package java.util.concurrent.locks; import java.util.concurrent.TimeUnit; import java.util.ArrayList; import java.util.Collection; import java.util.Date; import sun.misc.Unsafe;
public abstract class AbstractQueuedSynchronizer extends AbstractOwnableSynchronizer implements java.io.Serializable {
private static final long serialVersionUID = 7373984972572414691L;
protected AbstractQueuedSynchronizer() { }
static final 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 void cancelAcquire(Node node) { if (node == null) return;
node.thread = null;
Node pred = node.prev; while (pred.waitStatus > 0) node.prev = pred = pred.prev;
Node predNext = pred.next;
node.waitStatus = Node.CANCELLED;
if (node == tail && compareAndSetTail(node, pred)) { compareAndSetNext(pred, predNext, null); } else { int ws; if (pred != head && ((ws = pred.waitStatus) == Node.SIGNAL || (ws <= 0 && compareAndSetWaitStatus(pred, ws, Node.SIGNAL))) && pred.thread != null) { Node next = node.next; if (next != null && next.waitStatus <= 0) compareAndSetNext(pred, predNext, next); } else { unparkSuccessor(node); }
node.next = node; } }
private static boolean shouldParkAfterFailedAcquire(Node pred, Node node) { int ws = pred.waitStatus; if (ws == Node.SIGNAL)
return true; if (ws > 0) {
do { node.prev = pred = pred.prev; } while (pred.waitStatus > 0); pred.next = node; } else {
compareAndSetWaitStatus(pred, ws, Node.SIGNAL); } return false; }
static void selfInterrupt() { Thread.currentThread().interrupt(); }
private final boolean parkAndCheckInterrupt() { LockSupport.park(this); return Thread.interrupted(); }
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; failed = false; return interrupted; } if (shouldParkAfterFailedAcquire(p, node) && parkAndCheckInterrupt()) interrupted = true; } } finally { if (failed) cancelAcquire(node); } }
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; failed = false; return; } if (shouldParkAfterFailedAcquire(p, node) && parkAndCheckInterrupt()) throw new InterruptedException(); } } finally { if (failed) cancelAcquire(node); } }
private boolean doAcquireNanos(int arg, long nanosTimeout) throws InterruptedException { if (nanosTimeout <= 0L) return false; final long deadline = System.nanoTime() + nanosTimeout; 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; failed = false; return true; } nanosTimeout = deadline - System.nanoTime(); if (nanosTimeout <= 0L) return false; if (shouldParkAfterFailedAcquire(p, node) && nanosTimeout > spinForTimeoutThreshold) LockSupport.parkNanos(this, nanosTimeout); if (Thread.interrupted()) throw new InterruptedException(); } } finally { if (failed) cancelAcquire(node); } }
private void doAcquireShared(int arg) { final Node node = addWaiter(Node.SHARED); boolean failed = true; try { boolean interrupted = false; for (;;) { final Node p = node.predecessor(); if (p == head) { int r = tryAcquireShared(arg); if (r >= 0) { setHeadAndPropagate(node, r); p.next = null; if (interrupted) selfInterrupt(); failed = false; return; } } if (shouldParkAfterFailedAcquire(p, node) && parkAndCheckInterrupt()) interrupted = true; } } finally { if (failed) cancelAcquire(node); } }
private void doAcquireSharedInterruptibly(int arg) throws InterruptedException { final Node node = addWaiter(Node.SHARED); boolean failed = true; try { for (;;) { final Node p = node.predecessor(); if (p == head) { int r = tryAcquireShared(arg); if (r >= 0) { setHeadAndPropagate(node, r); p.next = null; failed = false; return; } } if (shouldParkAfterFailedAcquire(p, node) && parkAndCheckInterrupt()) throw new InterruptedException(); } } finally { if (failed) cancelAcquire(node); } }
private boolean doAcquireSharedNanos(int arg, long nanosTimeout) throws InterruptedException { if (nanosTimeout <= 0L) return false; final long deadline = System.nanoTime() + nanosTimeout; final Node node = addWaiter(Node.SHARED); boolean failed = true; try { for (;;) { final Node p = node.predecessor(); if (p == head) { int r = tryAcquireShared(arg); if (r >= 0) { setHeadAndPropagate(node, r); p.next = null; failed = false; return true; } } nanosTimeout = deadline - System.nanoTime(); if (nanosTimeout <= 0L) return false; if (shouldParkAfterFailedAcquire(p, node) && nanosTimeout > spinForTimeoutThreshold) LockSupport.parkNanos(this, nanosTimeout); if (Thread.interrupted()) throw new InterruptedException(); } } finally { if (failed) cancelAcquire(node); } }
protected boolean tryAcquire(int arg) { throw new UnsupportedOperationException(); }
protected boolean tryRelease(int arg) { throw new UnsupportedOperationException(); }
protected int tryAcquireShared(int arg) { throw new UnsupportedOperationException(); }
protected boolean tryReleaseShared(int arg) { throw new UnsupportedOperationException(); }
protected boolean isHeldExclusively() { throw new UnsupportedOperationException(); }
public final void acquire(int arg) { if (!tryAcquire(arg) && acquireQueued(addWaiter(Node.EXCLUSIVE), arg)) selfInterrupt(); }
public final void acquireInterruptibly(int arg) throws InterruptedException { if (Thread.interrupted()) throw new InterruptedException(); if (!tryAcquire(arg)) doAcquireInterruptibly(arg); }
public final boolean tryAcquireNanos(int arg, long nanosTimeout) throws InterruptedException { if (Thread.interrupted()) throw new InterruptedException(); return tryAcquire(arg) || doAcquireNanos(arg, nanosTimeout); }
public final boolean release(int arg) { if (tryRelease(arg)) { Node h = head; if (h != null && h.waitStatus != 0) unparkSuccessor(h); return true; } return false; }
public final void acquireShared(int arg) { if (tryAcquireShared(arg) < 0) doAcquireShared(arg); }
public final void acquireSharedInterruptibly(int arg) throws InterruptedException { if (Thread.interrupted()) throw new InterruptedException(); if (tryAcquireShared(arg) < 0) doAcquireSharedInterruptibly(arg); }
public final boolean tryAcquireSharedNanos(int arg, long nanosTimeout) throws InterruptedException { if (Thread.interrupted()) throw new InterruptedException(); return tryAcquireShared(arg) >= 0 || doAcquireSharedNanos(arg, nanosTimeout); }
public final boolean releaseShared(int arg) { if (tryReleaseShared(arg)) { doReleaseShared(); return true; } return false; }
public final boolean hasQueuedThreads() { return head != tail; }
public final boolean hasContended() { return head != null; }
public final Thread getFirstQueuedThread() { return (head == tail) ? null : fullGetFirstQueuedThread(); }
private Thread fullGetFirstQueuedThread() {
Node h, s; Thread st; if (((h = head) != null && (s = h.next) != null && s.prev == head && (st = s.thread) != null) || ((h = head) != null && (s = h.next) != null && s.prev == head && (st = s.thread) != null)) return st;
Node t = tail; Thread firstThread = null; while (t != null && t != head) { Thread tt = t.thread; if (tt != null) firstThread = tt; t = t.prev; } return firstThread; }
public final boolean isQueued(Thread thread) { if (thread == null) throw new NullPointerException(); for (Node p = tail; p != null; p = p.prev) if (p.thread == thread) return true; return false; }
final boolean apparentlyFirstQueuedIsExclusive() { Node h, s; return (h = head) != null && (s = h.next) != null && !s.isShared() && s.thread != null; }
public final boolean hasQueuedPredecessors() { Node t = tail; Node h = head; Node s; return h != t && ((s = h.next) == null || s.thread != Thread.currentThread()); }
public final int getQueueLength() { int n = 0; for (Node p = tail; p != null; p = p.prev) { if (p.thread != null) ++n; } return n; }
public final Collection<Thread> getQueuedThreads() { ArrayList<Thread> list = new ArrayList<Thread>(); for (Node p = tail; p != null; p = p.prev) { Thread t = p.thread; if (t != null) list.add(t); } return list; }
public final Collection<Thread> getExclusiveQueuedThreads() { ArrayList<Thread> list = new ArrayList<Thread>(); for (Node p = tail; p != null; p = p.prev) { if (!p.isShared()) { Thread t = p.thread; if (t != null) list.add(t); } } return list; }
public final Collection<Thread> getSharedQueuedThreads() { ArrayList<Thread> list = new ArrayList<Thread>(); for (Node p = tail; p != null; p = p.prev) { if (p.isShared()) { Thread t = p.thread; if (t != null) list.add(t); } } return list; }
public String toString() { int s = getState(); String q = hasQueuedThreads() ? "non" : ""; return super.toString() + "[State = " + s + ", " + q + "empty queue]"; }
final boolean isOnSyncQueue(Node node) { if (node.waitStatus == Node.CONDITION || node.prev == null) return false; if (node.next != null) return true;
return findNodeFromTail(node); }
private boolean findNodeFromTail(Node node) { Node t = tail; for (;;) { if (t == node) return true; if (t == null) return false; t = t.prev; } }
final boolean transferForSignal(Node node) {
if (!compareAndSetWaitStatus(node, Node.CONDITION, 0)) return false;
Node p = enq(node); int ws = p.waitStatus; if (ws > 0 || !compareAndSetWaitStatus(p, ws, Node.SIGNAL)) LockSupport.unpark(node.thread); return true; }
final boolean transferAfterCancelledWait(Node node) { if (compareAndSetWaitStatus(node, Node.CONDITION, 0)) { enq(node); return true; }
while (!isOnSyncQueue(node)) Thread.yield(); return false; }
final int fullyRelease(Node node) { boolean failed = true; try { int savedState = getState(); if (release(savedState)) { failed = false; return savedState; } else { throw new IllegalMonitorStateException(); } } finally { if (failed) node.waitStatus = Node.CANCELLED; } }
public final boolean owns(ConditionObject condition) { return condition.isOwnedBy(this); }
public final boolean hasWaiters(ConditionObject condition) { if (!owns(condition)) throw new IllegalArgumentException("Not owner"); return condition.hasWaiters(); }
public final int getWaitQueueLength(ConditionObject condition) { if (!owns(condition)) throw new IllegalArgumentException("Not owner"); return condition.getWaitQueueLength(); }
public final Collection<Thread> getWaitingThreads(ConditionObject condition) { if (!owns(condition)) throw new IllegalArgumentException("Not owner"); return condition.getWaitingThreads(); }
public class ConditionObject implements Condition, java.io.Serializable { private static final long serialVersionUID = 1173984872572414699L; private transient Node firstWaiter; private transient Node lastWaiter;
public ConditionObject() { }
private Node addConditionWaiter() { Node t = lastWaiter; if (t != null && t.waitStatus != Node.CONDITION) { unlinkCancelledWaiters(); t = lastWaiter; } Node node = new Node(Thread.currentThread(), Node.CONDITION); if (t == null) firstWaiter = node; else t.nextWaiter = node; lastWaiter = node; return node; }
private void doSignal(Node first) { do { if ( (firstWaiter = first.nextWaiter) == null) lastWaiter = null; first.nextWaiter = null; } while (!transferForSignal(first) && (first = firstWaiter) != null); }
private void doSignalAll(Node first) { lastWaiter = firstWaiter = null; do { Node next = first.nextWaiter; first.nextWaiter = null; transferForSignal(first); first = next; } while (first != null); }
private void unlinkCancelledWaiters() { Node t = firstWaiter; Node trail = null; while (t != null) { Node next = t.nextWaiter; if (t.waitStatus != Node.CONDITION) { t.nextWaiter = null; if (trail == null) firstWaiter = next; else trail.nextWaiter = next; if (next == null) lastWaiter = trail; } else trail = t; t = next; } }
public final void signal() { if (!isHeldExclusively()) throw new IllegalMonitorStateException(); Node first = firstWaiter; if (first != null) doSignal(first); }
public final void signalAll() { if (!isHeldExclusively()) throw new IllegalMonitorStateException(); Node first = firstWaiter; if (first != null) doSignalAll(first); }
public final void awaitUninterruptibly() { Node node = addConditionWaiter(); int savedState = fullyRelease(node); boolean interrupted = false; while (!isOnSyncQueue(node)) { LockSupport.park(this); if (Thread.interrupted()) interrupted = true; } if (acquireQueued(node, savedState) || interrupted) selfInterrupt(); }
private static final int REINTERRUPT = 1; private static final int THROW_IE = -1;
private int checkInterruptWhileWaiting(Node node) { return Thread.interrupted() ? (transferAfterCancelledWait(node) ? THROW_IE : REINTERRUPT) : 0; }
private void reportInterruptAfterWait(int interruptMode) throws InterruptedException { if (interruptMode == THROW_IE) throw new InterruptedException(); else if (interruptMode == REINTERRUPT) selfInterrupt(); }
public final void await() throws InterruptedException { if (Thread.interrupted()) throw new InterruptedException(); Node node = addConditionWaiter(); int savedState = fullyRelease(node); int interruptMode = 0; while (!isOnSyncQueue(node)) { LockSupport.park(this); if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) break; } if (acquireQueued(node, savedState) && interruptMode != THROW_IE) interruptMode = REINTERRUPT; if (node.nextWaiter != null) unlinkCancelledWaiters(); if (interruptMode != 0) reportInterruptAfterWait(interruptMode); }
public final long awaitNanos(long nanosTimeout) throws InterruptedException { if (Thread.interrupted()) throw new InterruptedException(); Node node = addConditionWaiter(); int savedState = fullyRelease(node); final long deadline = System.nanoTime() + nanosTimeout; int interruptMode = 0; while (!isOnSyncQueue(node)) { if (nanosTimeout <= 0L) { transferAfterCancelledWait(node); break; } if (nanosTimeout >= spinForTimeoutThreshold) LockSupport.parkNanos(this, nanosTimeout); if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) break; nanosTimeout = deadline - System.nanoTime(); } if (acquireQueued(node, savedState) && interruptMode != THROW_IE) interruptMode = REINTERRUPT; if (node.nextWaiter != null) unlinkCancelledWaiters(); if (interruptMode != 0) reportInterruptAfterWait(interruptMode); return deadline - System.nanoTime(); }
public final boolean awaitUntil(Date deadline) throws InterruptedException { long abstime = deadline.getTime(); if (Thread.interrupted()) throw new InterruptedException(); Node node = addConditionWaiter(); int savedState = fullyRelease(node); boolean timedout = false; int interruptMode = 0; while (!isOnSyncQueue(node)) { if (System.currentTimeMillis() > abstime) { timedout = transferAfterCancelledWait(node); break; } LockSupport.parkUntil(this, abstime); if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) break; } if (acquireQueued(node, savedState) && interruptMode != THROW_IE) interruptMode = REINTERRUPT; if (node.nextWaiter != null) unlinkCancelledWaiters(); if (interruptMode != 0) reportInterruptAfterWait(interruptMode); return !timedout; }
public final boolean await(long time, TimeUnit unit) throws InterruptedException { long nanosTimeout = unit.toNanos(time); if (Thread.interrupted()) throw new InterruptedException(); Node node = addConditionWaiter(); int savedState = fullyRelease(node); final long deadline = System.nanoTime() + nanosTimeout; boolean timedout = false; int interruptMode = 0; while (!isOnSyncQueue(node)) { if (nanosTimeout <= 0L) { timedout = transferAfterCancelledWait(node); break; } if (nanosTimeout >= spinForTimeoutThreshold) LockSupport.parkNanos(this, nanosTimeout); if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) break; nanosTimeout = deadline - System.nanoTime(); } if (acquireQueued(node, savedState) && interruptMode != THROW_IE) interruptMode = REINTERRUPT; if (node.nextWaiter != null) unlinkCancelledWaiters(); if (interruptMode != 0) reportInterruptAfterWait(interruptMode); return !timedout; }
final boolean isOwnedBy(AbstractQueuedSynchronizer sync) { return sync == AbstractQueuedSynchronizer.this; }
protected final boolean hasWaiters() { if (!isHeldExclusively()) throw new IllegalMonitorStateException(); for (Node w = firstWaiter; w != null; w = w.nextWaiter) { if (w.waitStatus == Node.CONDITION) return true; } return false; }
protected final int getWaitQueueLength() { if (!isHeldExclusively()) throw new IllegalMonitorStateException(); int n = 0; for (Node w = firstWaiter; w != null; w = w.nextWaiter) { if (w.waitStatus == Node.CONDITION) ++n; } return n; }
protected final Collection<Thread> getWaitingThreads() { if (!isHeldExclusively()) throw new IllegalMonitorStateException(); ArrayList<Thread> list = new ArrayList<Thread>(); for (Node w = firstWaiter; w != null; w = w.nextWaiter) { if (w.waitStatus == Node.CONDITION) { Thread t = w.thread; if (t != null) list.add(t); } } return list; } }
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 waitStatusOffset; 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")); waitStatusOffset = unsafe.objectFieldOffset (Node.class.getDeclaredField("waitStatus")); nextOffset = unsafe.objectFieldOffset (Node.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, waitStatusOffset, expect, update); }
private static final boolean compareAndSetNext(Node node, Node expect, Node update) { return unsafe.compareAndSwapObject(node, nextOffset, expect, update); } }
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