在java多线程中，我们知道可以用synchronize关键字来实现线程间的同步互斥工作，还有更加优秀的机制去实现同步互斥工作，Lock对象。重入锁和读写锁，他们具有比synchronize更加强大的功能，并且具有嗅探锁定，多路分支等功能。
一、ReentrantLock（重入锁）（详见JDK-API）
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());
}
}
二、锁的等待与通知
在使用synchronize的时候，如果需要多线程之间进行协作工作，则需要Object的wait（）和notify（）,notifyAll( )方法进行配合工作。那么同样，我们在使用Lock的时候，可以使用一个新的等待通知类，它就是Condition，这个Condition一定是针对具体某一把锁的。也就是在只有锁的基础上才会产生Condition。
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();
}
}
三、多Condition
我们可以通过一个Lock对象产生多个Condition进行多线程间的交互，非常的灵活。可以使得部分需要唤醒的线程唤醒，其他线程则继续等待通知。
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
}
四 . Lock / Condition其他方法和用法
1.公平锁和非公平锁: Lock lock = new ReentrantLock ( boolean isFair);
lock的用法:
tryLock():尝试获得锁,获得结果用true/false返回.
tryLock():在给定的时间内尝试获得锁,获得结果用true/false返回.
isFair():是否是公平锁
isLocked():是否锁定
getHoldCount():查询当前线程保持此锁的个数,也就是调用lock()的次数
lockInterruptibly:优先响应中断的锁