架构师养成记--14.重入锁ReentrantLock 和 读写锁 ReentrantReadWriteLock
2024-10-18 22:35:48
ReentrantLock
有嗅探锁定和多路分支等功能，其实就是synchronized，wait，notify的升级。
this锁定当前对象不方便，于是就有了用new Object()来作为锁的解决方案，后面jdk干脆就提供了一个Lock类。
伪代码：
Lock lock = new ReentrantLock();//新建一个lock
Condition condition = lock.newCondition();//获取条件
method1(){
try{
lock.lock();
代码块；
lock.unlock();
后续代码块；
}
}
method2(){
try{
lock.lock();
代码块；
lock.signal();
}
}
单condition操作：
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock; 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..");
Thread.sleep(3000);
System.out.println("当前线程：" + Thread.currentThread().getName() + "释放锁..");
condition.await(); // Object wait
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..");
condition.signal(); //Object notify
} 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();
} }
执行结果：
解释：线程1调用method1方法，线程2调用同一对象的method2方法，线程1先启动，线程1获取锁，进入method1的代码块，线程2也启动了，单是线程2被锁定，直到线程1发出lock.unlock()了，线程1才将锁释放，这时线程2获取锁，执行method2的代码块，线程2发出lock.signal(); 线程1才继续执行后续代码块。
多condition操作：
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock; 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 } }
执行结果：
解释：t1、t2线程都是用第一个condition c1，t3线程用第二个condition c2，t4线程发出c1.signalAll() 唤醒t1和t2线程，t5发出c2.signal()唤醒t3线程。
ReentrantReadWriteLock
读写分离锁，读读共享、写写互斥、读写互斥。
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();
}
}
解释：t1和t2都是读，是共享的，可同时获得readLock同时进入read方法执行。t1是读和t3是写，是互斥的，只有t1执行完t3才能执行。t3、t4都是写，是互斥的，只有等t3执行完t4才能继续。
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