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| public abstract class AbstractQueuedSynchronizer extends AbstractOwnableSynchronizer implements Serializable{
protected AbstractQueuedSynchronizer() {
}
static class Node {
static final Node SHARED = new Node();
static final Node EXCLUSIVE = null;
static final int CANCELLED = 1;
static final int SIGNAL = -1;
static final int CONDITION = -2;
static final int PROPAGATE = -3;
volatile int waitStatus;
volatile Node prev;
volatile Node next;
volatile Thread thread;
Node nextWaiter;
final boolean isShared() {
return nextWaiter == SHARED;
}
final Node predecessor() throws NullPointerException {
Node p = prev;
if (p == null) {
throw new NullPointerException();
} else {
return p;
}
}
Node() {
}
Node(Thread thread, Node mode) {
this.nextWaiter = mode;
this.thread = thread;
}
Node(Thread thread, int waitStatus) {
this.waitStatus = waitStatus;
this.thread = thread;
}
}
private transient volatile Node head;
private transient volatile Node tail;
private volatile int state;
protected final int getState() {
return state;
}
protected final void setState(int newState) {
state = newState;
}
protected final boolean compareAndSetState(int expect, int update) {
return unsafe.compareAndSwapInt(this, stateOffset, expect, update);
}
static final long spinForTimeoutThreshold = 1000L;
private Node enq(final Node node) {
for (; ; ) {
Node t = tail;
if (t == null) {
if (compareAndSetHead(new Node())) {
tail = head;
}
} else {
node.prev = t;
if (compareAndSetTail(t, node)) {
t.next = node;
return t;
}
}
}
}
private Node addWaiter(Node mode) {
Node node = new Node(Thread.currentThread(), mode);
Node pred = tail;
if (pred != null) {
node.prev = pred;
if (compareAndSetTail(pred, node)) {
pred.next = node;
return node;
}
}
enq(node);
return node;
}
private void setHead(Node node) {
head = node;
node.thread = null;
node.prev = null;
}
private void unparkSuccessor(Node node) {
int ws = node.waitStatus;
if (ws < 0) {
compareAndSetWaitStatus(node, ws, 0);
}
Node s = node.next;
if (s == null || s.waitStatus > 0) {
s = null;
for (Node t = tail; t != null && t != node; t = t.prev) {
if (t.waitStatus <= 0) {
s = t;
}
}
}
if (s != null) {
LockSupport.unpark(s.thread);
}
}
private void doReleaseShared() {
for (; ; ) {
Node h = head;
if (h != null && h != tail) {
int ws = h.waitStatus;
if (ws == Node.SIGNAL) {
if (!compareAndSetWaitStatus(h, Node.SIGNAL, 0)) {
continue;
}
unparkSuccessor(h);
} else if (ws == 0 && !compareAndSetWaitStatus(h, 0, Node.PROPAGATE)) {
continue;
}
}
if (h == head) {
break;
}
}
}
private void setHeadAndPropagate(Node node, int propagate) {
Node h = head;
setHead(node);
if (propagate > 0 || h == null || h.waitStatus < 0 || (h = head) == null || h.waitStatus < 0) {
Node s = node.next;
if (s == null || s.isShared()) {
doReleaseShared();
}
}
}
private static final Unsafe unsafe = Unsafe.getUnsafe();
private static final long stateOffset;
private static final long headOffset;
private static final long tailOffset;
private static final long waiteStatusOffset;
private static final long nextOffset;
static {
try {
stateOffset = unsafe.objectFieldOffset(AbstractQueuedSynchronizer.class.getDeclaredField("state"));
headOffset = unsafe.objectFieldOffset(AbstractQueuedSynchronizer.class.getDeclaredField("head"));
tailOffset = unsafe.objectFieldOffset(AbstractQueuedSynchronizer.class.getDeclaredField("tail"));
waiteStatusOffset =
unsafe.objectFieldOffset(AbstractQueuedSynchronizer.class.getDeclaredField("waitStatus"));
nextOffset = unsafe.objectFieldOffset(AbstractQueuedSynchronizer.class.getDeclaredField("next"));
} catch (Exception ex) {
throw new Error(ex);
}
}
private final boolean compareAndSetHead(Node update) {
return unsafe.compareAndSwapObject(this, headOffset, null, update);
}
private final boolean compareAndSetTail(Node expect, Node update) {
return unsafe.compareAndSwapObject(this, tailOffset, expect, update);
}
private static final boolean compareAndSetWaitStatus(Node node, int expect, int update) {
return unsafe.compareAndSwapInt(node, waiteStatusOffset, expect, update);
}
private static final boolean compareAndSetNext(Node node, Node expect, Node update) {
return unsafe.compareAndSwapObject(node, nextOffset, expect, update);
}
}
|