6 |
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7 |
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package jsr166e; |
8 |
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9 |
– |
import java.util.concurrent.ThreadLocalRandom; |
9 |
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import java.util.concurrent.TimeUnit; |
10 |
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import java.util.concurrent.locks.Lock; |
11 |
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import java.util.concurrent.locks.Condition; |
39 |
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* <li><b>Optimistic Reading.</b> Method {@link #tryOptimisticRead} |
40 |
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* returns a non-zero stamp only if the lock is not currently held |
41 |
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* in write mode. Method {@link #validate} returns true if the lock |
42 |
< |
* has not since been acquired in write mode. This mode can be |
43 |
< |
* thought of as an extremely weak version of a read-lock, that can |
44 |
< |
* be broken by a writer at any time. The use of optimistic mode |
45 |
< |
* for short read-only code segments often reduces contention and |
46 |
< |
* improves throughput. However, its use is inherently fragile. |
47 |
< |
* Optimistic read sections should only read fields and hold them in |
48 |
< |
* local variables for later use after validation. Fields read while |
49 |
< |
* in optimistic mode may be wildly inconsistent, so usage applies |
50 |
< |
* only when you are familiar enough with data representations to |
51 |
< |
* check consistency and/or repeatedly invoke method {@code |
52 |
< |
* validate()}. For example, such steps are typically required when |
53 |
< |
* first reading an object or array reference, and then accessing |
54 |
< |
* one of its fields, elements or methods. </li> |
42 |
> |
* has not been acquired in write mode since obtaining a given |
43 |
> |
* stamp. This mode can be thought of as an extremely weak version |
44 |
> |
* of a read-lock, that can be broken by a writer at any time. The |
45 |
> |
* use of optimistic mode for short read-only code segments often |
46 |
> |
* reduces contention and improves throughput. However, its use is |
47 |
> |
* inherently fragile. Optimistic read sections should only read |
48 |
> |
* fields and hold them in local variables for later use after |
49 |
> |
* validation. Fields read while in optimistic mode may be wildly |
50 |
> |
* inconsistent, so usage applies only when you are familiar enough |
51 |
> |
* with data representations to check consistency and/or repeatedly |
52 |
> |
* invoke method {@code validate()}. For example, such steps are |
53 |
> |
* typically required when first reading an object or array |
54 |
> |
* reference, and then accessing one of its fields, elements or |
55 |
> |
* methods. </li> |
56 |
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* |
57 |
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* </ul> |
58 |
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* |
118 |
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* } |
119 |
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* } |
120 |
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* |
121 |
< |
* double distanceFromOriginV1() { // A read-only method |
122 |
< |
* long stamp; |
123 |
< |
* if ((stamp = sl.tryOptimisticRead()) != 0L) { // optimistic |
124 |
< |
* double currentX = x; |
125 |
< |
* double currentY = y; |
126 |
< |
* if (sl.validate(stamp)) |
127 |
< |
* return Math.sqrt(currentX * currentX + currentY * currentY); |
128 |
< |
* } |
129 |
< |
* stamp = sl.readLock(); // fall back to read lock |
130 |
< |
* try { |
131 |
< |
* double currentX = x; |
132 |
< |
* double currentY = y; |
133 |
< |
* return Math.sqrt(currentX * currentX + currentY * currentY); |
134 |
< |
* } finally { |
135 |
< |
* sl.unlockRead(stamp); |
136 |
< |
* } |
137 |
< |
* } |
138 |
< |
* |
139 |
< |
* double distanceFromOriginV2() { // combines code paths |
140 |
< |
* double currentX = 0.0, currentY = 0.0; |
141 |
< |
* for (long stamp = sl.tryOptimisticRead(); ; stamp = sl.readLock()) { |
142 |
< |
* try { |
143 |
< |
* currentX = x; |
144 |
< |
* currentY = y; |
145 |
< |
* } finally { |
146 |
< |
* if (sl.tryConvertToOptimisticRead(stamp) != 0L) // unlock or validate |
147 |
< |
* break; |
148 |
< |
* } |
121 |
> |
* double distanceFromOrigin() { // A read-only method |
122 |
> |
* long stamp = sl.tryOptimisticRead(); |
123 |
> |
* double currentX = x, currentY = y; |
124 |
> |
* if (!sl.validate(stamp)) { |
125 |
> |
* stamp = sl.readLock(); |
126 |
> |
* try { |
127 |
> |
* currentX = x; |
128 |
> |
* currentY = y; |
129 |
> |
* } finally { |
130 |
> |
* sl.unlockRead(stamp); |
131 |
> |
* } |
132 |
|
* } |
133 |
|
* return Math.sqrt(currentX * currentX + currentY * currentY); |
134 |
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* } |
197 |
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* incoming reader arrives while read lock is held but there is a |
198 |
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* queued writer, this incoming reader is queued. (This rule is |
199 |
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* responsible for some of the complexity of method acquireRead, |
200 |
< |
* but without it, the lock becomes highly unfair.) |
200 |
> |
* but without it, the lock becomes highly unfair.) Method release |
201 |
> |
* does not (and sometimes cannot) itself wake up cowaiters. This |
202 |
> |
* is done by the primary thread, but helped by any other threads |
203 |
> |
* with nothing better to do in methods acquireRead and |
204 |
> |
* acquireWrite. |
205 |
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* |
206 |
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* These rules apply to threads actually queued. All tryLock forms |
207 |
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* opportunistically try to acquire locks regardless of preference |
219 |
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* |
220 |
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* Nearly all of these mechanics are carried out in methods |
221 |
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* acquireWrite and acquireRead, that, as typical of such code, |
222 |
< |
* sprawl out because actions and retries rely on consitent sets |
222 |
> |
* sprawl out because actions and retries rely on consistent sets |
223 |
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* of locally cached reads. |
224 |
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* |
225 |
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* As noted in Boehm's paper (above), sequence validation (mainly |
239 |
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* motivation to further spread out contended locations, but might |
240 |
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* be subject to future improvements. |
241 |
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*/ |
242 |
+ |
|
243 |
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private static final long serialVersionUID = -6001602636862214147L; |
244 |
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|
245 |
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/** Number of processors, for spin control */ |
246 |
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private static final int NCPU = Runtime.getRuntime().availableProcessors(); |
247 |
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|
248 |
< |
/** Maximum number of retries before blocking on acquisition */ |
248 |
> |
/** Maximum number of retries before enqueuing on acquisition */ |
249 |
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private static final int SPINS = (NCPU > 1) ? 1 << 6 : 0; |
250 |
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|
251 |
+ |
/** Maximum number of retries before blocking at head on acquisition */ |
252 |
+ |
private static final int HEAD_SPINS = (NCPU > 1) ? 1 << 10 : 0; |
253 |
+ |
|
254 |
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/** Maximum number of retries before re-blocking */ |
255 |
< |
private static final int MAX_HEAD_SPINS = (NCPU > 1) ? 1 << 12 : 0; |
255 |
> |
private static final int MAX_HEAD_SPINS = (NCPU > 1) ? 1 << 16 : 0; |
256 |
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|
257 |
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/** The period for yielding when waiting for overflow spinlock */ |
258 |
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private static final int OVERFLOW_YIELD_RATE = 7; // must be power 2 - 1 |
322 |
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* @return a stamp that can be used to unlock or convert mode |
323 |
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*/ |
324 |
|
public long writeLock() { |
325 |
< |
long s, next; // bypass acquireWrite in fully onlocked case only |
325 |
> |
long s, next; // bypass acquireWrite in fully unlocked case only |
326 |
|
return ((((s = state) & ABITS) == 0L && |
327 |
|
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) ? |
328 |
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next : acquireWrite(false, 0L)); |
347 |
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* Behavior under timeout and interruption matches that specified |
348 |
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* for method {@link Lock#tryLock(long,TimeUnit)}. |
349 |
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* |
350 |
+ |
* @param time the maximum time to wait for the lock |
351 |
+ |
* @param unit the time unit of the {@code time} argument |
352 |
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* @return a stamp that can be used to unlock or convert mode, |
353 |
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* or zero if the lock is not available |
354 |
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* @throws InterruptedException if the current thread is interrupted |
396 |
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* @return a stamp that can be used to unlock or convert mode |
397 |
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*/ |
398 |
|
public long readLock() { |
399 |
< |
long s, next; // bypass acquireRead on fully onlocked case only |
400 |
< |
return ((((s = state) & ABITS) == 0L && |
399 |
> |
long s = state, next; // bypass acquireRead on common uncontended case |
400 |
> |
return ((whead == wtail && (s & ABITS) < RFULL && |
401 |
|
U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) ? |
402 |
|
next : acquireRead(false, 0L)); |
403 |
|
} |
428 |
|
* Behavior under timeout and interruption matches that specified |
429 |
|
* for method {@link Lock#tryLock(long,TimeUnit)}. |
430 |
|
* |
431 |
+ |
* @param time the maximum time to wait for the lock |
432 |
+ |
* @param unit the time unit of the {@code time} argument |
433 |
|
* @return a stamp that can be used to unlock or convert mode, |
434 |
|
* or zero if the lock is not available |
435 |
|
* @throws InterruptedException if the current thread is interrupted |
437 |
|
*/ |
438 |
|
public long tryReadLock(long time, TimeUnit unit) |
439 |
|
throws InterruptedException { |
440 |
< |
long next, deadline; |
440 |
> |
long s, m, next, deadline; |
441 |
|
long nanos = unit.toNanos(time); |
442 |
|
if (!Thread.interrupted()) { |
443 |
< |
if ((next = tryReadLock()) != 0L) |
444 |
< |
return next; |
443 |
> |
if ((m = (s = state) & ABITS) != WBIT) { |
444 |
> |
if (m < RFULL) { |
445 |
> |
if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) |
446 |
> |
return next; |
447 |
> |
} |
448 |
> |
else if ((next = tryIncReaderOverflow(s)) != 0L) |
449 |
> |
return next; |
450 |
> |
} |
451 |
|
if (nanos <= 0L) |
452 |
|
return 0L; |
453 |
|
if ((deadline = System.nanoTime() + nanos) == 0L) |
491 |
|
* Returns true if the lock has not been exclusively acquired |
492 |
|
* since issuance of the given stamp. Always returns false if the |
493 |
|
* stamp is zero. Always returns true if the stamp represents a |
494 |
< |
* currently held lock. |
494 |
> |
* currently held lock. Invoking this method with a value not |
495 |
> |
* obtained from {@link #tryOptimisticRead} or a locking method |
496 |
> |
* for this lock has no defined effect or result. |
497 |
|
* |
498 |
< |
* @return true if the lock has not been exclusively acquired |
498 |
> |
* @param stamp a stamp |
499 |
> |
* @return {@code true} if the lock has not been exclusively acquired |
500 |
|
* since issuance of the given stamp; else false |
501 |
|
*/ |
502 |
|
public boolean validate(long stamp) { |
674 |
|
long a = stamp & ABITS, m, s, next; WNode h; |
675 |
|
for (;;) { |
676 |
|
s = U.getLongVolatile(this, STATE); // see above |
677 |
< |
if ((s & SBITS) != (stamp & SBITS)) |
677 |
> |
if (((s = state) & SBITS) != (stamp & SBITS)) |
678 |
|
break; |
679 |
|
if ((m = s & ABITS) == 0L) { |
680 |
|
if (a != 0L) |
709 |
|
* stamp value. This method may be useful for recovery after |
710 |
|
* errors. |
711 |
|
* |
712 |
< |
* @return true if the lock was held, else false |
712 |
> |
* @return {@code true} if the lock was held, else false |
713 |
|
*/ |
714 |
|
public boolean tryUnlockWrite() { |
715 |
|
long s; WNode h; |
727 |
|
* requiring a stamp value. This method may be useful for recovery |
728 |
|
* after errors. |
729 |
|
* |
730 |
< |
* @return true if the read lock was held, else false |
730 |
> |
* @return {@code true} if the read lock was held, else false |
731 |
|
*/ |
732 |
|
public boolean tryUnlockRead() { |
733 |
|
long s, m; WNode h; |
745 |
|
return false; |
746 |
|
} |
747 |
|
|
748 |
+ |
// status monitoring methods |
749 |
+ |
|
750 |
|
/** |
751 |
< |
* Returns true if the lock is currently held exclusively. |
751 |
> |
* Returns combined state-held and overflow read count for given |
752 |
> |
* state s. |
753 |
> |
*/ |
754 |
> |
private int getReadLockCount(long s) { |
755 |
> |
long readers; |
756 |
> |
if ((readers = s & RBITS) >= RFULL) |
757 |
> |
readers = RFULL + readerOverflow; |
758 |
> |
return (int) readers; |
759 |
> |
} |
760 |
> |
|
761 |
> |
/** |
762 |
> |
* Returns {@code true} if the lock is currently held exclusively. |
763 |
|
* |
764 |
< |
* @return true if the lock is currently held exclusively |
764 |
> |
* @return {@code true} if the lock is currently held exclusively |
765 |
|
*/ |
766 |
|
public boolean isWriteLocked() { |
767 |
|
return (state & WBIT) != 0L; |
768 |
|
} |
769 |
|
|
770 |
|
/** |
771 |
< |
* Returns true if the lock is currently held non-exclusively. |
771 |
> |
* Returns {@code true} if the lock is currently held non-exclusively. |
772 |
|
* |
773 |
< |
* @return true if the lock is currently held non-exclusively |
773 |
> |
* @return {@code true} if the lock is currently held non-exclusively |
774 |
|
*/ |
775 |
|
public boolean isReadLocked() { |
776 |
|
return (state & RBITS) != 0L; |
777 |
|
} |
778 |
|
|
779 |
< |
private void readObject(java.io.ObjectInputStream s) |
780 |
< |
throws java.io.IOException, ClassNotFoundException { |
781 |
< |
s.defaultReadObject(); |
782 |
< |
state = ORIGIN; // reset to unlocked state |
779 |
> |
/** |
780 |
> |
* Queries the number of read locks held for this lock. This |
781 |
> |
* method is designed for use in monitoring system state, not for |
782 |
> |
* synchronization control. |
783 |
> |
* @return the number of read locks held |
784 |
> |
*/ |
785 |
> |
public int getReadLockCount() { |
786 |
> |
return getReadLockCount(state); |
787 |
|
} |
788 |
|
|
789 |
|
/** |
790 |
+ |
* Returns a string identifying this lock, as well as its lock |
791 |
+ |
* state. The state, in brackets, includes the String {@code |
792 |
+ |
* "Unlocked"} or the String {@code "Write-locked"} or the String |
793 |
+ |
* {@code "Read-locks:"} followed by the current number of |
794 |
+ |
* read-locks held. |
795 |
+ |
* |
796 |
+ |
* @return a string identifying this lock, as well as its lock state |
797 |
+ |
*/ |
798 |
+ |
public String toString() { |
799 |
+ |
long s = state; |
800 |
+ |
return super.toString() + |
801 |
+ |
((s & ABITS) == 0L ? "[Unlocked]" : |
802 |
+ |
(s & WBIT) != 0L ? "[Write-locked]" : |
803 |
+ |
"[Read-locks:" + getReadLockCount(s) + "]"); |
804 |
+ |
} |
805 |
+ |
|
806 |
+ |
// views |
807 |
+ |
|
808 |
+ |
/** |
809 |
|
* Returns a plain {@link Lock} view of this StampedLock in which |
810 |
|
* the {@link Lock#lock} method is mapped to {@link #readLock}, |
811 |
|
* and similarly for other methods. The returned Lock does not |
919 |
|
} |
920 |
|
} |
921 |
|
|
922 |
+ |
private void readObject(java.io.ObjectInputStream s) |
923 |
+ |
throws java.io.IOException, ClassNotFoundException { |
924 |
+ |
s.defaultReadObject(); |
925 |
+ |
state = ORIGIN; // reset to unlocked state |
926 |
+ |
} |
927 |
+ |
|
928 |
|
// internals |
929 |
|
|
930 |
|
/** |
932 |
|
* access bits value to RBITS, indicating hold of spinlock, |
933 |
|
* then updating, then releasing. |
934 |
|
* |
935 |
< |
* @param s, assumed that (s & ABITS) >= RFULL |
935 |
> |
* @param s a reader overflow stamp: (s & ABITS) >= RFULL |
936 |
|
* @return new stamp on success, else zero |
937 |
|
*/ |
938 |
|
private long tryIncReaderOverflow(long s) { |
939 |
+ |
// assert (s & ABITS) >= RFULL; |
940 |
|
if ((s & ABITS) == RFULL) { |
941 |
|
if (U.compareAndSwapLong(this, STATE, s, s | RBITS)) { |
942 |
|
++readerOverflow; |
953 |
|
/** |
954 |
|
* Tries to decrement readerOverflow. |
955 |
|
* |
956 |
< |
* @param s, assumed that (s & ABITS) >= RFULL |
956 |
> |
* @param s a reader overflow stamp: (s & ABITS) >= RFULL |
957 |
|
* @return new stamp on success, else zero |
958 |
|
*/ |
959 |
|
private long tryDecReaderOverflow(long s) { |
960 |
+ |
// assert (s & ABITS) >= RFULL; |
961 |
|
if ((s & ABITS) == RFULL) { |
962 |
|
if (U.compareAndSwapLong(this, STATE, s, s | RBITS)) { |
963 |
|
int r; long next; |
977 |
|
return 0L; |
978 |
|
} |
979 |
|
|
980 |
< |
/* |
980 |
> |
/** |
981 |
|
* Wakes up the successor of h (normally whead). This is normally |
982 |
|
* just h.next, but may require traversal from wtail if next |
983 |
|
* pointers are lagging. This may fail to wake up an acquiring |
993 |
|
if (t.status <= 0) |
994 |
|
q = t; |
995 |
|
} |
996 |
< |
if (q != null) { |
997 |
< |
for (WNode r = q;;) { // release co-waiters too |
950 |
< |
if ((w = r.thread) != null) { |
951 |
< |
r.thread = null; |
952 |
< |
U.unpark(w); |
953 |
< |
} |
954 |
< |
if ((r = q.cowait) == null) |
955 |
< |
break; |
956 |
< |
U.compareAndSwapObject(q, WCOWAIT, r, r.cowait); |
957 |
< |
} |
958 |
< |
} |
996 |
> |
if (q != null && (w = q.thread) != null) |
997 |
> |
U.unpark(w); |
998 |
|
} |
999 |
|
} |
1000 |
|
|
1010 |
|
private long acquireWrite(boolean interruptible, long deadline) { |
1011 |
|
WNode node = null, p; |
1012 |
|
for (int spins = -1;;) { // spin while enqueuing |
1013 |
< |
long s, ns; |
1014 |
< |
if (((s = state) & ABITS) == 0L) { |
1013 |
> |
long m, s, ns; |
1014 |
> |
if ((m = (s = state) & ABITS) == 0L) { |
1015 |
|
if (U.compareAndSwapLong(this, STATE, s, ns = s + WBIT)) |
1016 |
|
return ns; |
1017 |
|
} |
1018 |
+ |
else if (spins < 0) |
1019 |
+ |
spins = (m == WBIT && wtail == whead) ? SPINS : 0; |
1020 |
|
else if (spins > 0) { |
1021 |
|
if (ThreadLocalRandom.current().nextInt() >= 0) |
1022 |
|
--spins; |
1023 |
|
} |
1024 |
|
else if ((p = wtail) == null) { // initialize queue |
1025 |
< |
WNode h = new WNode(WMODE, null); |
1026 |
< |
if (U.compareAndSwapObject(this, WHEAD, null, h)) |
1027 |
< |
wtail = h; |
1025 |
> |
WNode hd = new WNode(WMODE, null); |
1026 |
> |
if (U.compareAndSwapObject(this, WHEAD, null, hd)) |
1027 |
> |
wtail = hd; |
1028 |
|
} |
988 |
– |
else if (spins < 0) |
989 |
– |
spins = (p == whead) ? SPINS : 0; |
1029 |
|
else if (node == null) |
1030 |
|
node = new WNode(WMODE, p); |
1031 |
|
else if (node.prev != p) |
1036 |
|
} |
1037 |
|
} |
1038 |
|
|
1039 |
< |
for (int spins = SPINS;;) { |
1040 |
< |
WNode np, pp; int ps; long s, ns; Thread w; |
1041 |
< |
while ((np = node.prev) != p && np != null) |
1042 |
< |
(p = np).next = node; // stale |
1043 |
< |
if (whead == p) { |
1039 |
> |
for (int spins = -1;;) { |
1040 |
> |
WNode h, np, pp; int ps; |
1041 |
> |
if ((h = whead) == p) { |
1042 |
> |
if (spins < 0) |
1043 |
> |
spins = HEAD_SPINS; |
1044 |
> |
else if (spins < MAX_HEAD_SPINS) |
1045 |
> |
spins <<= 1; |
1046 |
|
for (int k = spins;;) { // spin at head |
1047 |
+ |
long s, ns; |
1048 |
|
if (((s = state) & ABITS) == 0L) { |
1049 |
< |
if (U.compareAndSwapLong(this, STATE, s, ns = s+WBIT)) { |
1049 |
> |
if (U.compareAndSwapLong(this, STATE, s, |
1050 |
> |
ns = s + WBIT)) { |
1051 |
|
whead = node; |
1052 |
|
node.prev = null; |
1053 |
|
return ns; |
1057 |
|
--k <= 0) |
1058 |
|
break; |
1059 |
|
} |
1017 |
– |
if (spins < MAX_HEAD_SPINS) |
1018 |
– |
spins <<= 1; |
1060 |
|
} |
1061 |
< |
if ((ps = p.status) == 0) |
1062 |
< |
U.compareAndSwapInt(p, WSTATUS, 0, WAITING); |
1063 |
< |
else if (ps == CANCELLED) { |
1064 |
< |
if ((pp = p.prev) != null) { |
1065 |
< |
node.prev = pp; |
1066 |
< |
pp.next = node; |
1061 |
> |
else if (h != null) { // help release stale waiters |
1062 |
> |
WNode c; Thread w; |
1063 |
> |
while ((c = h.cowait) != null) { |
1064 |
> |
if (U.compareAndSwapObject(h, WCOWAIT, c, c.cowait) && |
1065 |
> |
(w = c.thread) != null) |
1066 |
> |
U.unpark(w); |
1067 |
|
} |
1068 |
|
} |
1069 |
< |
else { |
1070 |
< |
long time; // 0 argument to park means no timeout |
1071 |
< |
if (deadline == 0L) |
1072 |
< |
time = 0L; |
1073 |
< |
else if ((time = deadline - System.nanoTime()) <= 0L) |
1074 |
< |
return cancelWaiter(node, null, false); |
1075 |
< |
node.thread = Thread.currentThread(); |
1076 |
< |
if (node.prev == p && p.status == WAITING && // recheck |
1077 |
< |
(p != whead || (state & ABITS) != 0L)) { |
1078 |
< |
U.park(false, time); |
1069 |
> |
if (whead == h) { |
1070 |
> |
if ((np = node.prev) != p) { |
1071 |
> |
if (np != null) |
1072 |
> |
(p = np).next = node; // stale |
1073 |
> |
} |
1074 |
> |
else if ((ps = p.status) == 0) |
1075 |
> |
U.compareAndSwapInt(p, WSTATUS, 0, WAITING); |
1076 |
> |
else if (ps == CANCELLED) { |
1077 |
> |
if ((pp = p.prev) != null) { |
1078 |
> |
node.prev = pp; |
1079 |
> |
pp.next = node; |
1080 |
> |
} |
1081 |
> |
} |
1082 |
> |
else { |
1083 |
> |
long time; // 0 argument to park means no timeout |
1084 |
> |
if (deadline == 0L) |
1085 |
> |
time = 0L; |
1086 |
> |
else if ((time = deadline - System.nanoTime()) <= 0L) |
1087 |
> |
return cancelWaiter(node, node, false); |
1088 |
> |
Thread wt = Thread.currentThread(); |
1089 |
> |
U.putObject(wt, PARKBLOCKER, this); |
1090 |
> |
node.thread = wt; |
1091 |
> |
if (p.status < 0 && (p != h || (state & ABITS) != 0L) && |
1092 |
> |
whead == h && node.prev == p) |
1093 |
> |
U.park(false, time); // emulate LockSupport.park |
1094 |
> |
node.thread = null; |
1095 |
> |
U.putObject(wt, PARKBLOCKER, null); |
1096 |
|
if (interruptible && Thread.interrupted()) |
1097 |
< |
return cancelWaiter(node, null, true); |
1097 |
> |
return cancelWaiter(node, node, true); |
1098 |
|
} |
1041 |
– |
node.thread = null; |
1099 |
|
} |
1100 |
|
} |
1101 |
|
} |
1110 |
|
* @return next state, or INTERRUPTED |
1111 |
|
*/ |
1112 |
|
private long acquireRead(boolean interruptible, long deadline) { |
1113 |
< |
WNode node = null, group = null, p; |
1113 |
> |
WNode node = null, p; |
1114 |
|
for (int spins = -1;;) { |
1115 |
< |
for (;;) { |
1116 |
< |
long s, m, ns; WNode h, q; Thread w; // anti-barging guard |
1117 |
< |
if (group == null && (h = whead) != null && |
1118 |
< |
(q = h.next) != null && q.mode != RMODE) |
1119 |
< |
break; |
1120 |
< |
if ((m = (s = state) & ABITS) < RFULL ? |
1121 |
< |
U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT) : |
1122 |
< |
(m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L)) { |
1123 |
< |
if (group != null) { // help release others |
1124 |
< |
for (WNode r = group;;) { |
1125 |
< |
if ((w = r.thread) != null) { |
1126 |
< |
r.thread = null; |
1127 |
< |
U.unpark(w); |
1115 |
> |
WNode h; |
1116 |
> |
if ((h = whead) == (p = wtail)) { |
1117 |
> |
for (long m, s, ns;;) { |
1118 |
> |
if ((m = (s = state) & ABITS) < RFULL ? |
1119 |
> |
U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT) : |
1120 |
> |
(m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L)) |
1121 |
> |
return ns; |
1122 |
> |
else if (m >= WBIT) { |
1123 |
> |
if (spins > 0) { |
1124 |
> |
if (ThreadLocalRandom.current().nextInt() >= 0) |
1125 |
> |
--spins; |
1126 |
> |
} |
1127 |
> |
else { |
1128 |
> |
if (spins == 0) { |
1129 |
> |
WNode nh = whead, np = wtail; |
1130 |
> |
if ((nh == h && np == p) || (h = nh) != (p = np)) |
1131 |
> |
break; |
1132 |
|
} |
1133 |
< |
if ((r = group.cowait) == null) |
1073 |
< |
break; |
1074 |
< |
U.compareAndSwapObject(group, WCOWAIT, r, r.cowait); |
1133 |
> |
spins = SPINS; |
1134 |
|
} |
1135 |
|
} |
1077 |
– |
return ns; |
1136 |
|
} |
1079 |
– |
if (m >= WBIT) |
1080 |
– |
break; |
1081 |
– |
} |
1082 |
– |
if (spins > 0) { |
1083 |
– |
if (ThreadLocalRandom.current().nextInt() >= 0) |
1084 |
– |
--spins; |
1137 |
|
} |
1138 |
< |
else if ((p = wtail) == null) { |
1139 |
< |
WNode h = new WNode(WMODE, null); |
1140 |
< |
if (U.compareAndSwapObject(this, WHEAD, null, h)) |
1141 |
< |
wtail = h; |
1138 |
> |
if (p == null) { // initialize queue |
1139 |
> |
WNode hd = new WNode(WMODE, null); |
1140 |
> |
if (U.compareAndSwapObject(this, WHEAD, null, hd)) |
1141 |
> |
wtail = hd; |
1142 |
|
} |
1091 |
– |
else if (spins < 0) |
1092 |
– |
spins = (p == whead) ? SPINS : 0; |
1143 |
|
else if (node == null) |
1144 |
< |
node = new WNode(WMODE, p); |
1145 |
< |
else if (node.prev != p) |
1146 |
< |
node.prev = p; |
1147 |
< |
else if (p.mode == RMODE && p != whead) { |
1148 |
< |
WNode pp = p.prev; // become co-waiter with group p |
1149 |
< |
if (pp != null && p == wtail && |
1150 |
< |
U.compareAndSwapObject(p, WCOWAIT, |
1151 |
< |
node.cowait = p.cowait, node)) { |
1152 |
< |
node.thread = Thread.currentThread(); |
1153 |
< |
for (long time;;) { |
1144 |
> |
node = new WNode(RMODE, p); |
1145 |
> |
else if (h == p || p.mode != RMODE) { |
1146 |
> |
if (node.prev != p) |
1147 |
> |
node.prev = p; |
1148 |
> |
else if (U.compareAndSwapObject(this, WTAIL, p, node)) { |
1149 |
> |
p.next = node; |
1150 |
> |
break; |
1151 |
> |
} |
1152 |
> |
} |
1153 |
> |
else if (!U.compareAndSwapObject(p, WCOWAIT, |
1154 |
> |
node.cowait = p.cowait, node)) |
1155 |
> |
node.cowait = null; |
1156 |
> |
else { |
1157 |
> |
for (;;) { |
1158 |
> |
WNode pp, c; Thread w; |
1159 |
> |
if ((h = whead) != null && (c = h.cowait) != null && |
1160 |
> |
U.compareAndSwapObject(h, WCOWAIT, c, c.cowait) && |
1161 |
> |
(w = c.thread) != null) // help release |
1162 |
> |
U.unpark(w); |
1163 |
> |
if (h == (pp = p.prev) || h == p || pp == null) { |
1164 |
> |
long m, s, ns; |
1165 |
> |
do { |
1166 |
> |
if ((m = (s = state) & ABITS) < RFULL ? |
1167 |
> |
U.compareAndSwapLong(this, STATE, s, |
1168 |
> |
ns = s + RUNIT) : |
1169 |
> |
(m < WBIT && |
1170 |
> |
(ns = tryIncReaderOverflow(s)) != 0L)) |
1171 |
> |
return ns; |
1172 |
> |
} while (m < WBIT); |
1173 |
> |
} |
1174 |
> |
if (whead == h && p.prev == pp) { |
1175 |
> |
long time; |
1176 |
> |
if (pp == null || h == p || p.status > 0) { |
1177 |
> |
node = null; // throw away |
1178 |
> |
break; |
1179 |
> |
} |
1180 |
|
if (deadline == 0L) |
1181 |
|
time = 0L; |
1182 |
|
else if ((time = deadline - System.nanoTime()) <= 0L) |
1183 |
|
return cancelWaiter(node, p, false); |
1184 |
< |
if (node.thread == null) |
1185 |
< |
break; |
1186 |
< |
if (p.prev != pp || p.status == CANCELLED || |
1187 |
< |
p == whead || p.prev != pp) { |
1188 |
< |
node.thread = null; |
1189 |
< |
break; |
1190 |
< |
} |
1191 |
< |
if (node.thread == null) // must recheck |
1116 |
< |
break; |
1117 |
< |
U.park(false, time); |
1184 |
> |
Thread wt = Thread.currentThread(); |
1185 |
> |
U.putObject(wt, PARKBLOCKER, this); |
1186 |
> |
node.thread = wt; |
1187 |
> |
if ((h != pp || (state & ABITS) == WBIT) && |
1188 |
> |
whead == h && p.prev == pp) |
1189 |
> |
U.park(false, time); |
1190 |
> |
node.thread = null; |
1191 |
> |
U.putObject(wt, PARKBLOCKER, null); |
1192 |
|
if (interruptible && Thread.interrupted()) |
1193 |
|
return cancelWaiter(node, p, true); |
1194 |
|
} |
1121 |
– |
group = p; |
1195 |
|
} |
1123 |
– |
node = null; // throw away |
1124 |
– |
} |
1125 |
– |
else if (U.compareAndSwapObject(this, WTAIL, p, node)) { |
1126 |
– |
p.next = node; |
1127 |
– |
break; |
1196 |
|
} |
1197 |
|
} |
1198 |
|
|
1199 |
< |
for (int spins = SPINS;;) { |
1200 |
< |
WNode np, pp, r; int ps; long m, s, ns; Thread w; |
1201 |
< |
while ((np = node.prev) != p && np != null) |
1202 |
< |
(p = np).next = node; |
1203 |
< |
if (whead == p) { |
1204 |
< |
for (int k = spins;;) { |
1205 |
< |
if ((m = (s = state) & ABITS) != WBIT) { |
1206 |
< |
if (m < RFULL ? |
1207 |
< |
U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT): |
1208 |
< |
(ns = tryIncReaderOverflow(s)) != 0L) { |
1209 |
< |
whead = node; |
1210 |
< |
node.prev = null; |
1211 |
< |
while ((r = node.cowait) != null) { |
1212 |
< |
if (U.compareAndSwapObject(node, WCOWAIT, |
1213 |
< |
r, r.cowait) && |
1214 |
< |
(w = r.thread) != null) { |
1215 |
< |
r.thread = null; |
1216 |
< |
U.unpark(w); // release co-waiter |
1217 |
< |
} |
1218 |
< |
} |
1151 |
< |
return ns; |
1199 |
> |
for (int spins = -1;;) { |
1200 |
> |
WNode h, np, pp; int ps; |
1201 |
> |
if ((h = whead) == p) { |
1202 |
> |
if (spins < 0) |
1203 |
> |
spins = HEAD_SPINS; |
1204 |
> |
else if (spins < MAX_HEAD_SPINS) |
1205 |
> |
spins <<= 1; |
1206 |
> |
for (int k = spins;;) { // spin at head |
1207 |
> |
long m, s, ns; |
1208 |
> |
if ((m = (s = state) & ABITS) < RFULL ? |
1209 |
> |
U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT) : |
1210 |
> |
(m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L)) { |
1211 |
> |
WNode c; Thread w; |
1212 |
> |
whead = node; |
1213 |
> |
node.prev = null; |
1214 |
> |
while ((c = node.cowait) != null) { |
1215 |
> |
if (U.compareAndSwapObject(node, WCOWAIT, |
1216 |
> |
c, c.cowait) && |
1217 |
> |
(w = c.thread) != null) |
1218 |
> |
U.unpark(w); |
1219 |
|
} |
1220 |
+ |
return ns; |
1221 |
|
} |
1222 |
< |
else if (ThreadLocalRandom.current().nextInt() >= 0 && |
1223 |
< |
--k <= 0) |
1222 |
> |
else if (m >= WBIT && |
1223 |
> |
ThreadLocalRandom.current().nextInt() >= 0 && --k <= 0) |
1224 |
|
break; |
1225 |
|
} |
1158 |
– |
if (spins < MAX_HEAD_SPINS) |
1159 |
– |
spins <<= 1; |
1226 |
|
} |
1227 |
< |
if ((ps = p.status) == 0) |
1228 |
< |
U.compareAndSwapInt(p, WSTATUS, 0, WAITING); |
1229 |
< |
else if (ps == CANCELLED) { |
1230 |
< |
if ((pp = p.prev) != null) { |
1231 |
< |
node.prev = pp; |
1232 |
< |
pp.next = node; |
1227 |
> |
else if (h != null) { |
1228 |
> |
WNode c; Thread w; |
1229 |
> |
while ((c = h.cowait) != null) { |
1230 |
> |
if (U.compareAndSwapObject(h, WCOWAIT, c, c.cowait) && |
1231 |
> |
(w = c.thread) != null) |
1232 |
> |
U.unpark(w); |
1233 |
|
} |
1234 |
|
} |
1235 |
< |
else { |
1236 |
< |
long time; |
1237 |
< |
if (deadline == 0L) |
1238 |
< |
time = 0L; |
1239 |
< |
else if ((time = deadline - System.nanoTime()) <= 0L) |
1240 |
< |
return cancelWaiter(node, null, false); |
1241 |
< |
node.thread = Thread.currentThread(); |
1242 |
< |
if (node.prev == p && p.status == WAITING && |
1243 |
< |
(p != whead || (state & ABITS) != WBIT)) { |
1244 |
< |
U.park(false, time); |
1235 |
> |
if (whead == h) { |
1236 |
> |
if ((np = node.prev) != p) { |
1237 |
> |
if (np != null) |
1238 |
> |
(p = np).next = node; // stale |
1239 |
> |
} |
1240 |
> |
else if ((ps = p.status) == 0) |
1241 |
> |
U.compareAndSwapInt(p, WSTATUS, 0, WAITING); |
1242 |
> |
else if (ps == CANCELLED) { |
1243 |
> |
if ((pp = p.prev) != null) { |
1244 |
> |
node.prev = pp; |
1245 |
> |
pp.next = node; |
1246 |
> |
} |
1247 |
> |
} |
1248 |
> |
else { |
1249 |
> |
long time; |
1250 |
> |
if (deadline == 0L) |
1251 |
> |
time = 0L; |
1252 |
> |
else if ((time = deadline - System.nanoTime()) <= 0L) |
1253 |
> |
return cancelWaiter(node, node, false); |
1254 |
> |
Thread wt = Thread.currentThread(); |
1255 |
> |
U.putObject(wt, PARKBLOCKER, this); |
1256 |
> |
node.thread = wt; |
1257 |
> |
if (p.status < 0 && |
1258 |
> |
(p != h || (state & ABITS) == WBIT) && |
1259 |
> |
whead == h && node.prev == p) |
1260 |
> |
U.park(false, time); |
1261 |
> |
node.thread = null; |
1262 |
> |
U.putObject(wt, PARKBLOCKER, null); |
1263 |
|
if (interruptible && Thread.interrupted()) |
1264 |
< |
return cancelWaiter(node, null, true); |
1264 |
> |
return cancelWaiter(node, node, true); |
1265 |
|
} |
1182 |
– |
node.thread = null; |
1266 |
|
} |
1267 |
|
} |
1268 |
|
} |
1269 |
|
|
1270 |
|
/** |
1271 |
< |
* If node non-null, forces cancel status and unsplices from queue |
1272 |
< |
* if possible. This is a variant of cancellation methods in |
1271 |
> |
* If node non-null, forces cancel status and unsplices it from |
1272 |
> |
* queue if possible and wakes up any cowaiters (of the node, or |
1273 |
> |
* group, as applicable), and in any case helps release current |
1274 |
> |
* first waiter if lock is free. (Calling with null arguments |
1275 |
> |
* serves as a conditional form of release, which is not currently |
1276 |
> |
* needed but may be needed under possible future cancellation |
1277 |
> |
* policies). This is a variant of cancellation methods in |
1278 |
|
* AbstractQueuedSynchronizer (see its detailed explanation in AQS |
1279 |
< |
* internal documentation) that more conservatively wakes up other |
1280 |
< |
* threads that may have had their links changed, so as to preserve |
1281 |
< |
* liveness in the main signalling methods. |
1279 |
> |
* internal documentation). |
1280 |
> |
* |
1281 |
> |
* @param node if nonnull, the waiter |
1282 |
> |
* @param group either node or the group node is cowaiting with |
1283 |
> |
* @param interrupted if already interrupted |
1284 |
> |
* @return INTERRUPTED if interrupted or Thread.interrupted, else zero |
1285 |
|
*/ |
1286 |
|
private long cancelWaiter(WNode node, WNode group, boolean interrupted) { |
1287 |
< |
if (node != null) { |
1288 |
< |
node.thread = null; |
1287 |
> |
if (node != null && group != null) { |
1288 |
> |
Thread w; |
1289 |
|
node.status = CANCELLED; |
1290 |
< |
if (group != null) { |
1291 |
< |
for (WNode p = group, q; p != null; p = q) { |
1292 |
< |
if ((q = p.cowait) != null && q.status == CANCELLED) { |
1293 |
< |
U.compareAndSwapObject(p, WCOWAIT, q, q.cowait); |
1294 |
< |
break; |
1204 |
< |
} |
1290 |
> |
// unsplice cancelled nodes from group |
1291 |
> |
for (WNode p = group, q; (q = p.cowait) != null;) { |
1292 |
> |
if (q.status == CANCELLED) { |
1293 |
> |
U.compareAndSwapObject(p, WCOWAIT, q, q.cowait); |
1294 |
> |
p = group; // restart |
1295 |
|
} |
1296 |
+ |
else |
1297 |
+ |
p = q; |
1298 |
|
} |
1299 |
< |
else { |
1300 |
< |
for (WNode pred = node.prev; pred != null; ) { |
1301 |
< |
WNode succ, pp; Thread w; |
1299 |
> |
if (group == node) { |
1300 |
> |
for (WNode r = group.cowait; r != null; r = r.cowait) { |
1301 |
> |
if ((w = r.thread) != null) |
1302 |
> |
U.unpark(w); // wake up uncancelled co-waiters |
1303 |
> |
} |
1304 |
> |
for (WNode pred = node.prev; pred != null; ) { // unsplice |
1305 |
> |
WNode succ, pp; // find valid successor |
1306 |
|
while ((succ = node.next) == null || |
1307 |
|
succ.status == CANCELLED) { |
1308 |
< |
WNode q = null; |
1308 |
> |
WNode q = null; // find successor the slow way |
1309 |
|
for (WNode t = wtail; t != null && t != node; t = t.prev) |
1310 |
|
if (t.status != CANCELLED) |
1311 |
< |
q = t; |
1312 |
< |
if (succ == q || |
1311 |
> |
q = t; // don't link if succ cancelled |
1312 |
> |
if (succ == q || // ensure accurate successor |
1313 |
|
U.compareAndSwapObject(node, WNEXT, |
1314 |
|
succ, succ = q)) { |
1315 |
|
if (succ == null && node == wtail) |
1317 |
|
break; |
1318 |
|
} |
1319 |
|
} |
1320 |
< |
if (pred.next == node) |
1320 |
> |
if (pred.next == node) // unsplice pred link |
1321 |
|
U.compareAndSwapObject(pred, WNEXT, node, succ); |
1322 |
< |
if (succ != null && (w = succ.thread) != null) |
1323 |
< |
U.unpark(w); |
1322 |
> |
if (succ != null && (w = succ.thread) != null) { |
1323 |
> |
succ.thread = null; |
1324 |
> |
U.unpark(w); // wake up succ to observe new pred |
1325 |
> |
} |
1326 |
|
if (pred.status != CANCELLED || (pp = pred.prev) == null) |
1327 |
|
break; |
1328 |
< |
node.prev = pp; // repeat for new pred |
1328 |
> |
node.prev = pp; // repeat if new pred wrong/cancelled |
1329 |
|
U.compareAndSwapObject(pp, WNEXT, pred, succ); |
1330 |
|
pred = pp; |
1331 |
|
} |
1332 |
|
} |
1333 |
|
} |
1334 |
< |
release(whead); |
1334 |
> |
WNode h; // Possibly release first waiter |
1335 |
> |
while ((h = whead) != null) { |
1336 |
> |
long s; WNode q; // similar to release() but check eligibility |
1337 |
> |
if ((q = h.next) == null || q.status == CANCELLED) { |
1338 |
> |
for (WNode t = wtail; t != null && t != h; t = t.prev) |
1339 |
> |
if (t.status <= 0) |
1340 |
> |
q = t; |
1341 |
> |
} |
1342 |
> |
if (h == whead) { |
1343 |
> |
if (q != null && h.status == 0 && |
1344 |
> |
((s = state) & ABITS) != WBIT && // waiter is eligible |
1345 |
> |
(s == 0L || q.mode == RMODE)) |
1346 |
> |
release(h); |
1347 |
> |
break; |
1348 |
> |
} |
1349 |
> |
} |
1350 |
|
return (interrupted || Thread.interrupted()) ? INTERRUPTED : 0L; |
1351 |
|
} |
1352 |
|
|
1358 |
|
private static final long WNEXT; |
1359 |
|
private static final long WSTATUS; |
1360 |
|
private static final long WCOWAIT; |
1361 |
+ |
private static final long PARKBLOCKER; |
1362 |
|
|
1363 |
|
static { |
1364 |
|
try { |
1377 |
|
(wk.getDeclaredField("next")); |
1378 |
|
WCOWAIT = U.objectFieldOffset |
1379 |
|
(wk.getDeclaredField("cowait")); |
1380 |
+ |
Class<?> tk = Thread.class; |
1381 |
+ |
PARKBLOCKER = U.objectFieldOffset |
1382 |
+ |
(tk.getDeclaredField("parkBlocker")); |
1383 |
|
|
1384 |
|
} catch (Exception e) { |
1385 |
|
throw new Error(e); |