Java锁机制ReentrantLock
2024-09-03 13:21:34
ReentrantLock 锁常用于保证程序的人为顺序执行。
写一个类模拟ReentrantLock类的功能
class MyLock{
private boolean lock = false;
private int holdCount = 0;
private Thread myThread = null; //当前占用锁的线程
public synchronized void lock(){ //线程同步，只允许一个线程来获取这把锁
Thread currThread = Thread.currentThread(); //当前访问线程
if(lock == true && currThread != myThread){
try {
wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
//给予锁
myThread = currThread;
lock = true;
holdCount ++;
}
public synchronized void unlock(){
Thread currThread = Thread.currentThread(); //当前访问线程
if(currThread == myThread && holdCount>0){
holdCount -- ;
if(holdCount == 0){
notifyAll();
lock = false;
myThread = null;
}
}
}
public int getHoldCount() {
return holdCount;
}
}
当一个线程不能得到一把锁时就会产生等待，等到其他线程释放锁后其将被唤醒，然后拿到所继续运行。
public class Test {
public static void main(String[] args) {
MyLock myLock = new MyLock();
new Thread(new Runnable() {
@Override
public void run() {
myLock.lock();
System.out.println(Thread.currentThread().getName()+"得到锁:"+myLock.getHoldCount());
myLock.lock(); //可重入锁
System.out.println(Thread.currentThread().getName()+"重入成功:"+myLock.getHoldCount());
myLock.unlock();
System.out.println(Thread.currentThread().getName()+"释放锁:"+myLock.getHoldCount());
myLock.unlock();
System.out.println(Thread.currentThread().getName()+"释放锁:"+myLock.getHoldCount());
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
myLock.lock();
System.out.println(Thread.currentThread().getName()+"得到锁:"+myLock.getHoldCount());
myLock.unlock();
System.out.println(Thread.currentThread().getName()+"释放锁:"+myLock.getHoldCount());
}
}).start();
}
}
ReentrantLock的使用
public class LockTest {
ReentrantLock lock = new ReentrantLock();
public void a() throws InterruptedException {
lock.lock();
System.out.println(lock.getHoldCount());
dosomething();
lock.unlock();
System.out.println(lock.getHoldCount());
}
public void dosomething() throws InterruptedException {
lock.lock();
System.out.println(lock.getHoldCount());
lock.unlock();
System.out.println(lock.getHoldCount());
}
public static void main(String[] args) throws InterruptedException {
LockTest lockTest = new LockTest();
lockTest.a();
}
}
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