java并发编程---ReentrantLock不可打断模式与可打断模式
文章目录
- ReentrantLock不可打断模式
- 可打断模式
ReentrantLock不可打断模式
在此模式下，即使它被打断，仍会驻留在AQS队列中，等获得锁后方能继续运行（是继续运行！只是打断标记被设置为true）
public ReentrantLock() {
sync = new NonfairSync();
}
public void lock() {
sync.lock();
}
static final class NonfairSync extends Sync {
lock，重点方法
final void lock() {
if (compareAndSetState(0, 1))
setExclusiveOwnerThread(Thread.currentThread());
else
acquire(1);
}
acquire方法
public final void acquire(int arg) {
if (!tryAcquire(arg) &&
acquireQueued(addWaiter(Node.EXCLUSIVE), arg))
selfInterrupt();
}
acquireQueued方法
final boolean acquireQueued(final Node node, int arg) {
boolean failed = true;
try {
boolean interrupted = false;
for (;;) {
final Node p = node.predecessor();
if (p == head && tryAcquire(arg)) {
setHead(node);
p.next = null; // help GC
failed = false;
return interrupted;
}
if (shouldParkAfterFailedAcquire(p, node) &&
parkAndCheckInterrupt())
interrupted = true;
}
} finally {
if (failed)
cancelAcquire(node);
}
}
parkAndCheckInterrupt方法
private final boolean parkAndCheckInterrupt() {
LockSupport.park(this);
return Thread.interrupted();
}
如果interrupted 返回真，就会返回到acquire方法，进入if块内容。
public final void acquire(int arg) {
if (!tryAcquire(arg) &&
acquireQueued(addWaiter(Node.EXCLUSIVE), arg))
selfInterrupt();
}
static void selfInterrupt() {
//重新产生一次中断
Thread.currentThread().interrupt();
}
可打断模式
static final class NonfairSync extends Sync {
public final void acquireInterruptibly(int arg)
throws InterruptedException {
if (Thread.interrupted())
throw new InterruptedException();
if (!tryAcquire(arg))
doAcquireInterruptibly(arg);
}
doAcquireInterruptibly方法
private void doAcquireInterruptibly(int arg)
throws InterruptedException {
final Node node = addWaiter(Node.EXCLUSIVE);
boolean failed = true;
try {
for (;;) {
final Node p = node.predecessor();
if (p == head && tryAcquire(arg)) {
setHead(node);
p.next = null; // help GC
failed = false;
return;
}
if (shouldParkAfterFailedAcquire(p, node) &&
parkAndCheckInterrupt())
//在park过程中如果被interrupt会进入此
//这时候抛出异常，而不会再次进入for(;;)
throw new InterruptedException();
}
} finally {
if (failed)
cancelAcquire(node);
}
}