锁类型:
可重入锁：在执行对象中所有同步方法不用再次获得锁
可中断锁：在等待获取锁过程中可中断
公平锁： 按等待获取锁的线程的等待时间进行获取，等待时间长的具有优先获取锁权利
读写锁：对资源读取和写入的时候拆分为2部分处理，读的时候可以多线程一起读，写的时候必须同步地写
Lock主要方法:
lock()：获取锁，如果锁被暂用则一直等待
unlock():释放锁
tryLock(): 注意返回类型是boolean，如果获取锁的时候锁被占用就返回false，否则返回true
tryLock(long time, TimeUnit unit)：比起tryLock()就是给了一个时间期限，保证等待参数时间
lockInterruptibly()：用该锁的获得方式，如果线程在获取锁的阶段进入了等待，那么可以中断此线程，先去做别的事
ReentrantLock:
lock()样例:
public class LockTest {
private Lock lock = new ReentrantLock();
//需要参与同步的方法
private void method(Thread thread){
lock.lock();
try {
System.out.println("线程名"+thread.getName() + "获得了锁");
}catch(Exception e){
e.printStackTrace();
} finally {
System.out.println("线程名"+thread.getName() + "释放了锁");
lock.unlock();
}
}
public static void main(String[] args) {
LockTest lockTest = new LockTest();
//线程1
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
lockTest.method(Thread.currentThread());
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
lockTest.method(Thread.currentThread());
}
}, "t2");
t1.start();
t2.start();
}
}
//执行情况：线程名t1获得了锁
// 线程名t1释放了锁
// 线程名t2获得了锁
// 线程名t2释放了锁
tryLock()样例:
public class LockTest {
private Lock lock = new ReentrantLock();
//需要参与同步的方法
private void method(Thread thread){
/* lock.lock();
try {
System.out.println("线程名"+thread.getName() + "获得了锁");
}catch(Exception e){
e.printStackTrace();
} finally {
System.out.println("线程名"+thread.getName() + "释放了锁");
lock.unlock();
}*/
if(lock.tryLock()){
try {
System.out.println("线程名"+thread.getName() + "获得了锁");
}catch(Exception e){
e.printStackTrace();
} finally {
System.out.println("线程名"+thread.getName() + "释放了锁");
lock.unlock();
}
}else{
System.out.println("我是"+Thread.currentThread().getName()+"有人占着锁，我就不要啦");
}
}
public static void main(String[] args) {
LockTest lockTest = new LockTest();
//线程1
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
lockTest.method(Thread.currentThread());
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
lockTest.method(Thread.currentThread());
}
}, "t2");
t1.start();
t2.start();
}
}
//执行结果： 线程名t2获得了锁
// 我是t1有人占着锁，我就不要啦
// 线程名t2释放了锁
使用Lock时可以使用新的等待/通知类Condition,Condition一定是针对某一把固定的锁，也就是说，只有在有锁的基础上才会产生Condition
Condition样例:
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..");
//释放锁，类似于 Object wait，阻塞于此
condition.await();
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..");
//不释放锁类，似于Object notify
condition.signal();
System.out.println("当前线程：" + Thread.currentThread().getName() + "没有释放锁");
} 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();
}
}
实现原理:ReentrantLock 实现原理
ReentrantReadWriteLock:
读写锁的机制本质上分为两把锁，读锁和写锁，在读锁情况下，多个线程可以并发访问资源，只有当是写锁时只能一个一个的顺序执行。
读读共享，写写互斥，读写互斥
public class UseReentrantReadWriteLock {
private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
private ReentrantReadWriteLock.ReadLock readLock = rwLock.readLock();
private ReentrantReadWriteLock.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();
}
}
实现原理:轻松掌握java读写锁(ReentrantReadWriteLock)的实现原理
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