1 |
dl |
1.1 |
/* |
2 |
|
|
* Written by Doug Lea with assistance from members of JCP JSR-166 |
3 |
|
|
* Expert Group and released to the public domain, as explained at |
4 |
|
|
* http://creativecommons.org/licenses/publicdomain |
5 |
|
|
*/ |
6 |
|
|
|
7 |
|
|
package jsr166y; |
8 |
jsr166 |
1.26 |
|
9 |
dl |
1.1 |
import java.util.concurrent.*; |
10 |
jsr166 |
1.26 |
|
11 |
|
|
import java.util.AbstractQueue; |
12 |
|
|
import java.util.Collection; |
13 |
jsr166 |
1.35 |
import java.util.ConcurrentModificationException; |
14 |
jsr166 |
1.26 |
import java.util.Iterator; |
15 |
|
|
import java.util.NoSuchElementException; |
16 |
jsr166 |
1.35 |
import java.util.Queue; |
17 |
jsr166 |
1.26 |
import java.util.concurrent.locks.LockSupport; |
18 |
dl |
1.1 |
/** |
19 |
jsr166 |
1.43 |
* An unbounded {@link TransferQueue} based on linked nodes. |
20 |
dl |
1.1 |
* This queue orders elements FIFO (first-in-first-out) with respect |
21 |
|
|
* to any given producer. The <em>head</em> of the queue is that |
22 |
|
|
* element that has been on the queue the longest time for some |
23 |
|
|
* producer. The <em>tail</em> of the queue is that element that has |
24 |
|
|
* been on the queue the shortest time for some producer. |
25 |
|
|
* |
26 |
jsr166 |
1.11 |
* <p>Beware that, unlike in most collections, the {@code size} |
27 |
dl |
1.1 |
* method is <em>NOT</em> a constant-time operation. Because of the |
28 |
|
|
* asynchronous nature of these queues, determining the current number |
29 |
|
|
* of elements requires a traversal of the elements. |
30 |
|
|
* |
31 |
|
|
* <p>This class and its iterator implement all of the |
32 |
|
|
* <em>optional</em> methods of the {@link Collection} and {@link |
33 |
|
|
* Iterator} interfaces. |
34 |
|
|
* |
35 |
|
|
* <p>Memory consistency effects: As with other concurrent |
36 |
|
|
* collections, actions in a thread prior to placing an object into a |
37 |
|
|
* {@code LinkedTransferQueue} |
38 |
|
|
* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> |
39 |
|
|
* actions subsequent to the access or removal of that element from |
40 |
|
|
* the {@code LinkedTransferQueue} in another thread. |
41 |
|
|
* |
42 |
|
|
* <p>This class is a member of the |
43 |
|
|
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
44 |
|
|
* Java Collections Framework</a>. |
45 |
|
|
* |
46 |
dl |
1.3 |
* @since 1.7 |
47 |
dl |
1.1 |
* @author Doug Lea |
48 |
|
|
* @param <E> the type of elements held in this collection |
49 |
|
|
*/ |
50 |
|
|
public class LinkedTransferQueue<E> extends AbstractQueue<E> |
51 |
|
|
implements TransferQueue<E>, java.io.Serializable { |
52 |
|
|
private static final long serialVersionUID = -3223113410248163686L; |
53 |
|
|
|
54 |
|
|
/* |
55 |
dl |
1.45 |
* *** Overview of Dual Queues with Slack *** |
56 |
dl |
1.1 |
* |
57 |
dl |
1.45 |
* Dual Queues, introduced by Scherer and Scott |
58 |
|
|
* (http://www.cs.rice.edu/~wns1/papers/2004-DISC-DDS.pdf) are |
59 |
|
|
* (linked) queues in which nodes may represent either data or |
60 |
|
|
* requests. When a thread tries to enqueue a data node, but |
61 |
|
|
* encounters a request node, it instead "matches" and removes it; |
62 |
|
|
* and vice versa for enqueuing requests. Blocking Dual Queues |
63 |
|
|
* arrange that threads enqueuing unmatched requests block until |
64 |
|
|
* other threads provide the match. Dual Synchronous Queues (see |
65 |
|
|
* Scherer, Lea, & Scott |
66 |
|
|
* http://www.cs.rochester.edu/u/scott/papers/2009_Scherer_CACM_SSQ.pdf) |
67 |
|
|
* additionally arrange that threads enqueuing unmatched data also |
68 |
|
|
* block. Dual Transfer Queues support all of these modes, as |
69 |
|
|
* dictated by callers. |
70 |
|
|
* |
71 |
|
|
* A FIFO dual queue may be implemented using a variation of the |
72 |
|
|
* Michael & Scott (M&S) lock-free queue algorithm |
73 |
|
|
* (http://www.cs.rochester.edu/u/scott/papers/1996_PODC_queues.pdf). |
74 |
|
|
* It maintains two pointer fields, "head", pointing to a |
75 |
|
|
* (matched) node that in turn points to the first actual |
76 |
|
|
* (unmatched) queue node (or null if empty); and "tail" that |
77 |
|
|
* points to the last node on the queue (or again null if |
78 |
|
|
* empty). For example, here is a possible queue with four data |
79 |
|
|
* elements: |
80 |
|
|
* |
81 |
|
|
* head tail |
82 |
|
|
* | | |
83 |
|
|
* v v |
84 |
|
|
* M -> U -> U -> U -> U |
85 |
|
|
* |
86 |
|
|
* The M&S queue algorithm is known to be prone to scalability and |
87 |
|
|
* overhead limitations when maintaining (via CAS) these head and |
88 |
|
|
* tail pointers. This has led to the development of |
89 |
|
|
* contention-reducing variants such as elimination arrays (see |
90 |
|
|
* Moir et al http://portal.acm.org/citation.cfm?id=1074013) and |
91 |
|
|
* optimistic back pointers (see Ladan-Mozes & Shavit |
92 |
|
|
* http://people.csail.mit.edu/edya/publications/OptimisticFIFOQueue-journal.pdf). |
93 |
|
|
* However, the nature of dual queues enables a simpler tactic for |
94 |
|
|
* improving M&S-style implementations when dual-ness is needed. |
95 |
|
|
* |
96 |
|
|
* In a dual queue, each node must atomically maintain its match |
97 |
|
|
* status. While there are other possible variants, we implement |
98 |
|
|
* this here as: for a data-mode node, matching entails CASing an |
99 |
|
|
* "item" field from a non-null data value to null upon match, and |
100 |
|
|
* vice-versa for request nodes, CASing from null to a data |
101 |
|
|
* value. (Note that the linearization properties of this style of |
102 |
|
|
* queue are easy to verify -- elements are made available by |
103 |
|
|
* linking, and unavailable by matching.) Compared to plain M&S |
104 |
|
|
* queues, this property of dual queues requires one additional |
105 |
|
|
* successful atomic operation per enq/deq pair. But it also |
106 |
|
|
* enables lower cost variants of queue maintenance mechanics. (A |
107 |
|
|
* variation of this idea applies even for non-dual queues that |
108 |
dl |
1.48 |
* support deletion of interior elements, such as |
109 |
dl |
1.45 |
* j.u.c.ConcurrentLinkedQueue.) |
110 |
|
|
* |
111 |
dl |
1.48 |
* Once a node is matched, its match status can never again |
112 |
|
|
* change. We may thus arrange that the linked list of them |
113 |
|
|
* contain a prefix of zero or more matched nodes, followed by a |
114 |
|
|
* suffix of zero or more unmatched nodes. (Note that we allow |
115 |
|
|
* both the prefix and suffix to be zero length, which in turn |
116 |
|
|
* means that we do not use a dummy header.) If we were not |
117 |
|
|
* concerned with either time or space efficiency, we could |
118 |
|
|
* correctly perform enqueue and dequeue operations by traversing |
119 |
|
|
* from a pointer to the initial node; CASing the item of the |
120 |
|
|
* first unmatched node on match and CASing the next field of the |
121 |
|
|
* trailing node on appends. (Plus some special-casing when |
122 |
|
|
* initially empty). While this would be a terrible idea in |
123 |
|
|
* itself, it does have the benefit of not requiring ANY atomic |
124 |
|
|
* updates on head/tail fields. |
125 |
dl |
1.45 |
* |
126 |
|
|
* We introduce here an approach that lies between the extremes of |
127 |
dl |
1.48 |
* never versus always updating queue (head and tail) pointers. |
128 |
|
|
* This offers a tradeoff between sometimes requiring extra |
129 |
|
|
* traversal steps to locate the first and/or last unmatched |
130 |
|
|
* nodes, versus the reduced overhead and contention of fewer |
131 |
|
|
* updates to queue pointers. For example, a possible snapshot of |
132 |
|
|
* a queue is: |
133 |
dl |
1.45 |
* |
134 |
|
|
* head tail |
135 |
|
|
* | | |
136 |
|
|
* v v |
137 |
|
|
* M -> M -> U -> U -> U -> U |
138 |
|
|
* |
139 |
|
|
* The best value for this "slack" (the targeted maximum distance |
140 |
|
|
* between the value of "head" and the first unmatched node, and |
141 |
|
|
* similarly for "tail") is an empirical matter. We have found |
142 |
|
|
* that using very small constants in the range of 1-3 work best |
143 |
|
|
* over a range of platforms. Larger values introduce increasing |
144 |
dl |
1.48 |
* costs of cache misses and risks of long traversal chains, while |
145 |
jsr166 |
1.49 |
* smaller values increase CAS contention and overhead. |
146 |
dl |
1.45 |
* |
147 |
|
|
* Dual queues with slack differ from plain M&S dual queues by |
148 |
|
|
* virtue of only sometimes updating head or tail pointers when |
149 |
|
|
* matching, appending, or even traversing nodes; in order to |
150 |
|
|
* maintain a targeted slack. The idea of "sometimes" may be |
151 |
|
|
* operationalized in several ways. The simplest is to use a |
152 |
|
|
* per-operation counter incremented on each traversal step, and |
153 |
|
|
* to try (via CAS) to update the associated queue pointer |
154 |
|
|
* whenever the count exceeds a threshold. Another, that requires |
155 |
|
|
* more overhead, is to use random number generators to update |
156 |
|
|
* with a given probability per traversal step. |
157 |
|
|
* |
158 |
|
|
* In any strategy along these lines, because CASes updating |
159 |
|
|
* fields may fail, the actual slack may exceed targeted |
160 |
|
|
* slack. However, they may be retried at any time to maintain |
161 |
|
|
* targets. Even when using very small slack values, this |
162 |
|
|
* approach works well for dual queues because it allows all |
163 |
|
|
* operations up to the point of matching or appending an item |
164 |
dl |
1.50 |
* (hence potentially allowing progress by another thread) to be |
165 |
|
|
* read-only, thus not introducing any further contention. As |
166 |
|
|
* described below, we implement this by performing slack |
167 |
|
|
* maintenance retries only after these points. |
168 |
dl |
1.45 |
* |
169 |
|
|
* As an accompaniment to such techniques, traversal overhead can |
170 |
|
|
* be further reduced without increasing contention of head |
171 |
dl |
1.50 |
* pointer updates: Threads may sometimes shortcut the "next" link |
172 |
|
|
* path from the current "head" node to be closer to the currently |
173 |
|
|
* known first unmatched node, and similarly for tail. Again, this |
174 |
|
|
* may be triggered with using thresholds or randomization. |
175 |
dl |
1.45 |
* |
176 |
|
|
* These ideas must be further extended to avoid unbounded amounts |
177 |
|
|
* of costly-to-reclaim garbage caused by the sequential "next" |
178 |
|
|
* links of nodes starting at old forgotten head nodes: As first |
179 |
|
|
* described in detail by Boehm |
180 |
|
|
* (http://portal.acm.org/citation.cfm?doid=503272.503282) if a GC |
181 |
|
|
* delays noticing that any arbitrarily old node has become |
182 |
|
|
* garbage, all newer dead nodes will also be unreclaimed. |
183 |
|
|
* (Similar issues arise in non-GC environments.) To cope with |
184 |
|
|
* this in our implementation, upon CASing to advance the head |
185 |
|
|
* pointer, we set the "next" link of the previous head to point |
186 |
jsr166 |
1.46 |
* only to itself; thus limiting the length of connected dead lists. |
187 |
dl |
1.45 |
* (We also take similar care to wipe out possibly garbage |
188 |
|
|
* retaining values held in other Node fields.) However, doing so |
189 |
|
|
* adds some further complexity to traversal: If any "next" |
190 |
|
|
* pointer links to itself, it indicates that the current thread |
191 |
|
|
* has lagged behind a head-update, and so the traversal must |
192 |
|
|
* continue from the "head". Traversals trying to find the |
193 |
|
|
* current tail starting from "tail" may also encounter |
194 |
|
|
* self-links, in which case they also continue at "head". |
195 |
|
|
* |
196 |
|
|
* It is tempting in slack-based scheme to not even use CAS for |
197 |
|
|
* updates (similarly to Ladan-Mozes & Shavit). However, this |
198 |
|
|
* cannot be done for head updates under the above link-forgetting |
199 |
|
|
* mechanics because an update may leave head at a detached node. |
200 |
|
|
* And while direct writes are possible for tail updates, they |
201 |
|
|
* increase the risk of long retraversals, and hence long garbage |
202 |
dl |
1.50 |
* chains, which can be much more costly than is worthwhile |
203 |
dl |
1.45 |
* considering that the cost difference of performing a CAS vs |
204 |
|
|
* write is smaller when they are not triggered on each operation |
205 |
|
|
* (especially considering that writes and CASes equally require |
206 |
|
|
* additional GC bookkeeping ("write barriers") that are sometimes |
207 |
|
|
* more costly than the writes themselves because of contention). |
208 |
|
|
* |
209 |
dl |
1.48 |
* Removal of interior nodes (due to timed out or interrupted |
210 |
dl |
1.50 |
* waits, or calls to remove(x) or Iterator.remove) can use a |
211 |
|
|
* scheme roughly similar to that described in Scherer, Lea, and |
212 |
|
|
* Scott's SynchronousQueue. Given a predecessor, we can unsplice |
213 |
|
|
* any node except the (actual) tail of the queue. To avoid |
214 |
|
|
* build-up of cancelled trailing nodes, upon a request to remove |
215 |
|
|
* a trailing node, it is placed in field "cleanMe" to be |
216 |
|
|
* unspliced upon the next call to unsplice any other node. |
217 |
|
|
* Situations needing such mechanics are not common but do occur |
218 |
|
|
* in practice; for example when an unbounded series of short |
219 |
|
|
* timed calls to poll repeatedly time out but never otherwise |
220 |
|
|
* fall off the list because of an untimed call to take at the |
221 |
|
|
* front of the queue. Note that maintaining field cleanMe does |
222 |
|
|
* not otherwise much impact garbage retention even if never |
223 |
|
|
* cleared by some other call because the held node will |
224 |
|
|
* eventually either directly or indirectly lead to a self-link |
225 |
|
|
* once off the list. |
226 |
dl |
1.45 |
* |
227 |
|
|
* *** Overview of implementation *** |
228 |
|
|
* |
229 |
dl |
1.50 |
* We use a threshold-based approach to updates, with a slack |
230 |
|
|
* threshold of two -- that is, we update head/tail when the |
231 |
|
|
* current pointer appears to be two or more steps away from the |
232 |
|
|
* first/last node. The slack value is hard-wired: a path greater |
233 |
dl |
1.45 |
* than one is naturally implemented by checking equality of |
234 |
|
|
* traversal pointers except when the list has only one element, |
235 |
dl |
1.50 |
* in which case we keep slack threshold at one. Avoiding tracking |
236 |
dl |
1.48 |
* explicit counts across method calls slightly simplifies an |
237 |
dl |
1.45 |
* already-messy implementation. Using randomization would |
238 |
|
|
* probably work better if there were a low-quality dirt-cheap |
239 |
|
|
* per-thread one available, but even ThreadLocalRandom is too |
240 |
|
|
* heavy for these purposes. |
241 |
|
|
* |
242 |
dl |
1.50 |
* With such a small slack threshold value, it is rarely |
243 |
|
|
* worthwhile to augment this with path short-circuiting; i.e., |
244 |
|
|
* unsplicing nodes between head and the first unmatched node, or |
245 |
|
|
* similarly for tail, rather than advancing head or tail |
246 |
|
|
* proper. However, it is used (in awaitMatch) immediately before |
247 |
|
|
* a waiting thread starts to block, as a final bit of helping at |
248 |
|
|
* a point when contention with others is extremely unlikely |
249 |
|
|
* (since if other threads that could release it are operating, |
250 |
|
|
* then the current thread wouldn't be blocking). |
251 |
dl |
1.48 |
* |
252 |
|
|
* We allow both the head and tail fields to be null before any |
253 |
|
|
* nodes are enqueued; initializing upon first append. This |
254 |
|
|
* simplifies some other logic, as well as providing more |
255 |
|
|
* efficient explicit control paths instead of letting JVMs insert |
256 |
|
|
* implicit NullPointerExceptions when they are null. While not |
257 |
|
|
* currently fully implemented, we also leave open the possibility |
258 |
jsr166 |
1.49 |
* of re-nulling these fields when empty (which is complicated to |
259 |
|
|
* arrange, for little benefit.) |
260 |
dl |
1.45 |
* |
261 |
|
|
* All enqueue/dequeue operations are handled by the single method |
262 |
|
|
* "xfer" with parameters indicating whether to act as some form |
263 |
|
|
* of offer, put, poll, take, or transfer (each possibly with |
264 |
|
|
* timeout). The relative complexity of using one monolithic |
265 |
|
|
* method outweighs the code bulk and maintenance problems of |
266 |
dl |
1.50 |
* using separate methods for each case. |
267 |
dl |
1.45 |
* |
268 |
|
|
* Operation consists of up to three phases. The first is |
269 |
|
|
* implemented within method xfer, the second in tryAppend, and |
270 |
|
|
* the third in method awaitMatch. |
271 |
|
|
* |
272 |
|
|
* 1. Try to match an existing node |
273 |
|
|
* |
274 |
|
|
* Starting at head, skip already-matched nodes until finding |
275 |
|
|
* an unmatched node of opposite mode, if one exists, in which |
276 |
|
|
* case matching it and returning, also if necessary updating |
277 |
|
|
* head to one past the matched node (or the node itself if the |
278 |
|
|
* list has no other unmatched nodes). If the CAS misses, then |
279 |
dl |
1.48 |
* a loop retries advancing head by two steps until either |
280 |
|
|
* success or the slack is at most two. By requiring that each |
281 |
|
|
* attempt advances head by two (if applicable), we ensure that |
282 |
|
|
* the slack does not grow without bound. Traversals also check |
283 |
|
|
* if the initial head is now off-list, in which case they |
284 |
|
|
* start at the new head. |
285 |
dl |
1.45 |
* |
286 |
|
|
* If no candidates are found and the call was untimed |
287 |
|
|
* poll/offer, (argument "how" is NOW) return. |
288 |
|
|
* |
289 |
|
|
* 2. Try to append a new node (method tryAppend) |
290 |
|
|
* |
291 |
dl |
1.50 |
* Starting at current tail pointer, find the actual last node |
292 |
|
|
* and try to append a new node (or if head was null, establish |
293 |
|
|
* the first node). Nodes can be appended only if their |
294 |
|
|
* predecessors are either already matched or are of the same |
295 |
|
|
* mode. If we detect otherwise, then a new node with opposite |
296 |
|
|
* mode must have been appended during traversal, so we must |
297 |
|
|
* restart at phase 1. The traversal and update steps are |
298 |
|
|
* otherwise similar to phase 1: Retrying upon CAS misses and |
299 |
|
|
* checking for staleness. In particular, if a self-link is |
300 |
|
|
* encountered, then we can safely jump to a node on the list |
301 |
|
|
* by continuing the traversal at current head. |
302 |
dl |
1.45 |
* |
303 |
jsr166 |
1.46 |
* On successful append, if the call was ASYNC, return. |
304 |
dl |
1.45 |
* |
305 |
|
|
* 3. Await match or cancellation (method awaitMatch) |
306 |
|
|
* |
307 |
|
|
* Wait for another thread to match node; instead cancelling if |
308 |
dl |
1.50 |
* the current thread was interrupted or the wait timed out. On |
309 |
dl |
1.45 |
* multiprocessors, we use front-of-queue spinning: If a node |
310 |
|
|
* appears to be the first unmatched node in the queue, it |
311 |
|
|
* spins a bit before blocking. In either case, before blocking |
312 |
|
|
* it tries to unsplice any nodes between the current "head" |
313 |
|
|
* and the first unmatched node. |
314 |
|
|
* |
315 |
|
|
* Front-of-queue spinning vastly improves performance of |
316 |
|
|
* heavily contended queues. And so long as it is relatively |
317 |
|
|
* brief and "quiet", spinning does not much impact performance |
318 |
|
|
* of less-contended queues. During spins threads check their |
319 |
|
|
* interrupt status and generate a thread-local random number |
320 |
|
|
* to decide to occasionally perform a Thread.yield. While |
321 |
|
|
* yield has underdefined specs, we assume that might it help, |
322 |
|
|
* and will not hurt in limiting impact of spinning on busy |
323 |
dl |
1.50 |
* systems. We also use smaller (1/2) spins for nodes that are |
324 |
|
|
* not known to be front but whose predecessors have not |
325 |
|
|
* blocked -- these "chained" spins avoid artifacts of |
326 |
dl |
1.45 |
* front-of-queue rules which otherwise lead to alternating |
327 |
|
|
* nodes spinning vs blocking. Further, front threads that |
328 |
|
|
* represent phase changes (from data to request node or vice |
329 |
|
|
* versa) compared to their predecessors receive additional |
330 |
dl |
1.50 |
* chained spins, reflecting longer paths typically required to |
331 |
|
|
* unblock threads during phase changes. |
332 |
dl |
1.45 |
*/ |
333 |
|
|
|
334 |
|
|
/** True if on multiprocessor */ |
335 |
|
|
private static final boolean MP = |
336 |
|
|
Runtime.getRuntime().availableProcessors() > 1; |
337 |
|
|
|
338 |
|
|
/** |
339 |
dl |
1.50 |
* The number of times to spin (with randomly interspersed calls |
340 |
|
|
* to Thread.yield) on multiprocessor before blocking when a node |
341 |
|
|
* is apparently the first waiter in the queue. See above for |
342 |
|
|
* explanation. Must be a power of two. The value is empirically |
343 |
|
|
* derived -- it works pretty well across a variety of processors, |
344 |
|
|
* numbers of CPUs, and OSes. |
345 |
dl |
1.45 |
*/ |
346 |
|
|
private static final int FRONT_SPINS = 1 << 7; |
347 |
|
|
|
348 |
|
|
/** |
349 |
|
|
* The number of times to spin before blocking when a node is |
350 |
dl |
1.50 |
* preceded by another node that is apparently spinning. Also |
351 |
|
|
* serves as an increment to FRONT_SPINS on phase changes, and as |
352 |
|
|
* base average frequency for yielding during spins. Must be a |
353 |
|
|
* power of two. |
354 |
dl |
1.45 |
*/ |
355 |
dl |
1.50 |
private static final int CHAINED_SPINS = FRONT_SPINS >>> 1; |
356 |
dl |
1.45 |
|
357 |
|
|
/** |
358 |
jsr166 |
1.46 |
* Queue nodes. Uses Object, not E, for items to allow forgetting |
359 |
dl |
1.45 |
* them after use. Relies heavily on Unsafe mechanics to minimize |
360 |
jsr166 |
1.46 |
* unnecessary ordering constraints: Writes that intrinsically |
361 |
dl |
1.45 |
* precede or follow CASes use simple relaxed forms. Other |
362 |
|
|
* cleanups use releasing/lazy writes. |
363 |
|
|
*/ |
364 |
jsr166 |
1.54 |
static final class Node<E> { |
365 |
dl |
1.45 |
final boolean isData; // false if this is a request node |
366 |
jsr166 |
1.46 |
volatile Object item; // initially non-null if isData; CASed to match |
367 |
jsr166 |
1.54 |
volatile Node<E> next; |
368 |
dl |
1.45 |
volatile Thread waiter; // null until waiting |
369 |
dl |
1.1 |
|
370 |
dl |
1.45 |
// CAS methods for fields |
371 |
jsr166 |
1.54 |
final boolean casNext(Node<E> cmp, Node<E> val) { |
372 |
dl |
1.45 |
return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val); |
373 |
|
|
} |
374 |
dl |
1.1 |
|
375 |
dl |
1.45 |
final boolean casItem(Object cmp, Object val) { |
376 |
jsr166 |
1.55 |
assert cmp == null || cmp.getClass() != Node.class; |
377 |
dl |
1.45 |
return UNSAFE.compareAndSwapObject(this, itemOffset, cmp, val); |
378 |
|
|
} |
379 |
dl |
1.1 |
|
380 |
dl |
1.45 |
/** |
381 |
jsr166 |
1.46 |
* Creates a new node. Uses relaxed write because item can only |
382 |
|
|
* be seen if followed by CAS. |
383 |
dl |
1.45 |
*/ |
384 |
jsr166 |
1.54 |
Node(E item, boolean isData) { |
385 |
dl |
1.45 |
UNSAFE.putObject(this, itemOffset, item); // relaxed write |
386 |
dl |
1.1 |
this.isData = isData; |
387 |
|
|
} |
388 |
|
|
|
389 |
dl |
1.45 |
/** |
390 |
|
|
* Links node to itself to avoid garbage retention. Called |
391 |
|
|
* only after CASing head field, so uses relaxed write. |
392 |
|
|
*/ |
393 |
|
|
final void forgetNext() { |
394 |
|
|
UNSAFE.putObject(this, nextOffset, this); |
395 |
|
|
} |
396 |
jsr166 |
1.32 |
|
397 |
dl |
1.45 |
/** |
398 |
|
|
* Sets item to self (using a releasing/lazy write) and waiter |
399 |
|
|
* to null, to avoid garbage retention after extracting or |
400 |
|
|
* cancelling. |
401 |
|
|
*/ |
402 |
|
|
final void forgetContents() { |
403 |
|
|
UNSAFE.putOrderedObject(this, itemOffset, this); |
404 |
|
|
UNSAFE.putOrderedObject(this, waiterOffset, null); |
405 |
|
|
} |
406 |
jsr166 |
1.32 |
|
407 |
dl |
1.45 |
/** |
408 |
|
|
* Returns true if this node has been matched, including the |
409 |
|
|
* case of artificial matches due to cancellation. |
410 |
|
|
*/ |
411 |
|
|
final boolean isMatched() { |
412 |
|
|
Object x = item; |
413 |
jsr166 |
1.57 |
return (x == this) || ((x == null) == isData); |
414 |
dl |
1.1 |
} |
415 |
dl |
1.15 |
|
416 |
dl |
1.45 |
/** |
417 |
jsr166 |
1.58 |
* Returns true if this is an unmatched request node. |
418 |
|
|
*/ |
419 |
|
|
final boolean isUnmatchedRequest() { |
420 |
|
|
return !isData && item == null; |
421 |
|
|
} |
422 |
|
|
|
423 |
|
|
/** |
424 |
dl |
1.45 |
* Returns true if a node with the given mode cannot be |
425 |
|
|
* appended to this node because this node is unmatched and |
426 |
|
|
* has opposite data mode. |
427 |
|
|
*/ |
428 |
|
|
final boolean cannotPrecede(boolean haveData) { |
429 |
|
|
boolean d = isData; |
430 |
|
|
Object x; |
431 |
|
|
return d != haveData && (x = item) != this && (x != null) == d; |
432 |
jsr166 |
1.31 |
} |
433 |
|
|
|
434 |
|
|
/** |
435 |
jsr166 |
1.46 |
* Tries to artificially match a data node -- used by remove. |
436 |
jsr166 |
1.31 |
*/ |
437 |
dl |
1.45 |
final boolean tryMatchData() { |
438 |
jsr166 |
1.58 |
assert isData; |
439 |
dl |
1.45 |
Object x = item; |
440 |
|
|
if (x != null && x != this && casItem(x, null)) { |
441 |
|
|
LockSupport.unpark(waiter); |
442 |
|
|
return true; |
443 |
jsr166 |
1.31 |
} |
444 |
dl |
1.45 |
return false; |
445 |
dl |
1.15 |
} |
446 |
|
|
|
447 |
dl |
1.45 |
// Unsafe mechanics |
448 |
|
|
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
449 |
|
|
private static final long nextOffset = |
450 |
|
|
objectFieldOffset(UNSAFE, "next", Node.class); |
451 |
|
|
private static final long itemOffset = |
452 |
|
|
objectFieldOffset(UNSAFE, "item", Node.class); |
453 |
|
|
private static final long waiterOffset = |
454 |
|
|
objectFieldOffset(UNSAFE, "waiter", Node.class); |
455 |
|
|
|
456 |
jsr166 |
1.24 |
private static final long serialVersionUID = -3375979862319811754L; |
457 |
dl |
1.1 |
} |
458 |
|
|
|
459 |
dl |
1.45 |
/** head of the queue; null until first enqueue */ |
460 |
jsr166 |
1.54 |
transient volatile Node<E> head; |
461 |
dl |
1.45 |
|
462 |
|
|
/** predecessor of dangling unspliceable node */ |
463 |
jsr166 |
1.54 |
private transient volatile Node<E> cleanMe; // decl here reduces contention |
464 |
dl |
1.1 |
|
465 |
dl |
1.45 |
/** tail of the queue; null until first append */ |
466 |
jsr166 |
1.54 |
private transient volatile Node<E> tail; |
467 |
dl |
1.1 |
|
468 |
dl |
1.45 |
// CAS methods for fields |
469 |
jsr166 |
1.54 |
private boolean casTail(Node<E> cmp, Node<E> val) { |
470 |
dl |
1.45 |
return UNSAFE.compareAndSwapObject(this, tailOffset, cmp, val); |
471 |
|
|
} |
472 |
jsr166 |
1.23 |
|
473 |
jsr166 |
1.54 |
private boolean casHead(Node<E> cmp, Node<E> val) { |
474 |
dl |
1.45 |
return UNSAFE.compareAndSwapObject(this, headOffset, cmp, val); |
475 |
|
|
} |
476 |
dl |
1.1 |
|
477 |
jsr166 |
1.54 |
private boolean casCleanMe(Node<E> cmp, Node<E> val) { |
478 |
dl |
1.45 |
return UNSAFE.compareAndSwapObject(this, cleanMeOffset, cmp, val); |
479 |
|
|
} |
480 |
dl |
1.1 |
|
481 |
dl |
1.45 |
/* |
482 |
|
|
* Possible values for "how" argument in xfer method. Beware that |
483 |
|
|
* the order of assigned numerical values matters. |
484 |
dl |
1.1 |
*/ |
485 |
dl |
1.45 |
private static final int NOW = 0; // for untimed poll, tryTransfer |
486 |
|
|
private static final int ASYNC = 1; // for offer, put, add |
487 |
|
|
private static final int SYNC = 2; // for transfer, take |
488 |
|
|
private static final int TIMEOUT = 3; // for timed poll, tryTransfer |
489 |
jsr166 |
1.5 |
|
490 |
jsr166 |
1.56 |
@SuppressWarnings("unchecked") |
491 |
|
|
static <E> E cast(Object item) { |
492 |
|
|
assert item == null || item.getClass() != Node.class; |
493 |
|
|
return (E) item; |
494 |
|
|
} |
495 |
|
|
|
496 |
dl |
1.1 |
/** |
497 |
dl |
1.45 |
* Implements all queuing methods. See above for explanation. |
498 |
jsr166 |
1.17 |
* |
499 |
dl |
1.45 |
* @param e the item or null for take |
500 |
jsr166 |
1.46 |
* @param haveData true if this is a put, else a take |
501 |
dl |
1.45 |
* @param how NOW, ASYNC, SYNC, or TIMEOUT |
502 |
dl |
1.1 |
* @param nanos timeout in nanosecs, used only if mode is TIMEOUT |
503 |
jsr166 |
1.46 |
* @return an item if matched, else e |
504 |
dl |
1.45 |
* @throws NullPointerException if haveData mode but e is null |
505 |
dl |
1.1 |
*/ |
506 |
jsr166 |
1.54 |
private E xfer(E e, boolean haveData, int how, long nanos) { |
507 |
dl |
1.45 |
if (haveData && (e == null)) |
508 |
|
|
throw new NullPointerException(); |
509 |
jsr166 |
1.54 |
Node<E> s = null; // the node to append, if needed |
510 |
dl |
1.1 |
|
511 |
dl |
1.45 |
retry: for (;;) { // restart on append race |
512 |
dl |
1.1 |
|
513 |
jsr166 |
1.54 |
for (Node<E> h = head, p = h; p != null;) { |
514 |
|
|
// find & match first node |
515 |
dl |
1.45 |
boolean isData = p.isData; |
516 |
|
|
Object item = p.item; |
517 |
|
|
if (item != p && (item != null) == isData) { // unmatched |
518 |
|
|
if (isData == haveData) // can't match |
519 |
|
|
break; |
520 |
|
|
if (p.casItem(item, e)) { // match |
521 |
jsr166 |
1.54 |
for (Node<E> q = p; q != h;) { |
522 |
|
|
Node<E> n = q.next; // update head by 2 |
523 |
dl |
1.52 |
if (n != null) // unless singleton |
524 |
|
|
q = n; |
525 |
|
|
if (head == h && casHead(h, q)) { |
526 |
dl |
1.45 |
h.forgetNext(); |
527 |
|
|
break; |
528 |
|
|
} // advance and retry |
529 |
|
|
if ((h = head) == null || |
530 |
dl |
1.52 |
(q = h.next) == null || !q.isMatched()) |
531 |
dl |
1.45 |
break; // unless slack < 2 |
532 |
|
|
} |
533 |
dl |
1.52 |
LockSupport.unpark(p.waiter); |
534 |
jsr166 |
1.54 |
return this.<E>cast(item); |
535 |
dl |
1.1 |
} |
536 |
|
|
} |
537 |
jsr166 |
1.54 |
Node<E> n = p.next; |
538 |
jsr166 |
1.47 |
p = (p != n) ? n : (h = head); // Use head if p offlist |
539 |
dl |
1.45 |
} |
540 |
|
|
|
541 |
|
|
if (how >= ASYNC) { // No matches available |
542 |
|
|
if (s == null) |
543 |
jsr166 |
1.54 |
s = new Node<E>(e, haveData); |
544 |
|
|
Node<E> pred = tryAppend(s, haveData); |
545 |
dl |
1.45 |
if (pred == null) |
546 |
|
|
continue retry; // lost race vs opposite mode |
547 |
|
|
if (how >= SYNC) |
548 |
dl |
1.50 |
return awaitMatch(s, pred, e, how, nanos); |
549 |
dl |
1.1 |
} |
550 |
dl |
1.45 |
return e; // not waiting |
551 |
dl |
1.1 |
} |
552 |
|
|
} |
553 |
|
|
|
554 |
|
|
/** |
555 |
jsr166 |
1.46 |
* Tries to append node s as tail. |
556 |
|
|
* |
557 |
dl |
1.48 |
* @param s the node to append |
558 |
dl |
1.45 |
* @param haveData true if appending in data mode |
559 |
|
|
* @return null on failure due to losing race with append in |
560 |
|
|
* different mode, else s's predecessor, or s itself if no |
561 |
|
|
* predecessor |
562 |
dl |
1.1 |
*/ |
563 |
jsr166 |
1.54 |
private Node<E> tryAppend(Node<E> s, boolean haveData) { |
564 |
|
|
for (Node<E> t = tail, p = t;;) { // move p to last node and append |
565 |
|
|
Node<E> n, u; // temps for reads of next & tail |
566 |
dl |
1.45 |
if (p == null && (p = head) == null) { |
567 |
|
|
if (casHead(null, s)) |
568 |
|
|
return s; // initialize |
569 |
|
|
} |
570 |
|
|
else if (p.cannotPrecede(haveData)) |
571 |
|
|
return null; // lost race vs opposite mode |
572 |
dl |
1.48 |
else if ((n = p.next) != null) // not last; keep traversing |
573 |
dl |
1.45 |
p = p != t && t != (u = tail) ? (t = u) : // stale tail |
574 |
jsr166 |
1.47 |
(p != n) ? n : null; // restart if off list |
575 |
dl |
1.45 |
else if (!p.casNext(null, s)) |
576 |
|
|
p = p.next; // re-read on CAS failure |
577 |
|
|
else { |
578 |
dl |
1.48 |
if (p != t) { // update if slack now >= 2 |
579 |
dl |
1.45 |
while ((tail != t || !casTail(t, s)) && |
580 |
|
|
(t = tail) != null && |
581 |
|
|
(s = t.next) != null && // advance and retry |
582 |
|
|
(s = s.next) != null && s != t); |
583 |
dl |
1.1 |
} |
584 |
dl |
1.45 |
return p; |
585 |
dl |
1.1 |
} |
586 |
|
|
} |
587 |
|
|
} |
588 |
|
|
|
589 |
|
|
/** |
590 |
dl |
1.45 |
* Spins/yields/blocks until node s is matched or caller gives up. |
591 |
dl |
1.1 |
* |
592 |
|
|
* @param s the waiting node |
593 |
dl |
1.50 |
* @param pred the predecessor of s, or s itself if it has no |
594 |
|
|
* predecessor, or null if unknown (the null case does not occur |
595 |
|
|
* in any current calls but may in possible future extensions) |
596 |
dl |
1.1 |
* @param e the comparison value for checking match |
597 |
dl |
1.45 |
* @param how either SYNC or TIMEOUT |
598 |
dl |
1.1 |
* @param nanos timeout value |
599 |
dl |
1.45 |
* @return matched item, or e if unmatched on interrupt or timeout |
600 |
dl |
1.1 |
*/ |
601 |
jsr166 |
1.54 |
private E awaitMatch(Node<E> s, Node<E> pred, E e, int how, long nanos) { |
602 |
dl |
1.45 |
long lastTime = (how == TIMEOUT) ? System.nanoTime() : 0L; |
603 |
|
|
Thread w = Thread.currentThread(); |
604 |
|
|
int spins = -1; // initialized after first item and cancel checks |
605 |
|
|
ThreadLocalRandom randomYields = null; // bound if needed |
606 |
dl |
1.1 |
|
607 |
|
|
for (;;) { |
608 |
dl |
1.45 |
Object item = s.item; |
609 |
|
|
if (item != e) { // matched |
610 |
jsr166 |
1.54 |
assert item != s; |
611 |
dl |
1.45 |
s.forgetContents(); // avoid garbage |
612 |
jsr166 |
1.54 |
return this.<E>cast(item); |
613 |
dl |
1.45 |
} |
614 |
|
|
if ((w.isInterrupted() || (how == TIMEOUT && nanos <= 0)) && |
615 |
jsr166 |
1.54 |
s.casItem(e, s)) { // cancel |
616 |
dl |
1.45 |
unsplice(pred, s); |
617 |
|
|
return e; |
618 |
|
|
} |
619 |
|
|
|
620 |
|
|
if (spins < 0) { // establish spins at/near front |
621 |
|
|
if ((spins = spinsFor(pred, s.isData)) > 0) |
622 |
|
|
randomYields = ThreadLocalRandom.current(); |
623 |
|
|
} |
624 |
dl |
1.50 |
else if (spins > 0) { // spin |
625 |
|
|
if (--spins == 0) |
626 |
|
|
shortenHeadPath(); // reduce slack before blocking |
627 |
|
|
else if (randomYields.nextInt(CHAINED_SPINS) == 0) |
628 |
|
|
Thread.yield(); // occasionally yield |
629 |
dl |
1.45 |
} |
630 |
|
|
else if (s.waiter == null) { |
631 |
dl |
1.51 |
s.waiter = w; // request unpark then recheck |
632 |
dl |
1.1 |
} |
633 |
dl |
1.45 |
else if (how == TIMEOUT) { |
634 |
dl |
1.1 |
long now = System.nanoTime(); |
635 |
dl |
1.45 |
if ((nanos -= now - lastTime) > 0) |
636 |
|
|
LockSupport.parkNanos(this, nanos); |
637 |
dl |
1.1 |
lastTime = now; |
638 |
|
|
} |
639 |
dl |
1.45 |
else { |
640 |
dl |
1.12 |
LockSupport.park(this); |
641 |
dl |
1.51 |
s.waiter = null; |
642 |
dl |
1.45 |
spins = -1; // spin if front upon wakeup |
643 |
dl |
1.1 |
} |
644 |
dl |
1.45 |
} |
645 |
|
|
} |
646 |
|
|
|
647 |
|
|
/** |
648 |
jsr166 |
1.46 |
* Returns spin/yield value for a node with given predecessor and |
649 |
dl |
1.45 |
* data mode. See above for explanation. |
650 |
|
|
*/ |
651 |
jsr166 |
1.54 |
private static int spinsFor(Node<?> pred, boolean haveData) { |
652 |
dl |
1.45 |
if (MP && pred != null) { |
653 |
dl |
1.50 |
if (pred.isData != haveData) // phase change |
654 |
|
|
return FRONT_SPINS + CHAINED_SPINS; |
655 |
|
|
if (pred.isMatched()) // probably at front |
656 |
dl |
1.45 |
return FRONT_SPINS; |
657 |
|
|
if (pred.waiter == null) // pred apparently spinning |
658 |
|
|
return CHAINED_SPINS; |
659 |
|
|
} |
660 |
|
|
return 0; |
661 |
|
|
} |
662 |
|
|
|
663 |
|
|
/** |
664 |
|
|
* Tries (once) to unsplice nodes between head and first unmatched |
665 |
|
|
* or trailing node; failing on contention. |
666 |
|
|
*/ |
667 |
|
|
private void shortenHeadPath() { |
668 |
jsr166 |
1.54 |
Node<E> h, hn, p, q; |
669 |
dl |
1.45 |
if ((p = h = head) != null && h.isMatched() && |
670 |
|
|
(q = hn = h.next) != null) { |
671 |
jsr166 |
1.54 |
Node<E> n; |
672 |
dl |
1.45 |
while ((n = q.next) != q) { |
673 |
|
|
if (n == null || !q.isMatched()) { |
674 |
|
|
if (hn != q && h.next == hn) |
675 |
|
|
h.casNext(hn, q); |
676 |
|
|
break; |
677 |
|
|
} |
678 |
|
|
p = q; |
679 |
|
|
q = n; |
680 |
dl |
1.1 |
} |
681 |
|
|
} |
682 |
|
|
} |
683 |
|
|
|
684 |
dl |
1.45 |
/* -------------- Traversal methods -------------- */ |
685 |
|
|
|
686 |
dl |
1.1 |
/** |
687 |
jsr166 |
1.46 |
* Returns the first unmatched node of the given mode, or null if |
688 |
dl |
1.45 |
* none. Used by methods isEmpty, hasWaitingConsumer. |
689 |
dl |
1.9 |
*/ |
690 |
jsr166 |
1.54 |
private Node<E> firstOfMode(boolean data) { |
691 |
|
|
for (Node<E> p = head; p != null; ) { |
692 |
dl |
1.45 |
if (!p.isMatched()) |
693 |
jsr166 |
1.47 |
return (p.isData == data) ? p : null; |
694 |
jsr166 |
1.54 |
Node<E> n = p.next; |
695 |
jsr166 |
1.47 |
p = (n != p) ? n : head; |
696 |
dl |
1.45 |
} |
697 |
|
|
return null; |
698 |
|
|
} |
699 |
|
|
|
700 |
|
|
/** |
701 |
|
|
* Returns the item in the first unmatched node with isData; or |
702 |
jsr166 |
1.54 |
* null if none. Used by peek. |
703 |
dl |
1.45 |
*/ |
704 |
jsr166 |
1.54 |
private E firstDataItem() { |
705 |
|
|
for (Node<E> p = head; p != null; ) { |
706 |
dl |
1.45 |
boolean isData = p.isData; |
707 |
|
|
Object item = p.item; |
708 |
|
|
if (item != p && (item != null) == isData) |
709 |
jsr166 |
1.54 |
return isData ? this.<E>cast(item) : null; |
710 |
|
|
Node<E> n = p.next; |
711 |
jsr166 |
1.47 |
p = (n != p) ? n : head; |
712 |
dl |
1.45 |
} |
713 |
|
|
return null; |
714 |
|
|
} |
715 |
|
|
|
716 |
|
|
/** |
717 |
jsr166 |
1.46 |
* Traverses and counts unmatched nodes of the given mode. |
718 |
|
|
* Used by methods size and getWaitingConsumerCount. |
719 |
dl |
1.45 |
*/ |
720 |
|
|
private int countOfMode(boolean data) { |
721 |
|
|
int count = 0; |
722 |
jsr166 |
1.54 |
for (Node<E> p = head; p != null; ) { |
723 |
dl |
1.45 |
if (!p.isMatched()) { |
724 |
|
|
if (p.isData != data) |
725 |
|
|
return 0; |
726 |
|
|
if (++count == Integer.MAX_VALUE) // saturated |
727 |
|
|
break; |
728 |
dl |
1.9 |
} |
729 |
jsr166 |
1.54 |
Node<E> n = p.next; |
730 |
dl |
1.45 |
if (n != p) |
731 |
|
|
p = n; |
732 |
|
|
else { |
733 |
|
|
count = 0; |
734 |
|
|
p = head; |
735 |
dl |
1.9 |
} |
736 |
|
|
} |
737 |
dl |
1.45 |
return count; |
738 |
jsr166 |
1.10 |
} |
739 |
dl |
1.9 |
|
740 |
dl |
1.45 |
final class Itr implements Iterator<E> { |
741 |
jsr166 |
1.54 |
private Node<E> nextNode; // next node to return item for |
742 |
|
|
private E nextItem; // the corresponding item |
743 |
|
|
private Node<E> lastRet; // last returned node, to support remove |
744 |
dl |
1.60 |
private Node<E> lastPred; // predecessor to unlink lastRet |
745 |
dl |
1.45 |
|
746 |
|
|
/** |
747 |
|
|
* Moves to next node after prev, or first node if prev null. |
748 |
|
|
*/ |
749 |
jsr166 |
1.54 |
private void advance(Node<E> prev) { |
750 |
dl |
1.60 |
lastPred = lastRet; |
751 |
dl |
1.45 |
lastRet = prev; |
752 |
jsr166 |
1.54 |
Node<E> p; |
753 |
dl |
1.45 |
if (prev == null || (p = prev.next) == prev) |
754 |
|
|
p = head; |
755 |
|
|
while (p != null) { |
756 |
|
|
Object item = p.item; |
757 |
|
|
if (p.isData) { |
758 |
|
|
if (item != null && item != p) { |
759 |
jsr166 |
1.54 |
nextItem = LinkedTransferQueue.this.<E>cast(item); |
760 |
dl |
1.45 |
nextNode = p; |
761 |
|
|
return; |
762 |
|
|
} |
763 |
|
|
} |
764 |
|
|
else if (item == null) |
765 |
|
|
break; |
766 |
jsr166 |
1.54 |
Node<E> n = p.next; |
767 |
jsr166 |
1.47 |
p = (n != p) ? n : head; |
768 |
dl |
1.45 |
} |
769 |
|
|
nextNode = null; |
770 |
|
|
} |
771 |
|
|
|
772 |
|
|
Itr() { |
773 |
|
|
advance(null); |
774 |
|
|
} |
775 |
|
|
|
776 |
|
|
public final boolean hasNext() { |
777 |
|
|
return nextNode != null; |
778 |
|
|
} |
779 |
|
|
|
780 |
|
|
public final E next() { |
781 |
jsr166 |
1.54 |
Node<E> p = nextNode; |
782 |
dl |
1.45 |
if (p == null) throw new NoSuchElementException(); |
783 |
jsr166 |
1.54 |
E e = nextItem; |
784 |
dl |
1.45 |
advance(p); |
785 |
jsr166 |
1.54 |
return e; |
786 |
dl |
1.45 |
} |
787 |
|
|
|
788 |
|
|
public final void remove() { |
789 |
jsr166 |
1.54 |
Node<E> p = lastRet; |
790 |
dl |
1.45 |
if (p == null) throw new IllegalStateException(); |
791 |
dl |
1.60 |
findAndRemoveDataNode(lastPred, p); |
792 |
dl |
1.45 |
} |
793 |
|
|
} |
794 |
|
|
|
795 |
|
|
/* -------------- Removal methods -------------- */ |
796 |
|
|
|
797 |
dl |
1.9 |
/** |
798 |
dl |
1.45 |
* Unsplices (now or later) the given deleted/cancelled node with |
799 |
|
|
* the given predecessor. |
800 |
jsr166 |
1.17 |
* |
801 |
dl |
1.45 |
* @param pred predecessor of node to be unspliced |
802 |
|
|
* @param s the node to be unspliced |
803 |
dl |
1.1 |
*/ |
804 |
jsr166 |
1.54 |
private void unsplice(Node<E> pred, Node<E> s) { |
805 |
dl |
1.45 |
s.forgetContents(); // clear unneeded fields |
806 |
dl |
1.9 |
/* |
807 |
|
|
* At any given time, exactly one node on list cannot be |
808 |
dl |
1.48 |
* unlinked -- the last inserted node. To accommodate this, if |
809 |
|
|
* we cannot unlink s, we save its predecessor as "cleanMe", |
810 |
dl |
1.45 |
* processing the previously saved version first. Because only |
811 |
|
|
* one node in the list can have a null next, at least one of |
812 |
|
|
* node s or the node previously saved can always be |
813 |
dl |
1.9 |
* processed, so this always terminates. |
814 |
|
|
*/ |
815 |
dl |
1.45 |
if (pred != null && pred != s) { |
816 |
|
|
while (pred.next == s) { |
817 |
jsr166 |
1.54 |
Node<E> oldpred = (cleanMe == null) ? null : reclean(); |
818 |
|
|
Node<E> n = s.next; |
819 |
dl |
1.45 |
if (n != null) { |
820 |
|
|
if (n != s) |
821 |
|
|
pred.casNext(s, n); |
822 |
dl |
1.9 |
break; |
823 |
dl |
1.45 |
} |
824 |
|
|
if (oldpred == pred || // Already saved |
825 |
jsr166 |
1.59 |
((oldpred == null || oldpred.next == s) && |
826 |
|
|
casCleanMe(oldpred, pred))) { |
827 |
|
|
break; |
828 |
|
|
} |
829 |
dl |
1.9 |
} |
830 |
|
|
} |
831 |
|
|
} |
832 |
jsr166 |
1.5 |
|
833 |
dl |
1.9 |
/** |
834 |
dl |
1.45 |
* Tries to unsplice the deleted/cancelled node held in cleanMe |
835 |
|
|
* that was previously uncleanable because it was at tail. |
836 |
jsr166 |
1.17 |
* |
837 |
dl |
1.9 |
* @return current cleanMe node (or null) |
838 |
|
|
*/ |
839 |
jsr166 |
1.54 |
private Node<E> reclean() { |
840 |
jsr166 |
1.10 |
/* |
841 |
dl |
1.45 |
* cleanMe is, or at one time was, predecessor of a cancelled |
842 |
|
|
* node s that was the tail so could not be unspliced. If it |
843 |
dl |
1.9 |
* is no longer the tail, try to unsplice if necessary and |
844 |
|
|
* make cleanMe slot available. This differs from similar |
845 |
dl |
1.45 |
* code in unsplice() because we must check that pred still |
846 |
|
|
* points to a matched node that can be unspliced -- if not, |
847 |
|
|
* we can (must) clear cleanMe without unsplicing. This can |
848 |
|
|
* loop only due to contention. |
849 |
dl |
1.9 |
*/ |
850 |
jsr166 |
1.54 |
Node<E> pred; |
851 |
dl |
1.45 |
while ((pred = cleanMe) != null) { |
852 |
jsr166 |
1.54 |
Node<E> s = pred.next; |
853 |
|
|
Node<E> n; |
854 |
dl |
1.45 |
if (s == null || s == pred || !s.isMatched()) |
855 |
|
|
casCleanMe(pred, null); // already gone |
856 |
|
|
else if ((n = s.next) != null) { |
857 |
|
|
if (n != s) |
858 |
|
|
pred.casNext(s, n); |
859 |
|
|
casCleanMe(pred, null); |
860 |
dl |
1.1 |
} |
861 |
dl |
1.45 |
else |
862 |
dl |
1.9 |
break; |
863 |
dl |
1.1 |
} |
864 |
dl |
1.9 |
return pred; |
865 |
dl |
1.1 |
} |
866 |
jsr166 |
1.5 |
|
867 |
dl |
1.1 |
/** |
868 |
dl |
1.45 |
* Main implementation of Iterator.remove(). Find |
869 |
jsr166 |
1.58 |
* and unsplice the given data node. |
870 |
dl |
1.60 |
* @param possiblePred possible predecessor of s |
871 |
|
|
* @param s the node to remove |
872 |
dl |
1.45 |
*/ |
873 |
dl |
1.60 |
final void findAndRemoveDataNode(Node<E> possiblePred, Node<E> s) { |
874 |
jsr166 |
1.58 |
assert s.isData; |
875 |
dl |
1.45 |
if (s.tryMatchData()) { |
876 |
dl |
1.60 |
if (possiblePred != null && possiblePred.next == s) |
877 |
|
|
unsplice(possiblePred, s); // was actual predecessor |
878 |
|
|
else { |
879 |
|
|
for (Node<E> pred = null, p = head; p != null; ) { |
880 |
|
|
if (p == s) { |
881 |
|
|
unsplice(pred, p); |
882 |
|
|
break; |
883 |
|
|
} |
884 |
|
|
if (p.isUnmatchedRequest()) |
885 |
|
|
break; |
886 |
|
|
pred = p; |
887 |
|
|
if ((p = p.next) == pred) { // stale |
888 |
|
|
pred = null; |
889 |
|
|
p = head; |
890 |
|
|
} |
891 |
dl |
1.45 |
} |
892 |
|
|
} |
893 |
|
|
} |
894 |
|
|
} |
895 |
|
|
|
896 |
|
|
/** |
897 |
|
|
* Main implementation of remove(Object) |
898 |
|
|
*/ |
899 |
|
|
private boolean findAndRemove(Object e) { |
900 |
|
|
if (e != null) { |
901 |
jsr166 |
1.58 |
for (Node<E> pred = null, p = head; p != null; ) { |
902 |
dl |
1.45 |
Object item = p.item; |
903 |
|
|
if (p.isData) { |
904 |
|
|
if (item != null && item != p && e.equals(item) && |
905 |
|
|
p.tryMatchData()) { |
906 |
|
|
unsplice(pred, p); |
907 |
|
|
return true; |
908 |
|
|
} |
909 |
|
|
} |
910 |
|
|
else if (item == null) |
911 |
|
|
break; |
912 |
|
|
pred = p; |
913 |
jsr166 |
1.58 |
if ((p = p.next) == pred) { // stale |
914 |
dl |
1.45 |
pred = null; |
915 |
|
|
p = head; |
916 |
|
|
} |
917 |
|
|
} |
918 |
|
|
} |
919 |
|
|
return false; |
920 |
|
|
} |
921 |
|
|
|
922 |
|
|
|
923 |
|
|
/** |
924 |
jsr166 |
1.11 |
* Creates an initially empty {@code LinkedTransferQueue}. |
925 |
dl |
1.1 |
*/ |
926 |
|
|
public LinkedTransferQueue() { |
927 |
|
|
} |
928 |
|
|
|
929 |
|
|
/** |
930 |
jsr166 |
1.11 |
* Creates a {@code LinkedTransferQueue} |
931 |
dl |
1.1 |
* initially containing the elements of the given collection, |
932 |
|
|
* added in traversal order of the collection's iterator. |
933 |
jsr166 |
1.17 |
* |
934 |
dl |
1.1 |
* @param c the collection of elements to initially contain |
935 |
|
|
* @throws NullPointerException if the specified collection or any |
936 |
|
|
* of its elements are null |
937 |
|
|
*/ |
938 |
|
|
public LinkedTransferQueue(Collection<? extends E> c) { |
939 |
dl |
1.7 |
this(); |
940 |
dl |
1.1 |
addAll(c); |
941 |
|
|
} |
942 |
|
|
|
943 |
jsr166 |
1.29 |
/** |
944 |
jsr166 |
1.35 |
* Inserts the specified element at the tail of this queue. |
945 |
|
|
* As the queue is unbounded, this method will never block. |
946 |
|
|
* |
947 |
|
|
* @throws NullPointerException if the specified element is null |
948 |
jsr166 |
1.29 |
*/ |
949 |
jsr166 |
1.35 |
public void put(E e) { |
950 |
dl |
1.45 |
xfer(e, true, ASYNC, 0); |
951 |
dl |
1.1 |
} |
952 |
|
|
|
953 |
jsr166 |
1.29 |
/** |
954 |
jsr166 |
1.35 |
* Inserts the specified element at the tail of this queue. |
955 |
|
|
* As the queue is unbounded, this method will never block or |
956 |
|
|
* return {@code false}. |
957 |
|
|
* |
958 |
|
|
* @return {@code true} (as specified by |
959 |
|
|
* {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer}) |
960 |
|
|
* @throws NullPointerException if the specified element is null |
961 |
jsr166 |
1.29 |
*/ |
962 |
jsr166 |
1.35 |
public boolean offer(E e, long timeout, TimeUnit unit) { |
963 |
dl |
1.45 |
xfer(e, true, ASYNC, 0); |
964 |
|
|
return true; |
965 |
dl |
1.1 |
} |
966 |
|
|
|
967 |
jsr166 |
1.29 |
/** |
968 |
jsr166 |
1.35 |
* Inserts the specified element at the tail of this queue. |
969 |
|
|
* As the queue is unbounded, this method will never return {@code false}. |
970 |
|
|
* |
971 |
|
|
* @return {@code true} (as specified by |
972 |
|
|
* {@link BlockingQueue#offer(Object) BlockingQueue.offer}) |
973 |
|
|
* @throws NullPointerException if the specified element is null |
974 |
jsr166 |
1.29 |
*/ |
975 |
dl |
1.1 |
public boolean offer(E e) { |
976 |
dl |
1.45 |
xfer(e, true, ASYNC, 0); |
977 |
dl |
1.1 |
return true; |
978 |
|
|
} |
979 |
|
|
|
980 |
jsr166 |
1.29 |
/** |
981 |
jsr166 |
1.35 |
* Inserts the specified element at the tail of this queue. |
982 |
jsr166 |
1.37 |
* As the queue is unbounded, this method will never throw |
983 |
jsr166 |
1.35 |
* {@link IllegalStateException} or return {@code false}. |
984 |
|
|
* |
985 |
|
|
* @return {@code true} (as specified by {@link Collection#add}) |
986 |
|
|
* @throws NullPointerException if the specified element is null |
987 |
jsr166 |
1.29 |
*/ |
988 |
dl |
1.15 |
public boolean add(E e) { |
989 |
dl |
1.45 |
xfer(e, true, ASYNC, 0); |
990 |
|
|
return true; |
991 |
jsr166 |
1.35 |
} |
992 |
|
|
|
993 |
|
|
/** |
994 |
jsr166 |
1.40 |
* Transfers the element to a waiting consumer immediately, if possible. |
995 |
|
|
* |
996 |
|
|
* <p>More precisely, transfers the specified element immediately |
997 |
|
|
* if there exists a consumer already waiting to receive it (in |
998 |
|
|
* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
999 |
|
|
* otherwise returning {@code false} without enqueuing the element. |
1000 |
jsr166 |
1.35 |
* |
1001 |
|
|
* @throws NullPointerException if the specified element is null |
1002 |
|
|
*/ |
1003 |
|
|
public boolean tryTransfer(E e) { |
1004 |
dl |
1.45 |
return xfer(e, true, NOW, 0) == null; |
1005 |
dl |
1.15 |
} |
1006 |
|
|
|
1007 |
jsr166 |
1.29 |
/** |
1008 |
jsr166 |
1.40 |
* Transfers the element to a consumer, waiting if necessary to do so. |
1009 |
|
|
* |
1010 |
|
|
* <p>More precisely, transfers the specified element immediately |
1011 |
|
|
* if there exists a consumer already waiting to receive it (in |
1012 |
|
|
* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
1013 |
|
|
* else inserts the specified element at the tail of this queue |
1014 |
|
|
* and waits until the element is received by a consumer. |
1015 |
jsr166 |
1.35 |
* |
1016 |
|
|
* @throws NullPointerException if the specified element is null |
1017 |
jsr166 |
1.29 |
*/ |
1018 |
dl |
1.1 |
public void transfer(E e) throws InterruptedException { |
1019 |
dl |
1.45 |
if (xfer(e, true, SYNC, 0) != null) { |
1020 |
|
|
Thread.interrupted(); // failure possible only due to interrupt |
1021 |
dl |
1.1 |
throw new InterruptedException(); |
1022 |
jsr166 |
1.6 |
} |
1023 |
dl |
1.1 |
} |
1024 |
|
|
|
1025 |
jsr166 |
1.29 |
/** |
1026 |
jsr166 |
1.40 |
* Transfers the element to a consumer if it is possible to do so |
1027 |
|
|
* before the timeout elapses. |
1028 |
|
|
* |
1029 |
|
|
* <p>More precisely, transfers the specified element immediately |
1030 |
|
|
* if there exists a consumer already waiting to receive it (in |
1031 |
|
|
* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
1032 |
|
|
* else inserts the specified element at the tail of this queue |
1033 |
|
|
* and waits until the element is received by a consumer, |
1034 |
|
|
* returning {@code false} if the specified wait time elapses |
1035 |
|
|
* before the element can be transferred. |
1036 |
jsr166 |
1.35 |
* |
1037 |
|
|
* @throws NullPointerException if the specified element is null |
1038 |
jsr166 |
1.29 |
*/ |
1039 |
dl |
1.1 |
public boolean tryTransfer(E e, long timeout, TimeUnit unit) |
1040 |
|
|
throws InterruptedException { |
1041 |
dl |
1.45 |
if (xfer(e, true, TIMEOUT, unit.toNanos(timeout)) == null) |
1042 |
dl |
1.1 |
return true; |
1043 |
|
|
if (!Thread.interrupted()) |
1044 |
|
|
return false; |
1045 |
|
|
throw new InterruptedException(); |
1046 |
|
|
} |
1047 |
|
|
|
1048 |
|
|
public E take() throws InterruptedException { |
1049 |
jsr166 |
1.54 |
E e = xfer(null, false, SYNC, 0); |
1050 |
dl |
1.1 |
if (e != null) |
1051 |
jsr166 |
1.54 |
return e; |
1052 |
jsr166 |
1.6 |
Thread.interrupted(); |
1053 |
dl |
1.1 |
throw new InterruptedException(); |
1054 |
|
|
} |
1055 |
|
|
|
1056 |
|
|
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
1057 |
jsr166 |
1.54 |
E e = xfer(null, false, TIMEOUT, unit.toNanos(timeout)); |
1058 |
dl |
1.1 |
if (e != null || !Thread.interrupted()) |
1059 |
jsr166 |
1.54 |
return e; |
1060 |
dl |
1.1 |
throw new InterruptedException(); |
1061 |
|
|
} |
1062 |
|
|
|
1063 |
|
|
public E poll() { |
1064 |
jsr166 |
1.54 |
return xfer(null, false, NOW, 0); |
1065 |
dl |
1.1 |
} |
1066 |
|
|
|
1067 |
jsr166 |
1.29 |
/** |
1068 |
jsr166 |
1.30 |
* @throws NullPointerException {@inheritDoc} |
1069 |
|
|
* @throws IllegalArgumentException {@inheritDoc} |
1070 |
jsr166 |
1.29 |
*/ |
1071 |
dl |
1.1 |
public int drainTo(Collection<? super E> c) { |
1072 |
|
|
if (c == null) |
1073 |
|
|
throw new NullPointerException(); |
1074 |
|
|
if (c == this) |
1075 |
|
|
throw new IllegalArgumentException(); |
1076 |
|
|
int n = 0; |
1077 |
|
|
E e; |
1078 |
|
|
while ( (e = poll()) != null) { |
1079 |
|
|
c.add(e); |
1080 |
|
|
++n; |
1081 |
|
|
} |
1082 |
|
|
return n; |
1083 |
|
|
} |
1084 |
|
|
|
1085 |
jsr166 |
1.29 |
/** |
1086 |
jsr166 |
1.30 |
* @throws NullPointerException {@inheritDoc} |
1087 |
|
|
* @throws IllegalArgumentException {@inheritDoc} |
1088 |
jsr166 |
1.29 |
*/ |
1089 |
dl |
1.1 |
public int drainTo(Collection<? super E> c, int maxElements) { |
1090 |
|
|
if (c == null) |
1091 |
|
|
throw new NullPointerException(); |
1092 |
|
|
if (c == this) |
1093 |
|
|
throw new IllegalArgumentException(); |
1094 |
|
|
int n = 0; |
1095 |
|
|
E e; |
1096 |
|
|
while (n < maxElements && (e = poll()) != null) { |
1097 |
|
|
c.add(e); |
1098 |
|
|
++n; |
1099 |
|
|
} |
1100 |
|
|
return n; |
1101 |
|
|
} |
1102 |
|
|
|
1103 |
jsr166 |
1.35 |
/** |
1104 |
|
|
* Returns an iterator over the elements in this queue in proper |
1105 |
|
|
* sequence, from head to tail. |
1106 |
|
|
* |
1107 |
|
|
* <p>The returned iterator is a "weakly consistent" iterator that |
1108 |
|
|
* will never throw |
1109 |
|
|
* {@link ConcurrentModificationException ConcurrentModificationException}, |
1110 |
|
|
* and guarantees to traverse elements as they existed upon |
1111 |
|
|
* construction of the iterator, and may (but is not guaranteed |
1112 |
|
|
* to) reflect any modifications subsequent to construction. |
1113 |
|
|
* |
1114 |
|
|
* @return an iterator over the elements in this queue in proper sequence |
1115 |
|
|
*/ |
1116 |
dl |
1.1 |
public Iterator<E> iterator() { |
1117 |
|
|
return new Itr(); |
1118 |
|
|
} |
1119 |
|
|
|
1120 |
|
|
public E peek() { |
1121 |
jsr166 |
1.54 |
return firstDataItem(); |
1122 |
dl |
1.1 |
} |
1123 |
|
|
|
1124 |
jsr166 |
1.41 |
/** |
1125 |
|
|
* Returns {@code true} if this queue contains no elements. |
1126 |
|
|
* |
1127 |
|
|
* @return {@code true} if this queue contains no elements |
1128 |
|
|
*/ |
1129 |
dl |
1.2 |
public boolean isEmpty() { |
1130 |
dl |
1.45 |
return firstOfMode(true) == null; |
1131 |
dl |
1.2 |
} |
1132 |
|
|
|
1133 |
dl |
1.1 |
public boolean hasWaitingConsumer() { |
1134 |
dl |
1.45 |
return firstOfMode(false) != null; |
1135 |
dl |
1.1 |
} |
1136 |
jsr166 |
1.5 |
|
1137 |
dl |
1.1 |
/** |
1138 |
|
|
* Returns the number of elements in this queue. If this queue |
1139 |
jsr166 |
1.11 |
* contains more than {@code Integer.MAX_VALUE} elements, returns |
1140 |
|
|
* {@code Integer.MAX_VALUE}. |
1141 |
dl |
1.1 |
* |
1142 |
|
|
* <p>Beware that, unlike in most collections, this method is |
1143 |
|
|
* <em>NOT</em> a constant-time operation. Because of the |
1144 |
|
|
* asynchronous nature of these queues, determining the current |
1145 |
|
|
* number of elements requires an O(n) traversal. |
1146 |
|
|
* |
1147 |
|
|
* @return the number of elements in this queue |
1148 |
|
|
*/ |
1149 |
|
|
public int size() { |
1150 |
dl |
1.45 |
return countOfMode(true); |
1151 |
dl |
1.1 |
} |
1152 |
|
|
|
1153 |
|
|
public int getWaitingConsumerCount() { |
1154 |
dl |
1.45 |
return countOfMode(false); |
1155 |
dl |
1.1 |
} |
1156 |
|
|
|
1157 |
jsr166 |
1.42 |
/** |
1158 |
|
|
* Removes a single instance of the specified element from this queue, |
1159 |
|
|
* if it is present. More formally, removes an element {@code e} such |
1160 |
|
|
* that {@code o.equals(e)}, if this queue contains one or more such |
1161 |
|
|
* elements. |
1162 |
|
|
* Returns {@code true} if this queue contained the specified element |
1163 |
|
|
* (or equivalently, if this queue changed as a result of the call). |
1164 |
|
|
* |
1165 |
|
|
* @param o element to be removed from this queue, if present |
1166 |
|
|
* @return {@code true} if this queue changed as a result of the call |
1167 |
|
|
*/ |
1168 |
dl |
1.15 |
public boolean remove(Object o) { |
1169 |
dl |
1.45 |
return findAndRemove(o); |
1170 |
dl |
1.15 |
} |
1171 |
|
|
|
1172 |
jsr166 |
1.35 |
/** |
1173 |
|
|
* Always returns {@code Integer.MAX_VALUE} because a |
1174 |
|
|
* {@code LinkedTransferQueue} is not capacity constrained. |
1175 |
|
|
* |
1176 |
|
|
* @return {@code Integer.MAX_VALUE} (as specified by |
1177 |
|
|
* {@link BlockingQueue#remainingCapacity()}) |
1178 |
|
|
*/ |
1179 |
dl |
1.33 |
public int remainingCapacity() { |
1180 |
|
|
return Integer.MAX_VALUE; |
1181 |
|
|
} |
1182 |
|
|
|
1183 |
dl |
1.1 |
/** |
1184 |
jsr166 |
1.46 |
* Saves the state to a stream (that is, serializes it). |
1185 |
dl |
1.1 |
* |
1186 |
jsr166 |
1.11 |
* @serialData All of the elements (each an {@code E}) in |
1187 |
dl |
1.1 |
* the proper order, followed by a null |
1188 |
|
|
* @param s the stream |
1189 |
|
|
*/ |
1190 |
|
|
private void writeObject(java.io.ObjectOutputStream s) |
1191 |
|
|
throws java.io.IOException { |
1192 |
|
|
s.defaultWriteObject(); |
1193 |
jsr166 |
1.16 |
for (E e : this) |
1194 |
|
|
s.writeObject(e); |
1195 |
dl |
1.1 |
// Use trailing null as sentinel |
1196 |
|
|
s.writeObject(null); |
1197 |
|
|
} |
1198 |
|
|
|
1199 |
|
|
/** |
1200 |
jsr166 |
1.46 |
* Reconstitutes the Queue instance from a stream (that is, |
1201 |
|
|
* deserializes it). |
1202 |
jsr166 |
1.19 |
* |
1203 |
dl |
1.1 |
* @param s the stream |
1204 |
|
|
*/ |
1205 |
|
|
private void readObject(java.io.ObjectInputStream s) |
1206 |
|
|
throws java.io.IOException, ClassNotFoundException { |
1207 |
|
|
s.defaultReadObject(); |
1208 |
|
|
for (;;) { |
1209 |
jsr166 |
1.25 |
@SuppressWarnings("unchecked") E item = (E) s.readObject(); |
1210 |
dl |
1.1 |
if (item == null) |
1211 |
|
|
break; |
1212 |
|
|
else |
1213 |
|
|
offer(item); |
1214 |
|
|
} |
1215 |
|
|
} |
1216 |
dl |
1.7 |
|
1217 |
jsr166 |
1.28 |
// Unsafe mechanics |
1218 |
|
|
|
1219 |
|
|
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
1220 |
|
|
private static final long headOffset = |
1221 |
jsr166 |
1.31 |
objectFieldOffset(UNSAFE, "head", LinkedTransferQueue.class); |
1222 |
jsr166 |
1.28 |
private static final long tailOffset = |
1223 |
jsr166 |
1.31 |
objectFieldOffset(UNSAFE, "tail", LinkedTransferQueue.class); |
1224 |
jsr166 |
1.28 |
private static final long cleanMeOffset = |
1225 |
jsr166 |
1.31 |
objectFieldOffset(UNSAFE, "cleanMe", LinkedTransferQueue.class); |
1226 |
|
|
|
1227 |
|
|
static long objectFieldOffset(sun.misc.Unsafe UNSAFE, |
1228 |
|
|
String field, Class<?> klazz) { |
1229 |
jsr166 |
1.28 |
try { |
1230 |
|
|
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
1231 |
|
|
} catch (NoSuchFieldException e) { |
1232 |
|
|
// Convert Exception to corresponding Error |
1233 |
|
|
NoSuchFieldError error = new NoSuchFieldError(field); |
1234 |
|
|
error.initCause(e); |
1235 |
|
|
throw error; |
1236 |
|
|
} |
1237 |
|
|
} |
1238 |
|
|
|
1239 |
jsr166 |
1.53 |
/** |
1240 |
|
|
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
1241 |
|
|
* Replace with a simple call to Unsafe.getUnsafe when integrating |
1242 |
|
|
* into a jdk. |
1243 |
|
|
* |
1244 |
|
|
* @return a sun.misc.Unsafe |
1245 |
|
|
*/ |
1246 |
jsr166 |
1.54 |
static sun.misc.Unsafe getUnsafe() { |
1247 |
jsr166 |
1.13 |
try { |
1248 |
jsr166 |
1.25 |
return sun.misc.Unsafe.getUnsafe(); |
1249 |
jsr166 |
1.13 |
} catch (SecurityException se) { |
1250 |
|
|
try { |
1251 |
|
|
return java.security.AccessController.doPrivileged |
1252 |
jsr166 |
1.28 |
(new java.security |
1253 |
|
|
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1254 |
jsr166 |
1.25 |
public sun.misc.Unsafe run() throws Exception { |
1255 |
jsr166 |
1.28 |
java.lang.reflect.Field f = sun.misc |
1256 |
|
|
.Unsafe.class.getDeclaredField("theUnsafe"); |
1257 |
|
|
f.setAccessible(true); |
1258 |
|
|
return (sun.misc.Unsafe) f.get(null); |
1259 |
jsr166 |
1.13 |
}}); |
1260 |
|
|
} catch (java.security.PrivilegedActionException e) { |
1261 |
jsr166 |
1.25 |
throw new RuntimeException("Could not initialize intrinsics", |
1262 |
|
|
e.getCause()); |
1263 |
jsr166 |
1.13 |
} |
1264 |
|
|
} |
1265 |
|
|
} |
1266 |
dl |
1.45 |
|
1267 |
dl |
1.1 |
} |