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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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package jsr166y; |
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import java.util.concurrent.*; |
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import java.util.AbstractQueue; |
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import java.util.Collection; |
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import java.util.ConcurrentModificationException; |
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import java.util.Iterator; |
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import java.util.NoSuchElementException; |
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import java.util.Queue; |
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import java.util.concurrent.TimeUnit; |
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import java.util.concurrent.locks.LockSupport; |
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import java.util.concurrent.atomic.AtomicReference; |
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/** |
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* An unbounded {@linkplain TransferQueue} based on linked nodes. |
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* An unbounded {@link TransferQueue} based on linked nodes. |
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* This queue orders elements FIFO (first-in-first-out) with respect |
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* to any given producer. The <em>head</em> of the queue is that |
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* element that has been on the queue the longest time for some |
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* producer. The <em>tail</em> of the queue is that element that has |
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* been on the queue the shortest time for some producer. |
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* |
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* <p>Beware that, unlike in most collections, the {@code size} |
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* method is <em>NOT</em> a constant-time operation. Because of the |
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* <p>Beware that, unlike in most collections, the {@code size} method |
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* is <em>NOT</em> a constant-time operation. Because of the |
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* asynchronous nature of these queues, determining the current number |
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* of elements requires a traversal of the elements. |
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* of elements requires a traversal of the elements, and so may report |
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* inaccurate results if this collection is modified during traversal. |
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* Additionally, the bulk operations {@code addAll}, |
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* {@code removeAll}, {@code retainAll}, {@code containsAll}, |
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* {@code equals}, and {@code toArray} are <em>not</em> guaranteed |
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* to be performed atomically. For example, an iterator operating |
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* concurrently with an {@code addAll} operation might view only some |
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* of the added elements. |
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* |
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* <p>This class and its iterator implement all of the |
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* <em>optional</em> methods of the {@link Collection} and {@link |
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private static final long serialVersionUID = -3223113410248163686L; |
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/* |
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* This class extends the approach used in FIFO-mode |
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* SynchronousQueues. See the internal documentation, as well as |
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* the PPoPP 2006 paper "Scalable Synchronous Queues" by Scherer, |
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* Lea & Scott |
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* (http://www.cs.rice.edu/~wns1/papers/2006-PPoPP-SQ.pdf) |
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* *** Overview of Dual Queues with Slack *** |
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* |
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* The main extension is to provide different Wait modes for the |
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* main "xfer" method that puts or takes items. These don't |
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* impact the basic dual-queue logic, but instead control whether |
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* or how threads block upon insertion of request or data nodes |
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* into the dual queue. It also uses slightly different |
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* conventions for tracking whether nodes are off-list or |
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* cancelled. |
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*/ |
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// Wait modes for xfer method |
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static final int NOWAIT = 0; |
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static final int TIMEOUT = 1; |
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static final int WAIT = 2; |
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|
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/** The number of CPUs, for spin control */ |
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static final int NCPUS = Runtime.getRuntime().availableProcessors(); |
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* Dual Queues, introduced by Scherer and Scott |
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* (http://www.cs.rice.edu/~wns1/papers/2004-DISC-DDS.pdf) are |
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* (linked) queues in which nodes may represent either data or |
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* requests. When a thread tries to enqueue a data node, but |
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* encounters a request node, it instead "matches" and removes it; |
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* and vice versa for enqueuing requests. Blocking Dual Queues |
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* arrange that threads enqueuing unmatched requests block until |
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* other threads provide the match. Dual Synchronous Queues (see |
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* Scherer, Lea, & Scott |
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* http://www.cs.rochester.edu/u/scott/papers/2009_Scherer_CACM_SSQ.pdf) |
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* additionally arrange that threads enqueuing unmatched data also |
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* block. Dual Transfer Queues support all of these modes, as |
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* dictated by callers. |
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* |
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* A FIFO dual queue may be implemented using a variation of the |
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* Michael & Scott (M&S) lock-free queue algorithm |
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* (http://www.cs.rochester.edu/u/scott/papers/1996_PODC_queues.pdf). |
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* It maintains two pointer fields, "head", pointing to a |
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* (matched) node that in turn points to the first actual |
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* (unmatched) queue node (or null if empty); and "tail" that |
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* points to the last node on the queue (or again null if |
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* empty). For example, here is a possible queue with four data |
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* elements: |
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* |
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* head tail |
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* | | |
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* v v |
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* M -> U -> U -> U -> U |
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* |
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* The M&S queue algorithm is known to be prone to scalability and |
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* overhead limitations when maintaining (via CAS) these head and |
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* tail pointers. This has led to the development of |
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* contention-reducing variants such as elimination arrays (see |
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* Moir et al http://portal.acm.org/citation.cfm?id=1074013) and |
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* optimistic back pointers (see Ladan-Mozes & Shavit |
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* http://people.csail.mit.edu/edya/publications/OptimisticFIFOQueue-journal.pdf). |
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* However, the nature of dual queues enables a simpler tactic for |
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* improving M&S-style implementations when dual-ness is needed. |
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* |
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* In a dual queue, each node must atomically maintain its match |
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* status. While there are other possible variants, we implement |
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* this here as: for a data-mode node, matching entails CASing an |
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* "item" field from a non-null data value to null upon match, and |
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* vice-versa for request nodes, CASing from null to a data |
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* value. (Note that the linearization properties of this style of |
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* queue are easy to verify -- elements are made available by |
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* linking, and unavailable by matching.) Compared to plain M&S |
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* queues, this property of dual queues requires one additional |
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* successful atomic operation per enq/deq pair. But it also |
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* enables lower cost variants of queue maintenance mechanics. (A |
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* variation of this idea applies even for non-dual queues that |
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* support deletion of interior elements, such as |
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* j.u.c.ConcurrentLinkedQueue.) |
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* |
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* Once a node is matched, its match status can never again |
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* change. We may thus arrange that the linked list of them |
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* contain a prefix of zero or more matched nodes, followed by a |
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* suffix of zero or more unmatched nodes. (Note that we allow |
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* both the prefix and suffix to be zero length, which in turn |
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* means that we do not use a dummy header.) If we were not |
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* concerned with either time or space efficiency, we could |
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* correctly perform enqueue and dequeue operations by traversing |
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* from a pointer to the initial node; CASing the item of the |
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* first unmatched node on match and CASing the next field of the |
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* trailing node on appends. (Plus some special-casing when |
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* initially empty). While this would be a terrible idea in |
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* itself, it does have the benefit of not requiring ANY atomic |
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* updates on head/tail fields. |
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* |
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* We introduce here an approach that lies between the extremes of |
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* never versus always updating queue (head and tail) pointers. |
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* This offers a tradeoff between sometimes requiring extra |
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* traversal steps to locate the first and/or last unmatched |
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* nodes, versus the reduced overhead and contention of fewer |
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* updates to queue pointers. For example, a possible snapshot of |
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* a queue is: |
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* |
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* head tail |
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* | | |
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* v v |
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* M -> M -> U -> U -> U -> U |
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* |
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* The best value for this "slack" (the targeted maximum distance |
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* between the value of "head" and the first unmatched node, and |
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* similarly for "tail") is an empirical matter. We have found |
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* that using very small constants in the range of 1-3 work best |
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* over a range of platforms. Larger values introduce increasing |
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* costs of cache misses and risks of long traversal chains, while |
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* smaller values increase CAS contention and overhead. |
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* |
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* Dual queues with slack differ from plain M&S dual queues by |
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* virtue of only sometimes updating head or tail pointers when |
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* matching, appending, or even traversing nodes; in order to |
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* maintain a targeted slack. The idea of "sometimes" may be |
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* operationalized in several ways. The simplest is to use a |
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* per-operation counter incremented on each traversal step, and |
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* to try (via CAS) to update the associated queue pointer |
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* whenever the count exceeds a threshold. Another, that requires |
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* more overhead, is to use random number generators to update |
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* with a given probability per traversal step. |
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* |
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* In any strategy along these lines, because CASes updating |
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* fields may fail, the actual slack may exceed targeted |
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* slack. However, they may be retried at any time to maintain |
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* targets. Even when using very small slack values, this |
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* approach works well for dual queues because it allows all |
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* operations up to the point of matching or appending an item |
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* (hence potentially allowing progress by another thread) to be |
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* read-only, thus not introducing any further contention. As |
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* described below, we implement this by performing slack |
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* maintenance retries only after these points. |
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* |
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* As an accompaniment to such techniques, traversal overhead can |
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* be further reduced without increasing contention of head |
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* pointer updates: Threads may sometimes shortcut the "next" link |
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* path from the current "head" node to be closer to the currently |
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* known first unmatched node, and similarly for tail. Again, this |
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* may be triggered with using thresholds or randomization. |
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* |
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* These ideas must be further extended to avoid unbounded amounts |
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* of costly-to-reclaim garbage caused by the sequential "next" |
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* links of nodes starting at old forgotten head nodes: As first |
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* described in detail by Boehm |
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* (http://portal.acm.org/citation.cfm?doid=503272.503282) if a GC |
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* delays noticing that any arbitrarily old node has become |
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* garbage, all newer dead nodes will also be unreclaimed. |
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* (Similar issues arise in non-GC environments.) To cope with |
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* this in our implementation, upon CASing to advance the head |
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* pointer, we set the "next" link of the previous head to point |
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* only to itself; thus limiting the length of connected dead lists. |
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* (We also take similar care to wipe out possibly garbage |
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* retaining values held in other Node fields.) However, doing so |
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* adds some further complexity to traversal: If any "next" |
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* pointer links to itself, it indicates that the current thread |
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* has lagged behind a head-update, and so the traversal must |
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* continue from the "head". Traversals trying to find the |
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* current tail starting from "tail" may also encounter |
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* self-links, in which case they also continue at "head". |
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* |
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* It is tempting in slack-based scheme to not even use CAS for |
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* updates (similarly to Ladan-Mozes & Shavit). However, this |
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* cannot be done for head updates under the above link-forgetting |
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* mechanics because an update may leave head at a detached node. |
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* And while direct writes are possible for tail updates, they |
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* increase the risk of long retraversals, and hence long garbage |
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* chains, which can be much more costly than is worthwhile |
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* considering that the cost difference of performing a CAS vs |
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* write is smaller when they are not triggered on each operation |
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* (especially considering that writes and CASes equally require |
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* additional GC bookkeeping ("write barriers") that are sometimes |
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* more costly than the writes themselves because of contention). |
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* |
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* *** Overview of implementation *** |
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* |
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* We use a threshold-based approach to updates, with a slack |
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* threshold of two -- that is, we update head/tail when the |
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* current pointer appears to be two or more steps away from the |
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* first/last node. The slack value is hard-wired: a path greater |
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* than one is naturally implemented by checking equality of |
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* traversal pointers except when the list has only one element, |
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* in which case we keep slack threshold at one. Avoiding tracking |
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* explicit counts across method calls slightly simplifies an |
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* already-messy implementation. Using randomization would |
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* probably work better if there were a low-quality dirt-cheap |
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* per-thread one available, but even ThreadLocalRandom is too |
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* heavy for these purposes. |
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* |
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* With such a small slack threshold value, it is not worthwhile |
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* to augment this with path short-circuiting (i.e., unsplicing |
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* interior nodes) except in the case of cancellation/removal (see |
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* below). |
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* |
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* We allow both the head and tail fields to be null before any |
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* nodes are enqueued; initializing upon first append. This |
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* simplifies some other logic, as well as providing more |
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* efficient explicit control paths instead of letting JVMs insert |
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* implicit NullPointerExceptions when they are null. While not |
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* currently fully implemented, we also leave open the possibility |
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* of re-nulling these fields when empty (which is complicated to |
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* arrange, for little benefit.) |
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* |
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* All enqueue/dequeue operations are handled by the single method |
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* "xfer" with parameters indicating whether to act as some form |
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* of offer, put, poll, take, or transfer (each possibly with |
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* timeout). The relative complexity of using one monolithic |
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* method outweighs the code bulk and maintenance problems of |
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* using separate methods for each case. |
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* |
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* Operation consists of up to three phases. The first is |
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* implemented within method xfer, the second in tryAppend, and |
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* the third in method awaitMatch. |
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* |
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* 1. Try to match an existing node |
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* |
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* Starting at head, skip already-matched nodes until finding |
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* an unmatched node of opposite mode, if one exists, in which |
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* case matching it and returning, also if necessary updating |
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* head to one past the matched node (or the node itself if the |
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* list has no other unmatched nodes). If the CAS misses, then |
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* a loop retries advancing head by two steps until either |
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* success or the slack is at most two. By requiring that each |
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* attempt advances head by two (if applicable), we ensure that |
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* the slack does not grow without bound. Traversals also check |
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* if the initial head is now off-list, in which case they |
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* start at the new head. |
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* |
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* If no candidates are found and the call was untimed |
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* poll/offer, (argument "how" is NOW) return. |
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* |
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* 2. Try to append a new node (method tryAppend) |
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* |
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* Starting at current tail pointer, find the actual last node |
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* and try to append a new node (or if head was null, establish |
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* the first node). Nodes can be appended only if their |
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* predecessors are either already matched or are of the same |
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* mode. If we detect otherwise, then a new node with opposite |
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* mode must have been appended during traversal, so we must |
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* restart at phase 1. The traversal and update steps are |
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* otherwise similar to phase 1: Retrying upon CAS misses and |
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* checking for staleness. In particular, if a self-link is |
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* encountered, then we can safely jump to a node on the list |
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* by continuing the traversal at current head. |
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* |
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* On successful append, if the call was ASYNC, return. |
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* |
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* 3. Await match or cancellation (method awaitMatch) |
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* |
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* Wait for another thread to match node; instead cancelling if |
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* the current thread was interrupted or the wait timed out. On |
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* multiprocessors, we use front-of-queue spinning: If a node |
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* appears to be the first unmatched node in the queue, it |
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* spins a bit before blocking. In either case, before blocking |
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* it tries to unsplice any nodes between the current "head" |
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* and the first unmatched node. |
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* |
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* Front-of-queue spinning vastly improves performance of |
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* heavily contended queues. And so long as it is relatively |
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* brief and "quiet", spinning does not much impact performance |
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* of less-contended queues. During spins threads check their |
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* interrupt status and generate a thread-local random number |
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* to decide to occasionally perform a Thread.yield. While |
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* yield has underdefined specs, we assume that it might help, |
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* and will not hurt, in limiting impact of spinning on busy |
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* systems. We also use smaller (1/2) spins for nodes that are |
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* not known to be front but whose predecessors have not |
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* blocked -- these "chained" spins avoid artifacts of |
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* front-of-queue rules which otherwise lead to alternating |
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* nodes spinning vs blocking. Further, front threads that |
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* represent phase changes (from data to request node or vice |
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* versa) compared to their predecessors receive additional |
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* chained spins, reflecting longer paths typically required to |
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* unblock threads during phase changes. |
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* |
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* |
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* ** Unlinking removed interior nodes ** |
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* |
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* In addition to minimizing garbage retention via self-linking |
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* described above, we also unlink removed interior nodes. These |
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* may arise due to timed out or interrupted waits, or calls to |
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* remove(x) or Iterator.remove. Normally, given a node that was |
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* at one time known to be the predecessor of some node s that is |
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* to be removed, we can unsplice s by CASing the next field of |
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* its predecessor if it still points to s (otherwise s must |
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* already have been removed or is now offlist). But there are two |
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* situations in which we cannot guarantee to make node s |
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* unreachable in this way: (1) If s is the trailing node of list |
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* (i.e., with null next), then it is pinned as the target node |
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* for appends, so can only be removed later after other nodes are |
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* appended. (2) We cannot necessarily unlink s given a |
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* predecessor node that is matched (including the case of being |
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* cancelled): the predecessor may already be unspliced, in which |
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* case some previous reachable node may still point to s. |
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* (For further explanation see Herlihy & Shavit "The Art of |
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* Multiprocessor Programming" chapter 9). Although, in both |
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* cases, we can rule out the need for further action if either s |
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* or its predecessor are (or can be made to be) at, or fall off |
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* from, the head of list. |
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* |
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* Without taking these into account, it would be possible for an |
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* unbounded number of supposedly removed nodes to remain |
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* reachable. Situations leading to such buildup are uncommon but |
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* can occur in practice; for example when a series of short timed |
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* calls to poll repeatedly time out but never otherwise fall off |
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* the list because of an untimed call to take at the front of the |
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* queue. |
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* |
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* When these cases arise, rather than always retraversing the |
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* entire list to find an actual predecessor to unlink (which |
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* won't help for case (1) anyway), we record a conservative |
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* estimate of possible unsplice failures (in "sweepVotes"). |
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* We trigger a full sweep when the estimate exceeds a threshold |
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* ("SWEEP_THRESHOLD") indicating the maximum number of estimated |
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* removal failures to tolerate before sweeping through, unlinking |
356 |
> |
* cancelled nodes that were not unlinked upon initial removal. |
357 |
> |
* We perform sweeps by the thread hitting threshold (rather than |
358 |
> |
* background threads or by spreading work to other threads) |
359 |
> |
* because in the main contexts in which removal occurs, the |
360 |
> |
* caller is already timed-out, cancelled, or performing a |
361 |
> |
* potentially O(n) operation (e.g. remove(x)), none of which are |
362 |
> |
* time-critical enough to warrant the overhead that alternatives |
363 |
> |
* would impose on other threads. |
364 |
> |
* |
365 |
> |
* Because the sweepVotes estimate is conservative, and because |
366 |
> |
* nodes become unlinked "naturally" as they fall off the head of |
367 |
> |
* the queue, and because we allow votes to accumulate even while |
368 |
> |
* sweeps are in progress, there are typically significantly fewer |
369 |
> |
* such nodes than estimated. Choice of a threshold value |
370 |
> |
* balances the likelihood of wasted effort and contention, versus |
371 |
> |
* providing a worst-case bound on retention of interior nodes in |
372 |
> |
* quiescent queues. The value defined below was chosen |
373 |
> |
* empirically to balance these under various timeout scenarios. |
374 |
> |
* |
375 |
> |
* Note that we cannot self-link unlinked interior nodes during |
376 |
> |
* sweeps. However, the associated garbage chains terminate when |
377 |
> |
* some successor ultimately falls off the head of the list and is |
378 |
> |
* self-linked. |
379 |
> |
*/ |
380 |
> |
|
381 |
> |
/** True if on multiprocessor */ |
382 |
> |
private static final boolean MP = |
383 |
> |
Runtime.getRuntime().availableProcessors() > 1; |
384 |
> |
|
385 |
> |
/** |
386 |
> |
* The number of times to spin (with randomly interspersed calls |
387 |
> |
* to Thread.yield) on multiprocessor before blocking when a node |
388 |
> |
* is apparently the first waiter in the queue. See above for |
389 |
> |
* explanation. Must be a power of two. The value is empirically |
390 |
> |
* derived -- it works pretty well across a variety of processors, |
391 |
> |
* numbers of CPUs, and OSes. |
392 |
> |
*/ |
393 |
> |
private static final int FRONT_SPINS = 1 << 7; |
394 |
> |
|
395 |
> |
/** |
396 |
> |
* The number of times to spin before blocking when a node is |
397 |
> |
* preceded by another node that is apparently spinning. Also |
398 |
> |
* serves as an increment to FRONT_SPINS on phase changes, and as |
399 |
> |
* base average frequency for yielding during spins. Must be a |
400 |
> |
* power of two. |
401 |
> |
*/ |
402 |
> |
private static final int CHAINED_SPINS = FRONT_SPINS >>> 1; |
403 |
> |
|
404 |
> |
/** |
405 |
> |
* The maximum number of estimated removal failures (sweepVotes) |
406 |
> |
* to tolerate before sweeping through the queue unlinking |
407 |
> |
* cancelled nodes that were not unlinked upon initial |
408 |
> |
* removal. See above for explanation. The value must be at least |
409 |
> |
* two to avoid useless sweeps when removing trailing nodes. |
410 |
> |
*/ |
411 |
> |
static final int SWEEP_THRESHOLD = 32; |
412 |
> |
|
413 |
> |
/** |
414 |
> |
* Queue nodes. Uses Object, not E, for items to allow forgetting |
415 |
> |
* them after use. Relies heavily on Unsafe mechanics to minimize |
416 |
> |
* unnecessary ordering constraints: Writes that are intrinsically |
417 |
> |
* ordered wrt other accesses or CASes use simple relaxed forms. |
418 |
> |
*/ |
419 |
> |
static final class Node { |
420 |
> |
final boolean isData; // false if this is a request node |
421 |
> |
volatile Object item; // initially non-null if isData; CASed to match |
422 |
> |
volatile Node next; |
423 |
> |
volatile Thread waiter; // null until waiting |
424 |
|
|
425 |
< |
/** |
426 |
< |
* The number of times to spin before blocking in timed waits. |
427 |
< |
* The value is empirically derived -- it works well across a |
428 |
< |
* variety of processors and OSes. Empirically, the best value |
84 |
< |
* seems not to vary with number of CPUs (beyond 2) so is just |
85 |
< |
* a constant. |
86 |
< |
*/ |
87 |
< |
static final int maxTimedSpins = (NCPUS < 2) ? 0 : 32; |
88 |
< |
|
89 |
< |
/** |
90 |
< |
* The number of times to spin before blocking in untimed waits. |
91 |
< |
* This is greater than timed value because untimed waits spin |
92 |
< |
* faster since they don't need to check times on each spin. |
93 |
< |
*/ |
94 |
< |
static final int maxUntimedSpins = maxTimedSpins * 16; |
95 |
< |
|
96 |
< |
/** |
97 |
< |
* The number of nanoseconds for which it is faster to spin |
98 |
< |
* rather than to use timed park. A rough estimate suffices. |
99 |
< |
*/ |
100 |
< |
static final long spinForTimeoutThreshold = 1000L; |
425 |
> |
// CAS methods for fields |
426 |
> |
final boolean casNext(Node cmp, Node val) { |
427 |
> |
return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val); |
428 |
> |
} |
429 |
|
|
430 |
< |
/** |
431 |
< |
* Node class for LinkedTransferQueue. Opportunistically |
432 |
< |
* subclasses from AtomicReference to represent item. Uses Object, |
433 |
< |
* not E, to allow setting item to "this" after use, to avoid |
106 |
< |
* garbage retention. Similarly, setting the next field to this is |
107 |
< |
* used as sentinel that node is off list. |
108 |
< |
*/ |
109 |
< |
static final class Node<E> extends AtomicReference<Object> { |
110 |
< |
volatile Node<E> next; |
111 |
< |
volatile Thread waiter; // to control park/unpark |
112 |
< |
final boolean isData; |
430 |
> |
final boolean casItem(Object cmp, Object val) { |
431 |
> |
// assert cmp == null || cmp.getClass() != Node.class; |
432 |
> |
return UNSAFE.compareAndSwapObject(this, itemOffset, cmp, val); |
433 |
> |
} |
434 |
|
|
435 |
< |
Node(E item, boolean isData) { |
436 |
< |
super(item); |
435 |
> |
/** |
436 |
> |
* Constructs a new node. Uses relaxed write because item can |
437 |
> |
* only be seen after publication via casNext. |
438 |
> |
*/ |
439 |
> |
Node(Object item, boolean isData) { |
440 |
> |
UNSAFE.putObject(this, itemOffset, item); // relaxed write |
441 |
|
this.isData = isData; |
442 |
|
} |
443 |
|
|
444 |
< |
// Unsafe mechanics |
444 |
> |
/** |
445 |
> |
* Links node to itself to avoid garbage retention. Called |
446 |
> |
* only after CASing head field, so uses relaxed write. |
447 |
> |
*/ |
448 |
> |
final void forgetNext() { |
449 |
> |
UNSAFE.putObject(this, nextOffset, this); |
450 |
> |
} |
451 |
|
|
452 |
< |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
453 |
< |
private static final long nextOffset = |
454 |
< |
objectFieldOffset(UNSAFE, "next", Node.class); |
452 |
> |
/** |
453 |
> |
* Sets item to self and waiter to null, to avoid garbage |
454 |
> |
* retention after matching or cancelling. Uses relaxed writes |
455 |
> |
* because order is already constrained in the only calling |
456 |
> |
* contexts: item is forgotten only after volatile/atomic |
457 |
> |
* mechanics that extract items. Similarly, clearing waiter |
458 |
> |
* follows either CAS or return from park (if ever parked; |
459 |
> |
* else we don't care). |
460 |
> |
*/ |
461 |
> |
final void forgetContents() { |
462 |
> |
UNSAFE.putObject(this, itemOffset, this); |
463 |
> |
UNSAFE.putObject(this, waiterOffset, null); |
464 |
> |
} |
465 |
|
|
466 |
< |
final boolean casNext(Node<E> cmp, Node<E> val) { |
467 |
< |
return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val); |
466 |
> |
/** |
467 |
> |
* Returns true if this node has been matched, including the |
468 |
> |
* case of artificial matches due to cancellation. |
469 |
> |
*/ |
470 |
> |
final boolean isMatched() { |
471 |
> |
Object x = item; |
472 |
> |
return (x == this) || ((x == null) == isData); |
473 |
|
} |
474 |
|
|
475 |
< |
final void clearNext() { |
476 |
< |
UNSAFE.putOrderedObject(this, nextOffset, this); |
475 |
> |
/** |
476 |
> |
* Returns true if this is an unmatched request node. |
477 |
> |
*/ |
478 |
> |
final boolean isUnmatchedRequest() { |
479 |
> |
return !isData && item == null; |
480 |
|
} |
481 |
|
|
482 |
|
/** |
483 |
< |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
484 |
< |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
485 |
< |
* into a jdk. |
137 |
< |
* |
138 |
< |
* @return a sun.misc.Unsafe |
483 |
> |
* Returns true if a node with the given mode cannot be |
484 |
> |
* appended to this node because this node is unmatched and |
485 |
> |
* has opposite data mode. |
486 |
|
*/ |
487 |
< |
private static sun.misc.Unsafe getUnsafe() { |
488 |
< |
try { |
489 |
< |
return sun.misc.Unsafe.getUnsafe(); |
490 |
< |
} catch (SecurityException se) { |
491 |
< |
try { |
492 |
< |
return java.security.AccessController.doPrivileged |
493 |
< |
(new java.security |
494 |
< |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
495 |
< |
public sun.misc.Unsafe run() throws Exception { |
496 |
< |
java.lang.reflect.Field f = sun.misc |
497 |
< |
.Unsafe.class.getDeclaredField("theUnsafe"); |
498 |
< |
f.setAccessible(true); |
499 |
< |
return (sun.misc.Unsafe) f.get(null); |
500 |
< |
}}); |
501 |
< |
} catch (java.security.PrivilegedActionException e) { |
155 |
< |
throw new RuntimeException("Could not initialize intrinsics", |
156 |
< |
e.getCause()); |
157 |
< |
} |
487 |
> |
final boolean cannotPrecede(boolean haveData) { |
488 |
> |
boolean d = isData; |
489 |
> |
Object x; |
490 |
> |
return d != haveData && (x = item) != this && (x != null) == d; |
491 |
> |
} |
492 |
> |
|
493 |
> |
/** |
494 |
> |
* Tries to artificially match a data node -- used by remove. |
495 |
> |
*/ |
496 |
> |
final boolean tryMatchData() { |
497 |
> |
// assert isData; |
498 |
> |
Object x = item; |
499 |
> |
if (x != null && x != this && casItem(x, null)) { |
500 |
> |
LockSupport.unpark(waiter); |
501 |
> |
return true; |
502 |
|
} |
503 |
+ |
return false; |
504 |
|
} |
505 |
|
|
506 |
|
private static final long serialVersionUID = -3375979862319811754L; |
162 |
– |
} |
507 |
|
|
508 |
< |
/** |
509 |
< |
* Padded version of AtomicReference used for head, tail and |
510 |
< |
* cleanMe, to alleviate contention across threads CASing one vs |
511 |
< |
* the other. |
512 |
< |
*/ |
513 |
< |
static final class PaddedAtomicReference<T> extends AtomicReference<T> { |
514 |
< |
// enough padding for 64bytes with 4byte refs |
515 |
< |
Object p0, p1, p2, p3, p4, p5, p6, p7, p8, p9, pa, pb, pc, pd, pe; |
516 |
< |
PaddedAtomicReference(T r) { super(r); } |
517 |
< |
private static final long serialVersionUID = 8170090609809740854L; |
508 |
> |
// Unsafe mechanics |
509 |
> |
private static final sun.misc.Unsafe UNSAFE; |
510 |
> |
private static final long itemOffset; |
511 |
> |
private static final long nextOffset; |
512 |
> |
private static final long waiterOffset; |
513 |
> |
static { |
514 |
> |
try { |
515 |
> |
UNSAFE = getUnsafe(); |
516 |
> |
Class<?> k = Node.class; |
517 |
> |
itemOffset = UNSAFE.objectFieldOffset |
518 |
> |
(k.getDeclaredField("item")); |
519 |
> |
nextOffset = UNSAFE.objectFieldOffset |
520 |
> |
(k.getDeclaredField("next")); |
521 |
> |
waiterOffset = UNSAFE.objectFieldOffset |
522 |
> |
(k.getDeclaredField("waiter")); |
523 |
> |
} catch (Exception e) { |
524 |
> |
throw new Error(e); |
525 |
> |
} |
526 |
> |
} |
527 |
|
} |
528 |
|
|
529 |
+ |
/** head of the queue; null until first enqueue */ |
530 |
+ |
transient volatile Node head; |
531 |
|
|
532 |
< |
/** head of the queue */ |
533 |
< |
private transient final PaddedAtomicReference<Node<E>> head; |
532 |
> |
/** tail of the queue; null until first append */ |
533 |
> |
private transient volatile Node tail; |
534 |
|
|
535 |
< |
/** tail of the queue */ |
536 |
< |
private transient final PaddedAtomicReference<Node<E>> tail; |
535 |
> |
/** The number of apparent failures to unsplice removed nodes */ |
536 |
> |
private transient volatile int sweepVotes; |
537 |
|
|
538 |
< |
/** |
539 |
< |
* Reference to a cancelled node that might not yet have been |
540 |
< |
* unlinked from queue because it was the last inserted node |
541 |
< |
* when it cancelled. |
187 |
< |
*/ |
188 |
< |
private transient final PaddedAtomicReference<Node<E>> cleanMe; |
538 |
> |
// CAS methods for fields |
539 |
> |
private boolean casTail(Node cmp, Node val) { |
540 |
> |
return UNSAFE.compareAndSwapObject(this, tailOffset, cmp, val); |
541 |
> |
} |
542 |
|
|
543 |
< |
/** |
544 |
< |
* Tries to cas nh as new head; if successful, unlink |
545 |
< |
* old head's next node to avoid garbage retention. |
543 |
> |
private boolean casHead(Node cmp, Node val) { |
544 |
> |
return UNSAFE.compareAndSwapObject(this, headOffset, cmp, val); |
545 |
> |
} |
546 |
> |
|
547 |
> |
private boolean casSweepVotes(int cmp, int val) { |
548 |
> |
return UNSAFE.compareAndSwapInt(this, sweepVotesOffset, cmp, val); |
549 |
> |
} |
550 |
> |
|
551 |
> |
/* |
552 |
> |
* Possible values for "how" argument in xfer method. |
553 |
|
*/ |
554 |
< |
private boolean advanceHead(Node<E> h, Node<E> nh) { |
555 |
< |
if (h == head.get() && head.compareAndSet(h, nh)) { |
556 |
< |
h.clearNext(); // forget old next |
557 |
< |
return true; |
558 |
< |
} |
559 |
< |
return false; |
554 |
> |
private static final int NOW = 0; // for untimed poll, tryTransfer |
555 |
> |
private static final int ASYNC = 1; // for offer, put, add |
556 |
> |
private static final int SYNC = 2; // for transfer, take |
557 |
> |
private static final int TIMED = 3; // for timed poll, tryTransfer |
558 |
> |
|
559 |
> |
@SuppressWarnings("unchecked") |
560 |
> |
static <E> E cast(Object item) { |
561 |
> |
// assert item == null || item.getClass() != Node.class; |
562 |
> |
return (E) item; |
563 |
|
} |
564 |
|
|
565 |
|
/** |
566 |
< |
* Puts or takes an item. Used for most queue operations (except |
567 |
< |
* poll() and tryTransfer()). See the similar code in |
568 |
< |
* SynchronousQueue for detailed explanation. |
569 |
< |
* |
570 |
< |
* @param e the item or if null, signifies that this is a take |
571 |
< |
* @param mode the wait mode: NOWAIT, TIMEOUT, WAIT |
572 |
< |
* @param nanos timeout in nanosecs, used only if mode is TIMEOUT |
573 |
< |
* @return an item, or null on failure |
574 |
< |
*/ |
575 |
< |
private E xfer(E e, int mode, long nanos) { |
576 |
< |
boolean isData = (e != null); |
577 |
< |
Node<E> s = null; |
578 |
< |
final PaddedAtomicReference<Node<E>> head = this.head; |
216 |
< |
final PaddedAtomicReference<Node<E>> tail = this.tail; |
566 |
> |
* Implements all queuing methods. See above for explanation. |
567 |
> |
* |
568 |
> |
* @param e the item or null for take |
569 |
> |
* @param haveData true if this is a put, else a take |
570 |
> |
* @param how NOW, ASYNC, SYNC, or TIMED |
571 |
> |
* @param nanos timeout in nanosecs, used only if mode is TIMED |
572 |
> |
* @return an item if matched, else e |
573 |
> |
* @throws NullPointerException if haveData mode but e is null |
574 |
> |
*/ |
575 |
> |
private E xfer(E e, boolean haveData, int how, long nanos) { |
576 |
> |
if (haveData && (e == null)) |
577 |
> |
throw new NullPointerException(); |
578 |
> |
Node s = null; // the node to append, if needed |
579 |
|
|
580 |
< |
for (;;) { |
581 |
< |
Node<E> t = tail.get(); |
220 |
< |
Node<E> h = head.get(); |
580 |
> |
retry: |
581 |
> |
for (;;) { // restart on append race |
582 |
|
|
583 |
< |
if (t != null && (t == h || t.isData == isData)) { |
584 |
< |
if (s == null) |
585 |
< |
s = new Node<E>(e, isData); |
586 |
< |
Node<E> last = t.next; |
587 |
< |
if (last != null) { |
588 |
< |
if (t == tail.get()) |
589 |
< |
tail.compareAndSet(t, last); |
590 |
< |
} |
591 |
< |
else if (t.casNext(null, s)) { |
592 |
< |
tail.compareAndSet(t, s); |
593 |
< |
return awaitFulfill(t, s, e, mode, nanos); |
594 |
< |
} |
595 |
< |
} |
596 |
< |
|
597 |
< |
else if (h != null) { |
598 |
< |
Node<E> first = h.next; |
599 |
< |
if (t == tail.get() && first != null && |
600 |
< |
advanceHead(h, first)) { |
601 |
< |
Object x = first.get(); |
241 |
< |
if (x != first && first.compareAndSet(x, e)) { |
242 |
< |
LockSupport.unpark(first.waiter); |
243 |
< |
return isData ? e : (E) x; |
583 |
> |
for (Node h = head, p = h; p != null;) { // find & match first node |
584 |
> |
boolean isData = p.isData; |
585 |
> |
Object item = p.item; |
586 |
> |
if (item != p && (item != null) == isData) { // unmatched |
587 |
> |
if (isData == haveData) // can't match |
588 |
> |
break; |
589 |
> |
if (p.casItem(item, e)) { // match |
590 |
> |
for (Node q = p; q != h;) { |
591 |
> |
Node n = q.next; // update by 2 unless singleton |
592 |
> |
if (head == h && casHead(h, n == null ? q : n)) { |
593 |
> |
h.forgetNext(); |
594 |
> |
break; |
595 |
> |
} // advance and retry |
596 |
> |
if ((h = head) == null || |
597 |
> |
(q = h.next) == null || !q.isMatched()) |
598 |
> |
break; // unless slack < 2 |
599 |
> |
} |
600 |
> |
LockSupport.unpark(p.waiter); |
601 |
> |
return LinkedTransferQueue.<E>cast(item); |
602 |
|
} |
603 |
|
} |
604 |
+ |
Node n = p.next; |
605 |
+ |
p = (p != n) ? n : (h = head); // Use head if p offlist |
606 |
|
} |
607 |
+ |
|
608 |
+ |
if (how != NOW) { // No matches available |
609 |
+ |
if (s == null) |
610 |
+ |
s = new Node(e, haveData); |
611 |
+ |
Node pred = tryAppend(s, haveData); |
612 |
+ |
if (pred == null) |
613 |
+ |
continue retry; // lost race vs opposite mode |
614 |
+ |
if (how != ASYNC) |
615 |
+ |
return awaitMatch(s, pred, e, (how == TIMED), nanos); |
616 |
+ |
} |
617 |
+ |
return e; // not waiting |
618 |
|
} |
619 |
|
} |
620 |
|
|
250 |
– |
|
621 |
|
/** |
622 |
< |
* Version of xfer for poll() and tryTransfer, which |
623 |
< |
* simplifies control paths both here and in xfer. |
624 |
< |
*/ |
625 |
< |
private E fulfill(E e) { |
626 |
< |
boolean isData = (e != null); |
627 |
< |
final PaddedAtomicReference<Node<E>> head = this.head; |
628 |
< |
final PaddedAtomicReference<Node<E>> tail = this.tail; |
629 |
< |
|
630 |
< |
for (;;) { |
631 |
< |
Node<E> t = tail.get(); |
632 |
< |
Node<E> h = head.get(); |
633 |
< |
|
634 |
< |
if (t != null && (t == h || t.isData == isData)) { |
635 |
< |
Node<E> last = t.next; |
636 |
< |
if (t == tail.get()) { |
637 |
< |
if (last != null) |
638 |
< |
tail.compareAndSet(t, last); |
639 |
< |
else |
640 |
< |
return null; |
641 |
< |
} |
642 |
< |
} |
643 |
< |
else if (h != null) { |
644 |
< |
Node<E> first = h.next; |
645 |
< |
if (t == tail.get() && |
646 |
< |
first != null && |
647 |
< |
advanceHead(h, first)) { |
648 |
< |
Object x = first.get(); |
649 |
< |
if (x != first && first.compareAndSet(x, e)) { |
280 |
< |
LockSupport.unpark(first.waiter); |
281 |
< |
return isData ? e : (E) x; |
282 |
< |
} |
622 |
> |
* Tries to append node s as tail. |
623 |
> |
* |
624 |
> |
* @param s the node to append |
625 |
> |
* @param haveData true if appending in data mode |
626 |
> |
* @return null on failure due to losing race with append in |
627 |
> |
* different mode, else s's predecessor, or s itself if no |
628 |
> |
* predecessor |
629 |
> |
*/ |
630 |
> |
private Node tryAppend(Node s, boolean haveData) { |
631 |
> |
for (Node t = tail, p = t;;) { // move p to last node and append |
632 |
> |
Node n, u; // temps for reads of next & tail |
633 |
> |
if (p == null && (p = head) == null) { |
634 |
> |
if (casHead(null, s)) |
635 |
> |
return s; // initialize |
636 |
> |
} |
637 |
> |
else if (p.cannotPrecede(haveData)) |
638 |
> |
return null; // lost race vs opposite mode |
639 |
> |
else if ((n = p.next) != null) // not last; keep traversing |
640 |
> |
p = p != t && t != (u = tail) ? (t = u) : // stale tail |
641 |
> |
(p != n) ? n : null; // restart if off list |
642 |
> |
else if (!p.casNext(null, s)) |
643 |
> |
p = p.next; // re-read on CAS failure |
644 |
> |
else { |
645 |
> |
if (p != t) { // update if slack now >= 2 |
646 |
> |
while ((tail != t || !casTail(t, s)) && |
647 |
> |
(t = tail) != null && |
648 |
> |
(s = t.next) != null && // advance and retry |
649 |
> |
(s = s.next) != null && s != t); |
650 |
|
} |
651 |
+ |
return p; |
652 |
|
} |
653 |
|
} |
654 |
|
} |
655 |
|
|
656 |
|
/** |
657 |
< |
* Spins/blocks until node s is fulfilled or caller gives up, |
290 |
< |
* depending on wait mode. |
657 |
> |
* Spins/yields/blocks until node s is matched or caller gives up. |
658 |
|
* |
292 |
– |
* @param pred the predecessor of waiting node |
659 |
|
* @param s the waiting node |
660 |
+ |
* @param pred the predecessor of s, or s itself if it has no |
661 |
+ |
* predecessor, or null if unknown (the null case does not occur |
662 |
+ |
* in any current calls but may in possible future extensions) |
663 |
|
* @param e the comparison value for checking match |
664 |
< |
* @param mode mode |
665 |
< |
* @param nanos timeout value |
666 |
< |
* @return matched item, or null if cancelled |
667 |
< |
*/ |
668 |
< |
private E awaitFulfill(Node<E> pred, Node<E> s, E e, |
669 |
< |
int mode, long nanos) { |
301 |
< |
if (mode == NOWAIT) |
302 |
< |
return null; |
303 |
< |
|
304 |
< |
long lastTime = (mode == TIMEOUT) ? System.nanoTime() : 0; |
664 |
> |
* @param timed if true, wait only until timeout elapses |
665 |
> |
* @param nanos timeout in nanosecs, used only if timed is true |
666 |
> |
* @return matched item, or e if unmatched on interrupt or timeout |
667 |
> |
*/ |
668 |
> |
private E awaitMatch(Node s, Node pred, E e, boolean timed, long nanos) { |
669 |
> |
long lastTime = timed ? System.nanoTime() : 0L; |
670 |
|
Thread w = Thread.currentThread(); |
671 |
< |
int spins = -1; // set to desired spin count below |
671 |
> |
int spins = -1; // initialized after first item and cancel checks |
672 |
> |
ThreadLocalRandom randomYields = null; // bound if needed |
673 |
> |
|
674 |
|
for (;;) { |
675 |
< |
if (w.isInterrupted()) |
676 |
< |
s.compareAndSet(e, s); |
677 |
< |
Object x = s.get(); |
678 |
< |
if (x != e) { // Node was matched or cancelled |
679 |
< |
advanceHead(pred, s); // unlink if head |
680 |
< |
if (x == s) { // was cancelled |
681 |
< |
clean(pred, s); |
682 |
< |
return null; |
683 |
< |
} |
684 |
< |
else if (x != null) { |
685 |
< |
s.set(s); // avoid garbage retention |
686 |
< |
return (E) x; |
687 |
< |
} |
688 |
< |
else |
689 |
< |
return e; |
675 |
> |
Object item = s.item; |
676 |
> |
if (item != e) { // matched |
677 |
> |
// assert item != s; |
678 |
> |
s.forgetContents(); // avoid garbage |
679 |
> |
return LinkedTransferQueue.<E>cast(item); |
680 |
> |
} |
681 |
> |
if ((w.isInterrupted() || (timed && nanos <= 0)) && |
682 |
> |
s.casItem(e, s)) { // cancel |
683 |
> |
unsplice(pred, s); |
684 |
> |
return e; |
685 |
> |
} |
686 |
> |
|
687 |
> |
if (spins < 0) { // establish spins at/near front |
688 |
> |
if ((spins = spinsFor(pred, s.isData)) > 0) |
689 |
> |
randomYields = ThreadLocalRandom.current(); |
690 |
|
} |
691 |
< |
if (mode == TIMEOUT) { |
691 |
> |
else if (spins > 0) { // spin |
692 |
> |
--spins; |
693 |
> |
if (randomYields.nextInt(CHAINED_SPINS) == 0) |
694 |
> |
Thread.yield(); // occasionally yield |
695 |
> |
} |
696 |
> |
else if (s.waiter == null) { |
697 |
> |
s.waiter = w; // request unpark then recheck |
698 |
> |
} |
699 |
> |
else if (timed) { |
700 |
|
long now = System.nanoTime(); |
701 |
< |
nanos -= now - lastTime; |
701 |
> |
if ((nanos -= now - lastTime) > 0) |
702 |
> |
LockSupport.parkNanos(this, nanos); |
703 |
|
lastTime = now; |
328 |
– |
if (nanos <= 0) { |
329 |
– |
s.compareAndSet(e, s); // try to cancel |
330 |
– |
continue; |
331 |
– |
} |
332 |
– |
} |
333 |
– |
if (spins < 0) { |
334 |
– |
Node<E> h = head.get(); // only spin if at head |
335 |
– |
spins = ((h != null && h.next == s) ? |
336 |
– |
((mode == TIMEOUT) ? |
337 |
– |
maxTimedSpins : maxUntimedSpins) : 0); |
704 |
|
} |
705 |
< |
if (spins > 0) |
340 |
< |
--spins; |
341 |
< |
else if (s.waiter == null) |
342 |
< |
s.waiter = w; |
343 |
< |
else if (mode != TIMEOUT) { |
705 |
> |
else { |
706 |
|
LockSupport.park(this); |
345 |
– |
s.waiter = null; |
346 |
– |
spins = -1; |
347 |
– |
} |
348 |
– |
else if (nanos > spinForTimeoutThreshold) { |
349 |
– |
LockSupport.parkNanos(this, nanos); |
350 |
– |
s.waiter = null; |
351 |
– |
spins = -1; |
707 |
|
} |
708 |
|
} |
709 |
|
} |
710 |
|
|
711 |
|
/** |
712 |
< |
* Returns validated tail for use in cleaning methods. |
712 |
> |
* Returns spin/yield value for a node with given predecessor and |
713 |
> |
* data mode. See above for explanation. |
714 |
|
*/ |
715 |
< |
private Node<E> getValidatedTail() { |
716 |
< |
for (;;) { |
717 |
< |
Node<E> h = head.get(); |
718 |
< |
Node<E> first = h.next; |
719 |
< |
if (first != null && first.get() == first) { // help advance |
720 |
< |
advanceHead(h, first); |
721 |
< |
continue; |
722 |
< |
} |
367 |
< |
Node<E> t = tail.get(); |
368 |
< |
Node<E> last = t.next; |
369 |
< |
if (t == tail.get()) { |
370 |
< |
if (last != null) |
371 |
< |
tail.compareAndSet(t, last); // help advance |
372 |
< |
else |
373 |
< |
return t; |
374 |
< |
} |
715 |
> |
private static int spinsFor(Node pred, boolean haveData) { |
716 |
> |
if (MP && pred != null) { |
717 |
> |
if (pred.isData != haveData) // phase change |
718 |
> |
return FRONT_SPINS + CHAINED_SPINS; |
719 |
> |
if (pred.isMatched()) // probably at front |
720 |
> |
return FRONT_SPINS; |
721 |
> |
if (pred.waiter == null) // pred apparently spinning |
722 |
> |
return CHAINED_SPINS; |
723 |
|
} |
724 |
+ |
return 0; |
725 |
|
} |
726 |
|
|
727 |
+ |
/* -------------- Traversal methods -------------- */ |
728 |
+ |
|
729 |
|
/** |
730 |
< |
* Gets rid of cancelled node s with original predecessor pred. |
731 |
< |
* |
732 |
< |
* @param pred predecessor of cancelled node |
382 |
< |
* @param s the cancelled node |
730 |
> |
* Returns the successor of p, or the head node if p.next has been |
731 |
> |
* linked to self, which will only be true if traversing with a |
732 |
> |
* stale pointer that is now off the list. |
733 |
|
*/ |
734 |
< |
private void clean(Node<E> pred, Node<E> s) { |
735 |
< |
Thread w = s.waiter; |
736 |
< |
if (w != null) { // Wake up thread |
737 |
< |
s.waiter = null; |
738 |
< |
if (w != Thread.currentThread()) |
739 |
< |
LockSupport.unpark(w); |
734 |
> |
final Node succ(Node p) { |
735 |
> |
Node next = p.next; |
736 |
> |
return (p == next) ? head : next; |
737 |
> |
} |
738 |
> |
|
739 |
> |
/** |
740 |
> |
* Returns the first unmatched node of the given mode, or null if |
741 |
> |
* none. Used by methods isEmpty, hasWaitingConsumer. |
742 |
> |
*/ |
743 |
> |
private Node firstOfMode(boolean isData) { |
744 |
> |
for (Node p = head; p != null; p = succ(p)) { |
745 |
> |
if (!p.isMatched()) |
746 |
> |
return (p.isData == isData) ? p : null; |
747 |
|
} |
748 |
+ |
return null; |
749 |
+ |
} |
750 |
|
|
751 |
< |
if (pred == null) |
752 |
< |
return; |
751 |
> |
/** |
752 |
> |
* Returns the item in the first unmatched node with isData; or |
753 |
> |
* null if none. Used by peek. |
754 |
> |
*/ |
755 |
> |
private E firstDataItem() { |
756 |
> |
for (Node p = head; p != null; p = succ(p)) { |
757 |
> |
Object item = p.item; |
758 |
> |
if (p.isData) { |
759 |
> |
if (item != null && item != p) |
760 |
> |
return LinkedTransferQueue.<E>cast(item); |
761 |
> |
} |
762 |
> |
else if (item == null) |
763 |
> |
return null; |
764 |
> |
} |
765 |
> |
return null; |
766 |
> |
} |
767 |
|
|
768 |
< |
/* |
769 |
< |
* At any given time, exactly one node on list cannot be |
770 |
< |
* deleted -- the last inserted node. To accommodate this, if |
771 |
< |
* we cannot delete s, we save its predecessor as "cleanMe", |
772 |
< |
* processing the previously saved version first. At least one |
773 |
< |
* of node s or the node previously saved can always be |
774 |
< |
* processed, so this always terminates. |
768 |
> |
/** |
769 |
> |
* Traverses and counts unmatched nodes of the given mode. |
770 |
> |
* Used by methods size and getWaitingConsumerCount. |
771 |
> |
*/ |
772 |
> |
private int countOfMode(boolean data) { |
773 |
> |
int count = 0; |
774 |
> |
for (Node p = head; p != null; ) { |
775 |
> |
if (!p.isMatched()) { |
776 |
> |
if (p.isData != data) |
777 |
> |
return 0; |
778 |
> |
if (++count == Integer.MAX_VALUE) // saturated |
779 |
> |
break; |
780 |
> |
} |
781 |
> |
Node n = p.next; |
782 |
> |
if (n != p) |
783 |
> |
p = n; |
784 |
> |
else { |
785 |
> |
count = 0; |
786 |
> |
p = head; |
787 |
> |
} |
788 |
> |
} |
789 |
> |
return count; |
790 |
> |
} |
791 |
> |
|
792 |
> |
final class Itr implements Iterator<E> { |
793 |
> |
private Node nextNode; // next node to return item for |
794 |
> |
private E nextItem; // the corresponding item |
795 |
> |
private Node lastRet; // last returned node, to support remove |
796 |
> |
private Node lastPred; // predecessor to unlink lastRet |
797 |
> |
|
798 |
> |
/** |
799 |
> |
* Moves to next node after prev, or first node if prev null. |
800 |
|
*/ |
801 |
< |
while (pred.next == s) { |
802 |
< |
Node<E> oldpred = reclean(); // First, help get rid of cleanMe |
803 |
< |
Node<E> t = getValidatedTail(); |
804 |
< |
if (s != t) { // If not tail, try to unsplice |
805 |
< |
Node<E> sn = s.next; // s.next == s means s already off list |
806 |
< |
if (sn == s || pred.casNext(s, sn)) |
801 |
> |
private void advance(Node prev) { |
802 |
> |
/* |
803 |
> |
* To track and avoid buildup of deleted nodes in the face |
804 |
> |
* of calls to both Queue.remove and Itr.remove, we must |
805 |
> |
* include variants of unsplice and sweep upon each |
806 |
> |
* advance: Upon Itr.remove, we may need to catch up links |
807 |
> |
* from lastPred, and upon other removes, we might need to |
808 |
> |
* skip ahead from stale nodes and unsplice deleted ones |
809 |
> |
* found while advancing. |
810 |
> |
*/ |
811 |
> |
|
812 |
> |
Node r, b; // reset lastPred upon possible deletion of lastRet |
813 |
> |
if ((r = lastRet) != null && !r.isMatched()) |
814 |
> |
lastPred = r; // next lastPred is old lastRet |
815 |
> |
else if ((b = lastPred) == null || b.isMatched()) |
816 |
> |
lastPred = null; // at start of list |
817 |
> |
else { |
818 |
> |
Node s, n; // help with removal of lastPred.next |
819 |
> |
while ((s = b.next) != null && |
820 |
> |
s != b && s.isMatched() && |
821 |
> |
(n = s.next) != null && n != s) |
822 |
> |
b.casNext(s, n); |
823 |
> |
} |
824 |
> |
|
825 |
> |
this.lastRet = prev; |
826 |
> |
|
827 |
> |
for (Node p = prev, s, n;;) { |
828 |
> |
s = (p == null) ? head : p.next; |
829 |
> |
if (s == null) |
830 |
> |
break; |
831 |
> |
else if (s == p) { |
832 |
> |
p = null; |
833 |
> |
continue; |
834 |
> |
} |
835 |
> |
Object item = s.item; |
836 |
> |
if (s.isData) { |
837 |
> |
if (item != null && item != s) { |
838 |
> |
nextItem = LinkedTransferQueue.<E>cast(item); |
839 |
> |
nextNode = s; |
840 |
> |
return; |
841 |
> |
} |
842 |
> |
} |
843 |
> |
else if (item == null) |
844 |
> |
break; |
845 |
> |
// assert s.isMatched(); |
846 |
> |
if (p == null) |
847 |
> |
p = s; |
848 |
> |
else if ((n = s.next) == null) |
849 |
|
break; |
850 |
+ |
else if (s == n) |
851 |
+ |
p = null; |
852 |
+ |
else |
853 |
+ |
p.casNext(s, n); |
854 |
|
} |
855 |
< |
else if (oldpred == pred || // Already saved |
856 |
< |
(oldpred == null && cleanMe.compareAndSet(null, pred))) |
857 |
< |
break; // Postpone cleaning |
855 |
> |
nextNode = null; |
856 |
> |
nextItem = null; |
857 |
> |
} |
858 |
> |
|
859 |
> |
Itr() { |
860 |
> |
advance(null); |
861 |
> |
} |
862 |
> |
|
863 |
> |
public final boolean hasNext() { |
864 |
> |
return nextNode != null; |
865 |
> |
} |
866 |
> |
|
867 |
> |
public final E next() { |
868 |
> |
Node p = nextNode; |
869 |
> |
if (p == null) throw new NoSuchElementException(); |
870 |
> |
E e = nextItem; |
871 |
> |
advance(p); |
872 |
> |
return e; |
873 |
> |
} |
874 |
> |
|
875 |
> |
public final void remove() { |
876 |
> |
final Node lastRet = this.lastRet; |
877 |
> |
if (lastRet == null) |
878 |
> |
throw new IllegalStateException(); |
879 |
> |
this.lastRet = null; |
880 |
> |
if (lastRet.tryMatchData()) |
881 |
> |
unsplice(lastPred, lastRet); |
882 |
|
} |
883 |
|
} |
884 |
|
|
885 |
+ |
/* -------------- Removal methods -------------- */ |
886 |
+ |
|
887 |
|
/** |
888 |
< |
* Tries to unsplice the cancelled node held in cleanMe that was |
889 |
< |
* previously uncleanable because it was at tail. |
888 |
> |
* Unsplices (now or later) the given deleted/cancelled node with |
889 |
> |
* the given predecessor. |
890 |
|
* |
891 |
< |
* @return current cleanMe node (or null) |
891 |
> |
* @param pred a node that was at one time known to be the |
892 |
> |
* predecessor of s, or null or s itself if s is/was at head |
893 |
> |
* @param s the node to be unspliced |
894 |
|
*/ |
895 |
< |
private Node<E> reclean() { |
895 |
> |
final void unsplice(Node pred, Node s) { |
896 |
> |
s.forgetContents(); // forget unneeded fields |
897 |
|
/* |
898 |
< |
* cleanMe is, or at one time was, predecessor of cancelled |
899 |
< |
* node s that was the tail so could not be unspliced. If s |
900 |
< |
* is no longer the tail, try to unsplice if necessary and |
901 |
< |
* make cleanMe slot available. This differs from similar |
902 |
< |
* code in clean() because we must check that pred still |
430 |
< |
* points to a cancelled node that must be unspliced -- if |
431 |
< |
* not, we can (must) clear cleanMe without unsplicing. |
432 |
< |
* This can loop only due to contention on casNext or |
433 |
< |
* clearing cleanMe. |
898 |
> |
* See above for rationale. Briefly: if pred still points to |
899 |
> |
* s, try to unlink s. If s cannot be unlinked, because it is |
900 |
> |
* trailing node or pred might be unlinked, and neither pred |
901 |
> |
* nor s are head or offlist, add to sweepVotes, and if enough |
902 |
> |
* votes have accumulated, sweep. |
903 |
|
*/ |
904 |
< |
Node<E> pred; |
905 |
< |
while ((pred = cleanMe.get()) != null) { |
906 |
< |
Node<E> t = getValidatedTail(); |
907 |
< |
Node<E> s = pred.next; |
908 |
< |
if (s != t) { |
909 |
< |
Node<E> sn; |
910 |
< |
if (s == null || s == pred || s.get() != s || |
911 |
< |
(sn = s.next) == s || pred.casNext(s, sn)) |
912 |
< |
cleanMe.compareAndSet(pred, null); |
904 |
> |
if (pred != null && pred != s && pred.next == s) { |
905 |
> |
Node n = s.next; |
906 |
> |
if (n == null || |
907 |
> |
(n != s && pred.casNext(s, n) && pred.isMatched())) { |
908 |
> |
for (;;) { // check if at, or could be, head |
909 |
> |
Node h = head; |
910 |
> |
if (h == pred || h == s || h == null) |
911 |
> |
return; // at head or list empty |
912 |
> |
if (!h.isMatched()) |
913 |
> |
break; |
914 |
> |
Node hn = h.next; |
915 |
> |
if (hn == null) |
916 |
> |
return; // now empty |
917 |
> |
if (hn != h && casHead(h, hn)) |
918 |
> |
h.forgetNext(); // advance head |
919 |
> |
} |
920 |
> |
if (pred.next != pred && s.next != s) { // recheck if offlist |
921 |
> |
for (;;) { // sweep now if enough votes |
922 |
> |
int v = sweepVotes; |
923 |
> |
if (v < SWEEP_THRESHOLD) { |
924 |
> |
if (casSweepVotes(v, v + 1)) |
925 |
> |
break; |
926 |
> |
} |
927 |
> |
else if (casSweepVotes(v, 0)) { |
928 |
> |
sweep(); |
929 |
> |
break; |
930 |
> |
} |
931 |
> |
} |
932 |
> |
} |
933 |
|
} |
934 |
< |
else // s is still tail; cannot clean |
934 |
> |
} |
935 |
> |
} |
936 |
> |
|
937 |
> |
/** |
938 |
> |
* Unlinks matched (typically cancelled) nodes encountered in a |
939 |
> |
* traversal from head. |
940 |
> |
*/ |
941 |
> |
private void sweep() { |
942 |
> |
for (Node p = head, s, n; p != null && (s = p.next) != null; ) { |
943 |
> |
if (!s.isMatched()) |
944 |
> |
// Unmatched nodes are never self-linked |
945 |
> |
p = s; |
946 |
> |
else if ((n = s.next) == null) // trailing node is pinned |
947 |
|
break; |
948 |
+ |
else if (s == n) // stale |
949 |
+ |
// No need to also check for p == s, since that implies s == n |
950 |
+ |
p = head; |
951 |
+ |
else |
952 |
+ |
p.casNext(s, n); |
953 |
|
} |
448 |
– |
return pred; |
954 |
|
} |
955 |
|
|
956 |
|
/** |
957 |
+ |
* Main implementation of remove(Object) |
958 |
+ |
*/ |
959 |
+ |
private boolean findAndRemove(Object e) { |
960 |
+ |
if (e != null) { |
961 |
+ |
for (Node pred = null, p = head; p != null; ) { |
962 |
+ |
Object item = p.item; |
963 |
+ |
if (p.isData) { |
964 |
+ |
if (item != null && item != p && e.equals(item) && |
965 |
+ |
p.tryMatchData()) { |
966 |
+ |
unsplice(pred, p); |
967 |
+ |
return true; |
968 |
+ |
} |
969 |
+ |
} |
970 |
+ |
else if (item == null) |
971 |
+ |
break; |
972 |
+ |
pred = p; |
973 |
+ |
if ((p = p.next) == pred) { // stale |
974 |
+ |
pred = null; |
975 |
+ |
p = head; |
976 |
+ |
} |
977 |
+ |
} |
978 |
+ |
} |
979 |
+ |
return false; |
980 |
+ |
} |
981 |
+ |
|
982 |
+ |
|
983 |
+ |
/** |
984 |
|
* Creates an initially empty {@code LinkedTransferQueue}. |
985 |
|
*/ |
986 |
|
public LinkedTransferQueue() { |
455 |
– |
Node<E> dummy = new Node<E>(null, false); |
456 |
– |
head = new PaddedAtomicReference<Node<E>>(dummy); |
457 |
– |
tail = new PaddedAtomicReference<Node<E>>(dummy); |
458 |
– |
cleanMe = new PaddedAtomicReference<Node<E>>(null); |
987 |
|
} |
988 |
|
|
989 |
|
/** |
1007 |
|
* @throws NullPointerException if the specified element is null |
1008 |
|
*/ |
1009 |
|
public void put(E e) { |
1010 |
< |
offer(e); |
1010 |
> |
xfer(e, true, ASYNC, 0); |
1011 |
|
} |
1012 |
|
|
1013 |
|
/** |
1016 |
|
* return {@code false}. |
1017 |
|
* |
1018 |
|
* @return {@code true} (as specified by |
1019 |
< |
* {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer}) |
1019 |
> |
* {@link java.util.concurrent.BlockingQueue#offer(Object,long,TimeUnit) |
1020 |
> |
* BlockingQueue.offer}) |
1021 |
|
* @throws NullPointerException if the specified element is null |
1022 |
|
*/ |
1023 |
|
public boolean offer(E e, long timeout, TimeUnit unit) { |
1024 |
< |
return offer(e); |
1024 |
> |
xfer(e, true, ASYNC, 0); |
1025 |
> |
return true; |
1026 |
|
} |
1027 |
|
|
1028 |
|
/** |
1029 |
|
* Inserts the specified element at the tail of this queue. |
1030 |
|
* As the queue is unbounded, this method will never return {@code false}. |
1031 |
|
* |
1032 |
< |
* @return {@code true} (as specified by |
503 |
< |
* {@link BlockingQueue#offer(Object) BlockingQueue.offer}) |
1032 |
> |
* @return {@code true} (as specified by {@link Queue#offer}) |
1033 |
|
* @throws NullPointerException if the specified element is null |
1034 |
|
*/ |
1035 |
|
public boolean offer(E e) { |
1036 |
< |
if (e == null) throw new NullPointerException(); |
508 |
< |
xfer(e, NOWAIT, 0); |
1036 |
> |
xfer(e, true, ASYNC, 0); |
1037 |
|
return true; |
1038 |
|
} |
1039 |
|
|
1046 |
|
* @throws NullPointerException if the specified element is null |
1047 |
|
*/ |
1048 |
|
public boolean add(E e) { |
1049 |
< |
return offer(e); |
1049 |
> |
xfer(e, true, ASYNC, 0); |
1050 |
> |
return true; |
1051 |
|
} |
1052 |
|
|
1053 |
|
/** |
1061 |
|
* @throws NullPointerException if the specified element is null |
1062 |
|
*/ |
1063 |
|
public boolean tryTransfer(E e) { |
1064 |
< |
if (e == null) throw new NullPointerException(); |
536 |
< |
return fulfill(e) != null; |
1064 |
> |
return xfer(e, true, NOW, 0) == null; |
1065 |
|
} |
1066 |
|
|
1067 |
|
/** |
1076 |
|
* @throws NullPointerException if the specified element is null |
1077 |
|
*/ |
1078 |
|
public void transfer(E e) throws InterruptedException { |
1079 |
< |
if (e == null) throw new NullPointerException(); |
1080 |
< |
if (xfer(e, WAIT, 0) == null) { |
553 |
< |
Thread.interrupted(); |
1079 |
> |
if (xfer(e, true, SYNC, 0) != null) { |
1080 |
> |
Thread.interrupted(); // failure possible only due to interrupt |
1081 |
|
throw new InterruptedException(); |
1082 |
|
} |
1083 |
|
} |
1098 |
|
*/ |
1099 |
|
public boolean tryTransfer(E e, long timeout, TimeUnit unit) |
1100 |
|
throws InterruptedException { |
1101 |
< |
if (e == null) throw new NullPointerException(); |
575 |
< |
if (xfer(e, TIMEOUT, unit.toNanos(timeout)) != null) |
1101 |
> |
if (xfer(e, true, TIMED, unit.toNanos(timeout)) == null) |
1102 |
|
return true; |
1103 |
|
if (!Thread.interrupted()) |
1104 |
|
return false; |
1106 |
|
} |
1107 |
|
|
1108 |
|
public E take() throws InterruptedException { |
1109 |
< |
E e = xfer(null, WAIT, 0); |
1109 |
> |
E e = xfer(null, false, SYNC, 0); |
1110 |
|
if (e != null) |
1111 |
|
return e; |
1112 |
|
Thread.interrupted(); |
1114 |
|
} |
1115 |
|
|
1116 |
|
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
1117 |
< |
E e = xfer(null, TIMEOUT, unit.toNanos(timeout)); |
1117 |
> |
E e = xfer(null, false, TIMED, unit.toNanos(timeout)); |
1118 |
|
if (e != null || !Thread.interrupted()) |
1119 |
|
return e; |
1120 |
|
throw new InterruptedException(); |
1121 |
|
} |
1122 |
|
|
1123 |
|
public E poll() { |
1124 |
< |
return fulfill(null); |
1124 |
> |
return xfer(null, false, NOW, 0); |
1125 |
|
} |
1126 |
|
|
1127 |
|
/** |
1134 |
|
if (c == this) |
1135 |
|
throw new IllegalArgumentException(); |
1136 |
|
int n = 0; |
1137 |
< |
E e; |
612 |
< |
while ( (e = poll()) != null) { |
1137 |
> |
for (E e; (e = poll()) != null;) { |
1138 |
|
c.add(e); |
1139 |
|
++n; |
1140 |
|
} |
1151 |
|
if (c == this) |
1152 |
|
throw new IllegalArgumentException(); |
1153 |
|
int n = 0; |
1154 |
< |
E e; |
630 |
< |
while (n < maxElements && (e = poll()) != null) { |
1154 |
> |
for (E e; n < maxElements && (e = poll()) != null;) { |
1155 |
|
c.add(e); |
1156 |
|
++n; |
1157 |
|
} |
1158 |
|
return n; |
1159 |
|
} |
1160 |
|
|
637 |
– |
// Traversal-based methods |
638 |
– |
|
639 |
– |
/** |
640 |
– |
* Returns head after performing any outstanding helping steps. |
641 |
– |
*/ |
642 |
– |
private Node<E> traversalHead() { |
643 |
– |
for (;;) { |
644 |
– |
Node<E> t = tail.get(); |
645 |
– |
Node<E> h = head.get(); |
646 |
– |
if (h != null && t != null) { |
647 |
– |
Node<E> last = t.next; |
648 |
– |
Node<E> first = h.next; |
649 |
– |
if (t == tail.get()) { |
650 |
– |
if (last != null) |
651 |
– |
tail.compareAndSet(t, last); |
652 |
– |
else if (first != null) { |
653 |
– |
Object x = first.get(); |
654 |
– |
if (x == first) |
655 |
– |
advanceHead(h, first); |
656 |
– |
else |
657 |
– |
return h; |
658 |
– |
} |
659 |
– |
else |
660 |
– |
return h; |
661 |
– |
} |
662 |
– |
} |
663 |
– |
reclean(); |
664 |
– |
} |
665 |
– |
} |
666 |
– |
|
1161 |
|
/** |
1162 |
< |
* Returns an iterator over the elements in this queue in proper |
1163 |
< |
* sequence, from head to tail. |
1162 |
> |
* Returns an iterator over the elements in this queue in proper sequence. |
1163 |
> |
* The elements will be returned in order from first (head) to last (tail). |
1164 |
|
* |
1165 |
|
* <p>The returned iterator is a "weakly consistent" iterator that |
1166 |
< |
* will never throw |
1167 |
< |
* {@link ConcurrentModificationException ConcurrentModificationException}, |
1168 |
< |
* and guarantees to traverse elements as they existed upon |
1169 |
< |
* construction of the iterator, and may (but is not guaranteed |
1170 |
< |
* to) reflect any modifications subsequent to construction. |
1166 |
> |
* will never throw {@link java.util.ConcurrentModificationException |
1167 |
> |
* ConcurrentModificationException}, and guarantees to traverse |
1168 |
> |
* elements as they existed upon construction of the iterator, and |
1169 |
> |
* may (but is not guaranteed to) reflect any modifications |
1170 |
> |
* subsequent to construction. |
1171 |
|
* |
1172 |
|
* @return an iterator over the elements in this queue in proper sequence |
1173 |
|
*/ |
1175 |
|
return new Itr(); |
1176 |
|
} |
1177 |
|
|
684 |
– |
/** |
685 |
– |
* Iterators. Basic strategy is to traverse list, treating |
686 |
– |
* non-data (i.e., request) nodes as terminating list. |
687 |
– |
* Once a valid data node is found, the item is cached |
688 |
– |
* so that the next call to next() will return it even |
689 |
– |
* if subsequently removed. |
690 |
– |
*/ |
691 |
– |
class Itr implements Iterator<E> { |
692 |
– |
Node<E> next; // node to return next |
693 |
– |
Node<E> pnext; // predecessor of next |
694 |
– |
Node<E> curr; // last returned node, for remove() |
695 |
– |
Node<E> pcurr; // predecessor of curr, for remove() |
696 |
– |
E nextItem; // Cache of next item, once committed to in next |
697 |
– |
|
698 |
– |
Itr() { |
699 |
– |
advance(); |
700 |
– |
} |
701 |
– |
|
702 |
– |
/** |
703 |
– |
* Moves to next valid node and returns item to return for |
704 |
– |
* next(), or null if no such. |
705 |
– |
*/ |
706 |
– |
private E advance() { |
707 |
– |
pcurr = pnext; |
708 |
– |
curr = next; |
709 |
– |
E item = nextItem; |
710 |
– |
|
711 |
– |
for (;;) { |
712 |
– |
pnext = (next == null) ? traversalHead() : next; |
713 |
– |
next = pnext.next; |
714 |
– |
if (next == pnext) { |
715 |
– |
next = null; |
716 |
– |
continue; // restart |
717 |
– |
} |
718 |
– |
if (next == null) |
719 |
– |
break; |
720 |
– |
Object x = next.get(); |
721 |
– |
if (x != null && x != next) { |
722 |
– |
nextItem = (E) x; |
723 |
– |
break; |
724 |
– |
} |
725 |
– |
} |
726 |
– |
return item; |
727 |
– |
} |
728 |
– |
|
729 |
– |
public boolean hasNext() { |
730 |
– |
return next != null; |
731 |
– |
} |
732 |
– |
|
733 |
– |
public E next() { |
734 |
– |
if (next == null) |
735 |
– |
throw new NoSuchElementException(); |
736 |
– |
return advance(); |
737 |
– |
} |
738 |
– |
|
739 |
– |
public void remove() { |
740 |
– |
Node<E> p = curr; |
741 |
– |
if (p == null) |
742 |
– |
throw new IllegalStateException(); |
743 |
– |
Object x = p.get(); |
744 |
– |
if (x != null && x != p && p.compareAndSet(x, p)) |
745 |
– |
clean(pcurr, p); |
746 |
– |
} |
747 |
– |
} |
748 |
– |
|
1178 |
|
public E peek() { |
1179 |
< |
for (;;) { |
751 |
< |
Node<E> h = traversalHead(); |
752 |
< |
Node<E> p = h.next; |
753 |
< |
if (p == null) |
754 |
< |
return null; |
755 |
< |
Object x = p.get(); |
756 |
< |
if (p != x) { |
757 |
< |
if (!p.isData) |
758 |
< |
return null; |
759 |
< |
if (x != null) |
760 |
< |
return (E) x; |
761 |
< |
} |
762 |
< |
} |
1179 |
> |
return firstDataItem(); |
1180 |
|
} |
1181 |
|
|
1182 |
|
/** |
1185 |
|
* @return {@code true} if this queue contains no elements |
1186 |
|
*/ |
1187 |
|
public boolean isEmpty() { |
1188 |
< |
for (;;) { |
1189 |
< |
Node<E> h = traversalHead(); |
1190 |
< |
Node<E> p = h.next; |
774 |
< |
if (p == null) |
775 |
< |
return true; |
776 |
< |
Object x = p.get(); |
777 |
< |
if (p != x) { |
778 |
< |
if (!p.isData) |
779 |
< |
return true; |
780 |
< |
if (x != null) |
781 |
< |
return false; |
782 |
< |
} |
1188 |
> |
for (Node p = head; p != null; p = succ(p)) { |
1189 |
> |
if (!p.isMatched()) |
1190 |
> |
return !p.isData; |
1191 |
|
} |
1192 |
+ |
return true; |
1193 |
|
} |
1194 |
|
|
1195 |
|
public boolean hasWaitingConsumer() { |
1196 |
< |
for (;;) { |
788 |
< |
Node<E> h = traversalHead(); |
789 |
< |
Node<E> p = h.next; |
790 |
< |
if (p == null) |
791 |
< |
return false; |
792 |
< |
Object x = p.get(); |
793 |
< |
if (p != x) |
794 |
< |
return !p.isData; |
795 |
< |
} |
1196 |
> |
return firstOfMode(false) != null; |
1197 |
|
} |
1198 |
|
|
1199 |
|
/** |
1209 |
|
* @return the number of elements in this queue |
1210 |
|
*/ |
1211 |
|
public int size() { |
1212 |
< |
for (;;) { |
812 |
< |
int count = 0; |
813 |
< |
Node<E> pred = traversalHead(); |
814 |
< |
for (;;) { |
815 |
< |
Node<E> q = pred.next; |
816 |
< |
if (q == pred) // restart |
817 |
< |
break; |
818 |
< |
if (q == null || !q.isData) |
819 |
< |
return count; |
820 |
< |
Object x = q.get(); |
821 |
< |
if (x != null && x != q) { |
822 |
< |
if (++count == Integer.MAX_VALUE) // saturated |
823 |
< |
return count; |
824 |
< |
} |
825 |
< |
pred = q; |
826 |
< |
} |
827 |
< |
} |
1212 |
> |
return countOfMode(true); |
1213 |
|
} |
1214 |
|
|
1215 |
|
public int getWaitingConsumerCount() { |
1216 |
< |
// converse of size -- count valid non-data nodes |
832 |
< |
for (;;) { |
833 |
< |
int count = 0; |
834 |
< |
Node<E> pred = traversalHead(); |
835 |
< |
for (;;) { |
836 |
< |
Node<E> q = pred.next; |
837 |
< |
if (q == pred) // restart |
838 |
< |
break; |
839 |
< |
if (q == null || q.isData) |
840 |
< |
return count; |
841 |
< |
Object x = q.get(); |
842 |
< |
if (x == null) { |
843 |
< |
if (++count == Integer.MAX_VALUE) // saturated |
844 |
< |
return count; |
845 |
< |
} |
846 |
< |
pred = q; |
847 |
< |
} |
848 |
< |
} |
1216 |
> |
return countOfMode(false); |
1217 |
|
} |
1218 |
|
|
1219 |
|
/** |
1228 |
|
* @return {@code true} if this queue changed as a result of the call |
1229 |
|
*/ |
1230 |
|
public boolean remove(Object o) { |
1231 |
< |
if (o == null) |
1232 |
< |
return false; |
1233 |
< |
for (;;) { |
1234 |
< |
Node<E> pred = traversalHead(); |
1235 |
< |
for (;;) { |
1236 |
< |
Node<E> q = pred.next; |
1237 |
< |
if (q == pred) // restart |
1238 |
< |
break; |
1239 |
< |
if (q == null || !q.isData) |
1240 |
< |
return false; |
1241 |
< |
Object x = q.get(); |
1242 |
< |
if (x != null && x != q && o.equals(x) && |
1243 |
< |
q.compareAndSet(x, q)) { |
1244 |
< |
clean(pred, q); |
1231 |
> |
return findAndRemove(o); |
1232 |
> |
} |
1233 |
> |
|
1234 |
> |
/** |
1235 |
> |
* Returns {@code true} if this queue contains the specified element. |
1236 |
> |
* More formally, returns {@code true} if and only if this queue contains |
1237 |
> |
* at least one element {@code e} such that {@code o.equals(e)}. |
1238 |
> |
* |
1239 |
> |
* @param o object to be checked for containment in this queue |
1240 |
> |
* @return {@code true} if this queue contains the specified element |
1241 |
> |
*/ |
1242 |
> |
public boolean contains(Object o) { |
1243 |
> |
if (o == null) return false; |
1244 |
> |
for (Node p = head; p != null; p = succ(p)) { |
1245 |
> |
Object item = p.item; |
1246 |
> |
if (p.isData) { |
1247 |
> |
if (item != null && item != p && o.equals(item)) |
1248 |
|
return true; |
878 |
– |
} |
879 |
– |
pred = q; |
1249 |
|
} |
1250 |
+ |
else if (item == null) |
1251 |
+ |
break; |
1252 |
|
} |
1253 |
+ |
return false; |
1254 |
|
} |
1255 |
|
|
1256 |
|
/** |
1258 |
|
* {@code LinkedTransferQueue} is not capacity constrained. |
1259 |
|
* |
1260 |
|
* @return {@code Integer.MAX_VALUE} (as specified by |
1261 |
< |
* {@link BlockingQueue#remainingCapacity()}) |
1261 |
> |
* {@link java.util.concurrent.BlockingQueue#remainingCapacity() |
1262 |
> |
* BlockingQueue.remainingCapacity}) |
1263 |
|
*/ |
1264 |
|
public int remainingCapacity() { |
1265 |
|
return Integer.MAX_VALUE; |
1266 |
|
} |
1267 |
|
|
1268 |
|
/** |
1269 |
< |
* Save the state to a stream (that is, serialize it). |
1269 |
> |
* Saves the state to a stream (that is, serializes it). |
1270 |
|
* |
1271 |
|
* @serialData All of the elements (each an {@code E}) in |
1272 |
|
* the proper order, followed by a null |
1282 |
|
} |
1283 |
|
|
1284 |
|
/** |
1285 |
< |
* Reconstitute the Queue instance from a stream (that is, |
1286 |
< |
* deserialize it). |
1285 |
> |
* Reconstitutes the Queue instance from a stream (that is, |
1286 |
> |
* deserializes it). |
1287 |
|
* |
1288 |
|
* @param s the stream |
1289 |
|
*/ |
1290 |
|
private void readObject(java.io.ObjectInputStream s) |
1291 |
|
throws java.io.IOException, ClassNotFoundException { |
1292 |
|
s.defaultReadObject(); |
920 |
– |
resetHeadAndTail(); |
1293 |
|
for (;;) { |
1294 |
< |
@SuppressWarnings("unchecked") E item = (E) s.readObject(); |
1294 |
> |
@SuppressWarnings("unchecked") |
1295 |
> |
E item = (E) s.readObject(); |
1296 |
|
if (item == null) |
1297 |
|
break; |
1298 |
|
else |
1300 |
|
} |
1301 |
|
} |
1302 |
|
|
930 |
– |
// Support for resetting head/tail while deserializing |
931 |
– |
private void resetHeadAndTail() { |
932 |
– |
Node<E> dummy = new Node<E>(null, false); |
933 |
– |
UNSAFE.putObjectVolatile(this, headOffset, |
934 |
– |
new PaddedAtomicReference<Node<E>>(dummy)); |
935 |
– |
UNSAFE.putObjectVolatile(this, tailOffset, |
936 |
– |
new PaddedAtomicReference<Node<E>>(dummy)); |
937 |
– |
UNSAFE.putObjectVolatile(this, cleanMeOffset, |
938 |
– |
new PaddedAtomicReference<Node<E>>(null)); |
939 |
– |
} |
940 |
– |
|
1303 |
|
// Unsafe mechanics |
1304 |
|
|
1305 |
< |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
1306 |
< |
private static final long headOffset = |
1307 |
< |
objectFieldOffset(UNSAFE, "head", LinkedTransferQueue.class); |
1308 |
< |
private static final long tailOffset = |
1309 |
< |
objectFieldOffset(UNSAFE, "tail", LinkedTransferQueue.class); |
948 |
< |
private static final long cleanMeOffset = |
949 |
< |
objectFieldOffset(UNSAFE, "cleanMe", LinkedTransferQueue.class); |
950 |
< |
|
951 |
< |
|
952 |
< |
static long objectFieldOffset(sun.misc.Unsafe UNSAFE, |
953 |
< |
String field, Class<?> klazz) { |
1305 |
> |
private static final sun.misc.Unsafe UNSAFE; |
1306 |
> |
private static final long headOffset; |
1307 |
> |
private static final long tailOffset; |
1308 |
> |
private static final long sweepVotesOffset; |
1309 |
> |
static { |
1310 |
|
try { |
1311 |
< |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
1312 |
< |
} catch (NoSuchFieldException e) { |
1313 |
< |
// Convert Exception to corresponding Error |
1314 |
< |
NoSuchFieldError error = new NoSuchFieldError(field); |
1315 |
< |
error.initCause(e); |
1316 |
< |
throw error; |
1311 |
> |
UNSAFE = getUnsafe(); |
1312 |
> |
Class<?> k = LinkedTransferQueue.class; |
1313 |
> |
headOffset = UNSAFE.objectFieldOffset |
1314 |
> |
(k.getDeclaredField("head")); |
1315 |
> |
tailOffset = UNSAFE.objectFieldOffset |
1316 |
> |
(k.getDeclaredField("tail")); |
1317 |
> |
sweepVotesOffset = UNSAFE.objectFieldOffset |
1318 |
> |
(k.getDeclaredField("sweepVotes")); |
1319 |
> |
} catch (Exception e) { |
1320 |
> |
throw new Error(e); |
1321 |
|
} |
1322 |
|
} |
1323 |
|
|
1328 |
|
* |
1329 |
|
* @return a sun.misc.Unsafe |
1330 |
|
*/ |
1331 |
< |
private static sun.misc.Unsafe getUnsafe() { |
1331 |
> |
static sun.misc.Unsafe getUnsafe() { |
1332 |
|
try { |
1333 |
|
return sun.misc.Unsafe.getUnsafe(); |
1334 |
|
} catch (SecurityException se) { |
1348 |
|
} |
1349 |
|
} |
1350 |
|
} |
1351 |
+ |
|
1352 |
|
} |