ReentrantReadWriteLock_读写锁-蒲公英云

ReentrantReadWriteLock_读写锁

读写锁的核心是实现读与写的分离,在高并发的情况下,尤其是读多写少的情况下,性能要远高于重入锁.对于Synchronize,ReentrantLock时,同一个时间内,只能由一个线程进行访问被锁定的代码,而读写锁则不同,其本质是分成两个锁,即读锁和写锁. 在读锁下,多个线程可以并发的进行访问,但是在写锁的时候,只能一个个的顺序访问.
读读共享,写写互斥,读写互斥
一、读写锁代码示例

public class UseReentrantReadWriteLock { 
    private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
    private ReadLock readLock = rwLock.readLock();
    private WriteLock writeLock = rwLock.writeLock();
    public void read(){ 
        try { 
            readLock.lock();
            System.out.println("当前线程:" + Thread.currentThread().getName() + "进入...");
            Thread.sleep(3000);
            System.out.println("当前线程:" + Thread.currentThread().getName() + "退出...");
        } catch (Exception e) { 
            e.printStackTrace();
        } finally { 
            readLock.unlock();
        }
    }
    public void write(){ 
        try { 
            writeLock.lock();
            System.out.println("当前线程:" + Thread.currentThread().getName() + "进入...");
            Thread.sleep(3000);
            System.out.println("当前线程:" + Thread.currentThread().getName() + "退出...");
        } catch (Exception e) { 
            e.printStackTrace();
        } finally { 
            writeLock.unlock();
        }
    }
    public static void main(String[] args) { 
        final UseReentrantReadWriteLock urrw = new UseReentrantReadWriteLock();
        Thread t1 = new Thread(new Runnable() { 
            @Override
            public void run() { 
                urrw.read();
            }
        }, "t1");
        Thread t2 = new Thread(new Runnable() { 
            @Override
            public void run() { 
                urrw.read();
            }
        }, "t2");
        Thread t3 = new Thread(new Runnable() { 
            @Override
            public void run() { 
                urrw.write();
            }
        }, "t3");
        Thread t4 = new Thread(new Runnable() { 
            @Override
            public void run() { 
                urrw.write();
            }
        }, "t4");        
// t1.start();
// t2.start();
// t1.start(); // R 
// t3.start(); // W
        t3.start();
        t4.start();
    }
}