并发编程-锁

概念：

　　１、重入锁 ReenTrantLock

　　　　功能类似于synchronized,但又比它更加灵活。

　　　　synchronized一般需要配合wait,notify一起使用。

　　　　ReenTrantLock配合Condition一起使用

　　　　private Lock lock = new ReentrantLock();
　　private Condition condition = lock.newCondition();　

　　　　可以在一个lock对象中设置多个condition.

实例：

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

}



}

　　２、读写锁 ReentrantReadWriteLock

　　　　一般使用场景是在读多写少的时候用的比较多。

              读写互斥，写写互斥。

import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;


public class UseReentrantReadWriteLock {


private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
private ReadLock readLock = rwLock.readLock();
private 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();








}
}