5 |
|
*/ |
6 |
|
|
7 |
|
package jsr166y; |
8 |
+ |
|
9 |
|
import java.util.concurrent.*; |
10 |
< |
import java.util.concurrent.locks.*; |
11 |
< |
import java.util.concurrent.atomic.*; |
12 |
< |
import java.util.*; |
13 |
< |
import java.io.*; |
10 |
> |
|
11 |
> |
import java.util.AbstractQueue; |
12 |
> |
import java.util.Collection; |
13 |
> |
import java.util.ConcurrentModificationException; |
14 |
> |
import java.util.Iterator; |
15 |
> |
import java.util.NoSuchElementException; |
16 |
> |
import java.util.Queue; |
17 |
> |
import java.util.concurrent.locks.LockSupport; |
18 |
> |
import java.util.concurrent.atomic.AtomicReference; |
19 |
|
|
20 |
|
/** |
21 |
< |
* An unbounded {@linkplain TransferQueue} based on linked nodes. |
21 |
> |
* An unbounded {@link TransferQueue} based on linked nodes. |
22 |
|
* This queue orders elements FIFO (first-in-first-out) with respect |
23 |
|
* to any given producer. The <em>head</em> of the queue is that |
24 |
|
* element that has been on the queue the longest time for some |
25 |
|
* producer. The <em>tail</em> of the queue is that element that has |
26 |
|
* been on the queue the shortest time for some producer. |
27 |
|
* |
28 |
< |
* <p>Beware that, unlike in most collections, the <tt>size</tt> |
28 |
> |
* <p>Beware that, unlike in most collections, the {@code size} |
29 |
|
* method is <em>NOT</em> a constant-time operation. Because of the |
30 |
|
* asynchronous nature of these queues, determining the current number |
31 |
|
* of elements requires a traversal of the elements. |
48 |
|
* @since 1.7 |
49 |
|
* @author Doug Lea |
50 |
|
* @param <E> the type of elements held in this collection |
45 |
– |
* |
51 |
|
*/ |
52 |
|
public class LinkedTransferQueue<E> extends AbstractQueue<E> |
53 |
|
implements TransferQueue<E>, java.io.Serializable { |
54 |
|
private static final long serialVersionUID = -3223113410248163686L; |
55 |
|
|
56 |
|
/* |
52 |
– |
* This is still a work in progress... |
53 |
– |
* |
57 |
|
* This class extends the approach used in FIFO-mode |
58 |
|
* SynchronousQueues. See the internal documentation, as well as |
59 |
|
* the PPoPP 2006 paper "Scalable Synchronous Queues" by Scherer, |
60 |
|
* Lea & Scott |
61 |
|
* (http://www.cs.rice.edu/~wns1/papers/2006-PPoPP-SQ.pdf) |
62 |
|
* |
63 |
< |
* The main extension is to provide different Wait modes |
64 |
< |
* for the main "xfer" method that puts or takes items. |
65 |
< |
* These don't impact the basic dual-queue logic, but instead |
66 |
< |
* control whether or how threads block upon insertion |
67 |
< |
* of request or data nodes into the dual queue. |
63 |
> |
* The main extension is to provide different Wait modes for the |
64 |
> |
* main "xfer" method that puts or takes items. These don't |
65 |
> |
* impact the basic dual-queue logic, but instead control whether |
66 |
> |
* or how threads block upon insertion of request or data nodes |
67 |
> |
* into the dual queue. It also uses slightly different |
68 |
> |
* conventions for tracking whether nodes are off-list or |
69 |
> |
* cancelled. |
70 |
|
*/ |
71 |
|
|
72 |
|
// Wait modes for xfer method |
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; |
87 |
> |
static final int maxTimedSpins = (NCPUS < 2) ? 0 : 32; |
88 |
|
|
89 |
|
/** |
90 |
|
* The number of times to spin before blocking in untimed waits. |
99 |
|
*/ |
100 |
|
static final long spinForTimeoutThreshold = 1000L; |
101 |
|
|
102 |
< |
/** |
103 |
< |
* Node class for LinkedTransferQueue. Opportunistically subclasses from |
104 |
< |
* AtomicReference to represent item. Uses Object, not E, to allow |
105 |
< |
* setting item to "this" after use, to avoid garbage |
106 |
< |
* retention. Similarly, setting the next field to this is used as |
107 |
< |
* sentinel that node is off list. |
102 |
> |
/** |
103 |
> |
* Node class for LinkedTransferQueue. Opportunistically |
104 |
> |
* subclasses from AtomicReference to represent item. Uses Object, |
105 |
> |
* 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 QNode extends AtomicReference<Object> { |
110 |
< |
volatile QNode next; |
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; |
113 |
< |
QNode(Object item, boolean isData) { |
113 |
> |
|
114 |
> |
Node(E item, boolean isData) { |
115 |
|
super(item); |
116 |
|
this.isData = isData; |
117 |
|
} |
118 |
|
|
119 |
< |
static final AtomicReferenceFieldUpdater<QNode, QNode> |
114 |
< |
nextUpdater = AtomicReferenceFieldUpdater.newUpdater |
115 |
< |
(QNode.class, QNode.class, "next"); |
119 |
> |
// Unsafe mechanics |
120 |
|
|
121 |
< |
boolean casNext(QNode cmp, QNode val) { |
122 |
< |
return nextUpdater.compareAndSet(this, cmp, val); |
121 |
> |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
122 |
> |
private static final long nextOffset = |
123 |
> |
objectFieldOffset(UNSAFE, "next", Node.class); |
124 |
> |
|
125 |
> |
final boolean casNext(Node<E> cmp, Node<E> val) { |
126 |
> |
return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val); |
127 |
> |
} |
128 |
> |
|
129 |
> |
final void clearNext() { |
130 |
> |
UNSAFE.putOrderedObject(this, nextOffset, this); |
131 |
> |
} |
132 |
> |
|
133 |
> |
/** |
134 |
> |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
135 |
> |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
136 |
> |
* into a jdk. |
137 |
> |
* |
138 |
> |
* @return a sun.misc.Unsafe |
139 |
> |
*/ |
140 |
> |
private static sun.misc.Unsafe getUnsafe() { |
141 |
> |
try { |
142 |
> |
return sun.misc.Unsafe.getUnsafe(); |
143 |
> |
} catch (SecurityException se) { |
144 |
> |
try { |
145 |
> |
return java.security.AccessController.doPrivileged |
146 |
> |
(new java.security |
147 |
> |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
148 |
> |
public sun.misc.Unsafe run() throws Exception { |
149 |
> |
java.lang.reflect.Field f = sun.misc |
150 |
> |
.Unsafe.class.getDeclaredField("theUnsafe"); |
151 |
> |
f.setAccessible(true); |
152 |
> |
return (sun.misc.Unsafe) f.get(null); |
153 |
> |
}}); |
154 |
> |
} catch (java.security.PrivilegedActionException e) { |
155 |
> |
throw new RuntimeException("Could not initialize intrinsics", |
156 |
> |
e.getCause()); |
157 |
> |
} |
158 |
> |
} |
159 |
|
} |
160 |
+ |
|
161 |
+ |
private static final long serialVersionUID = -3375979862319811754L; |
162 |
|
} |
163 |
|
|
164 |
|
/** |
170 |
|
// enough padding for 64bytes with 4byte refs |
171 |
|
Object p0, p1, p2, p3, p4, p5, p6, p7, p8, p9, pa, pb, pc, pd, pe; |
172 |
|
PaddedAtomicReference(T r) { super(r); } |
173 |
+ |
private static final long serialVersionUID = 8170090609809740854L; |
174 |
|
} |
175 |
|
|
176 |
|
|
177 |
< |
private final QNode dummy = new QNode(null, false); |
178 |
< |
private final PaddedAtomicReference<QNode> head = |
179 |
< |
new PaddedAtomicReference<QNode>(dummy); |
180 |
< |
private final PaddedAtomicReference<QNode> tail = |
181 |
< |
new PaddedAtomicReference<QNode>(dummy); |
177 |
> |
/** head of the queue */ |
178 |
> |
private transient final PaddedAtomicReference<Node<E>> head; |
179 |
> |
|
180 |
> |
/** tail of the queue */ |
181 |
> |
private transient final PaddedAtomicReference<Node<E>> tail; |
182 |
|
|
183 |
|
/** |
184 |
|
* Reference to a cancelled node that might not yet have been |
185 |
|
* unlinked from queue because it was the last inserted node |
186 |
|
* when it cancelled. |
187 |
|
*/ |
188 |
< |
private final PaddedAtomicReference<QNode> cleanMe = |
146 |
< |
new PaddedAtomicReference<QNode>(null); |
188 |
> |
private transient final PaddedAtomicReference<Node<E>> cleanMe; |
189 |
|
|
190 |
|
/** |
191 |
|
* Tries to cas nh as new head; if successful, unlink |
192 |
|
* old head's next node to avoid garbage retention. |
193 |
|
*/ |
194 |
< |
private boolean advanceHead(QNode h, QNode nh) { |
194 |
> |
private boolean advanceHead(Node<E> h, Node<E> nh) { |
195 |
|
if (h == head.get() && head.compareAndSet(h, nh)) { |
196 |
< |
h.next = h; // forget old next |
196 |
> |
h.clearNext(); // forget old next |
197 |
|
return true; |
198 |
|
} |
199 |
|
return false; |
200 |
|
} |
201 |
< |
|
201 |
> |
|
202 |
|
/** |
203 |
|
* Puts or takes an item. Used for most queue operations (except |
204 |
< |
* poll() and tryTransfer()) |
204 |
> |
* poll() and tryTransfer()). See the similar code in |
205 |
> |
* SynchronousQueue for detailed explanation. |
206 |
> |
* |
207 |
|
* @param e the item or if null, signifies that this is a take |
208 |
|
* @param mode the wait mode: NOWAIT, TIMEOUT, WAIT |
209 |
|
* @param nanos timeout in nanosecs, used only if mode is TIMEOUT |
210 |
|
* @return an item, or null on failure |
211 |
|
*/ |
212 |
< |
private Object xfer(Object e, int mode, long nanos) { |
212 |
> |
private E xfer(E e, int mode, long nanos) { |
213 |
|
boolean isData = (e != null); |
214 |
< |
QNode s = null; |
215 |
< |
final PaddedAtomicReference<QNode> head = this.head; |
216 |
< |
final PaddedAtomicReference<QNode> tail = this.tail; |
214 |
> |
Node<E> s = null; |
215 |
> |
final PaddedAtomicReference<Node<E>> head = this.head; |
216 |
> |
final PaddedAtomicReference<Node<E>> tail = this.tail; |
217 |
|
|
218 |
|
for (;;) { |
219 |
< |
QNode t = tail.get(); |
220 |
< |
QNode h = head.get(); |
219 |
> |
Node<E> t = tail.get(); |
220 |
> |
Node<E> h = head.get(); |
221 |
|
|
222 |
< |
if (t != null && (t == h || t.isData == isData)) { |
222 |
> |
if (t == h || t.isData == isData) { |
223 |
|
if (s == null) |
224 |
< |
s = new QNode(e, isData); |
225 |
< |
QNode last = t.next; |
224 |
> |
s = new Node<E>(e, isData); |
225 |
> |
Node<E> last = t.next; |
226 |
|
if (last != null) { |
227 |
|
if (t == tail.get()) |
228 |
|
tail.compareAndSet(t, last); |
231 |
|
tail.compareAndSet(t, s); |
232 |
|
return awaitFulfill(t, s, e, mode, nanos); |
233 |
|
} |
234 |
< |
} |
235 |
< |
|
236 |
< |
else if (h != null) { |
193 |
< |
QNode first = h.next; |
194 |
< |
if (t == tail.get() && first != null && |
234 |
> |
} else { |
235 |
> |
Node<E> first = h.next; |
236 |
> |
if (t == tail.get() && first != null && |
237 |
|
advanceHead(h, first)) { |
238 |
|
Object x = first.get(); |
239 |
|
if (x != first && first.compareAndSet(x, e)) { |
240 |
|
LockSupport.unpark(first.waiter); |
241 |
< |
return isData? e : x; |
241 |
> |
return isData ? e : (E) x; |
242 |
|
} |
243 |
|
} |
244 |
|
} |
248 |
|
|
249 |
|
/** |
250 |
|
* Version of xfer for poll() and tryTransfer, which |
251 |
< |
* simplifies control paths both here and in xfer |
251 |
> |
* simplifies control paths both here and in xfer. |
252 |
|
*/ |
253 |
< |
private Object fulfill(Object e) { |
253 |
> |
private E fulfill(E e) { |
254 |
|
boolean isData = (e != null); |
255 |
< |
final PaddedAtomicReference<QNode> head = this.head; |
256 |
< |
final PaddedAtomicReference<QNode> tail = this.tail; |
255 |
> |
final PaddedAtomicReference<Node<E>> head = this.head; |
256 |
> |
final PaddedAtomicReference<Node<E>> tail = this.tail; |
257 |
|
|
258 |
|
for (;;) { |
259 |
< |
QNode t = tail.get(); |
260 |
< |
QNode h = head.get(); |
259 |
> |
Node<E> t = tail.get(); |
260 |
> |
Node<E> h = head.get(); |
261 |
|
|
262 |
< |
if (t != null && (t == h || t.isData == isData)) { |
263 |
< |
QNode last = t.next; |
262 |
> |
if (t == h || t.isData == isData) { |
263 |
> |
Node<E> last = t.next; |
264 |
|
if (t == tail.get()) { |
265 |
|
if (last != null) |
266 |
|
tail.compareAndSet(t, last); |
267 |
|
else |
268 |
|
return null; |
269 |
|
} |
270 |
< |
} |
271 |
< |
else if (h != null) { |
272 |
< |
QNode first = h.next; |
231 |
< |
if (t == tail.get() && |
270 |
> |
} else { |
271 |
> |
Node<E> first = h.next; |
272 |
> |
if (t == tail.get() && |
273 |
|
first != null && |
274 |
|
advanceHead(h, first)) { |
275 |
|
Object x = first.get(); |
276 |
|
if (x != first && first.compareAndSet(x, e)) { |
277 |
|
LockSupport.unpark(first.waiter); |
278 |
< |
return isData? e : x; |
278 |
> |
return isData ? e : (E) x; |
279 |
|
} |
280 |
|
} |
281 |
|
} |
291 |
|
* @param e the comparison value for checking match |
292 |
|
* @param mode mode |
293 |
|
* @param nanos timeout value |
294 |
< |
* @return matched item, or s if cancelled |
294 |
> |
* @return matched item, or null if cancelled |
295 |
|
*/ |
296 |
< |
private Object awaitFulfill(QNode pred, QNode s, Object e, |
297 |
< |
int mode, long nanos) { |
296 |
> |
private E awaitFulfill(Node<E> pred, Node<E> s, E e, |
297 |
> |
int mode, long nanos) { |
298 |
|
if (mode == NOWAIT) |
299 |
|
return null; |
300 |
|
|
301 |
< |
long lastTime = (mode == TIMEOUT)? System.nanoTime() : 0; |
301 |
> |
long lastTime = (mode == TIMEOUT) ? System.nanoTime() : 0; |
302 |
|
Thread w = Thread.currentThread(); |
303 |
|
int spins = -1; // set to desired spin count below |
304 |
|
for (;;) { |
307 |
|
Object x = s.get(); |
308 |
|
if (x != e) { // Node was matched or cancelled |
309 |
|
advanceHead(pred, s); // unlink if head |
310 |
< |
if (x == s) // was cancelled |
311 |
< |
return clean(pred, s); |
312 |
< |
else if (x != null) { |
310 |
> |
if (x == s) { // was cancelled |
311 |
> |
clean(pred, s); |
312 |
> |
return null; |
313 |
> |
} |
314 |
> |
else if (x != null) { |
315 |
|
s.set(s); // avoid garbage retention |
316 |
< |
return x; |
316 |
> |
return (E) x; |
317 |
|
} |
318 |
|
else |
319 |
|
return e; |
320 |
|
} |
278 |
– |
|
321 |
|
if (mode == TIMEOUT) { |
322 |
|
long now = System.nanoTime(); |
323 |
|
nanos -= now - lastTime; |
328 |
|
} |
329 |
|
} |
330 |
|
if (spins < 0) { |
331 |
< |
QNode h = head.get(); // only spin if at head |
332 |
< |
spins = ((h != null && h.next == s) ? |
333 |
< |
(mode == TIMEOUT? |
334 |
< |
maxTimedSpins : maxUntimedSpins) : 0); |
331 |
> |
Node<E> h = head.get(); // only spin if at head |
332 |
> |
spins = ((h.next != s) ? 0 : |
333 |
> |
(mode == TIMEOUT) ? maxTimedSpins : |
334 |
> |
maxUntimedSpins); |
335 |
|
} |
336 |
|
if (spins > 0) |
337 |
|
--spins; |
338 |
|
else if (s.waiter == null) |
339 |
|
s.waiter = w; |
340 |
|
else if (mode != TIMEOUT) { |
341 |
< |
// LockSupport.park(this); |
300 |
< |
LockSupport.park(); // allows run on java5 |
341 |
> |
LockSupport.park(this); |
342 |
|
s.waiter = null; |
343 |
|
spins = -1; |
344 |
|
} |
345 |
|
else if (nanos > spinForTimeoutThreshold) { |
346 |
< |
// LockSupport.parkNanos(this, nanos); |
306 |
< |
LockSupport.parkNanos(nanos); |
346 |
> |
LockSupport.parkNanos(this, nanos); |
347 |
|
s.waiter = null; |
348 |
|
spins = -1; |
349 |
|
} |
351 |
|
} |
352 |
|
|
353 |
|
/** |
354 |
+ |
* Returns validated tail for use in cleaning methods. |
355 |
+ |
*/ |
356 |
+ |
private Node<E> getValidatedTail() { |
357 |
+ |
for (;;) { |
358 |
+ |
Node<E> h = head.get(); |
359 |
+ |
Node<E> first = h.next; |
360 |
+ |
if (first != null && first.get() == first) { // help advance |
361 |
+ |
advanceHead(h, first); |
362 |
+ |
continue; |
363 |
+ |
} |
364 |
+ |
Node<E> t = tail.get(); |
365 |
+ |
Node<E> last = t.next; |
366 |
+ |
if (t == tail.get()) { |
367 |
+ |
if (last != null) |
368 |
+ |
tail.compareAndSet(t, last); // help advance |
369 |
+ |
else |
370 |
+ |
return t; |
371 |
+ |
} |
372 |
+ |
} |
373 |
+ |
} |
374 |
+ |
|
375 |
+ |
/** |
376 |
|
* Gets rid of cancelled node s with original predecessor pred. |
377 |
< |
* @return null (to simplify use by callers) |
377 |
> |
* |
378 |
> |
* @param pred predecessor of cancelled node |
379 |
> |
* @param s the cancelled node |
380 |
|
*/ |
381 |
< |
private Object clean(QNode pred, QNode s) { |
381 |
> |
private void clean(Node<E> pred, Node<E> s) { |
382 |
|
Thread w = s.waiter; |
383 |
|
if (w != null) { // Wake up thread |
384 |
|
s.waiter = null; |
385 |
|
if (w != Thread.currentThread()) |
386 |
|
LockSupport.unpark(w); |
387 |
|
} |
388 |
< |
|
389 |
< |
for (;;) { |
390 |
< |
if (pred.next != s) // already cleaned |
391 |
< |
return null; |
392 |
< |
QNode h = head.get(); |
393 |
< |
QNode hn = h.next; // Absorb cancelled first node as head |
394 |
< |
if (hn != null && hn.next == hn) { |
395 |
< |
advanceHead(h, hn); |
396 |
< |
continue; |
397 |
< |
} |
398 |
< |
QNode t = tail.get(); // Ensure consistent read for tail |
399 |
< |
if (t == h) |
400 |
< |
return null; |
401 |
< |
QNode tn = t.next; |
402 |
< |
if (t != tail.get()) |
403 |
< |
continue; |
404 |
< |
if (tn != null) { // Help advance tail |
341 |
< |
tail.compareAndSet(t, tn); |
342 |
< |
continue; |
343 |
< |
} |
344 |
< |
if (s != t) { // If not tail, try to unsplice |
345 |
< |
QNode sn = s.next; |
388 |
> |
|
389 |
> |
if (pred == null) |
390 |
> |
return; |
391 |
> |
|
392 |
> |
/* |
393 |
> |
* At any given time, exactly one node on list cannot be |
394 |
> |
* deleted -- the last inserted node. To accommodate this, if |
395 |
> |
* we cannot delete s, we save its predecessor as "cleanMe", |
396 |
> |
* processing the previously saved version first. At least one |
397 |
> |
* of node s or the node previously saved can always be |
398 |
> |
* processed, so this always terminates. |
399 |
> |
*/ |
400 |
> |
while (pred.next == s) { |
401 |
> |
Node<E> oldpred = reclean(); // First, help get rid of cleanMe |
402 |
> |
Node<E> t = getValidatedTail(); |
403 |
> |
if (s != t) { // If not tail, try to unsplice |
404 |
> |
Node<E> sn = s.next; // s.next == s means s already off list |
405 |
|
if (sn == s || pred.casNext(s, sn)) |
406 |
< |
return null; |
406 |
> |
break; |
407 |
|
} |
408 |
< |
QNode dp = cleanMe.get(); |
409 |
< |
if (dp != null) { // Try unlinking previous cancelled node |
410 |
< |
QNode d = dp.next; |
352 |
< |
QNode dn; |
353 |
< |
if (d == null || // d is gone or |
354 |
< |
d == dp || // d is off list or |
355 |
< |
d.get() != d || // d not cancelled or |
356 |
< |
(d != t && // d not tail and |
357 |
< |
(dn = d.next) != null && // has successor |
358 |
< |
dn != d && // that is on list |
359 |
< |
dp.casNext(d, dn))) // d unspliced |
360 |
< |
cleanMe.compareAndSet(dp, null); |
361 |
< |
if (dp == pred) |
362 |
< |
return null; // s is already saved node |
363 |
< |
} |
364 |
< |
else if (cleanMe.compareAndSet(null, pred)) |
365 |
< |
return null; // Postpone cleaning s |
408 |
> |
else if (oldpred == pred || // Already saved |
409 |
> |
(oldpred == null && cleanMe.compareAndSet(null, pred))) |
410 |
> |
break; // Postpone cleaning |
411 |
|
} |
412 |
|
} |
413 |
< |
|
413 |
> |
|
414 |
> |
/** |
415 |
> |
* Tries to unsplice the cancelled node held in cleanMe that was |
416 |
> |
* previously uncleanable because it was at tail. |
417 |
> |
* |
418 |
> |
* @return current cleanMe node (or null) |
419 |
> |
*/ |
420 |
> |
private Node<E> reclean() { |
421 |
> |
/* |
422 |
> |
* cleanMe is, or at one time was, predecessor of cancelled |
423 |
> |
* node s that was the tail so could not be unspliced. If s |
424 |
> |
* is no longer the tail, try to unsplice if necessary and |
425 |
> |
* make cleanMe slot available. This differs from similar |
426 |
> |
* code in clean() because we must check that pred still |
427 |
> |
* points to a cancelled node that must be unspliced -- if |
428 |
> |
* not, we can (must) clear cleanMe without unsplicing. |
429 |
> |
* This can loop only due to contention on casNext or |
430 |
> |
* clearing cleanMe. |
431 |
> |
*/ |
432 |
> |
Node<E> pred; |
433 |
> |
while ((pred = cleanMe.get()) != null) { |
434 |
> |
Node<E> t = getValidatedTail(); |
435 |
> |
Node<E> s = pred.next; |
436 |
> |
if (s != t) { |
437 |
> |
Node<E> sn; |
438 |
> |
if (s == null || s == pred || s.get() != s || |
439 |
> |
(sn = s.next) == s || pred.casNext(s, sn)) |
440 |
> |
cleanMe.compareAndSet(pred, null); |
441 |
> |
} |
442 |
> |
else // s is still tail; cannot clean |
443 |
> |
break; |
444 |
> |
} |
445 |
> |
return pred; |
446 |
> |
} |
447 |
> |
|
448 |
|
/** |
449 |
< |
* Creates an initially empty <tt>LinkedTransferQueue</tt>. |
449 |
> |
* Creates an initially empty {@code LinkedTransferQueue}. |
450 |
|
*/ |
451 |
|
public LinkedTransferQueue() { |
452 |
+ |
Node<E> dummy = new Node<E>(null, false); |
453 |
+ |
head = new PaddedAtomicReference<Node<E>>(dummy); |
454 |
+ |
tail = new PaddedAtomicReference<Node<E>>(dummy); |
455 |
+ |
cleanMe = new PaddedAtomicReference<Node<E>>(null); |
456 |
|
} |
457 |
|
|
458 |
|
/** |
459 |
< |
* Creates a <tt>LinkedTransferQueue</tt> |
459 |
> |
* Creates a {@code LinkedTransferQueue} |
460 |
|
* initially containing the elements of the given collection, |
461 |
|
* added in traversal order of the collection's iterator. |
462 |
+ |
* |
463 |
|
* @param c the collection of elements to initially contain |
464 |
|
* @throws NullPointerException if the specified collection or any |
465 |
|
* of its elements are null |
466 |
|
*/ |
467 |
|
public LinkedTransferQueue(Collection<? extends E> c) { |
468 |
+ |
this(); |
469 |
|
addAll(c); |
470 |
|
} |
471 |
|
|
472 |
< |
public void put(E e) throws InterruptedException { |
473 |
< |
if (e == null) throw new NullPointerException(); |
474 |
< |
if (Thread.interrupted()) throw new InterruptedException(); |
475 |
< |
xfer(e, NOWAIT, 0); |
472 |
> |
/** |
473 |
> |
* Inserts the specified element at the tail of this queue. |
474 |
> |
* As the queue is unbounded, this method will never block. |
475 |
> |
* |
476 |
> |
* @throws NullPointerException if the specified element is null |
477 |
> |
*/ |
478 |
> |
public void put(E e) { |
479 |
> |
offer(e); |
480 |
|
} |
481 |
|
|
482 |
< |
public boolean offer(E e, long timeout, TimeUnit unit) |
483 |
< |
throws InterruptedException { |
484 |
< |
if (e == null) throw new NullPointerException(); |
485 |
< |
if (Thread.interrupted()) throw new InterruptedException(); |
486 |
< |
xfer(e, NOWAIT, 0); |
487 |
< |
return true; |
482 |
> |
/** |
483 |
> |
* Inserts the specified element at the tail of this queue. |
484 |
> |
* As the queue is unbounded, this method will never block or |
485 |
> |
* return {@code false}. |
486 |
> |
* |
487 |
> |
* @return {@code true} (as specified by |
488 |
> |
* {@link BlockingQueue#offer(Object,long,TimeUnit) BlockingQueue.offer}) |
489 |
> |
* @throws NullPointerException if the specified element is null |
490 |
> |
*/ |
491 |
> |
public boolean offer(E e, long timeout, TimeUnit unit) { |
492 |
> |
return offer(e); |
493 |
|
} |
494 |
|
|
495 |
+ |
/** |
496 |
+ |
* Inserts the specified element at the tail of this queue. |
497 |
+ |
* As the queue is unbounded, this method will never return {@code false}. |
498 |
+ |
* |
499 |
+ |
* @return {@code true} (as specified by |
500 |
+ |
* {@link BlockingQueue#offer(Object) BlockingQueue.offer}) |
501 |
+ |
* @throws NullPointerException if the specified element is null |
502 |
+ |
*/ |
503 |
|
public boolean offer(E e) { |
504 |
|
if (e == null) throw new NullPointerException(); |
505 |
|
xfer(e, NOWAIT, 0); |
506 |
|
return true; |
507 |
|
} |
508 |
|
|
509 |
+ |
/** |
510 |
+ |
* Inserts the specified element at the tail of this queue. |
511 |
+ |
* As the queue is unbounded, this method will never throw |
512 |
+ |
* {@link IllegalStateException} or return {@code false}. |
513 |
+ |
* |
514 |
+ |
* @return {@code true} (as specified by {@link Collection#add}) |
515 |
+ |
* @throws NullPointerException if the specified element is null |
516 |
+ |
*/ |
517 |
+ |
public boolean add(E e) { |
518 |
+ |
return offer(e); |
519 |
+ |
} |
520 |
+ |
|
521 |
+ |
/** |
522 |
+ |
* Transfers the element to a waiting consumer immediately, if possible. |
523 |
+ |
* |
524 |
+ |
* <p>More precisely, transfers the specified element immediately |
525 |
+ |
* if there exists a consumer already waiting to receive it (in |
526 |
+ |
* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
527 |
+ |
* otherwise returning {@code false} without enqueuing the element. |
528 |
+ |
* |
529 |
+ |
* @throws NullPointerException if the specified element is null |
530 |
+ |
*/ |
531 |
+ |
public boolean tryTransfer(E e) { |
532 |
+ |
if (e == null) throw new NullPointerException(); |
533 |
+ |
return fulfill(e) != null; |
534 |
+ |
} |
535 |
+ |
|
536 |
+ |
/** |
537 |
+ |
* Transfers the element to a consumer, waiting if necessary to do so. |
538 |
+ |
* |
539 |
+ |
* <p>More precisely, transfers the specified element immediately |
540 |
+ |
* if there exists a consumer already waiting to receive it (in |
541 |
+ |
* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
542 |
+ |
* else inserts the specified element at the tail of this queue |
543 |
+ |
* and waits until the element is received by a consumer. |
544 |
+ |
* |
545 |
+ |
* @throws NullPointerException if the specified element is null |
546 |
+ |
*/ |
547 |
|
public void transfer(E e) throws InterruptedException { |
548 |
|
if (e == null) throw new NullPointerException(); |
549 |
|
if (xfer(e, WAIT, 0) == null) { |
550 |
< |
Thread.interrupted(); |
550 |
> |
Thread.interrupted(); |
551 |
|
throw new InterruptedException(); |
552 |
< |
} |
552 |
> |
} |
553 |
|
} |
554 |
|
|
555 |
+ |
/** |
556 |
+ |
* Transfers the element to a consumer if it is possible to do so |
557 |
+ |
* before the timeout elapses. |
558 |
+ |
* |
559 |
+ |
* <p>More precisely, transfers the specified element immediately |
560 |
+ |
* if there exists a consumer already waiting to receive it (in |
561 |
+ |
* {@link #take} or timed {@link #poll(long,TimeUnit) poll}), |
562 |
+ |
* else inserts the specified element at the tail of this queue |
563 |
+ |
* and waits until the element is received by a consumer, |
564 |
+ |
* returning {@code false} if the specified wait time elapses |
565 |
+ |
* before the element can be transferred. |
566 |
+ |
* |
567 |
+ |
* @throws NullPointerException if the specified element is null |
568 |
+ |
*/ |
569 |
|
public boolean tryTransfer(E e, long timeout, TimeUnit unit) |
570 |
|
throws InterruptedException { |
571 |
|
if (e == null) throw new NullPointerException(); |
576 |
|
throw new InterruptedException(); |
577 |
|
} |
578 |
|
|
425 |
– |
public boolean tryTransfer(E e) { |
426 |
– |
if (e == null) throw new NullPointerException(); |
427 |
– |
return fulfill(e) != null; |
428 |
– |
} |
429 |
– |
|
579 |
|
public E take() throws InterruptedException { |
580 |
< |
Object e = xfer(null, WAIT, 0); |
580 |
> |
E e = xfer(null, WAIT, 0); |
581 |
|
if (e != null) |
582 |
< |
return (E)e; |
583 |
< |
Thread.interrupted(); |
582 |
> |
return e; |
583 |
> |
Thread.interrupted(); |
584 |
|
throw new InterruptedException(); |
585 |
|
} |
586 |
|
|
587 |
|
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
588 |
< |
Object e = xfer(null, TIMEOUT, unit.toNanos(timeout)); |
588 |
> |
E e = xfer(null, TIMEOUT, unit.toNanos(timeout)); |
589 |
|
if (e != null || !Thread.interrupted()) |
590 |
< |
return (E)e; |
590 |
> |
return e; |
591 |
|
throw new InterruptedException(); |
592 |
|
} |
593 |
|
|
594 |
|
public E poll() { |
595 |
< |
return (E)fulfill(null); |
595 |
> |
return fulfill(null); |
596 |
|
} |
597 |
|
|
598 |
+ |
/** |
599 |
+ |
* @throws NullPointerException {@inheritDoc} |
600 |
+ |
* @throws IllegalArgumentException {@inheritDoc} |
601 |
+ |
*/ |
602 |
|
public int drainTo(Collection<? super E> c) { |
603 |
|
if (c == null) |
604 |
|
throw new NullPointerException(); |
613 |
|
return n; |
614 |
|
} |
615 |
|
|
616 |
+ |
/** |
617 |
+ |
* @throws NullPointerException {@inheritDoc} |
618 |
+ |
* @throws IllegalArgumentException {@inheritDoc} |
619 |
+ |
*/ |
620 |
|
public int drainTo(Collection<? super E> c, int maxElements) { |
621 |
|
if (c == null) |
622 |
|
throw new NullPointerException(); |
634 |
|
// Traversal-based methods |
635 |
|
|
636 |
|
/** |
637 |
< |
* Return head after performing any outstanding helping steps |
637 |
> |
* Returns head after performing any outstanding helping steps. |
638 |
|
*/ |
639 |
< |
private QNode traversalHead() { |
639 |
> |
private Node<E> traversalHead() { |
640 |
|
for (;;) { |
641 |
< |
QNode t = tail.get(); |
642 |
< |
QNode h = head.get(); |
643 |
< |
if (h != null && t != null) { |
644 |
< |
QNode last = t.next; |
645 |
< |
QNode first = h.next; |
646 |
< |
if (t == tail.get()) { |
647 |
< |
if (last != null) |
648 |
< |
tail.compareAndSet(t, last); |
649 |
< |
else if (first != null) { |
650 |
< |
Object x = first.get(); |
651 |
< |
if (x == first) |
495 |
< |
advanceHead(h, first); |
496 |
< |
else |
497 |
< |
return h; |
498 |
< |
} |
641 |
> |
Node<E> t = tail.get(); |
642 |
> |
Node<E> h = head.get(); |
643 |
> |
Node<E> last = t.next; |
644 |
> |
Node<E> first = h.next; |
645 |
> |
if (t == tail.get()) { |
646 |
> |
if (last != null) |
647 |
> |
tail.compareAndSet(t, last); |
648 |
> |
else if (first != null) { |
649 |
> |
Object x = first.get(); |
650 |
> |
if (x == first) |
651 |
> |
advanceHead(h, first); |
652 |
|
else |
653 |
|
return h; |
654 |
|
} |
655 |
+ |
else |
656 |
+ |
return h; |
657 |
|
} |
658 |
+ |
reclean(); |
659 |
|
} |
660 |
|
} |
661 |
|
|
662 |
< |
|
662 |
> |
/** |
663 |
> |
* Returns an iterator over the elements in this queue in proper |
664 |
> |
* sequence, from head to tail. |
665 |
> |
* |
666 |
> |
* <p>The returned iterator is a "weakly consistent" iterator that |
667 |
> |
* will never throw |
668 |
> |
* {@link ConcurrentModificationException ConcurrentModificationException}, |
669 |
> |
* and guarantees to traverse elements as they existed upon |
670 |
> |
* construction of the iterator, and may (but is not guaranteed |
671 |
> |
* to) reflect any modifications subsequent to construction. |
672 |
> |
* |
673 |
> |
* @return an iterator over the elements in this queue in proper sequence |
674 |
> |
*/ |
675 |
|
public Iterator<E> iterator() { |
676 |
|
return new Itr(); |
677 |
|
} |
684 |
|
* if subsequently removed. |
685 |
|
*/ |
686 |
|
class Itr implements Iterator<E> { |
687 |
< |
QNode nextNode; // Next node to return next |
688 |
< |
QNode currentNode; // last returned node, for remove() |
689 |
< |
QNode prevNode; // predecessor of last returned node |
690 |
< |
E nextItem; // Cache of next item, once commited to in next |
691 |
< |
|
687 |
> |
Node<E> next; // node to return next |
688 |
> |
Node<E> pnext; // predecessor of next |
689 |
> |
Node<E> curr; // last returned node, for remove() |
690 |
> |
Node<E> pcurr; // predecessor of curr, for remove() |
691 |
> |
E nextItem; // Cache of next item, once committed to in next |
692 |
> |
|
693 |
|
Itr() { |
525 |
– |
nextNode = traversalHead(); |
694 |
|
advance(); |
695 |
|
} |
696 |
< |
|
697 |
< |
E advance() { |
698 |
< |
prevNode = currentNode; |
699 |
< |
currentNode = nextNode; |
700 |
< |
E x = nextItem; |
701 |
< |
|
702 |
< |
QNode p = nextNode.next; |
696 |
> |
|
697 |
> |
/** |
698 |
> |
* Moves to next valid node and returns item to return for |
699 |
> |
* next(), or null if no such. |
700 |
> |
*/ |
701 |
> |
private E advance() { |
702 |
> |
pcurr = pnext; |
703 |
> |
curr = next; |
704 |
> |
E item = nextItem; |
705 |
> |
|
706 |
|
for (;;) { |
707 |
< |
if (p == null || !p.isData) { |
708 |
< |
nextNode = null; |
709 |
< |
nextItem = null; |
710 |
< |
return x; |
711 |
< |
} |
712 |
< |
Object item = p.get(); |
713 |
< |
if (item != p && item != null) { |
714 |
< |
nextNode = p; |
715 |
< |
nextItem = (E)item; |
716 |
< |
return x; |
717 |
< |
} |
718 |
< |
prevNode = p; |
719 |
< |
p = p.next; |
707 |
> |
pnext = (next == null) ? traversalHead() : next; |
708 |
> |
next = pnext.next; |
709 |
> |
if (next == pnext) { |
710 |
> |
next = null; |
711 |
> |
continue; // restart |
712 |
> |
} |
713 |
> |
if (next == null) |
714 |
> |
break; |
715 |
> |
Object x = next.get(); |
716 |
> |
if (x != null && x != next) { |
717 |
> |
nextItem = (E) x; |
718 |
> |
break; |
719 |
> |
} |
720 |
|
} |
721 |
+ |
return item; |
722 |
|
} |
723 |
< |
|
723 |
> |
|
724 |
|
public boolean hasNext() { |
725 |
< |
return nextNode != null; |
725 |
> |
return next != null; |
726 |
|
} |
727 |
< |
|
727 |
> |
|
728 |
|
public E next() { |
729 |
< |
if (nextNode == null) throw new NoSuchElementException(); |
729 |
> |
if (next == null) |
730 |
> |
throw new NoSuchElementException(); |
731 |
|
return advance(); |
732 |
|
} |
733 |
< |
|
733 |
> |
|
734 |
|
public void remove() { |
735 |
< |
QNode p = currentNode; |
736 |
< |
QNode prev = prevNode; |
564 |
< |
if (prev == null || p == null) |
735 |
> |
Node<E> p = curr; |
736 |
> |
if (p == null) |
737 |
|
throw new IllegalStateException(); |
738 |
|
Object x = p.get(); |
739 |
|
if (x != null && x != p && p.compareAndSet(x, p)) |
740 |
< |
clean(prev, p); |
740 |
> |
clean(pcurr, p); |
741 |
|
} |
742 |
|
} |
743 |
|
|
744 |
|
public E peek() { |
745 |
|
for (;;) { |
746 |
< |
QNode h = traversalHead(); |
747 |
< |
QNode p = h.next; |
746 |
> |
Node<E> h = traversalHead(); |
747 |
> |
Node<E> p = h.next; |
748 |
|
if (p == null) |
749 |
|
return null; |
750 |
|
Object x = p.get(); |
752 |
|
if (!p.isData) |
753 |
|
return null; |
754 |
|
if (x != null) |
755 |
< |
return (E)x; |
755 |
> |
return (E) x; |
756 |
|
} |
757 |
|
} |
758 |
|
} |
759 |
|
|
760 |
+ |
/** |
761 |
+ |
* Returns {@code true} if this queue contains no elements. |
762 |
+ |
* |
763 |
+ |
* @return {@code true} if this queue contains no elements |
764 |
+ |
*/ |
765 |
|
public boolean isEmpty() { |
766 |
|
for (;;) { |
767 |
< |
QNode h = traversalHead(); |
768 |
< |
QNode p = h.next; |
767 |
> |
Node<E> h = traversalHead(); |
768 |
> |
Node<E> p = h.next; |
769 |
|
if (p == null) |
770 |
|
return true; |
771 |
|
Object x = p.get(); |
780 |
|
|
781 |
|
public boolean hasWaitingConsumer() { |
782 |
|
for (;;) { |
783 |
< |
QNode h = traversalHead(); |
784 |
< |
QNode p = h.next; |
783 |
> |
Node<E> h = traversalHead(); |
784 |
> |
Node<E> p = h.next; |
785 |
|
if (p == null) |
786 |
|
return false; |
787 |
|
Object x = p.get(); |
788 |
< |
if (p != x) |
788 |
> |
if (p != x) |
789 |
|
return !p.isData; |
790 |
|
} |
791 |
|
} |
792 |
< |
|
792 |
> |
|
793 |
|
/** |
794 |
|
* Returns the number of elements in this queue. If this queue |
795 |
< |
* contains more than <tt>Integer.MAX_VALUE</tt> elements, returns |
796 |
< |
* <tt>Integer.MAX_VALUE</tt>. |
795 |
> |
* contains more than {@code Integer.MAX_VALUE} elements, returns |
796 |
> |
* {@code Integer.MAX_VALUE}. |
797 |
|
* |
798 |
|
* <p>Beware that, unlike in most collections, this method is |
799 |
|
* <em>NOT</em> a constant-time operation. Because of the |
803 |
|
* @return the number of elements in this queue |
804 |
|
*/ |
805 |
|
public int size() { |
806 |
< |
int count = 0; |
807 |
< |
QNode h = traversalHead(); |
808 |
< |
for (QNode p = h.next; p != null && p.isData; p = p.next) { |
809 |
< |
Object x = p.get(); |
810 |
< |
if (x != null && x != p) { |
811 |
< |
if (++count == Integer.MAX_VALUE) // saturated |
806 |
> |
for (;;) { |
807 |
> |
int count = 0; |
808 |
> |
Node<E> pred = traversalHead(); |
809 |
> |
for (;;) { |
810 |
> |
Node<E> q = pred.next; |
811 |
> |
if (q == pred) // restart |
812 |
|
break; |
813 |
+ |
if (q == null || !q.isData) |
814 |
+ |
return count; |
815 |
+ |
Object x = q.get(); |
816 |
+ |
if (x != null && x != q) { |
817 |
+ |
if (++count == Integer.MAX_VALUE) // saturated |
818 |
+ |
return count; |
819 |
+ |
} |
820 |
+ |
pred = q; |
821 |
|
} |
822 |
|
} |
638 |
– |
return count; |
823 |
|
} |
824 |
|
|
825 |
|
public int getWaitingConsumerCount() { |
826 |
< |
int count = 0; |
827 |
< |
QNode h = traversalHead(); |
828 |
< |
for (QNode p = h.next; p != null && !p.isData; p = p.next) { |
829 |
< |
if (p.get() == null) { |
830 |
< |
if (++count == Integer.MAX_VALUE) |
826 |
> |
// converse of size -- count valid non-data nodes |
827 |
> |
for (;;) { |
828 |
> |
int count = 0; |
829 |
> |
Node<E> pred = traversalHead(); |
830 |
> |
for (;;) { |
831 |
> |
Node<E> q = pred.next; |
832 |
> |
if (q == pred) // restart |
833 |
|
break; |
834 |
+ |
if (q == null || q.isData) |
835 |
+ |
return count; |
836 |
+ |
Object x = q.get(); |
837 |
+ |
if (x == null) { |
838 |
+ |
if (++count == Integer.MAX_VALUE) // saturated |
839 |
+ |
return count; |
840 |
+ |
} |
841 |
+ |
pred = q; |
842 |
|
} |
843 |
|
} |
650 |
– |
return count; |
844 |
|
} |
845 |
|
|
846 |
+ |
/** |
847 |
+ |
* Removes a single instance of the specified element from this queue, |
848 |
+ |
* if it is present. More formally, removes an element {@code e} such |
849 |
+ |
* that {@code o.equals(e)}, if this queue contains one or more such |
850 |
+ |
* elements. |
851 |
+ |
* Returns {@code true} if this queue contained the specified element |
852 |
+ |
* (or equivalently, if this queue changed as a result of the call). |
853 |
+ |
* |
854 |
+ |
* @param o element to be removed from this queue, if present |
855 |
+ |
* @return {@code true} if this queue changed as a result of the call |
856 |
+ |
*/ |
857 |
+ |
public boolean remove(Object o) { |
858 |
+ |
if (o == null) |
859 |
+ |
return false; |
860 |
+ |
for (;;) { |
861 |
+ |
Node<E> pred = traversalHead(); |
862 |
+ |
for (;;) { |
863 |
+ |
Node<E> q = pred.next; |
864 |
+ |
if (q == pred) // restart |
865 |
+ |
break; |
866 |
+ |
if (q == null || !q.isData) |
867 |
+ |
return false; |
868 |
+ |
Object x = q.get(); |
869 |
+ |
if (x != null && x != q && o.equals(x) && |
870 |
+ |
q.compareAndSet(x, q)) { |
871 |
+ |
clean(pred, q); |
872 |
+ |
return true; |
873 |
+ |
} |
874 |
+ |
pred = q; |
875 |
+ |
} |
876 |
+ |
} |
877 |
+ |
} |
878 |
+ |
|
879 |
+ |
/** |
880 |
+ |
* Always returns {@code Integer.MAX_VALUE} because a |
881 |
+ |
* {@code LinkedTransferQueue} is not capacity constrained. |
882 |
+ |
* |
883 |
+ |
* @return {@code Integer.MAX_VALUE} (as specified by |
884 |
+ |
* {@link BlockingQueue#remainingCapacity()}) |
885 |
+ |
*/ |
886 |
|
public int remainingCapacity() { |
887 |
|
return Integer.MAX_VALUE; |
888 |
|
} |
890 |
|
/** |
891 |
|
* Save the state to a stream (that is, serialize it). |
892 |
|
* |
893 |
< |
* @serialData All of the elements (each an <tt>E</tt>) in |
893 |
> |
* @serialData All of the elements (each an {@code E}) in |
894 |
|
* the proper order, followed by a null |
895 |
|
* @param s the stream |
896 |
|
*/ |
897 |
|
private void writeObject(java.io.ObjectOutputStream s) |
898 |
|
throws java.io.IOException { |
899 |
|
s.defaultWriteObject(); |
900 |
< |
for (Iterator<E> it = iterator(); it.hasNext(); ) |
901 |
< |
s.writeObject(it.next()); |
900 |
> |
for (E e : this) |
901 |
> |
s.writeObject(e); |
902 |
|
// Use trailing null as sentinel |
903 |
|
s.writeObject(null); |
904 |
|
} |
906 |
|
/** |
907 |
|
* Reconstitute the Queue instance from a stream (that is, |
908 |
|
* deserialize it). |
909 |
+ |
* |
910 |
|
* @param s the stream |
911 |
|
*/ |
912 |
|
private void readObject(java.io.ObjectInputStream s) |
913 |
|
throws java.io.IOException, ClassNotFoundException { |
914 |
|
s.defaultReadObject(); |
915 |
+ |
resetHeadAndTail(); |
916 |
|
for (;;) { |
917 |
< |
E item = (E)s.readObject(); |
917 |
> |
@SuppressWarnings("unchecked") E item = (E) s.readObject(); |
918 |
|
if (item == null) |
919 |
|
break; |
920 |
|
else |
921 |
|
offer(item); |
922 |
|
} |
923 |
|
} |
924 |
+ |
|
925 |
+ |
// Support for resetting head/tail while deserializing |
926 |
+ |
private void resetHeadAndTail() { |
927 |
+ |
Node<E> dummy = new Node<E>(null, false); |
928 |
+ |
UNSAFE.putObjectVolatile(this, headOffset, |
929 |
+ |
new PaddedAtomicReference<Node<E>>(dummy)); |
930 |
+ |
UNSAFE.putObjectVolatile(this, tailOffset, |
931 |
+ |
new PaddedAtomicReference<Node<E>>(dummy)); |
932 |
+ |
UNSAFE.putObjectVolatile(this, cleanMeOffset, |
933 |
+ |
new PaddedAtomicReference<Node<E>>(null)); |
934 |
+ |
} |
935 |
+ |
|
936 |
+ |
// Unsafe mechanics |
937 |
+ |
|
938 |
+ |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
939 |
+ |
private static final long headOffset = |
940 |
+ |
objectFieldOffset(UNSAFE, "head", LinkedTransferQueue.class); |
941 |
+ |
private static final long tailOffset = |
942 |
+ |
objectFieldOffset(UNSAFE, "tail", LinkedTransferQueue.class); |
943 |
+ |
private static final long cleanMeOffset = |
944 |
+ |
objectFieldOffset(UNSAFE, "cleanMe", LinkedTransferQueue.class); |
945 |
+ |
|
946 |
+ |
|
947 |
+ |
static long objectFieldOffset(sun.misc.Unsafe UNSAFE, |
948 |
+ |
String field, Class<?> klazz) { |
949 |
+ |
try { |
950 |
+ |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
951 |
+ |
} catch (NoSuchFieldException e) { |
952 |
+ |
// Convert Exception to corresponding Error |
953 |
+ |
NoSuchFieldError error = new NoSuchFieldError(field); |
954 |
+ |
error.initCause(e); |
955 |
+ |
throw error; |
956 |
+ |
} |
957 |
+ |
} |
958 |
+ |
|
959 |
+ |
/** |
960 |
+ |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
961 |
+ |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
962 |
+ |
* into a jdk. |
963 |
+ |
* |
964 |
+ |
* @return a sun.misc.Unsafe |
965 |
+ |
*/ |
966 |
+ |
private static sun.misc.Unsafe getUnsafe() { |
967 |
+ |
try { |
968 |
+ |
return sun.misc.Unsafe.getUnsafe(); |
969 |
+ |
} catch (SecurityException se) { |
970 |
+ |
try { |
971 |
+ |
return java.security.AccessController.doPrivileged |
972 |
+ |
(new java.security |
973 |
+ |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
974 |
+ |
public sun.misc.Unsafe run() throws Exception { |
975 |
+ |
java.lang.reflect.Field f = sun.misc |
976 |
+ |
.Unsafe.class.getDeclaredField("theUnsafe"); |
977 |
+ |
f.setAccessible(true); |
978 |
+ |
return (sun.misc.Unsafe) f.get(null); |
979 |
+ |
}}); |
980 |
+ |
} catch (java.security.PrivilegedActionException e) { |
981 |
+ |
throw new RuntimeException("Could not initialize intrinsics", |
982 |
+ |
e.getCause()); |
983 |
+ |
} |
984 |
+ |
} |
985 |
+ |
} |
986 |
|
} |