介绍
ReentrantLock是互斥排他锁,同一时间只能有一个线程在执行任务,ReentrantLock支持锁的重入功能,虽然保证了线程的安全性,但是效率不高,实际上应该是写操作互斥,读操作共享。而jdk提供了读写锁ReentrantReadWriteLock。
公共代码(下面四种情况代码根据时间等候判断区别)
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();
}
}
}
读读共享
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(); // 读
}
});
t1.setName("t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
myTask.read(); // 读
}
});
t2.setName("t2");
t1.start();
t2.start();
}
}
// 输出
t2 start
t1 start
// 10s
t1 end
t2 end
写写互斥
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(); // 写
}
});
t1.setName("t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
myTask.write(); // 写
}
});
t2.setName("t2");
t1.start();
t2.start();
}
}
// 输出
t1 start
// 10s
t1 end
t2 start
// 10s
t2 end
读写互斥
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.read(); // 读
}
});
t1.setName("t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
myTask.write(); // 写
}
});
t2.setName("t2");
t1.start();
t2.start();
}
}
// 输出
t1 start
// 10s
t1 end
t2 start
// 10s
t2 end
写读互斥
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(); // 写
}
});
t1.setName("t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
myTask.read(); // 读
}
});
t2.setName("t2");
t1.start();
t2.start();
}
}
// 输出
t1 start
// 10s
t1 end
t2 start
// 10s
t2 end
总结
- 记住一句话:读读共享;写写、读写、写读都互斥。