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锁的简介 在Lock接口出现之前，Java程序是靠synchronized关键字实现锁功能的。JDK1.5之后并发包中新增了Lock接口以及相关实现类来实现锁功能。 Lock比synchorinized更灵活。
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使用示例
public class ReentrantLockTest implements Runnable {
Lock lock = new ReentrantLock();
public static void main(String[] args) {
ReentrantLockTest reentrantLockTest = new ReentrantLockTest();
Thread t1 = new Thread(reentrantLockTest);
Thread t2 = new Thread(reentrantLockTest);
Thread t3 = new Thread(reentrantLockTest);
Thread t4 = new Thread(reentrantLockTest);
Thread t5 = new Thread(reentrantLockTest);
t1.start();
t2.start();
t3.start();
t4.start();
t5.start();
}
@Override
public void run() {
lock.lock();
try {
for (int i = 0; i < 5; i++) {
Thread.sleep(1000);
System.out.println("ThreadName=" + Thread.currentThread().getName() + (" " + (i + 1)));
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}运行结果
ThreadName=Thread-0 1
ThreadName=Thread-0 2
ThreadName=Thread-0 3
ThreadName=Thread-0 4
ThreadName=Thread-0 5
ThreadName=Thread-1 1
ThreadName=Thread-1 2
ThreadName=Thread-1 3
ThreadName=Thread-1 4
ThreadName=Thread-1 5
ThreadName=Thread-2 1
ThreadName=Thread-2 2
ThreadName=Thread-2 3
ThreadName=Thread-2 4
ThreadName=Thread-2 5
ThreadName=Thread-3 1
ThreadName=Thread-3 2
ThreadName=Thread-3 3
ThreadName=Thread-3 4
ThreadName=Thread-3 5
ThreadName=Thread-4 1
ThreadName=Thread-4 2
ThreadName=Thread-4 3
ThreadName=Thread-4 4
ThreadName=Thread-4 5从运行结果可以看出，当一个线程运行完毕后才把锁释放，其他线程才能执行，其他线程的执行顺序是不确定的。
- 使用Condition实现等待/通知机制
public class UseSingleConditionWaitNotify {
public static void main(String[] args) throws InterruptedException {
MyService service = new MyService();
ThreadA a = new ThreadA(service);
a.start();
Thread.sleep(3000);
service.signal();
}
static public class MyService {
private Lock lock = new ReentrantLock();
public Condition condition = lock.newCondition();
public void await() {
lock.lock();
try {
System.out.println(" await时间为" + System.currentTimeMillis());
condition.await();
System.out.println("这是condition.await()方法之后的语句，condition.signal()方法之后我才被执行");
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void signal() throws InterruptedException {
lock.lock();
try {
System.out.println("signal时间为" + System.currentTimeMillis());
condition.signal();
Thread.sleep(3000);
System.out.println("这是condition.signal()方法之后的语句");
} finally {
lock.unlock();
}
}
}
static public class ThreadA extends Thread {
private MyService service;
public ThreadA(MyService service) {
super();
this.service = service;
}
@Override
public void run() {
service.await();
}
}
}- 公平锁与非公平锁 Lock锁分为：公平锁 和 非公平锁。公平锁表示线程获取锁的顺序是按照线程加锁的顺序来分配的，即先来先得的FIFO先进先出顺序。 而非公平锁就是一种获取锁的抢占机制，是随机获取锁的，和公平锁不一样的就是先来的不一定先的到锁，这样可能造成某些线程一直拿不到锁， 结果也就是不公平的了。
public class FairorNofairLock {
public static void main(String[] args) throws InterruptedException {
final Service service = new Service(true);//true为公平锁，false为非公平锁
Runnable runnable = new Runnable() {
@Override
public void run() {
System.out.println("★线程" + Thread.currentThread().getName()
+ "运行了");
service.serviceMethod();
}
};
Thread[] threadArray = new Thread[10];
for (int i = 0; i < 10; i++) {
threadArray[i] = new Thread(runnable);
}
for (int i = 0; i < 10; i++) {
threadArray[i].start();
}
}
static public class Service {
private ReentrantLock lock;
public Service(boolean isFair) {
super();
lock = new ReentrantLock(isFair);
}
public void serviceMethod() {
lock.lock();
try {
System.out.println("ThreadName=" + Thread.currentThread().getName()
+ "获得锁定");
} finally {
lock.unlock();
}
}
}
}运行结果
★线程Thread-0运行了
ThreadName=Thread-0获得锁定
★线程Thread-1运行了
ThreadName=Thread-1获得锁定
★线程Thread-2运行了
ThreadName=Thread-2获得锁定
★线程Thread-3运行了
ThreadName=Thread-3获得锁定
★线程Thread-4运行了
ThreadName=Thread-4获得锁定
★线程Thread-5运行了
ThreadName=Thread-5获得锁定
★线程Thread-6运行了
ThreadName=Thread-6获得锁定
★线程Thread-7运行了
ThreadName=Thread-7获得锁定
★线程Thread-8运行了
ThreadName=Thread-8获得锁定
★线程Thread-9运行了
ThreadName=Thread-9获得锁定不加锁的运行效果
★线程Thread-0运行了
★线程Thread-4运行了
★线程Thread-3运行了
★线程Thread-1运行了
★线程Thread-2运行了
ThreadName=Thread-0获得锁定
★线程Thread-5运行了
ThreadName=Thread-5获得锁定
★线程Thread-6运行了
ThreadName=Thread-6获得锁定
ThreadName=Thread-4获得锁定
ThreadName=Thread-3获得锁定
ThreadName=Thread-1获得锁定
★线程Thread-7运行了
ThreadName=Thread-2获得锁定
★线程Thread-8运行了
ThreadName=Thread-7获得锁定
ThreadName=Thread-8获得锁定
★线程Thread-9运行了
ThreadName=Thread-9获得锁定