并发控制(6)ReentrantLock 重入锁

并发控制(6)ReentrantLock 重入锁

• 这个锁基本上概念和synchronized关键字用法很像，但是在实现上和使用上的稳定性上貌似比synchronized要好.

• 但是你在调用锁的时候，要注意释放，不然就麻烦了。。。其他线程没有办法使用资源了

• 下面有4个例子注意区别

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有如下代码

import java.util.concurrent.CopyOnWriteArrayList;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;public class UseReentrantLock {    private Lock lock = new ReentrantLock();    public void method1(){        try {            lock.lock();            System.out.println("当前线程:" + Thread.currentThread().getName() + "进入method1..");            Thread.sleep(1000);            System.out.println("当前线程:" + Thread.currentThread().getName() + "退出method1..");            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        } finally {            lock.unlock();        }    }    public void method2(){        try {            lock.lock();            System.out.println("当前线程:" + Thread.currentThread().getName() + "进入method2..");            Thread.sleep(2000);            System.out.println("当前线程:" + Thread.currentThread().getName() + "退出method2..");            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        } finally {            lock.unlock();        }    }    public static void main(String[] args) {        final UseReentrantLock ur = new UseReentrantLock();        Thread t1 = new Thread(new Runnable() {            @Override            public void run() {                ur.method1();                ur.method2();            }        }, "t1");        t1.start();        try {            Thread.sleep(10);        } catch (InterruptedException e) {            e.printStackTrace();        }        //System.out.println(ur.lock.getQueueLength());    }}

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下面一个例子是使用condition的情况，这个比synchronized要灵活不少

import java.util.concurrent.CopyOnWriteArrayList;import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;public class UseCondition {    private Lock lock = new ReentrantLock();    private Condition condition = lock.newCondition();    public void method1(){        try {            lock.lock();            System.out.println("当前线程：" + Thread.currentThread().getName() + "进入等待状态..");            Thread.sleep(3000);            System.out.println("当前线程：" + Thread.currentThread().getName() + "释放锁..");            condition.await();  // Object wait            System.out.println("当前线程：" + Thread.currentThread().getName() +"继续执行...");        } catch (Exception e) {            e.printStackTrace();        } finally {            lock.unlock();        }    }    public void method2(){        try {            lock.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() + "发出唤醒..");            condition.signal();     //Object notify        } catch (Exception e) {            e.printStackTrace();        } finally {            lock.unlock();        }    }    public static void main(String[] args) {        final UseCondition uc = new UseCondition();        Thread t1 = new Thread(new Runnable() {            @Override            public void run() {                uc.method1();            }        }, "t1");        Thread t2 = new Thread(new Runnable() {            @Override            public void run() {                uc.method2();            }        }, "t2");        t1.start();        t2.start();    }}

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使用多个condition的情况，看看就可以了，其实很简单

import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;public class UseManyCondition {    private ReentrantLock lock = new ReentrantLock();    private Condition c1 = lock.newCondition();    private Condition c2 = lock.newCondition();    public void m1(){        try {            lock.lock();            System.out.println("当前线程：" +Thread.currentThread().getName() + "进入方法m1等待..");            c1.await();            System.out.println("当前线程：" +Thread.currentThread().getName() + "方法m1继续..");        } catch (Exception e) {            e.printStackTrace();        } finally {            lock.unlock();        }    }    public void m2(){        try {            lock.lock();            System.out.println("当前线程：" +Thread.currentThread().getName() + "进入方法m2等待..");            c1.await();            System.out.println("当前线程：" +Thread.currentThread().getName() + "方法m2继续..");        } catch (Exception e) {            e.printStackTrace();        } finally {            lock.unlock();        }    }    public void m3(){        try {            lock.lock();            System.out.println("当前线程：" +Thread.currentThread().getName() + "进入方法m3等待..");            c2.await();            System.out.println("当前线程：" +Thread.currentThread().getName() + "方法m3继续..");        } catch (Exception e) {            e.printStackTrace();        } finally {            lock.unlock();        }    }    public void m4(){        try {            lock.lock();            System.out.println("当前线程：" +Thread.currentThread().getName() + "唤醒..");            c1.signalAll();        } catch (Exception e) {            e.printStackTrace();        } finally {            lock.unlock();        }    }    public void m5(){        try {            lock.lock();            System.out.println("当前线程：" +Thread.currentThread().getName() + "唤醒..");            c2.signal();        } catch (Exception e) {            e.printStackTrace();        } finally {            lock.unlock();        }    }    public static void main(String[] args) {        final UseManyCondition umc = new UseManyCondition();        Thread t1 = new Thread(new Runnable() {            @Override            public void run() {                umc.m1();            }        },"t1");        Thread t2 = new Thread(new Runnable() {            @Override            public void run() {                umc.m2();            }        },"t2");        Thread t3 = new Thread(new Runnable() {            @Override            public void run() {                umc.m3();            }        },"t3");        Thread t4 = new Thread(new Runnable() {            @Override            public void run() {                umc.m4();            }        },"t4");        Thread t5 = new Thread(new Runnable() {            @Override            public void run() {                umc.m5();            }        },"t5");        t1.start(); // c1        t2.start(); // c1        t3.start(); // c2        try {            Thread.sleep(2000);        } catch (InterruptedException e) {            e.printStackTrace();        }        t4.start(); // c1        try {            Thread.sleep(2000);        } catch (InterruptedException e) {            e.printStackTrace();        }        t5.start(); // c2    }}

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这是使用读写锁例子，看一下就可以了

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();