Return-Path: X-Original-To: apmail-geode-commits-archive@minotaur.apache.org Delivered-To: apmail-geode-commits-archive@minotaur.apache.org Received: from mail.apache.org (hermes.apache.org [140.211.11.3]) by minotaur.apache.org (Postfix) with SMTP id D46F6183D8 for ; Thu, 15 Oct 2015 21:35:45 +0000 (UTC) Received: (qmail 78738 invoked by uid 500); 15 Oct 2015 21:35:45 -0000 Delivered-To: apmail-geode-commits-archive@geode.apache.org Received: (qmail 78703 invoked by uid 500); 15 Oct 2015 21:35:45 -0000 Mailing-List: contact commits-help@geode.incubator.apache.org; run by ezmlm Precedence: bulk List-Help: List-Unsubscribe: List-Post: List-Id: Reply-To: dev@geode.incubator.apache.org Delivered-To: mailing list commits@geode.incubator.apache.org Received: (qmail 78694 invoked by uid 99); 15 Oct 2015 21:35:45 -0000 Received: from Unknown (HELO spamd2-us-west.apache.org) (209.188.14.142) by apache.org (qpsmtpd/0.29) with ESMTP; Thu, 15 Oct 2015 21:35:45 +0000 Received: from localhost (localhost [127.0.0.1]) by spamd2-us-west.apache.org (ASF Mail Server at spamd2-us-west.apache.org) with ESMTP id 359221A2564 for ; Thu, 15 Oct 2015 21:35:45 +0000 (UTC) X-Virus-Scanned: Debian amavisd-new at spamd2-us-west.apache.org X-Spam-Flag: NO X-Spam-Score: 1.791 X-Spam-Level: * X-Spam-Status: No, score=1.791 tagged_above=-999 required=6.31 tests=[KAM_ASCII_DIVIDERS=0.8, KAM_LAZY_DOMAIN_SECURITY=1, T_RP_MATCHES_RCVD=-0.01, URIBL_BLOCKED=0.001] autolearn=disabled Received: from mx1-us-east.apache.org ([10.40.0.8]) by localhost (spamd2-us-west.apache.org [10.40.0.9]) (amavisd-new, port 10024) with ESMTP id rcLWnHwJ1_05 for ; Thu, 15 Oct 2015 21:35:26 +0000 (UTC) Received: from mail.apache.org (hermes.apache.org [140.211.11.3]) by mx1-us-east.apache.org (ASF Mail Server at mx1-us-east.apache.org) with SMTP id 7508A439E9 for ; Thu, 15 Oct 2015 21:35:25 +0000 (UTC) Received: (qmail 76554 invoked by uid 99); 15 Oct 2015 21:35:25 -0000 Received: from git1-us-west.apache.org (HELO git1-us-west.apache.org) (140.211.11.23) by apache.org (qpsmtpd/0.29) with ESMTP; Thu, 15 Oct 2015 21:35:25 +0000 Received: by git1-us-west.apache.org (ASF Mail Server at git1-us-west.apache.org, from userid 33) id A1D35E1138; Thu, 15 Oct 2015 21:35:24 +0000 (UTC) Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit From: bschuchardt@apache.org To: commits@geode.incubator.apache.org Date: Thu, 15 Oct 2015 21:35:26 -0000 Message-Id: <9633a47e998948cfa528cdfe310e118e@git.apache.org> In-Reply-To: <68405af159b8460d805532caa8b92ee6@git.apache.org> References: <68405af159b8460d805532caa8b92ee6@git.apache.org> X-Mailer: ASF-Git Admin Mailer Subject: [03/38] incubator-geode git commit: GEODE-378: use SynchronousQueue to prevent deadlock GEODE-378: use SynchronousQueue to prevent deadlock The SynchronousQueueNoSpin class has been completely removed. The JDK SynchronousQueue is now used in its place. Project: http://git-wip-us.apache.org/repos/asf/incubator-geode/repo Commit: http://git-wip-us.apache.org/repos/asf/incubator-geode/commit/9e4a94e0 Tree: http://git-wip-us.apache.org/repos/asf/incubator-geode/tree/9e4a94e0 Diff: http://git-wip-us.apache.org/repos/asf/incubator-geode/diff/9e4a94e0 Branch: refs/heads/feature/GEODE-77 Commit: 9e4a94e06377094336cb31882b96e8aff2ebe8dd Parents: 35d3f06 Author: Darrel Schneider Authored: Thu Oct 1 11:45:37 2015 -0700 Committer: Darrel Schneider Committed: Fri Oct 2 09:36:45 2015 -0700 ---------------------------------------------------------------------- .../FunctionExecutionPooledExecutor.java | 7 +- .../internal/PooledExecutorWithDMStats.java | 7 +- .../util/concurrent/SynchronousQueueNoSpin.java | 1144 ------------------ 3 files changed, 6 insertions(+), 1152 deletions(-) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/incubator-geode/blob/9e4a94e0/gemfire-core/src/main/java/com/gemstone/gemfire/distributed/internal/FunctionExecutionPooledExecutor.java ---------------------------------------------------------------------- diff --git a/gemfire-core/src/main/java/com/gemstone/gemfire/distributed/internal/FunctionExecutionPooledExecutor.java b/gemfire-core/src/main/java/com/gemstone/gemfire/distributed/internal/FunctionExecutionPooledExecutor.java index 501b83c..698bc86 100644 --- a/gemfire-core/src/main/java/com/gemstone/gemfire/distributed/internal/FunctionExecutionPooledExecutor.java +++ b/gemfire-core/src/main/java/com/gemstone/gemfire/distributed/internal/FunctionExecutionPooledExecutor.java @@ -21,7 +21,6 @@ import com.gemstone.gemfire.i18n.LogWriterI18n; import com.gemstone.gemfire.internal.i18n.LocalizedStrings; import com.gemstone.gemfire.internal.logging.LocalLogWriter; import com.gemstone.gemfire.internal.logging.LogWriterImpl; -import com.gemstone.java.util.concurrent.SynchronousQueueNoSpin; import java.util.List; @@ -75,10 +74,10 @@ public class FunctionExecutionPooledExecutor extends ThreadPoolExecutor { Thread bufferConsumer; private static BlockingQueue initQ(BlockingQueue q) { - if (q instanceof SynchronousQueue || q instanceof SynchronousQueueNoSpin) { + if (q instanceof SynchronousQueue) { return q; } else { - return new SynchronousQueueNoSpin(); + return new SynchronousQueue(); } } @@ -124,7 +123,7 @@ public class FunctionExecutionPooledExecutor extends ThreadPoolExecutor { } else { - if (q instanceof SynchronousQueue || q instanceof SynchronousQueueNoSpin) { + if (q instanceof SynchronousQueue) { return new CallerRunsPolicy(); // return new BlockHandler(); } http://git-wip-us.apache.org/repos/asf/incubator-geode/blob/9e4a94e0/gemfire-core/src/main/java/com/gemstone/gemfire/distributed/internal/PooledExecutorWithDMStats.java ---------------------------------------------------------------------- diff --git a/gemfire-core/src/main/java/com/gemstone/gemfire/distributed/internal/PooledExecutorWithDMStats.java b/gemfire-core/src/main/java/com/gemstone/gemfire/distributed/internal/PooledExecutorWithDMStats.java index 05f9dd5..a50e594 100644 --- a/gemfire-core/src/main/java/com/gemstone/gemfire/distributed/internal/PooledExecutorWithDMStats.java +++ b/gemfire-core/src/main/java/com/gemstone/gemfire/distributed/internal/PooledExecutorWithDMStats.java @@ -17,7 +17,6 @@ import java.util.concurrent.TimeUnit; import java.util.concurrent.ThreadFactory; import com.gemstone.gemfire.SystemFailure; import com.gemstone.gemfire.internal.i18n.LocalizedStrings; -import com.gemstone.java.util.concurrent.SynchronousQueueNoSpin; import java.util.List; @@ -55,15 +54,15 @@ public class PooledExecutorWithDMStats extends ThreadPoolExecutor { private Thread bufferConsumer; private static BlockingQueue initQ(BlockingQueue q) { - if (q instanceof SynchronousQueue || q instanceof SynchronousQueueNoSpin) { + if (q instanceof SynchronousQueue) { return q; } else { - return new SynchronousQueueNoSpin(); + return new SynchronousQueue(); } } private static RejectedExecutionHandler initREH(BlockingQueue q) { - if (q instanceof SynchronousQueue || q instanceof SynchronousQueueNoSpin) { + if (q instanceof SynchronousQueue) { return new CallerRunsPolicy(); //return new BlockHandler(); } else { http://git-wip-us.apache.org/repos/asf/incubator-geode/blob/9e4a94e0/gemfire-core/src/main/java/com/gemstone/java/util/concurrent/SynchronousQueueNoSpin.java ---------------------------------------------------------------------- diff --git a/gemfire-core/src/main/java/com/gemstone/java/util/concurrent/SynchronousQueueNoSpin.java b/gemfire-core/src/main/java/com/gemstone/java/util/concurrent/SynchronousQueueNoSpin.java deleted file mode 100644 index ca2c1d9..0000000 --- a/gemfire-core/src/main/java/com/gemstone/java/util/concurrent/SynchronousQueueNoSpin.java +++ /dev/null @@ -1,1144 +0,0 @@ -/* - * Written by Doug Lea, Bill Scherer, and Michael Scott with - * assistance from members of JCP JSR-166 Expert Group and released to - * the public domain, as explained at - * http://creativecommons.org/licenses/publicdomain - * - */ - -package com.gemstone.java.util.concurrent; -import java.util.AbstractQueue; -import java.util.Collection; -import java.util.Collections; -import java.util.Iterator; -import java.util.concurrent.BlockingQueue; -import java.util.concurrent.TimeUnit; -import java.util.concurrent.atomic.AtomicReferenceFieldUpdater; -import java.util.concurrent.locks.LockSupport; -import java.util.concurrent.locks.ReentrantLock; - -/** - * A {@linkplain BlockingQueue blocking queue} in which each insert - * operation must wait for a corresponding remove operation by another - * thread, and vice versa. A synchronous queue does not have any - * internal capacity, not even a capacity of one. You cannot - * peek at a synchronous queue because an element is only - * present when you try to remove it; you cannot insert an element - * (using any method) unless another thread is trying to remove it; - * you cannot iterate as there is nothing to iterate. The - * head of the queue is the element that the first queued - * inserting thread is trying to add to the queue; if there is no such - * queued thread then no element is available for removal and - * poll() will return null. For purposes of other - * Collection methods (for example contains), a - * SynchronousQueue acts as an empty collection. This queue - * does not permit null elements. - * - *

Synchronous queues are similar to rendezvous channels used in - * CSP and Ada. They are well suited for handoff designs, in which an - * object running in one thread must sync up with an object running - * in another thread in order to hand it some information, event, or - * task. - * - *

This class supports an optional fairness policy for ordering - * waiting producer and consumer threads. By default, this ordering - * is not guaranteed. However, a queue constructed with fairness set - * to true grants threads access in FIFO order. - * - *

This class and its iterator implement all of the - * optional methods of the {@link Collection} and {@link - * Iterator} interfaces. - * - *

This class is a member of the - * - * Java Collections Framework. - * - * @since 1.5 - * @author Doug Lea and Bill Scherer and Michael Scott - * @param the type of elements held in this collection - * - * GemstoneAddition - * ------------------ - * This version was taken from the jsr166 CVS repository - * http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/main/java/util/concurrent/SynchronousQueue.java revision 1.68 - * - * The JSR version is identical java 1.6_10 version except for formatting - * and licensing. - * - * It has been modified by gemstone to remove the spin waiting which is hard coded - * into the java 1.6 version. We found through performance testing - * that this spin waiting was causing up to a 50% throughput decrease - * for some of our perf tests (eg perf081). - * - * In addition, the calls to LockSupport.park(Object) have been changed - * to LockSupport.park() to compile with java 1.5. - */ -public class SynchronousQueueNoSpin extends AbstractQueue - implements BlockingQueue, java.io.Serializable { - private static final long serialVersionUID = -3223113410248163686L; - - /* - * This class implements extensions of the dual stack and dual - * queue algorithms described in "Nonblocking Concurrent Objects - * with Condition Synchronization", by W. N. Scherer III and - * M. L. Scott. 18th Annual Conf. on Distributed Computing, - * Oct. 2004 (see also - * http://www.cs.rochester.edu/u/scott/synchronization/pseudocode/duals.html). - * The (Lifo) stack is used for non-fair mode, and the (Fifo) - * queue for fair mode. The performance of the two is generally - * similar. Fifo usually supports higher throughput under - * contention but Lifo maintains higher thread locality in common - * applications. - * - * A dual queue (and similarly stack) is one that at any given - * time either holds "data" -- items provided by put operations, - * or "requests" -- slots representing take operations, or is - * empty. A call to "fulfill" (i.e., a call requesting an item - * from a queue holding data or vice versa) dequeues a - * complementary node. The most interesting feature of these - * queues is that any operation can figure out which mode the - * queue is in, and act accordingly without needing locks. - * - * Both the queue and stack extend abstract class Transferer - * defining the single method transfer that does a put or a - * take. These are unified into a single method because in dual - * data structures, the put and take operations are symmetrical, - * so nearly all code can be combined. The resulting transfer - * methods are on the long side, but are easier to follow than - * they would be if broken up into nearly-duplicated parts. - * - * The queue and stack data structures share many conceptual - * similarities but very few concrete details. For simplicity, - * they are kept distinct so that they can later evolve - * separately. - * - * The algorithms here differ from the versions in the above paper - * in extending them for use in synchronous queues, as well as - * dealing with cancellation. The main differences include: - * - * 1. The original algorithms used bit-marked pointers, but - * the ones here use mode bits in nodes, leading to a number - * of further adaptations. - * 2. SynchronousQueues must block threads waiting to become - * fulfilled. - * 3. Support for cancellation via timeout and interrupts, - * including cleaning out cancelled nodes/threads - * from lists to avoid garbage retention and memory depletion. - * - * Blocking is mainly accomplished using LockSupport park/unpark, - * except that nodes that appear to be the next ones to become - * fulfilled first spin a bit (on multiprocessors only). On very - * busy synchronous queues, spinning can dramatically improve - * throughput. And on less busy ones, the amount of spinning is - * small enough not to be noticeable. - * - * Cleaning is done in different ways in queues vs stacks. For - * queues, we can almost always remove a node immediately in O(1) - * time (modulo retries for consistency checks) when it is - * cancelled. But if it may be pinned as the current tail, it must - * wait until some subsequent cancellation. For stacks, we need a - * potentially O(n) traversal to be sure that we can remove the - * node, but this can run concurrently with other threads - * accessing the stack. - * - * While garbage collection takes care of most node reclamation - * issues that otherwise complicate nonblocking algorithms, care - * is taken to "forget" references to data, other nodes, and - * threads that might be held on to long-term by blocked - * threads. In cases where setting to null would otherwise - * conflict with main algorithms, this is done by changing a - * node's link to now point to the node itself. This doesn't arise - * much for Stack nodes (because blocked threads do not hang on to - * old head pointers), but references in Queue nodes must be - * aggressively forgotten to avoid reachability of everything any - * node has ever referred to since arrival. - */ - - /** - * Shared internal API for dual stacks and queues. - */ - static abstract class Transferer { - /** - * Performs a put or take. - * - * @param e if non-null, the item to be handed to a consumer; - * if null, requests that transfer return an item - * offered by producer. - * @param timed if this operation should timeout - * @param nanos the timeout, in nanoseconds - * @return if non-null, the item provided or received; if null, - * the operation failed due to timeout or interrupt -- - * the caller can distinguish which of these occurred - * by checking Thread.interrupted. - */ - abstract Object transfer(Object e, boolean timed, long nanos); - } - - /** The number of CPUs, for spin control */ - static final int NCPUS = Runtime.getRuntime().availableProcessors(); - - /** - * The number of times to spin before blocking in timed waits. - * The value is empirically derived -- it works well across a - * variety of processors and OSes. Empirically, the best value - * seems not to vary with number of CPUs (beyond 2) so is just - * a constant. - */ - //@GemstoneAddition - //static final int maxTimedSpins = (NCPUS < 2)? 0 : 32; - static final int maxTimedSpins = 0; - - /** - * The number of times to spin before blocking in untimed waits. - * This is greater than timed value because untimed waits spin - * faster since they don't need to check times on each spin. - */ - static final int maxUntimedSpins = maxTimedSpins * 16; - - /** - * The number of nanoseconds for which it is faster to spin - * rather than to use timed park. A rough estimate suffices. - */ - //@GemstoneAddition - //static final long spinForTimeoutThreshold = 1000L; - static final long spinForTimeoutThreshold = 0L; - - /** Dual stack */ - static final class TransferStack extends Transferer { - /* - * This extends Scherer-Scott dual stack algorithm, differing, - * among other ways, by using "covering" nodes rather than - * bit-marked pointers: Fulfilling operations push on marker - * nodes (with FULFILLING bit set in mode) to reserve a spot - * to match a waiting node. - */ - - /* Modes for SNodes, ORed together in node fields */ - /** Node represents an unfulfilled consumer */ - static final int REQUEST = 0; - /** Node represents an unfulfilled producer */ - static final int DATA = 1; - /** Node is fulfilling another unfulfilled DATA or REQUEST */ - static final int FULFILLING = 2; - - /** Return true if m has fulfilling bit set */ - static boolean isFulfilling(int m) { return (m & FULFILLING) != 0; } - - /** Node class for TransferStacks. */ - static final class SNode { - volatile SNode next; // next node in stack - volatile SNode match; // the node matched to this - volatile Thread waiter; // to control park/unpark - Object item; // data; or null for REQUESTs - int mode; - // Note: item and mode fields don't need to be volatile - // since they are always written before, and read after, - // other volatile/atomic operations. - - SNode(Object item) { - this.item = item; - } - - static final AtomicReferenceFieldUpdater - nextUpdater = AtomicReferenceFieldUpdater.newUpdater - (SNode.class, SNode.class, "next"); - - boolean casNext(SNode cmp, SNode val) { - return (cmp == next && - nextUpdater.compareAndSet(this, cmp, val)); - } - - static final AtomicReferenceFieldUpdater - matchUpdater = AtomicReferenceFieldUpdater.newUpdater - (SNode.class, SNode.class, "match"); - - /** - * Tries to match node s to this node, if so, waking up thread. - * Fulfillers call tryMatch to identify their waiters. - * Waiters block until they have been matched. - * - * @param s the node to match - * @return true if successfully matched to s - */ - boolean tryMatch(SNode s) { - if (match == null && - matchUpdater.compareAndSet(this, null, s)) { - Thread w = waiter; - if (w != null) { // waiters need at most one unpark - waiter = null; - LockSupport.unpark(w); - } - return true; - } - return match == s; - } - - /** - * Tries to cancel a wait by matching node to itself. - */ - void tryCancel() { - matchUpdater.compareAndSet(this, null, this); - } - - boolean isCancelled() { - return match == this; - } - } - - /** The head (top) of the stack */ - volatile SNode head; - - static final AtomicReferenceFieldUpdater - headUpdater = AtomicReferenceFieldUpdater.newUpdater - (TransferStack.class, SNode.class, "head"); - - boolean casHead(SNode h, SNode nh) { - return h == head && headUpdater.compareAndSet(this, h, nh); - } - - /** - * Creates or resets fields of a node. Called only from transfer - * where the node to push on stack is lazily created and - * reused when possible to help reduce intervals between reads - * and CASes of head and to avoid surges of garbage when CASes - * to push nodes fail due to contention. - */ - static SNode snode(SNode s, Object e, SNode next, int mode) { - if (s == null) s = new SNode(e); - s.mode = mode; - s.next = next; - return s; - } - - /** - * Puts or takes an item. - */ - Object transfer(Object e, boolean timed, long nanos) { - /* - * Basic algorithm is to loop trying one of three actions: - * - * 1. If apparently empty or already containing nodes of same - * mode, try to push node on stack and wait for a match, - * returning it, or null if cancelled. - * - * 2. If apparently containing node of complementary mode, - * try to push a fulfilling node on to stack, match - * with corresponding waiting node, pop both from - * stack, and return matched item. The matching or - * unlinking might not actually be necessary because of - * other threads performing action 3: - * - * 3. If top of stack already holds another fulfilling node, - * help it out by doing its match and/or pop - * operations, and then continue. The code for helping - * is essentially the same as for fulfilling, except - * that it doesn't return the item. - */ - - SNode s = null; // constructed/reused as needed - int mode = (e == null)? REQUEST : DATA; - - for (;;) { - SNode h = head; - if (h == null || h.mode == mode) { // empty or same-mode - if (timed && nanos <= 0) { // can't wait - if (h != null && h.isCancelled()) - casHead(h, h.next); // pop cancelled node - else - return null; - } else if (casHead(h, s = snode(s, e, h, mode))) { - SNode m = awaitFulfill(s, timed, nanos); - if (m == s) { // wait was cancelled - clean(s); - return null; - } - if ((h = head) != null && h.next == s) - casHead(h, s.next); // help s's fulfiller - return mode == REQUEST? m.item : s.item; - } - } else if (!isFulfilling(h.mode)) { // try to fulfill - if (h.isCancelled()) // already cancelled - casHead(h, h.next); // pop and retry - else if (casHead(h, s=snode(s, e, h, FULFILLING|mode))) { - for (;;) { // loop until matched or waiters disappear - SNode m = s.next; // m is s's match - if (m == null) { // all waiters are gone - casHead(s, null); // pop fulfill node - s = null; // use new node next time - break; // restart main loop - } - SNode mn = m.next; - if (m.tryMatch(s)) { - casHead(s, mn); // pop both s and m - return (mode == REQUEST)? m.item : s.item; - } else // lost match - s.casNext(m, mn); // help unlink - } - } - } else { // help a fulfiller - SNode m = h.next; // m is h's match - if (m == null) // waiter is gone - casHead(h, null); // pop fulfilling node - else { - SNode mn = m.next; - if (m.tryMatch(h)) // help match - casHead(h, mn); // pop both h and m - else // lost match - h.casNext(m, mn); // help unlink - } - } - } - } - - /** - * Spins/blocks until node s is matched by a fulfill operation. - * - * @param s the waiting node - * @param timed true if timed wait - * @param nanos timeout value - * @return matched node, or s if cancelled - */ - SNode awaitFulfill(SNode s, boolean timed, long nanos) { - /* - * When a node/thread is about to block, it sets its waiter - * field and then rechecks state at least one more time - * before actually parking, thus covering race vs - * fulfiller noticing that waiter is non-null so should be - * woken. - * - * When invoked by nodes that appear at the point of call - * to be at the head of the stack, calls to park are - * preceded by spins to avoid blocking when producers and - * consumers are arriving very close in time. This can - * happen enough to bother only on multiprocessors. - * - * The order of checks for returning out of main loop - * reflects fact that interrupts have precedence over - * normal returns, which have precedence over - * timeouts. (So, on timeout, one last check for match is - * done before giving up.) Except that calls from untimed - * SynchronousQueue.{poll/offer} don't check interrupts - * and don't wait at all, so are trapped in transfer - * method rather than calling awaitFulfill. - */ - long lastTime = (timed)? System.nanoTime() : 0; - Thread w = Thread.currentThread(); - SNode h = head; - int spins = (shouldSpin(s)? - (timed? maxTimedSpins : maxUntimedSpins) : 0); - for (;;) { - if (w.isInterrupted()) - s.tryCancel(); - SNode m = s.match; - if (m != null) - return m; - if (timed) { - long now = System.nanoTime(); - nanos -= now - lastTime; - lastTime = now; - if (nanos <= 0) { - s.tryCancel(); - continue; - } - } - if (spins > 0) - spins = shouldSpin(s)? (spins-1) : 0; - else if (s.waiter == null) - s.waiter = w; // establish waiter so can park next iter - else if (!timed) - LockSupport.park(); - else if (nanos > spinForTimeoutThreshold) - LockSupport.parkNanos(nanos); - } - } - - /** - * Returns true if node s is at head or there is an active - * fulfiller. - */ - boolean shouldSpin(SNode s) { - SNode h = head; - return (h == s || h == null || isFulfilling(h.mode)); - } - - /** - * Unlinks s from the stack. - */ - void clean(SNode s) { - s.item = null; // forget item - s.waiter = null; // forget thread - - /* - * At worst we may need to traverse entire stack to unlink - * s. If there are multiple concurrent calls to clean, we - * might not see s if another thread has already removed - * it. But we can stop when we see any node known to - * follow s. We use s.next unless it too is cancelled, in - * which case we try the node one past. We don't check any - * further because we don't want to doubly traverse just to - * find sentinel. - */ - - SNode past = s.next; - if (past != null && past.isCancelled()) - past = past.next; - - // Absorb cancelled nodes at head - SNode p; - while ((p = head) != null && p != past && p.isCancelled()) - casHead(p, p.next); - - // Unsplice embedded nodes - while (p != null && p != past) { - SNode n = p.next; - if (n != null && n.isCancelled()) - p.casNext(n, n.next); - else - p = n; - } - } - } - - /** Dual Queue */ - static final class TransferQueue extends Transferer { - /* - * This extends Scherer-Scott dual queue algorithm, differing, - * among other ways, by using modes within nodes rather than - * marked pointers. The algorithm is a little simpler than - * that for stacks because fulfillers do not need explicit - * nodes, and matching is done by CAS'ing QNode.item field - * from non-null to null (for put) or vice versa (for take). - */ - - /** Node class for TransferQueue. */ - static final class QNode { - volatile QNode next; // next node in queue - volatile Object item; // CAS'ed to or from null - volatile Thread waiter; // to control park/unpark - final boolean isData; - - QNode(Object item, boolean isData) { - this.item = item; - this.isData = isData; - } - - static final AtomicReferenceFieldUpdater - nextUpdater = AtomicReferenceFieldUpdater.newUpdater - (QNode.class, QNode.class, "next"); - - boolean casNext(QNode cmp, QNode val) { - return (next == cmp && - nextUpdater.compareAndSet(this, cmp, val)); - } - - static final AtomicReferenceFieldUpdater - itemUpdater = AtomicReferenceFieldUpdater.newUpdater - (QNode.class, Object.class, "item"); - - boolean casItem(Object cmp, Object val) { - return (item == cmp && - itemUpdater.compareAndSet(this, cmp, val)); - } - - /** - * Tries to cancel by CAS'ing ref to this as item. - */ - void tryCancel(Object cmp) { - itemUpdater.compareAndSet(this, cmp, this); - } - - boolean isCancelled() { - return item == this; - } - - /** - * Returns true if this node is known to be off the queue - * because its next pointer has been forgotten due to - * an advanceHead operation. - */ - boolean isOffList() { - return next == this; - } - } - - /** Head of queue */ - transient volatile QNode head; - /** Tail of queue */ - transient volatile QNode tail; - /** - * Reference to a cancelled node that might not yet have been - * unlinked from queue because it was the last inserted node - * when it cancelled. - */ - transient volatile QNode cleanMe; - - TransferQueue() { - QNode h = new QNode(null, false); // initialize to dummy node. - head = h; - tail = h; - } - - static final AtomicReferenceFieldUpdater - headUpdater = AtomicReferenceFieldUpdater.newUpdater - (TransferQueue.class, QNode.class, "head"); - - /** - * Tries to cas nh as new head; if successful, unlink - * old head's next node to avoid garbage retention. - */ - void advanceHead(QNode h, QNode nh) { - if (h == head && headUpdater.compareAndSet(this, h, nh)) - h.next = h; // forget old next - } - - static final AtomicReferenceFieldUpdater - tailUpdater = AtomicReferenceFieldUpdater.newUpdater - (TransferQueue.class, QNode.class, "tail"); - - /** - * Tries to cas nt as new tail. - */ - void advanceTail(QNode t, QNode nt) { - if (tail == t) - tailUpdater.compareAndSet(this, t, nt); - } - - static final AtomicReferenceFieldUpdater - cleanMeUpdater = AtomicReferenceFieldUpdater.newUpdater - (TransferQueue.class, QNode.class, "cleanMe"); - - /** - * Tries to CAS cleanMe slot. - */ - boolean casCleanMe(QNode cmp, QNode val) { - return (cleanMe == cmp && - cleanMeUpdater.compareAndSet(this, cmp, val)); - } - - /** - * Puts or takes an item. - */ - Object transfer(Object e, boolean timed, long nanos) { - /* Basic algorithm is to loop trying to take either of - * two actions: - * - * 1. If queue apparently empty or holding same-mode nodes, - * try to add node to queue of waiters, wait to be - * fulfilled (or cancelled) and return matching item. - * - * 2. If queue apparently contains waiting items, and this - * call is of complementary mode, try to fulfill by CAS'ing - * item field of waiting node and dequeuing it, and then - * returning matching item. - * - * In each case, along the way, check for and try to help - * advance head and tail on behalf of other stalled/slow - * threads. - * - * The loop starts off with a null check guarding against - * seeing uninitialized head or tail values. This never - * happens in current SynchronousQueue, but could if - * callers held non-volatile/final ref to the - * transferer. The check is here anyway because it places - * null checks at top of loop, which is usually faster - * than having them implicitly interspersed. - */ - - QNode s = null; // constructed/reused as needed - boolean isData = (e != null); - - for (;;) { - QNode t = tail; - QNode h = head; - if (t == null || h == null) // saw uninitialized value - continue; // spin - - if (h == t || t.isData == isData) { // empty or same-mode - QNode tn = t.next; - if (t != tail) // inconsistent read - continue; - if (tn != null) { // lagging tail - advanceTail(t, tn); - continue; - } - if (timed && nanos <= 0) // can't wait - return null; - if (s == null) - s = new QNode(e, isData); - if (!t.casNext(null, s)) // failed to link in - continue; - - advanceTail(t, s); // swing tail and wait - Object x = awaitFulfill(s, e, timed, nanos); - if (x == s) { // wait was cancelled - clean(t, s); - return null; - } - - if (!s.isOffList()) { // not already unlinked - advanceHead(t, s); // unlink if head - if (x != null) // and forget fields - s.item = s; - s.waiter = null; - } - return (x != null)? x : e; - - } else { // complementary-mode - QNode m = h.next; // node to fulfill - if (t != tail || m == null || h != head) - continue; // inconsistent read - - Object x = m.item; - if (isData == (x != null) || // m already fulfilled - x == m || // m cancelled - !m.casItem(x, e)) { // lost CAS - advanceHead(h, m); // dequeue and retry - continue; - } - - advanceHead(h, m); // successfully fulfilled - LockSupport.unpark(m.waiter); - return (x != null)? x : e; - } - } - } - - /** - * Spins/blocks until node s is fulfilled. - * - * @param s the waiting node - * @param e the comparison value for checking match - * @param timed true if timed wait - * @param nanos timeout value - * @return matched item, or s if cancelled - */ - Object awaitFulfill(QNode s, Object e, boolean timed, long nanos) { - /* Same idea as TransferStack.awaitFulfill */ - long lastTime = (timed)? System.nanoTime() : 0; - Thread w = Thread.currentThread(); - int spins = ((head.next == s) ? - (timed? maxTimedSpins : maxUntimedSpins) : 0); - for (;;) { - if (w.isInterrupted()) - s.tryCancel(e); - Object x = s.item; - if (x != e) - return x; - if (timed) { - long now = System.nanoTime(); - nanos -= now - lastTime; - lastTime = now; - if (nanos <= 0) { - s.tryCancel(e); - continue; - } - } - if (spins > 0) - --spins; - else if (s.waiter == null) - s.waiter = w; - else if (!timed) - LockSupport.park(); - else if (nanos > spinForTimeoutThreshold) - LockSupport.parkNanos(nanos); - } - } - - /** - * Gets rid of cancelled node s with original predecessor pred. - */ - void clean(QNode pred, QNode s) { - s.waiter = null; // forget thread - /* - * At any given time, exactly one node on list cannot be - * deleted -- the last inserted node. To accommodate this, - * if we cannot delete s, we save its predecessor as - * "cleanMe", deleting the previously saved version - * first. At least one of node s or the node previously - * saved can always be deleted, so this always terminates. - */ - while (pred.next == s) { // Return early if already unlinked - QNode h = head; - QNode hn = h.next; // Absorb cancelled first node as head - if (hn != null && hn.isCancelled()) { - advanceHead(h, hn); - continue; - } - QNode t = tail; // Ensure consistent read for tail - if (t == h) - return; - QNode tn = t.next; - if (t != tail) - continue; - if (tn != null) { - advanceTail(t, tn); - continue; - } - if (s != t) { // If not tail, try to unsplice - QNode sn = s.next; - if (sn == s || pred.casNext(s, sn)) - return; - } - QNode dp = cleanMe; - if (dp != null) { // Try unlinking previous cancelled node - QNode d = dp.next; - QNode dn; - if (d == null || // d is gone or - d == dp || // d is off list or - !d.isCancelled() || // d not cancelled or - (d != t && // d not tail and - (dn = d.next) != null && // has successor - dn != d && // that is on list - dp.casNext(d, dn))) // d unspliced - casCleanMe(dp, null); - if (dp == pred) - return; // s is already saved node - } else if (casCleanMe(null, pred)) - return; // Postpone cleaning s - } - } - } - - /** - * The transferer. Set only in constructor, but cannot be declared - * as final without further complicating serialization. Since - * this is accessed only at most once per public method, there - * isn't a noticeable performance penalty for using volatile - * instead of final here. - */ - private transient volatile Transferer transferer; - - /** - * Creates a SynchronousQueue with nonfair access policy. - */ - public SynchronousQueueNoSpin() { - this(false); - } - - /** - * Creates a SynchronousQueue with the specified fairness policy. - * - * @param fair if true, waiting threads contend in FIFO order for - * access; otherwise the order is unspecified. - */ - public SynchronousQueueNoSpin(boolean fair) { - transferer = (fair)? new TransferQueue() : new TransferStack(); - } - - /** - * Adds the specified element to this queue, waiting if necessary for - * another thread to receive it. - * - * @throws InterruptedException {@inheritDoc} - * @throws NullPointerException {@inheritDoc} - */ - public void put(E o) throws InterruptedException { - if (o == null) throw new NullPointerException(); - if (transferer.transfer(o, false, 0) == null) { - Thread.interrupted(); - throw new InterruptedException(); - } - } - - /** - * Inserts the specified element into this queue, waiting if necessary - * up to the specified wait time for another thread to receive it. - * - * @return true if successful, or false if the - * specified waiting time elapses before a consumer appears. - * @throws InterruptedException {@inheritDoc} - * @throws NullPointerException {@inheritDoc} - */ - public boolean offer(E o, long timeout, TimeUnit unit) - throws InterruptedException { - if (o == null) throw new NullPointerException(); - if (transferer.transfer(o, true, unit.toNanos(timeout)) != null) - return true; - if (!Thread.interrupted()) - return false; - throw new InterruptedException(); - } - - /** - * Inserts the specified element into this queue, if another thread is - * waiting to receive it. - * - * @param e the element to add - * @return true if the element was added to this queue, else - * false - * @throws NullPointerException if the specified element is null - */ - public boolean offer(E e) { - if (e == null) throw new NullPointerException(); - return transferer.transfer(e, true, 0) != null; - } - - /** - * Retrieves and removes the head of this queue, waiting if necessary - * for another thread to insert it. - * - * @return the head of this queue - * @throws InterruptedException {@inheritDoc} - */ - public E take() throws InterruptedException { - Object e = transferer.transfer(null, false, 0); - if (e != null) - return (E)e; - Thread.interrupted(); - throw new InterruptedException(); - } - - /** - * Retrieves and removes the head of this queue, waiting - * if necessary up to the specified wait time, for another thread - * to insert it. - * - * @return the head of this queue, or null if the - * specified waiting time elapses before an element is present. - * @throws InterruptedException {@inheritDoc} - */ - public E poll(long timeout, TimeUnit unit) throws InterruptedException { - Object e = transferer.transfer(null, true, unit.toNanos(timeout)); - if (e != null || !Thread.interrupted()) - return (E)e; - throw new InterruptedException(); - } - - /** - * Retrieves and removes the head of this queue, if another thread - * is currently making an element available. - * - * @return the head of this queue, or null if no - * element is available. - */ - public E poll() { - return (E)transferer.transfer(null, true, 0); - } - - /** - * Always returns true. - * A SynchronousQueue has no internal capacity. - * - * @return true - */ - public boolean isEmpty() { - return true; - } - - /** - * Always returns zero. - * A SynchronousQueue has no internal capacity. - * - * @return zero. - */ - public int size() { - return 0; - } - - /** - * Always returns zero. - * A SynchronousQueue has no internal capacity. - * - * @return zero. - */ - public int remainingCapacity() { - return 0; - } - - /** - * Does nothing. - * A SynchronousQueue has no internal capacity. - */ - public void clear() { - } - - /** - * Always returns false. - * A SynchronousQueue has no internal capacity. - * - * @param o the element - * @return false - */ - public boolean contains(Object o) { - return false; - } - - /** - * Always returns false. - * A SynchronousQueue has no internal capacity. - * - * @param o the element to remove - * @return false - */ - public boolean remove(Object o) { - return false; - } - - /** - * Returns false unless the given collection is empty. - * A SynchronousQueue has no internal capacity. - * - * @param c the collection - * @return false unless given collection is empty - */ - public boolean containsAll(Collection c) { - return c.isEmpty(); - } - - /** - * Always returns false. - * A SynchronousQueue has no internal capacity. - * - * @param c the collection - * @return false - */ - public boolean removeAll(Collection c) { - return false; - } - - /** - * Always returns false. - * A SynchronousQueue has no internal capacity. - * - * @param c the collection - * @return false - */ - public boolean retainAll(Collection c) { - return false; - } - - /** - * Always returns null. - * A SynchronousQueue does not return elements - * unless actively waited on. - * - * @return null - */ - public E peek() { - return null; - } - - /** - * Returns an empty iterator in which hasNext always returns - * false. - * - * @return an empty iterator - */ - public Iterator iterator() { - return Collections.emptyList().iterator(); - } - - /** - * Returns a zero-length array. - * @return a zero-length array - */ - public Object[] toArray() { - return new Object[0]; - } - - /** - * Sets the zeroeth element of the specified array to null - * (if the array has non-zero length) and returns it. - * - * @param a the array - * @return the specified array - * @throws NullPointerException if the specified array is null - */ - public T[] toArray(T[] a) { - if (a.length > 0) - a[0] = null; - return a; - } - - /** - * @throws UnsupportedOperationException {@inheritDoc} - * @throws ClassCastException {@inheritDoc} - * @throws NullPointerException {@inheritDoc} - * @throws IllegalArgumentException {@inheritDoc} - */ - public int drainTo(Collection c) { - if (c == null) - throw new NullPointerException(); - if (c == this) - throw new IllegalArgumentException(); - int n = 0; - E e; - while ( (e = poll()) != null) { - c.add(e); - ++n; - } - return n; - } - - /** - * @throws UnsupportedOperationException {@inheritDoc} - * @throws ClassCastException {@inheritDoc} - * @throws NullPointerException {@inheritDoc} - * @throws IllegalArgumentException {@inheritDoc} - */ - public int drainTo(Collection c, int maxElements) { - if (c == null) - throw new NullPointerException(); - if (c == this) - throw new IllegalArgumentException(); - int n = 0; - E e; - while (n < maxElements && (e = poll()) != null) { - c.add(e); - ++n; - } - return n; - } - - /* - * To cope with serialization strategy in the 1.5 version of - * SynchronousQueue, we declare some unused classes and fields - * that exist solely to enable serializability across versions. - * These fields are never used, so are initialized only if this - * object is ever serialized or deserialized. - */ - - static class WaitQueue implements java.io.Serializable { - private static final long serialVersionUID = 423369940180943459L; - } - static class LifoWaitQueue extends WaitQueue { - private static final long serialVersionUID = -3633113410248163686L; - } - static class FifoWaitQueue extends WaitQueue { - private static final long serialVersionUID = -3623113410248163686L; - } - private ReentrantLock qlock; - private WaitQueue waitingProducers; - private WaitQueue waitingConsumers; - - /** - * Save the state to a stream (that is, serialize it). - * - * @param s the stream - */ - private void writeObject(java.io.ObjectOutputStream s) - throws java.io.IOException { - boolean fair = transferer instanceof TransferQueue; - if (fair) { - qlock = new ReentrantLock(true); - waitingProducers = new FifoWaitQueue(); - waitingConsumers = new FifoWaitQueue(); - } - else { - qlock = new ReentrantLock(); - waitingProducers = new LifoWaitQueue(); - waitingConsumers = new LifoWaitQueue(); - } - s.defaultWriteObject(); - } - - private void readObject(final java.io.ObjectInputStream s) - throws java.io.IOException, ClassNotFoundException { - s.defaultReadObject(); - if (waitingProducers instanceof FifoWaitQueue) - transferer = new TransferQueue(); - else - transferer = new TransferStack(); - } - -}