--- jsr166/src/jsr166e/StampedLock.java 2013/01/26 01:22:37 1.32 +++ jsr166/src/jsr166e/StampedLock.java 2013/01/26 15:00:15 1.33 @@ -253,6 +253,7 @@ public class StampedLock implements java * motivation to further spread out contended locations, but might * be subject to future improvements. */ + private static final long serialVersionUID = -6001602636862214147L; /** Number of processors, for spin control */ @@ -443,11 +444,17 @@ public class StampedLock implements java */ public long tryReadLock(long time, TimeUnit unit) throws InterruptedException { - long next, deadline; + long s, m, next, deadline; long nanos = unit.toNanos(time); if (!Thread.interrupted()) { - if ((next = tryReadLock()) != 0L) - return next; + if ((m = (s = state) & ABITS) != WBIT) { + if (m < RFULL) { + if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) + return next; + } + else if ((next = tryIncReaderOverflow(s)) != 0L) + return next; + } if (nanos <= 0L) return 0L; if ((deadline = System.nanoTime() + nanos) == 0L) @@ -1033,14 +1040,14 @@ public class StampedLock implements java if (deadline == 0L) time = 0L; else if ((time = deadline - System.nanoTime()) <= 0L) - return cancelWaiter(node, null, false); + return cancelWaiter(node, node, false); node.thread = Thread.currentThread(); if (node.prev == p && p.status == WAITING && // recheck (p != whead || (state & ABITS) != 0L)) U.park(false, time); node.thread = null; if (interruptible && Thread.interrupted()) - return cancelWaiter(node, null, true); + return cancelWaiter(node, node, true); } } } @@ -1173,59 +1180,64 @@ public class StampedLock implements java if (deadline == 0L) time = 0L; else if ((time = deadline - System.nanoTime()) <= 0L) - return cancelWaiter(node, null, false); + return cancelWaiter(node, node, false); node.thread = Thread.currentThread(); if (node.prev == p && p.status == WAITING && (p != whead || (state & ABITS) != WBIT)) U.park(false, time); node.thread = null; if (interruptible && Thread.interrupted()) - return cancelWaiter(node, null, true); + return cancelWaiter(node, node, true); } } } /** * If node non-null, forces cancel status and unsplices it from - * queue if possible and wakes up any cowaiters. This is a variant - * of cancellation methods in AbstractQueuedSynchronizer (see its - * detailed explanation in AQS internal documentation) that more - * conservatively wakes up other threads that may have had their - * links changed, so as to preserve liveness in the main - * signalling methods. + * queue if possible and wakes up any cowaiters (of the node, or + * group, as applicable), and in any case helps release current + * first waiter if lock is free. (Calling with null arguments + * serves as a conditional form of release, which is not currently + * needed but may be needed under possible future cancellation + * policies). This is a variant of cancellation methods in + * AbstractQueuedSynchronizer (see its detailed explanation in AQS + * internal documentation). * * @param node if nonnull, the waiter - * @param group, if nonnull, the group current thread is cowaiting with + * @param group, either node or the group node is cowaiting with * @param interrupted if already interrupted * @return INTERRUPTED if interrupted or Thread.interrupted, else zero */ private long cancelWaiter(WNode node, WNode group, boolean interrupted) { - if (node != null) { - node.thread = null; + if (node != null && group != null) { + Thread w; node.status = CANCELLED; - Thread w; // wake up co-waiters; unsplice cancelled ones - for (WNode q, p = (group != null) ? group : node; p != null; ) { - if ((q = p.cowait) == null) - break; - if ((w = q.thread) != null) { - q.thread = null; - U.unpark(w); - } + node.thread = null; + // unsplice cancelled nodes from group + for (WNode p = group, q; (q = p.cowait) != null;) { if (q.status == CANCELLED) - U.compareAndSwapObject(p, WCOWAIT, q, q.cowait); + U.compareAndSwapObject(p, WNEXT, q, q.next); else p = q; } - if (group == null) { // unsplice both prev and next links - for (WNode pred = node.prev; pred != null; ) { - WNode succ, pp; // first unsplice next + if (group == node) { + WNode r; // detach and wake up uncancelled co-waiters + while ((r = node.cowait) != null) { + if (U.compareAndSwapObject(node, WCOWAIT, r, r.cowait) && + (w = r.thread) != null) { + r.thread = null; + U.unpark(w); + } + } + for (WNode pred = node.prev; pred != null; ) { // unsplice + WNode succ, pp; // find valid successor while ((succ = node.next) == null || succ.status == CANCELLED) { - WNode q = null; // find successor the slow way + WNode q = null; // find successor the slow way for (WNode t = wtail; t != null && t != node; t = t.prev) if (t.status != CANCELLED) - q = t; // don't link if succ cancelled - if (succ == q || // ensure accurate successor + q = t; // don't link if succ cancelled + if (succ == q || // ensure accurate successor U.compareAndSwapObject(node, WNEXT, succ, succ = q)) { if (succ == null && node == wtail) @@ -1237,17 +1249,32 @@ public class StampedLock implements java U.compareAndSwapObject(pred, WNEXT, node, succ); if (succ != null && (w = succ.thread) != null) { succ.thread = null; - U.unpark(w); // conservatively wake up new succ + U.unpark(w); // wake up succ to observe new pred } if (pred.status != CANCELLED || (pp = pred.prev) == null) break; - node.prev = pp; // repeat in case new pred wrong/cancelled + node.prev = pp; // repeat if new pred wrong/cancelled U.compareAndSwapObject(pp, WNEXT, pred, succ); pred = pp; } } } - release(whead); + WNode h; // Possibly release first waiter + while ((h = whead) != null) { + long s; WNode q; // similar to release() but check eligibility + if ((q = h.next) == null || q.status == CANCELLED) { + for (WNode t = wtail; t != null && t != h; t = t.prev) + if (t.status <= 0) + q = t; + } + if (h == whead) { + if (q != null && h.status == 0 && + ((s = state) & ABITS) != WBIT && // waiter is eligible + (s == 0L || q.mode == RMODE)) + release(h); + break; + } + } return (interrupted || Thread.interrupted()) ? INTERRUPTED : 0L; }