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Posted to commits@geode.apache.org by vf...@apache.org on 2015/11/25 20:07:34 UTC
[21/50] [abbrv] 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-78
Commit: 9e4a94e06377094336cb31882b96e8aff2ebe8dd
Parents: 35d3f06
Author: Darrel Schneider <ds...@pivotal.io>
Authored: Thu Oct 1 11:45:37 2015 -0700
Committer: Darrel Schneider <ds...@pivotal.io>
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<Runnable> initQ(BlockingQueue<Runnable> q) {
- if (q instanceof SynchronousQueue || q instanceof SynchronousQueueNoSpin) {
+ if (q instanceof SynchronousQueue) {
return q;
} else {
- return new SynchronousQueueNoSpin<Runnable>();
+ return new SynchronousQueue<Runnable>();
}
}
@@ -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<Runnable> initQ(BlockingQueue<Runnable> q) {
- if (q instanceof SynchronousQueue || q instanceof SynchronousQueueNoSpin) {
+ if (q instanceof SynchronousQueue) {
return q;
} else {
- return new SynchronousQueueNoSpin<Runnable>();
+ return new SynchronousQueue<Runnable>();
}
}
private static RejectedExecutionHandler initREH(BlockingQueue<Runnable> 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
- * <tt>peek</tt> 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
- * <em>head</em> 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
- * <tt>poll()</tt> will return <tt>null</tt>. For purposes of other
- * <tt>Collection</tt> methods (for example <tt>contains</tt>), a
- * <tt>SynchronousQueue</tt> acts as an empty collection. This queue
- * does not permit <tt>null</tt> elements.
- *
- * <p>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.
- *
- * <p> 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 <tt>true</tt> grants threads access in FIFO order.
- *
- * <p>This class and its iterator implement all of the
- * <em>optional</em> methods of the {@link Collection} and {@link
- * Iterator} interfaces.
- *
- * <p>This class is a member of the
- * <a href="{@docRoot}/../technotes/guides/collections/index.html">
- * Java Collections Framework</a>.
- *
- * @since 1.5
- * @author Doug Lea and Bill Scherer and Michael Scott
- * @param <E> 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<E> extends AbstractQueue<E>
- implements BlockingQueue<E>, 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<SNode, SNode>
- 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<SNode, SNode>
- 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<TransferStack, SNode>
- 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<QNode, QNode>
- 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<QNode, Object>
- 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<TransferQueue, QNode>
- 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<TransferQueue, QNode>
- 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<TransferQueue, QNode>
- 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 <tt>SynchronousQueue</tt> with nonfair access policy.
- */
- public SynchronousQueueNoSpin() {
- this(false);
- }
-
- /**
- * Creates a <tt>SynchronousQueue</tt> 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 <tt>true</tt> if successful, or <tt>false</tt> 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 <tt>true</tt> if the element was added to this queue, else
- * <tt>false</tt>
- * @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 <tt>null</tt> 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 <tt>null</tt> if no
- * element is available.
- */
- public E poll() {
- return (E)transferer.transfer(null, true, 0);
- }
-
- /**
- * Always returns <tt>true</tt>.
- * A <tt>SynchronousQueue</tt> has no internal capacity.
- *
- * @return <tt>true</tt>
- */
- public boolean isEmpty() {
- return true;
- }
-
- /**
- * Always returns zero.
- * A <tt>SynchronousQueue</tt> has no internal capacity.
- *
- * @return zero.
- */
- public int size() {
- return 0;
- }
-
- /**
- * Always returns zero.
- * A <tt>SynchronousQueue</tt> has no internal capacity.
- *
- * @return zero.
- */
- public int remainingCapacity() {
- return 0;
- }
-
- /**
- * Does nothing.
- * A <tt>SynchronousQueue</tt> has no internal capacity.
- */
- public void clear() {
- }
-
- /**
- * Always returns <tt>false</tt>.
- * A <tt>SynchronousQueue</tt> has no internal capacity.
- *
- * @param o the element
- * @return <tt>false</tt>
- */
- public boolean contains(Object o) {
- return false;
- }
-
- /**
- * Always returns <tt>false</tt>.
- * A <tt>SynchronousQueue</tt> has no internal capacity.
- *
- * @param o the element to remove
- * @return <tt>false</tt>
- */
- public boolean remove(Object o) {
- return false;
- }
-
- /**
- * Returns <tt>false</tt> unless the given collection is empty.
- * A <tt>SynchronousQueue</tt> has no internal capacity.
- *
- * @param c the collection
- * @return <tt>false</tt> unless given collection is empty
- */
- public boolean containsAll(Collection<?> c) {
- return c.isEmpty();
- }
-
- /**
- * Always returns <tt>false</tt>.
- * A <tt>SynchronousQueue</tt> has no internal capacity.
- *
- * @param c the collection
- * @return <tt>false</tt>
- */
- public boolean removeAll(Collection<?> c) {
- return false;
- }
-
- /**
- * Always returns <tt>false</tt>.
- * A <tt>SynchronousQueue</tt> has no internal capacity.
- *
- * @param c the collection
- * @return <tt>false</tt>
- */
- public boolean retainAll(Collection<?> c) {
- return false;
- }
-
- /**
- * Always returns <tt>null</tt>.
- * A <tt>SynchronousQueue</tt> does not return elements
- * unless actively waited on.
- *
- * @return <tt>null</tt>
- */
- public E peek() {
- return null;
- }
-
- /**
- * Returns an empty iterator in which <tt>hasNext</tt> always returns
- * <tt>false</tt>.
- *
- * @return an empty iterator
- */
- public Iterator<E> iterator() {
- return Collections.<E>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 <tt>null</tt>
- * (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> 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<? super E> 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<? super E> 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();
- }
-
-}