ReentrantReadWriteLock用法

介紹

ReentrantLock是互斥排他鎖，同一時間只能有一個線程在執行任務，ReentrantLock支持鎖的重入功能，雖然保證了線程的安全性，但是效率不高，實際上應該是寫操作互斥，讀操作共享。而jdk提供了讀寫鎖ReentrantReadWriteLock。

讀讀共享

 

public class MyTask {

    private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
    
    public void read() {
        try {
            lock.readLock().lock();
            System.out.println(Thread.currentThread().getName() + " start");
            Thread.sleep(10000);
            System.out.println(Thread.currentThread().getName() + " end");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.readLock().unlock();
        }
    }
}

public class ReadReadTest {

    public static void main(String[] args) {
        final MyTask myTask = new MyTask();
        
        Thread t1 = new Thread(new Runnable() {

            @Override
            public void run() {
                myTask.read();
            }
        });
        t1.setName("t1");
        
        Thread t2 = new Thread(new Runnable() {

            @Override
            public void run() {
                myTask.read();
            }
        });
        t2.setName("t2");
        
        t1.start();
        t2.start();
    }
}

結果：

 

t2 start
t1 start
t1 end
t2 end

寫寫互斥

 

public class MyTask {

    private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
    
    public void write() {
        try {
            lock.writeLock().lock();
            System.out.println(Thread.currentThread().getName() + " start");
            Thread.sleep(10000);
            System.out.println(Thread.currentThread().getName() + " end");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.writeLock().unlock();
        }
    }
}

public class ReadReadTest {

    public static void main(String[] args) {
        final MyTask myTask = new MyTask();
        
        Thread t1 = new Thread(new Runnable() {

            @Override
            public void run() {
                myTask.write();
            }
        });
        t1.setName("t1");
        
        Thread t2 = new Thread(new Runnable() {

            @Override
            public void run() {
                myTask.write();
            }
        });
        t2.setName("t2");
        
        t1.start();
        t2.start();
    }
}

結果：

 

t1 start
t1 end
t2 start
t2 end

讀寫互斥

 

public class MyTask {

    private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
    
    public void read() {
        try {
            lock.readLock().lock();
            System.out.println(Thread.currentThread().getName() + " start");
            Thread.sleep(10000);
            System.out.println(Thread.currentThread().getName() + " end");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.readLock().unlock();
        }
    }
    
    public void write() {
        try {
            lock.writeLock().lock();
            System.out.println(Thread.currentThread().getName() + " start");
            Thread.sleep(10000);
            System.out.println(Thread.currentThread().getName() + " end");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.writeLock().unlock();
        }
    }
}

public class ReadReadTest {

    public static void main(String[] args) {
        final MyTask myTask = new MyTask();
        
        Thread t1 = new Thread(new Runnable() {

            @Override
            public void run() {
                myTask.read();
            }
        });
        t1.setName("t1");
        
        Thread t2 = new Thread(new Runnable() {

            @Override
            public void run() {
                myTask.write();
            }
        });
        t2.setName("t2");
        
        t1.start();
        
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        t2.start();
    }
}

結果：

 

t1 start
t1 end
t2 start
t2 end

寫讀互斥

 

public class ReadReadTest {

    public static void main(String[] args) {
        final MyTask myTask = new MyTask();
        
        Thread t1 = new Thread(new Runnable() {

            @Override
            public void run() {
                myTask.write();
            }
        });
        t1.setName("t1");
        
        Thread t2 = new Thread(new Runnable() {

            @Override
            public void run() {
                myTask.read();
            }
        });
        t2.setName("t2");
        
        t1.start();
        
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        t2.start();
    }
}

結果：

 

t1 start
t1 end
t2 start
t2 end

總結

讀操作的鎖叫共享鎖，寫操作的鎖叫排他鎖。就是遇見寫鎖就需互斥。那麼以此可得出讀讀共享，寫寫互斥，讀寫互斥，寫讀互斥。