详解Java多线程tryLock()方法使用
tryLock(long time, TimeUnit unit) 的作用在给定等待时长内锁没有被另外的线程持有，并且当前线程也没有被中断,则获得该锁，通过该方法可以实现锁对象的限时等待。
package com.wkcto.lock.reentrant;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;
/**
*tryLock(long time, TimeUnit unit) 的基本使用
*/
public class Test07 {
static class TimeLock implements Runnable{
private static ReentrantLock lock = new ReentrantLock(); //定义锁对象
@Override
public void run() {
try {
if ( lock.tryLock(3, TimeUnit.SECONDS) ){ //获得锁返回true
System.out.println(Thread.currentThread().getName() + "获得锁,执行耗时任务");
// Thread.sleep(4000); //假设Thread-0线程先持有锁,完成任务需要4秒钟,Thread-1线程尝试获得锁,Thread-1线程在3秒内还没有获得锁的话,Thread-1线程会放弃
Thread.sleep(2000); //假设Thread-0线程先持有锁,完成任务需要2秒钟,Thread-1线程尝试获得锁,Thread-1线程会一直尝试,在它约定尝试的3秒内可以获得锁对象
}else { //没有获得锁
System.out.println(Thread.currentThread().getName() + "没有获得锁");
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
if (lock.isHeldByCurrentThread()){
lock.unlock();
}
}
}
}
public static void main(String[] args) {
TimeLock timeLock = new TimeLock();
Thread t1 = new Thread(timeLock);
Thread t2 = new Thread(timeLock);
t1.start();
t2.start();
}
}
tryLock()仅在调用时锁定未被其他线程持有的锁，如果调用方法时，锁对象对其他线程持有，则放弃，调用方法尝试获得没，如果该锁没有被其他线程占用则返回true表示锁定成功; 如果锁被其他线程占用则返回false,不等待。
package com.wkcto.lock.reentrant;
import java.util.concurrent.locks.ReentrantLock;
/**
*tryLock()
* 当锁对象没有被其他线程持有的情况下才会获得该锁定
*/
public class Test08 {
static class Service{
private ReentrantLock lock = new ReentrantLock();
public void serviceMethod(){
try {
if (lock.tryLock()){
System.out.println(Thread.currentThread().getName() + "获得锁定");
Thread.sleep(3000); //模拟执行任务的时长
}else {
System.out.println(Thread.currentThread().getName() + "没有获得锁定");
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
if (lock.isHeldByCurrentThread()){
lock.unlock();
}
}
}
}
public static void main(String[] args) throws InterruptedException {
Service service = new Service();
Runnable r = new Runnable() {
@Override
public void run() {
service.serviceMethod();
}
};
Thread t1 = new Thread(r);
t1.start();
Thread.sleep(50); //睡眠50毫秒,确保t1线程锁定
Thread t2 = new Thread(r);
t2.start();
}
}
package com.wkcto.lock.reentrant;
import java.util.Random;
import java.util.concurrent.locks.ReentrantLock;
/**
* 使用tryLock()可以避免死锁
*/
public class Test09 {
static class IntLock implements Runnable{
private static ReentrantLock lock1 = new ReentrantLock();
private static ReentrantLock lock2 = new ReentrantLock();
private int lockNum; //用于控制锁的顺序
public IntLock(int lockNum) {
this.lockNum = lockNum;
}
@Override
public void run() {
if ( lockNum % 2 == 0 ){ //偶数先锁1,再锁2
while (true){
try {
if (lock1.tryLock()){
System.out.println(Thread.currentThread().getName() + "获得锁1, 还想获得锁2");
Thread.sleep(new Random().nextInt(100));
try {
if (lock2.tryLock()){
System.out.println(Thread.currentThread().getName() + "同时获得锁1与锁2 ----完成任务了");
return; //结束run()方法执行,即当前线程结束
}
} finally {
if (lock2.isHeldByCurrentThread()){
lock2.unlock();
}
}
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
if (lock1.isHeldByCurrentThread()){
lock1.unlock();
}
}
}
}else { //奇数就先锁2,再锁1
while (true){
try {
if (lock2.tryLock()){
System.out.println(Thread.currentThread().getName() + "获得锁2, 还想获得锁1");
Thread.sleep(new Random().nextInt(100));
try {
if (lock1.tryLock()){
System.out.println(Thread.currentThread().getName() + "同时获得锁1与锁2 ----完成任务了");
return; //结束run()方法执行,即当前线程结束
}
} finally {
if (lock1.isHeldByCurrentThread()){
lock1.unlock();
}
}
}
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
if (lock2.isHeldByCurrentThread()){
lock2.unlock();
}
}
}
}
}
}
public static void main(String[] args) {
IntLock intLock1 = new IntLock(11);
IntLock intLock2 = new IntLock(22);
Thread t1 = new Thread(intLock1);
Thread t2 = new Thread(intLock2);
t1.start();
t2.start();
//运行后,使用tryLock()尝试获得锁,不会傻傻的等待,通过循环不停的再次尝试,如果等待的时间足够长,线程总是会获得想要的资源
}
}
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