Lock应用之 可中断
Thread.interrupt()方法可用于中断指定线程，但线程并不是在任何状态下可被立即中断，一般只有当线程处于阻塞状态（调用wait(),join(),sleep()等方法）时才会被立即中断，如果线程处于不可被立即中断状态，那么Thread.interrupt()只会标志线程的中断状态，以便后续操作用于判断，即isInterrupted()方法会返回true.
线程等待获取内部锁的时候，是一种不可立即中断状态，即线程不会立即响应中断而是会继续等待，这种无义无反顾的等待可能会造成资源浪费或者死锁等问题，后果非常严重。新Lock锁提供了等待锁资源时可立即响应中断的lockInterruptibly()方法和tryLock(long time, TimeUnit unit)方法及其实现，当使用这两个方法去请求锁时，如果主通过Thread.interrupt()对它们发起中断，那么它们会立即响应中断，不再继续等待获取锁，这让主线程（管理调度线程）在特殊情况下可以使用生杀大权，以避免系统陷于死锁状态或者避免资源严重浪费。
tryLock(long time, TimeUnit unit)是加强版的tryLock()，又具有lockInterruptibly()的可被中断特性，既可任其超时主动退出又可中断让其被动退出，很多场合可以使用，但如果想让线程只有当被动中断时才退出，那么就使用lockInterruptibly()方法。
通过测试可以得出以下结论：
内部锁(synchronized) 优先响应锁获取再响应中断
Lock.lock() 优先响应锁获取再响应中断
Lock.tryLock() 判断锁的状态不可用后马上返回不等待
tryLock(long time, TimeUnit unit) 优先响应中断再响应锁获取
Lock.lockInterruptibly() 优先响应中断再响应锁获取
代码示例：
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class TestLockInterrupt {
private Lock mLock1;
private Lock mLock2;
private Lock mLock3;
public TestLockInterrupt(){
mLock1 = new ReentrantLock();
mLock2 = new ReentrantLock();
mLock3 = new ReentrantLock();
}
public void f(){
System.out.println(Thread.currentThread().getName() + ":try to get lock in f().");
try{
synchronized(this){
System.out.println(Thread.currentThread().getName() + ":get the lock.");
if(Thread.currentThread().isInterrupted()){
System.out.println(Thread.currentThread().getName() + ":already marked as interrupted but still running.");
}
TimeUnit.SECONDS.sleep(100);
}
System.out.println(Thread.currentThread().getName() + ":release the lock.");
}
catch(InterruptedException e){
System.out.println(Thread.currentThread().getName() + ":interrupted.");
}
}
public void fWithLock(){
System.out.println(Thread.currentThread().getName() + ":try to get lock in fWithLock().");
mLock1.lock();
try{
System.out.println(Thread.currentThread().getName() + ":get the lock.");
if(Thread.currentThread().isInterrupted()){
System.out.println(Thread.currentThread().getName() + ":already marked as interrupted but still running.");
}
TimeUnit.SECONDS.sleep(100);
}
catch(InterruptedException e){
System.out.println(Thread.currentThread().getName() + ":interrupted.");
}
finally{
mLock1.unlock();
System.out.println(Thread.currentThread().getName() + ":release the lock.");
}
}
public void fWithTryLock(){
System.out.println(Thread.currentThread().getName() + ":try to get lock in fWithTryLock().");
try{
if(mLock2.tryLock(50, TimeUnit.SECONDS)){
try{
System.out.println(Thread.currentThread().getName() + ":get the lock.");
if(Thread.currentThread().isInterrupted()){
System.out.println(Thread.currentThread().getName() + ":already marked as interrupted but still running.");
}
TimeUnit.SECONDS.sleep(100);
}
finally{
mLock2.unlock();
System.out.println(Thread.currentThread().getName() + ":release the lock.");
}
}
}
catch(InterruptedException e){
System.out.println(Thread.currentThread().getName() + ":interrupted.");
}
}
public void fWithLockInterruptibly(){
System.out.println(Thread.currentThread().getName() + ":try to get lock in fWithLockInterruptibly().");
try{
mLock3.lockInterruptibly();
System.out.println(Thread.currentThread().getName() + ":get the lock.");
try{
if(Thread.currentThread().isInterrupted()){
System.out.println(Thread.currentThread().getName() + ":already marked as interrupted but still running.");
}
TimeUnit.SECONDS.sleep(100);
}
finally{
mLock3.unlock();
System.out.println(Thread.currentThread().getName() + ":release the lock.");
}
}
catch(InterruptedException e){
System.out.println(Thread.currentThread().getName() + ":interrupted.");
}
}
private class Worker implements Runnable{
private int index;
public Worker(int index){
this.index = index;
}
@Override
public void run() {
switch(index){
case 1:
f();
break;
case 2:
fWithLock();
break;
case 3:
fWithTryLock();
break;
case 4:
fWithLockInterruptibly();
break;
}
}
}
public static void main(String[] args) {
TestLockInterrupt testLockInterrupt = new TestLockInterrupt();
for(int i=1; i<=4; i++){
Thread t1 = new Thread(testLockInterrupt.new Worker(i));
Thread t2 = new Thread(testLockInterrupt.new Worker(i));
t1.start();
t2.start();
t1.interrupt();
t2.interrupt();
}
}
}
代码输出结果：
Thread-0:try to get lock in f(). Thread-1:try to get lock in f(). Thread-1:get the lock. Thread-3:try to get lock in fWithLock(). Thread-1:already marked as interrupted but still running. Thread-3:get the lock. Thread-3:already marked as interrupted but still running. Thread-7:try to get lock in fWithLockInterruptibly(). Thread-2:try to get lock in fWithLock(). Thread-1:interrupted. Thread-7:interrupted. Thread-3:interrupted. Thread-3:release the lock. Thread-2:get the lock. Thread-2:already marked as interrupted but still running. Thread-2:interrupted. Thread-2:release the lock. Thread-4:try to get lock in fWithTryLock(). Thread-4:interrupted. Thread-0:get the lock. Thread-0:already marked as interrupted but still running. Thread-0:interrupted. Thread-5:try to get lock in fWithTryLock(). Thread-5:interrupted. Thread-6:try to get lock in fWithLockInterruptibly(). Thread-6:interrupted.