1、ReentrantLock锁

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock; public class Test_01 {
Lock lock = new ReentrantLock(); public static void main(String[] args) {
final Test_01 t = new Test_01();
new Thread(new Runnable() {
@Override
public void run() {
t.m1();
}
}).start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(new Runnable() {
@Override
public void run() {
t.m2();
}
}).start();
} void m1() {
try {
lock.lock(); // 加锁
for (int i = 0; i < 10; i++) {
TimeUnit.SECONDS.sleep(1);
System.out.println("m1() method " + i);
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock(); // 解锁
}
} void m2() {
lock.lock();
System.out.println("m2() method");
lock.unlock();
}
}

  结果:

m1() method 0
m1() method 1
m1() method 2
m1() method 3
m1() method 4
m1() method 5
m1() method 6
m1() method 7
m1() method 8
m1() method 9
m2() method

2、ReentrantLock尝试锁

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock; public class Test_02 {
Lock lock = new ReentrantLock(); public static void main(String[] args) {
final Test_02 t = new Test_02();
new Thread(new Runnable() {
@Override
public void run() {
t.m1();
}
}).start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
new Thread(new Runnable() {
@Override
public void run() {
t.m2();
}
}).start();
} void m1() {
try {
lock.lock();
for (int i = 0; i < 10; i++) {
TimeUnit.SECONDS.sleep(1);
System.out.println("m1() method " + i);
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
} void m2() {
boolean isLocked = false;
try {
// 尝试锁, 如果有锁,无法获取锁标记,返回false。
// 如果获取锁标记,返回true
// isLocked = lock.tryLock(); // 阻塞尝试锁,阻塞参数代表的时长,尝试获取锁标记。
// 如果超时,不等待。直接返回。
isLocked = lock.tryLock(5, TimeUnit.SECONDS); if (isLocked) {
System.out.println("m2() method synchronized");
} else {
System.out.println("m2() method unsynchronized");
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (isLocked) {
// 尝试锁在解除锁标记的时候,一定要判断是否获取到锁标记。
// 如果当前线程没有获取到锁标记,会抛出异常。
lock.unlock();
}
}
}
}

  结果:

m1() method 0
m1() method 1
m1() method 2
m1() method 3
m1() method 4
m2() method unsynchronized
m1() method 5
m1() method 6
m1() method 7
m1() method 8
m1() method 9

3、ReentrantLock可打断锁

/**
* 可打断
* <p>
* 阻塞状态: 包括普通阻塞,等待队列,锁池队列。
* 普通阻塞: sleep(10000), 可以被打断。调用thread.interrupt()方法,可以打断阻塞状态,抛出异常。
* 等待队列: wait()方法被调用,也是一种阻塞状态,只能由notify唤醒。无法打断
* 锁池队列: 无法获取锁标记。不是所有的锁池队列都可被打断。
* 使用ReentrantLock的lock方法,获取锁标记的时候,如果需要阻塞等待锁标记,无法被打断。
* 使用ReentrantLock的lockInterruptibly方法,获取锁标记的时候,如果需要阻塞等待,可以被打断。
*/
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock; public class Test_03 {
Lock lock = new ReentrantLock(); public static void main(String[] args) {
final Test_03 t = new Test_03();
new Thread(new Runnable() {
@Override
public void run() {
t.m1();
}
}).start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
t.m2();
}
});
t2.start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
t2.interrupt();// 打断线程休眠。非正常结束阻塞状态的线程,都会抛出异常。
} void m1() {
try {
lock.lock();
for (int i = 0; i < 5; i++) {
TimeUnit.SECONDS.sleep(1);
System.out.println("m1() method " + i);
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
} void m2() {
try {
lock.lockInterruptibly(); // 可尝试打断,阻塞等待锁。可以被其他的线程打断阻塞状态
System.out.println("m2() method");
} catch (InterruptedException e) {
System.out.println("m2() method interrupted");
} finally {
try {
lock.unlock();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}

  结果:

m1() method 0
m1() method 1
java.lang.IllegalMonitorStateException
m2() method interrupted
at java.base/java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:149)
at java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1300)
at java.base/java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:439)
at concurrent.t03.Test_03.m2(Test_03.java:72)
at concurrent.t03.Test_03$2.run(Test_03.java:37)
at java.base/java.lang.Thread.run(Thread.java:844)
m1() method 2
m1() method 3
m1() method 4

4、ReentrantLock公平锁

/*
*在公平的锁上,线程按照他们发出请求的顺序获取锁,但在非公平锁上,则允许‘插队’:当一个线程请求非公平锁时,如果在发出请求的同时该锁变成可用状态,那么这个线程会跳过队列中所有的等待线程而获得锁。
非公平的ReentrantLock 并不提倡插队行为,但是无法防止某个线程在合适的时候进行插队。
*在公平的锁中,如果有另一个线程持有锁或者有其他线程在等待队列中等待这个所,那么新发出的请求的线程将被放入到队列中。而非公平锁上,只有当锁被某个线程持有时,新发出请求的线程才会被放入队列中。
*非公平锁性能高于公平锁性能的原因:
*在恢复一个被挂起的线程与该线程真正运行之间存在着严重的延迟。
*假设线程A持有一个锁,并且线程B请求这个锁。由于锁被A持有,因此B将被挂起。当A释放锁时,B将被唤醒,因此B会再次尝试获取这个锁。与此同时,如果线程C也请求这个锁,那么C很可能会在B被完全唤醒之前获得、使用以及释放这个锁。这样就是一种双赢的局面:B获得锁的时刻并没有推迟,C更早的获得了锁,并且吞吐量也提高了。
*当持有锁的时间相对较长或者请求锁的平均时间间隔较长,应该使用公平锁。在这些情况下,插队带来的吞吐量提升(当锁处于可用状态时,线程却还处于被唤醒的过程中)可能不会出现。
**/
import java.util.concurrent.locks.ReentrantLock; public class Test_04 { public static void main(String[] args) {
TestReentrantlock t = new TestReentrantlock();
//TestSync t = new TestSync();
Thread t1 = new Thread(t);
Thread t2 = new Thread(t);
t1.start();
t2.start();

}
} class TestReentrantlock extends Thread {
// 定义一个公平锁
private static ReentrantLock lock = new ReentrantLock(true); public void run() {
for (int i = 0; i < 5; i++) {
lock.lock();
try {
System.out.println(Thread.currentThread().getName() + " get lock in TestReentrantLock");
} finally {
lock.unlock();
}
}
} } class TestSync extends Thread {
public void run() {
for (int i = 0; i < 5; i++) {
synchronized (this) {
System.out.println(Thread.currentThread().getName() + " get lock in TestSync");
}
}
}
}

  结果(ReentrantLock两种都与可能,但是TestSync只可能出现后一种):

Thread-2 get lock in TestReentrantlock
Thread-2 get lock in TestReentrantlock
Thread-2 get lock in TestReentrantlock
Thread-2 get lock in TestReentrantlock
Thread-2 get lock in TestReentrantlock
Thread-1 get lock in TestReentrantlock
Thread-1 get lock in TestReentrantlock
Thread-1 get lock in TestReentrantlock
Thread-1 get lock in TestReentrantlock
Thread-1 get lock in TestReentrantlock
Thread-1 get lock in TestReentrantlock
Thread-1 get lock in TestReentrantlock
Thread-1 get lock in TestReentrantlock
Thread-1 get lock in TestReentrantlock
Thread-1 get lock in TestReentrantlock
Thread-2 get lock in TestReentrantlock
Thread-2 get lock in TestReentrantlock
Thread-2 get lock in TestReentrantlock
Thread-2 get lock in TestReentrantlock
Thread-2 get lock in TestReentrantlock
04-17 23:01