implements Runnable
    {
        @Override
        public void run()
        {
            try
            {
                String thName = Thread.currentThread().getName();
                // System.out.printf("%s: start. /n", thName); 
                
                // 隨機等待0-9秒 
                int t = (int)(Math.random() * 10);
                System.out.printf("%s: sleep for %d seconds. /n", thName, t);
                Thread.sleep(t * 1000);
                
                // 等待barrier 
                barrier.await();
                System.out.printf("%s: end. /n", thName);
            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
                return;
            }
            catch (BrokenBarrierException e)
            {
                e.printStackTrace();
                return;
            }
        }
    }
    
    private static class BarrierAction implements Runnable
    {
        @Override
        public void run()
        {
            String thName = Thread.currentThread().getName();
            
            System.out.printf("%s: barrier action. /n", thName);
        }
    }
}

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