5 |
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*/ |
6 |
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|
7 |
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package jsr166e; |
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|
9 |
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import java.util.concurrent.ThreadLocalRandom; |
8 |
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import java.util.concurrent.TimeUnit; |
9 |
+ |
import java.util.concurrent.locks.Lock; |
10 |
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import java.util.concurrent.locks.Condition; |
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import java.util.concurrent.locks.ReadWriteLock; |
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import java.util.concurrent.locks.LockSupport; |
13 |
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|
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/** |
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* A capability-based lock with three modes for controlling read/write |
16 |
< |
* access. The state of a StampedLock consists of a version and |
17 |
< |
* mode. Lock acquisition methods return a stamp that represents and |
16 |
> |
* access. The state of a StampedLock consists of a version and mode. |
17 |
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* Lock acquisition methods return a stamp that represents and |
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* controls access with respect to a lock state; "try" versions of |
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* these methods may instead return the special value zero to |
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* represent failure to acquire access. Lock release and conversion |
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* <li><b>Optimistic Reading.</b> Method {@link #tryOptimisticRead} |
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* returns a non-zero stamp only if the lock is not currently held |
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* in write mode. Method {@link #validate} returns true if the lock |
41 |
< |
* has not since been acquired in write mode. This mode can be |
42 |
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* thought of as an extremely weak version of a read-lock, that can |
43 |
< |
* be broken by a writer at any time. The use of optimistic mode |
44 |
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* for short read-only code segments often reduces contention and |
45 |
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* improves throughput. However, its use is inherently fragile. |
46 |
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* Optimistic read sections should only read fields and hold them in |
47 |
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* local variables for later use after validation. Fields read while |
48 |
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* in optimistic mode may be wildly inconsistent, so usage applies |
49 |
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* only when you are familiar enough with data representations to |
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* check consistency and/or repeatedly invoke method {@code |
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* validate()}. For example, such steps are typically required when |
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* first reading an object or array reference, and then accessing |
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* one of its fields, elements or methods. </li> |
41 |
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* has not been acquired in write mode since obtaining a given |
42 |
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* stamp. This mode can be thought of as an extremely weak version |
43 |
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* of a read-lock, that can be broken by a writer at any time. The |
44 |
> |
* use of optimistic mode for short read-only code segments often |
45 |
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* reduces contention and improves throughput. However, its use is |
46 |
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* inherently fragile. Optimistic read sections should only read |
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* fields and hold them in local variables for later use after |
48 |
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* validation. Fields read while in optimistic mode may be wildly |
49 |
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* inconsistent, so usage applies only when you are familiar enough |
50 |
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* with data representations to check consistency and/or repeatedly |
51 |
> |
* invoke method {@code validate()}. For example, such steps are |
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* typically required when first reading an object or array |
53 |
> |
* reference, and then accessing one of its fields, elements or |
54 |
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* methods. </li> |
55 |
|
* |
56 |
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* </ul> |
57 |
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* |
58 |
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* <p>This class also supports methods that conditionally provide |
59 |
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* conversions across the three modes. For example, method {@link |
60 |
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* #tryConvertToWriteLock} attempts to "upgrade" a mode, returning |
61 |
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* valid write stamp if (1) already in writing mode (2) in reading |
61 |
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* a valid write stamp if (1) already in writing mode (2) in reading |
62 |
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* mode and there are no other readers or (3) in optimistic mode and |
63 |
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* the lock is available. The forms of these methods are designed to |
64 |
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* help reduce some of the code bloat that otherwise occurs in |
65 |
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* retry-based designs. |
66 |
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* |
67 |
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* <p>StampedLocks are designed for use in a different (and generally |
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* narrower) range of contexts than most other locks: They are not |
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* reentrant, so locked bodies should not call other unknown methods |
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* that may try to re-acquire locks (although you may pass a stamp to |
71 |
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* other methods that can use or convert it). Unvalidated optimistic |
72 |
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* read sections should further not call methods that are not known to |
67 |
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* <p>StampedLocks are designed for use as internal utilities in the |
68 |
> |
* development of thread-safe components. Their use relies on |
69 |
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* knowledge of the internal properties of the data, objects, and |
70 |
> |
* methods they are protecting. They are not reentrant, so locked |
71 |
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* bodies should not call other unknown methods that may try to |
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* re-acquire locks (although you may pass a stamp to other methods |
73 |
> |
* that can use or convert it). The use of read lock modes relies on |
74 |
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* the associated code sections being side-effect-free. Unvalidated |
75 |
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* optimistic read sections cannot call methods that are not known to |
76 |
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* tolerate potential inconsistencies. Stamps use finite |
77 |
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* representations, and are not cryptographically secure (i.e., a |
78 |
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* valid stamp may be guessable). Stamp values may recycle after (no |
83 |
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* locking. |
84 |
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* |
85 |
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* <p>The scheduling policy of StampedLock does not consistently |
86 |
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* prefer readers over writers or vice versa. A zero return from any |
87 |
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* "try" method for acquiring or converting locks does carry any |
88 |
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* information about the state of the lock; a subsequent invocation |
89 |
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* may succeed. |
86 |
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* prefer readers over writers or vice versa. All "try" methods are |
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* best-effort and do not necessarily conform to any scheduling or |
88 |
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* fairness policy. A zero return from any "try" method for acquiring |
89 |
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* or converting locks does not carry any information about the state |
90 |
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* of the lock; a subsequent invocation may succeed. |
91 |
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* |
92 |
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* <p>Because it supports coordinated usage across multiple lock |
93 |
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* modes, this class does not directly implement the {@link Lock} or |
94 |
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* {@link ReadWriteLock} interfaces. However, a StampedLock may be |
95 |
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* viewed {@link #asReadLock()}, {@link #asWriteLock()}, or {@link |
96 |
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* #asReadWriteLock()} in applications requiring only the associated |
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* set of functionality. |
98 |
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* |
99 |
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* <p><b>Sample Usage.</b> The following illustrates some usage idioms |
100 |
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* in a class that maintains simple two-dimensional points. The sample |
117 |
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* } |
118 |
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* } |
119 |
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* |
120 |
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* double distanceFromOriginV1() { // A read-only method |
121 |
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* long stamp; |
122 |
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* if ((stamp = sl.tryOptimisticRead()) != 0L) { // optimistic |
123 |
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* double currentX = x; |
124 |
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* double currentY = y; |
125 |
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* if (sl.validate(stamp)) |
126 |
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* return Math.sqrt(currentX * currentX + currentY * currentY); |
127 |
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* } |
128 |
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* stamp = sl.readLock(); // fall back to read lock |
129 |
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* try { |
130 |
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* double currentX = x; |
117 |
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* double currentY = y; |
118 |
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* return Math.sqrt(currentX * currentX + currentY * currentY); |
119 |
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* } finally { |
120 |
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* sl.unlockRead(stamp); |
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* } |
122 |
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* } |
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* |
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* double distanceFromOriginV2() { // combines code paths |
125 |
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* for (long stamp = sl.tryOptimisticRead(); ; stamp = sl.readLock()) { |
126 |
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* double currentX, currentY; |
127 |
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* try { |
128 |
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* currentX = x; |
129 |
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* currentY = y; |
130 |
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* } finally { |
131 |
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* if (sl.tryConvertToOptimisticRead(stamp) != 0L) // unlock or validate |
132 |
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* return Math.sqrt(currentX * currentX + currentY * currentY); |
133 |
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* } |
120 |
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* double distanceFromOrigin() { // A read-only method |
121 |
> |
* long stamp = sl.tryOptimisticRead(); |
122 |
> |
* double currentX = x, currentY = y; |
123 |
> |
* if (!sl.validate(stamp)) { |
124 |
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* stamp = sl.readLock(); |
125 |
> |
* try { |
126 |
> |
* currentX = x; |
127 |
> |
* currentY = y; |
128 |
> |
* } finally { |
129 |
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* sl.unlockRead(stamp); |
130 |
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* } |
131 |
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* } |
132 |
+ |
* return Math.sqrt(currentX * currentX + currentY * currentY); |
133 |
|
* } |
134 |
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* |
135 |
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* void moveIfAtOrigin(double newX, double newY) { // upgrade |
137 |
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* long stamp = sl.readLock(); |
138 |
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* try { |
139 |
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* while (x == 0.0 && y == 0.0) { |
140 |
< |
* long ws = tryConvertToWriteLock(stamp); |
140 |
> |
* long ws = sl.tryConvertToWriteLock(stamp); |
141 |
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* if (ws != 0L) { |
142 |
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* stamp = ws; |
143 |
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* x = newX; |
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* } |
151 |
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* } |
152 |
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* } finally { |
153 |
< |
* sl.unlock(stamp); |
153 |
> |
* sl.unlock(stamp); |
154 |
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* } |
155 |
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* } |
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* }}</pre> |
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* http://www.lameter.com/gelato2005.pdf |
168 |
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* and elsewhere; see |
169 |
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* Boehm's http://www.hpl.hp.com/techreports/2012/HPL-2012-68.html) |
170 |
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* Ordered RW locks (see Shirako et al |
170 |
> |
* and Ordered RW locks (see Shirako et al |
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* http://dl.acm.org/citation.cfm?id=2312015) |
174 |
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* and Phase-Fair locks (see Brandenburg & Anderson, especially |
175 |
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* http://www.cs.unc.edu/~bbb/diss/). |
172 |
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* |
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* Conceptually, the primary state of the lock includes a sequence |
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* number that is odd when write-locked and even otherwise. |
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* read-locked. The read count is ignored when validating |
177 |
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* "optimistic" seqlock-reader-style stamps. Because we must use |
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* a small finite number of bits (currently 7) for readers, a |
179 |
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* supplementary reader overflow word is used when then number of |
179 |
> |
* supplementary reader overflow word is used when the number of |
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* readers exceeds the count field. We do this by treating the max |
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* reader count value (RBITS) as a spinlock protecting overflow |
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* updates. |
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* |
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* Waiting readers and writers use different queues. The writer |
185 |
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* queue is a modified form of CLH lock. (For discussion of CLH, |
186 |
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* see the internal documentation of AbstractQueuedSynchronizer.) |
187 |
< |
* The reader "queue" is a form of Treiber stack, that supports |
188 |
< |
* simpler/faster operations because order within a queue doesn't |
189 |
< |
* matter and all are signalled at once. However the sequence of |
190 |
< |
* threads within the queue vs the current stamp does matter (see |
191 |
< |
* Shirako et al) so each carries its incoming stamp value. |
192 |
< |
* Waiting writers never need to track sequence values, so they |
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* don't. |
194 |
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* |
195 |
< |
* These queue mechanics hardwire the scheduling policy. Ignoring |
196 |
< |
* trylocks, cancellation, and spinning, they implement Phase-Fair |
197 |
< |
* preferences: |
198 |
< |
* 1. Unlocked writers prefer to signal waiting readers |
199 |
< |
* 2. Fully unlocked readers prefer to signal waiting writers |
204 |
< |
* 3. When read-locked and a waiting writer exists, the writer |
205 |
< |
* is preferred to incoming readers |
184 |
> |
* Waiters use a modified form of CLH lock used in |
185 |
> |
* AbstractQueuedSynchronizer (see its internal documentation for |
186 |
> |
* a fuller account), where each node is tagged (field mode) as |
187 |
> |
* either a reader or writer. Sets of waiting readers are grouped |
188 |
> |
* (linked) under a common node (field cowait) so act as a single |
189 |
> |
* node with respect to most CLH mechanics. By virtue of the |
190 |
> |
* queue structure, wait nodes need not actually carry sequence |
191 |
> |
* numbers; we know each is greater than its predecessor. This |
192 |
> |
* simplifies the scheduling policy to a mainly-FIFO scheme that |
193 |
> |
* incorporates elements of Phase-Fair locks (see Brandenburg & |
194 |
> |
* Anderson, especially http://www.cs.unc.edu/~bbb/diss/). In |
195 |
> |
* particular, we use the phase-fair anti-barging rule: If an |
196 |
> |
* incoming reader arrives while read lock is held but there is a |
197 |
> |
* queued writer, this incoming reader is queued. (This rule is |
198 |
> |
* responsible for some of the complexity of method acquireRead, |
199 |
> |
* but without it, the lock becomes highly unfair.) |
200 |
|
* |
201 |
|
* These rules apply to threads actually queued. All tryLock forms |
202 |
|
* opportunistically try to acquire locks regardless of preference |
203 |
< |
* rules, and so may "barge" their way in. Additionally, initial |
204 |
< |
* phases of the await* methods (invoked from readLock() and |
205 |
< |
* writeLock()) use controlled spins that have similar effect. |
206 |
< |
* Phase-fair preferences may also be broken on cancellations due |
207 |
< |
* to timeouts and interrupts. Rule #3 (incoming readers when a |
208 |
< |
* waiting writer) is approximated with varying precision in |
209 |
< |
* different contexts -- some checks do not account for |
210 |
< |
* in-progress spins/signals, and others do not account for |
211 |
< |
* cancellations. |
203 |
> |
* rules, and so may "barge" their way in. Randomized spinning is |
204 |
> |
* used in the acquire methods to reduce (increasingly expensive) |
205 |
> |
* context switching while also avoiding sustained memory |
206 |
> |
* thrashing among many threads. We limit spins to the head of |
207 |
> |
* queue. A thread spin-waits up to SPINS times (where each |
208 |
> |
* iteration decreases spin count with 50% probability) before |
209 |
> |
* blocking. If, upon wakening it fails to obtain lock, and is |
210 |
> |
* still (or becomes) the first waiting thread (which indicates |
211 |
> |
* that some other thread barged and obtained lock), it escalates |
212 |
> |
* spins (up to MAX_HEAD_SPINS) to reduce the likelihood of |
213 |
> |
* continually losing to barging threads. |
214 |
> |
* |
215 |
> |
* Nearly all of these mechanics are carried out in methods |
216 |
> |
* acquireWrite and acquireRead, that, as typical of such code, |
217 |
> |
* sprawl out because actions and retries rely on consistent sets |
218 |
> |
* of locally cached reads. |
219 |
|
* |
220 |
|
* As noted in Boehm's paper (above), sequence validation (mainly |
221 |
|
* method validate()) requires stricter ordering rules than apply |
235 |
|
* be subject to future improvements. |
236 |
|
*/ |
237 |
|
|
238 |
+ |
private static final long serialVersionUID = -6001602636862214147L; |
239 |
+ |
|
240 |
|
/** Number of processors, for spin control */ |
241 |
|
private static final int NCPU = Runtime.getRuntime().availableProcessors(); |
242 |
|
|
243 |
|
/** Maximum number of retries before blocking on acquisition */ |
244 |
< |
private static final int SPINS = (NCPU > 1) ? 1 << 6 : 1; |
244 |
> |
private static final int SPINS = (NCPU > 1) ? 1 << 6 : 0; |
245 |
|
|
246 |
|
/** Maximum number of retries before re-blocking */ |
247 |
< |
private static final int MAX_HEAD_SPINS = (NCPU > 1) ? 1 << 12 : 1; |
247 |
> |
private static final int MAX_HEAD_SPINS = (NCPU > 1) ? 1 << 12 : 0; |
248 |
|
|
249 |
|
/** The period for yielding when waiting for overflow spinlock */ |
250 |
|
private static final int OVERFLOW_YIELD_RATE = 7; // must be power 2 - 1 |
251 |
|
|
252 |
|
/** The number of bits to use for reader count before overflowing */ |
253 |
< |
private static final int LG_READERS = 7; |
253 |
> |
private static final int LG_READERS = 7; |
254 |
|
|
255 |
|
// Values for lock state and stamp operations |
256 |
|
private static final long RUNIT = 1L; |
263 |
|
// Initial value for lock state; avoid failure value zero |
264 |
|
private static final long ORIGIN = WBIT << 1; |
265 |
|
|
266 |
< |
// Special value from cancelled await methods so caller can throw IE |
266 |
> |
// Special value from cancelled acquire methods so caller can throw IE |
267 |
|
private static final long INTERRUPTED = 1L; |
268 |
|
|
269 |
< |
// Values for writer status; order matters |
269 |
> |
// Values for node status; order matters |
270 |
|
private static final int WAITING = -1; |
271 |
|
private static final int CANCELLED = 1; |
272 |
|
|
273 |
< |
/** Wait nodes for readers */ |
274 |
< |
static final class RNode { |
275 |
< |
final long seq; // stamp value upon enqueue |
273 |
< |
volatile Thread waiter; // null if no longer waiting |
274 |
< |
volatile RNode next; |
275 |
< |
RNode(long s, Thread w) { seq = s; waiter = w; } |
276 |
< |
} |
273 |
> |
// Modes for nodes (int not boolean to allow arithmetic) |
274 |
> |
private static final int RMODE = 0; |
275 |
> |
private static final int WMODE = 1; |
276 |
|
|
277 |
< |
/** Wait nodes for writers */ |
277 |
> |
/** Wait nodes */ |
278 |
|
static final class WNode { |
280 |
– |
volatile int status; // 0, WAITING, or CANCELLED |
279 |
|
volatile WNode prev; |
280 |
|
volatile WNode next; |
281 |
< |
volatile Thread thread; |
282 |
< |
WNode(Thread t, WNode p) { thread = t; prev = p; } |
281 |
> |
volatile WNode cowait; // list of linked readers |
282 |
> |
volatile Thread thread; // non-null while possibly parked |
283 |
> |
volatile int status; // 0, WAITING, or CANCELLED |
284 |
> |
final int mode; // RMODE or WMODE |
285 |
> |
WNode(int m, WNode p) { mode = m; prev = p; } |
286 |
|
} |
287 |
|
|
288 |
< |
/** Head of writer CLH queue */ |
288 |
> |
/** Head of CLH queue */ |
289 |
|
private transient volatile WNode whead; |
290 |
< |
/** Tail (last) of writer CLH queue */ |
290 |
> |
/** Tail (last) of CLH queue */ |
291 |
|
private transient volatile WNode wtail; |
292 |
< |
/** Head of read queue */ |
293 |
< |
private transient volatile RNode rhead; |
294 |
< |
/** The state of the lock -- high bits hold sequence, low bits read count */ |
292 |
> |
|
293 |
> |
// views |
294 |
> |
transient ReadLockView readLockView; |
295 |
> |
transient WriteLockView writeLockView; |
296 |
> |
transient ReadWriteLockView readWriteLockView; |
297 |
> |
|
298 |
> |
/** Lock sequence/state */ |
299 |
|
private transient volatile long state; |
300 |
|
/** extra reader count when state read count saturated */ |
301 |
|
private transient int readerOverflow; |
302 |
|
|
303 |
|
/** |
304 |
< |
* Creates a new lock initially in unlocked state. |
304 |
> |
* Creates a new lock, initially in unlocked state. |
305 |
|
*/ |
306 |
|
public StampedLock() { |
307 |
|
state = ORIGIN; |
314 |
|
* @return a stamp that can be used to unlock or convert mode |
315 |
|
*/ |
316 |
|
public long writeLock() { |
317 |
< |
long s, next; |
318 |
< |
if (((s = state) & ABITS) == 0L && |
319 |
< |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) |
320 |
< |
return next; |
316 |
< |
return awaitWrite(false, 0L); |
317 |
> |
long s, next; // bypass acquireWrite in fully unlocked case only |
318 |
> |
return ((((s = state) & ABITS) == 0L && |
319 |
> |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) ? |
320 |
> |
next : acquireWrite(false, 0L)); |
321 |
|
} |
322 |
|
|
323 |
|
/** |
324 |
|
* Exclusively acquires the lock if it is immediately available. |
325 |
|
* |
326 |
|
* @return a stamp that can be used to unlock or convert mode, |
327 |
< |
* or zero if the lock is not available. |
327 |
> |
* or zero if the lock is not available |
328 |
|
*/ |
329 |
|
public long tryWriteLock() { |
330 |
|
long s, next; |
331 |
< |
if (((s = state) & ABITS) == 0L && |
332 |
< |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) |
333 |
< |
return next; |
330 |
< |
return 0L; |
331 |
> |
return ((((s = state) & ABITS) == 0L && |
332 |
> |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) ? |
333 |
> |
next : 0L); |
334 |
|
} |
335 |
|
|
336 |
|
/** |
337 |
|
* Exclusively acquires the lock if it is available within the |
338 |
|
* given time and the current thread has not been interrupted. |
339 |
+ |
* Behavior under timeout and interruption matches that specified |
340 |
+ |
* for method {@link Lock#tryLock(long,TimeUnit)}. |
341 |
|
* |
342 |
+ |
* @param time the maximum time to wait for the lock |
343 |
+ |
* @param unit the time unit of the {@code time} argument |
344 |
|
* @return a stamp that can be used to unlock or convert mode, |
345 |
|
* or zero if the lock is not available |
346 |
|
* @throws InterruptedException if the current thread is interrupted |
350 |
|
throws InterruptedException { |
351 |
|
long nanos = unit.toNanos(time); |
352 |
|
if (!Thread.interrupted()) { |
353 |
< |
long s, next, deadline; |
354 |
< |
if (((s = state) & ABITS) == 0L && |
348 |
< |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) |
353 |
> |
long next, deadline; |
354 |
> |
if ((next = tryWriteLock()) != 0L) |
355 |
|
return next; |
356 |
|
if (nanos <= 0L) |
357 |
|
return 0L; |
358 |
|
if ((deadline = System.nanoTime() + nanos) == 0L) |
359 |
|
deadline = 1L; |
360 |
< |
if ((next = awaitWrite(true, deadline)) != INTERRUPTED) |
360 |
> |
if ((next = acquireWrite(true, deadline)) != INTERRUPTED) |
361 |
|
return next; |
362 |
|
} |
363 |
|
throw new InterruptedException(); |
366 |
|
/** |
367 |
|
* Exclusively acquires the lock, blocking if necessary |
368 |
|
* until available or the current thread is interrupted. |
369 |
+ |
* Behavior under interruption matches that specified |
370 |
+ |
* for method {@link Lock#lockInterruptibly()}. |
371 |
|
* |
372 |
|
* @return a stamp that can be used to unlock or convert mode |
373 |
|
* @throws InterruptedException if the current thread is interrupted |
374 |
|
* before acquiring the lock |
375 |
|
*/ |
376 |
|
public long writeLockInterruptibly() throws InterruptedException { |
377 |
< |
if (!Thread.interrupted()) { |
378 |
< |
long s, next; |
379 |
< |
if (((s = state) & ABITS) == 0L && |
380 |
< |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) |
373 |
< |
return next; |
374 |
< |
if ((next = awaitWrite(true, 0L)) != INTERRUPTED) |
375 |
< |
return next; |
376 |
< |
} |
377 |
> |
long next; |
378 |
> |
if (!Thread.interrupted() && |
379 |
> |
(next = acquireWrite(true, 0L)) != INTERRUPTED) |
380 |
> |
return next; |
381 |
|
throw new InterruptedException(); |
382 |
|
} |
383 |
|
|
388 |
|
* @return a stamp that can be used to unlock or convert mode |
389 |
|
*/ |
390 |
|
public long readLock() { |
391 |
< |
for (;;) { |
392 |
< |
long s, m, next; |
393 |
< |
if ((m = (s = state) & ABITS) == 0L || |
394 |
< |
(m < WBIT && whead == wtail)) { |
391 |
< |
if (m < RFULL) { |
392 |
< |
if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) |
393 |
< |
return next; |
394 |
< |
} |
395 |
< |
else if ((next = tryIncReaderOverflow(s)) != 0L) |
396 |
< |
return next; |
397 |
< |
} |
398 |
< |
else |
399 |
< |
return awaitRead(s, false, 0L); |
400 |
< |
} |
391 |
> |
long s, next; // bypass acquireRead on fully unlocked case only |
392 |
> |
return ((((s = state) & ABITS) == 0L && |
393 |
> |
U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) ? |
394 |
> |
next : acquireRead(false, 0L)); |
395 |
|
} |
396 |
|
|
397 |
|
/** |
417 |
|
/** |
418 |
|
* Non-exclusively acquires the lock if it is available within the |
419 |
|
* given time and the current thread has not been interrupted. |
420 |
+ |
* Behavior under timeout and interruption matches that specified |
421 |
+ |
* for method {@link Lock#tryLock(long,TimeUnit)}. |
422 |
|
* |
423 |
+ |
* @param time the maximum time to wait for the lock |
424 |
+ |
* @param unit the time unit of the {@code time} argument |
425 |
|
* @return a stamp that can be used to unlock or convert mode, |
426 |
|
* or zero if the lock is not available |
427 |
|
* @throws InterruptedException if the current thread is interrupted |
429 |
|
*/ |
430 |
|
public long tryReadLock(long time, TimeUnit unit) |
431 |
|
throws InterruptedException { |
432 |
+ |
long s, m, next, deadline; |
433 |
|
long nanos = unit.toNanos(time); |
434 |
|
if (!Thread.interrupted()) { |
435 |
< |
for (;;) { |
436 |
< |
long s, m, next, deadline; |
438 |
< |
if ((m = (s = state) & ABITS) == WBIT || |
439 |
< |
(m != 0L && whead != wtail)) { |
440 |
< |
if (nanos <= 0L) |
441 |
< |
return 0L; |
442 |
< |
if ((deadline = System.nanoTime() + nanos) == 0L) |
443 |
< |
deadline = 1L; |
444 |
< |
if ((next = awaitRead(s, true, deadline)) != INTERRUPTED) |
445 |
< |
return next; |
446 |
< |
break; |
447 |
< |
} |
448 |
< |
else if (m < RFULL) { |
435 |
> |
if ((m = (s = state) & ABITS) != WBIT) { |
436 |
> |
if (m < RFULL) { |
437 |
|
if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) |
438 |
|
return next; |
439 |
|
} |
440 |
|
else if ((next = tryIncReaderOverflow(s)) != 0L) |
441 |
|
return next; |
442 |
|
} |
443 |
+ |
if (nanos <= 0L) |
444 |
+ |
return 0L; |
445 |
+ |
if ((deadline = System.nanoTime() + nanos) == 0L) |
446 |
+ |
deadline = 1L; |
447 |
+ |
if ((next = acquireRead(true, deadline)) != INTERRUPTED) |
448 |
+ |
return next; |
449 |
|
} |
450 |
|
throw new InterruptedException(); |
451 |
|
} |
453 |
|
/** |
454 |
|
* Non-exclusively acquires the lock, blocking if necessary |
455 |
|
* until available or the current thread is interrupted. |
456 |
+ |
* Behavior under interruption matches that specified |
457 |
+ |
* for method {@link Lock#lockInterruptibly()}. |
458 |
|
* |
459 |
|
* @return a stamp that can be used to unlock or convert mode |
460 |
|
* @throws InterruptedException if the current thread is interrupted |
461 |
|
* before acquiring the lock |
462 |
|
*/ |
463 |
|
public long readLockInterruptibly() throws InterruptedException { |
464 |
< |
if (!Thread.interrupted()) { |
465 |
< |
for (;;) { |
466 |
< |
long s, next, m; |
467 |
< |
if ((m = (s = state) & ABITS) == WBIT || |
472 |
< |
(m != 0L && whead != wtail)) { |
473 |
< |
if ((next = awaitRead(s, true, 0L)) != INTERRUPTED) |
474 |
< |
return next; |
475 |
< |
break; |
476 |
< |
} |
477 |
< |
else if (m < RFULL) { |
478 |
< |
if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) |
479 |
< |
return next; |
480 |
< |
} |
481 |
< |
else if ((next = tryIncReaderOverflow(s)) != 0L) |
482 |
< |
return next; |
483 |
< |
} |
484 |
< |
} |
464 |
> |
long next; |
465 |
> |
if (!Thread.interrupted() && |
466 |
> |
(next = acquireRead(true, 0L)) != INTERRUPTED) |
467 |
> |
return next; |
468 |
|
throw new InterruptedException(); |
469 |
|
} |
470 |
|
|
480 |
|
} |
481 |
|
|
482 |
|
/** |
483 |
< |
* Returns true if the lock has not been exclusively held since |
484 |
< |
* issuance of the given stamp. Always returns false if the stamp |
485 |
< |
* is zero. Always returns true if the stamp represents a |
486 |
< |
* currently held lock. |
483 |
> |
* Returns true if the lock has not been exclusively acquired |
484 |
> |
* since issuance of the given stamp. Always returns false if the |
485 |
> |
* stamp is zero. Always returns true if the stamp represents a |
486 |
> |
* currently held lock. Invoking this method with a value not |
487 |
> |
* obtained from {@link #tryOptimisticRead} or a locking method |
488 |
> |
* for this lock has no defined effect or result. |
489 |
|
* |
490 |
< |
* @return true if the lock has not been exclusively held since |
491 |
< |
* issuance of the given stamp; else false |
490 |
> |
* @param stamp a stamp |
491 |
> |
* @return {@code true} if the lock has not been exclusively acquired |
492 |
> |
* since issuance of the given stamp; else false |
493 |
|
*/ |
494 |
|
public boolean validate(long stamp) { |
495 |
+ |
// See above about current use of getLongVolatile here |
496 |
|
return (stamp & SBITS) == (U.getLongVolatile(this, STATE) & SBITS); |
497 |
|
} |
498 |
|
|
505 |
|
* not match the current state of this lock |
506 |
|
*/ |
507 |
|
public void unlockWrite(long stamp) { |
508 |
+ |
WNode h; |
509 |
|
if (state != stamp || (stamp & WBIT) == 0L) |
510 |
|
throw new IllegalMonitorStateException(); |
511 |
|
state = (stamp += WBIT) == 0L ? ORIGIN : stamp; |
512 |
< |
readerPrefSignal(); |
512 |
> |
if ((h = whead) != null && h.status != 0) |
513 |
> |
release(h); |
514 |
|
} |
515 |
|
|
516 |
|
/** |
517 |
< |
* If the lock state matches the given stamp, releases |
517 |
> |
* If the lock state matches the given stamp, releases the |
518 |
|
* non-exclusive lock. |
519 |
|
* |
520 |
|
* @param stamp a stamp returned by a read-lock operation |
522 |
|
* not match the current state of this lock |
523 |
|
*/ |
524 |
|
public void unlockRead(long stamp) { |
525 |
< |
long s, m; |
526 |
< |
if ((stamp & RBITS) != 0L) { |
527 |
< |
while (((s = state) & SBITS) == (stamp & SBITS)) { |
528 |
< |
if ((m = s & ABITS) == 0L) |
525 |
> |
long s, m; WNode h; |
526 |
> |
for (;;) { |
527 |
> |
if (((s = state) & SBITS) != (stamp & SBITS) || |
528 |
> |
(stamp & ABITS) == 0L || (m = s & ABITS) == 0L || m == WBIT) |
529 |
> |
throw new IllegalMonitorStateException(); |
530 |
> |
if (m < RFULL) { |
531 |
> |
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) { |
532 |
> |
if (m == RUNIT && (h = whead) != null && h.status != 0) |
533 |
> |
release(h); |
534 |
|
break; |
541 |
– |
else if (m < RFULL) { |
542 |
– |
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) { |
543 |
– |
if (m == RUNIT) |
544 |
– |
writerPrefSignal(); |
545 |
– |
return; |
546 |
– |
} |
535 |
|
} |
548 |
– |
else if (m >= WBIT) |
549 |
– |
break; |
550 |
– |
else if (tryDecReaderOverflow(s) != 0L) |
551 |
– |
return; |
536 |
|
} |
537 |
+ |
else if (tryDecReaderOverflow(s) != 0L) |
538 |
+ |
break; |
539 |
|
} |
554 |
– |
throw new IllegalMonitorStateException(); |
540 |
|
} |
541 |
|
|
542 |
|
/** |
548 |
|
* not match the current state of this lock |
549 |
|
*/ |
550 |
|
public void unlock(long stamp) { |
551 |
< |
long a = stamp & ABITS, m, s; |
551 |
> |
long a = stamp & ABITS, m, s; WNode h; |
552 |
|
while (((s = state) & SBITS) == (stamp & SBITS)) { |
553 |
|
if ((m = s & ABITS) == 0L) |
554 |
|
break; |
556 |
|
if (a != m) |
557 |
|
break; |
558 |
|
state = (s += WBIT) == 0L ? ORIGIN : s; |
559 |
< |
readerPrefSignal(); |
559 |
> |
if ((h = whead) != null && h.status != 0) |
560 |
> |
release(h); |
561 |
|
return; |
562 |
|
} |
563 |
|
else if (a == 0L || a >= WBIT) |
564 |
|
break; |
565 |
|
else if (m < RFULL) { |
566 |
|
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) { |
567 |
< |
if (m == RUNIT) |
568 |
< |
writerPrefSignal(); |
567 |
> |
if (m == RUNIT && (h = whead) != null && h.status != 0) |
568 |
> |
release(h); |
569 |
|
return; |
570 |
|
} |
571 |
|
} |
576 |
|
} |
577 |
|
|
578 |
|
/** |
579 |
< |
* If the lock state matches the given stamp then performs one of |
579 |
> |
* If the lock state matches the given stamp, performs one of |
580 |
|
* the following actions. If the stamp represents holding a write |
581 |
< |
* lock, returns it. Or, if a read lock, if the write lock is |
582 |
< |
* available, releases the read and returns a write stamp. Or, if |
583 |
< |
* an optimistic read, returns a write stamp only if immediately |
584 |
< |
* available. This method returns zero in all other cases. |
581 |
> |
* lock, returns it. Or, if a read lock, if the write lock is |
582 |
> |
* available, releases the read lock and returns a write stamp. |
583 |
> |
* Or, if an optimistic read, returns a write stamp only if |
584 |
> |
* immediately available. This method returns zero in all other |
585 |
> |
* cases. |
586 |
|
* |
587 |
|
* @param stamp a stamp |
588 |
|
* @return a valid write stamp, or zero on failure |
601 |
|
break; |
602 |
|
return stamp; |
603 |
|
} |
604 |
< |
else if (m == RUNIT && a != 0L && a < WBIT) { |
604 |
> |
else if (m == RUNIT && a != 0L) { |
605 |
|
if (U.compareAndSwapLong(this, STATE, s, |
606 |
|
next = s - RUNIT + WBIT)) |
607 |
|
return next; |
613 |
|
} |
614 |
|
|
615 |
|
/** |
616 |
< |
* If the lock state matches the given stamp then performs one of |
616 |
> |
* If the lock state matches the given stamp, performs one of |
617 |
|
* the following actions. If the stamp represents holding a write |
618 |
|
* lock, releases it and obtains a read lock. Or, if a read lock, |
619 |
|
* returns it. Or, if an optimistic read, acquires a read lock and |
624 |
|
* @return a valid read stamp, or zero on failure |
625 |
|
*/ |
626 |
|
public long tryConvertToReadLock(long stamp) { |
627 |
< |
long a = stamp & ABITS, m, s, next; |
627 |
> |
long a = stamp & ABITS, m, s, next; WNode h; |
628 |
|
while (((s = state) & SBITS) == (stamp & SBITS)) { |
629 |
|
if ((m = s & ABITS) == 0L) { |
630 |
|
if (a != 0L) |
639 |
|
else if (m == WBIT) { |
640 |
|
if (a != m) |
641 |
|
break; |
642 |
< |
next = state = s + (WBIT + RUNIT); |
643 |
< |
readerPrefSignal(); |
642 |
> |
state = next = s + (WBIT + RUNIT); |
643 |
> |
if ((h = whead) != null && h.status != 0) |
644 |
> |
release(h); |
645 |
|
return next; |
646 |
|
} |
647 |
|
else if (a != 0L && a < WBIT) |
663 |
|
* @return a valid optimistic read stamp, or zero on failure |
664 |
|
*/ |
665 |
|
public long tryConvertToOptimisticRead(long stamp) { |
666 |
< |
long a = stamp & ABITS, m, s, next; |
667 |
< |
while (((s = U.getLongVolatile(this, STATE)) & |
668 |
< |
SBITS) == (stamp & SBITS)) { |
666 |
> |
long a = stamp & ABITS, m, s, next; WNode h; |
667 |
> |
for (;;) { |
668 |
> |
s = U.getLongVolatile(this, STATE); // see above |
669 |
> |
if ((s & SBITS) != (stamp & SBITS)) |
670 |
> |
break; |
671 |
|
if ((m = s & ABITS) == 0L) { |
672 |
|
if (a != 0L) |
673 |
|
break; |
676 |
|
else if (m == WBIT) { |
677 |
|
if (a != m) |
678 |
|
break; |
679 |
< |
next = state = (s += WBIT) == 0L ? ORIGIN : s; |
680 |
< |
readerPrefSignal(); |
679 |
> |
state = next = (s += WBIT) == 0L ? ORIGIN : s; |
680 |
> |
if ((h = whead) != null && h.status != 0) |
681 |
> |
release(h); |
682 |
|
return next; |
683 |
|
} |
684 |
|
else if (a == 0L || a >= WBIT) |
685 |
|
break; |
686 |
|
else if (m < RFULL) { |
687 |
|
if (U.compareAndSwapLong(this, STATE, s, next = s - RUNIT)) { |
688 |
< |
if (m == RUNIT) |
689 |
< |
writerPrefSignal(); |
688 |
> |
if (m == RUNIT && (h = whead) != null && h.status != 0) |
689 |
> |
release(h); |
690 |
|
return next & SBITS; |
691 |
|
} |
692 |
|
} |
701 |
|
* stamp value. This method may be useful for recovery after |
702 |
|
* errors. |
703 |
|
* |
704 |
< |
* @return true if the lock was held, else false |
704 |
> |
* @return {@code true} if the lock was held, else false |
705 |
|
*/ |
706 |
|
public boolean tryUnlockWrite() { |
707 |
< |
long s; |
707 |
> |
long s; WNode h; |
708 |
|
if (((s = state) & WBIT) != 0L) { |
709 |
|
state = (s += WBIT) == 0L ? ORIGIN : s; |
710 |
< |
readerPrefSignal(); |
710 |
> |
if ((h = whead) != null && h.status != 0) |
711 |
> |
release(h); |
712 |
|
return true; |
713 |
|
} |
714 |
|
return false; |
719 |
|
* requiring a stamp value. This method may be useful for recovery |
720 |
|
* after errors. |
721 |
|
* |
722 |
< |
* @return true if the read lock was held, else false |
722 |
> |
* @return {@code true} if the read lock was held, else false |
723 |
|
*/ |
724 |
|
public boolean tryUnlockRead() { |
725 |
< |
long s, m; |
725 |
> |
long s, m; WNode h; |
726 |
|
while ((m = (s = state) & ABITS) != 0L && m < WBIT) { |
727 |
|
if (m < RFULL) { |
728 |
|
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) { |
729 |
< |
if (m == RUNIT) |
730 |
< |
writerPrefSignal(); |
729 |
> |
if (m == RUNIT && (h = whead) != null && h.status != 0) |
730 |
> |
release(h); |
731 |
|
return true; |
732 |
|
} |
733 |
|
} |
737 |
|
return false; |
738 |
|
} |
739 |
|
|
740 |
+ |
// status monitoring methods |
741 |
+ |
|
742 |
|
/** |
743 |
< |
* Returns true if the lock is currently held exclusively. |
743 |
> |
* Returns combined state-held and overflow read count for given |
744 |
> |
* state s. |
745 |
> |
*/ |
746 |
> |
private int getReadLockCount(long s) { |
747 |
> |
long readers; |
748 |
> |
if ((readers = s & RBITS) >= RFULL) |
749 |
> |
readers = RFULL + readerOverflow; |
750 |
> |
return (int) readers; |
751 |
> |
} |
752 |
> |
|
753 |
> |
/** |
754 |
> |
* Returns {@code true} if the lock is currently held exclusively. |
755 |
|
* |
756 |
< |
* @return true if the lock is currently held exclusively |
756 |
> |
* @return {@code true} if the lock is currently held exclusively |
757 |
|
*/ |
758 |
|
public boolean isWriteLocked() { |
759 |
|
return (state & WBIT) != 0L; |
760 |
|
} |
761 |
|
|
762 |
|
/** |
763 |
< |
* Returns true if the lock is currently held non-exclusively. |
763 |
> |
* Returns {@code true} if the lock is currently held non-exclusively. |
764 |
|
* |
765 |
< |
* @return true if the lock is currently held non-exclusively |
765 |
> |
* @return {@code true} if the lock is currently held non-exclusively |
766 |
|
*/ |
767 |
|
public boolean isReadLocked() { |
768 |
< |
long m; |
769 |
< |
return (m = state & ABITS) > 0L && m < WBIT; |
768 |
> |
return (state & RBITS) != 0L; |
769 |
> |
} |
770 |
> |
|
771 |
> |
/** |
772 |
> |
* Queries the number of read locks held for this lock. This |
773 |
> |
* method is designed for use in monitoring system state, not for |
774 |
> |
* synchronization control. |
775 |
> |
* @return the number of read locks held |
776 |
> |
*/ |
777 |
> |
public int getReadLockCount() { |
778 |
> |
return getReadLockCount(state); |
779 |
> |
} |
780 |
> |
|
781 |
> |
/** |
782 |
> |
* Returns a string identifying this lock, as well as its lock |
783 |
> |
* state. The state, in brackets, includes the String {@code |
784 |
> |
* "Unlocked"} or the String {@code "Write-locked"} or the String |
785 |
> |
* {@code "Read-locks:"} followed by the current number of |
786 |
> |
* read-locks held. |
787 |
> |
* |
788 |
> |
* @return a string identifying this lock, as well as its lock state |
789 |
> |
*/ |
790 |
> |
public String toString() { |
791 |
> |
long s = state; |
792 |
> |
return super.toString() + |
793 |
> |
((s & ABITS) == 0L ? "[Unlocked]" : |
794 |
> |
(s & WBIT) != 0L ? "[Write-locked]" : |
795 |
> |
"[Read-locks:" + getReadLockCount(s) + "]"); |
796 |
> |
} |
797 |
> |
|
798 |
> |
// views |
799 |
> |
|
800 |
> |
/** |
801 |
> |
* Returns a plain {@link Lock} view of this StampedLock in which |
802 |
> |
* the {@link Lock#lock} method is mapped to {@link #readLock}, |
803 |
> |
* and similarly for other methods. The returned Lock does not |
804 |
> |
* support a {@link Condition}; method {@link |
805 |
> |
* Lock#newCondition()} throws {@code |
806 |
> |
* UnsupportedOperationException}. |
807 |
> |
* |
808 |
> |
* @return the lock |
809 |
> |
*/ |
810 |
> |
public Lock asReadLock() { |
811 |
> |
ReadLockView v; |
812 |
> |
return ((v = readLockView) != null ? v : |
813 |
> |
(readLockView = new ReadLockView())); |
814 |
> |
} |
815 |
> |
|
816 |
> |
/** |
817 |
> |
* Returns a plain {@link Lock} view of this StampedLock in which |
818 |
> |
* the {@link Lock#lock} method is mapped to {@link #writeLock}, |
819 |
> |
* and similarly for other methods. The returned Lock does not |
820 |
> |
* support a {@link Condition}; method {@link |
821 |
> |
* Lock#newCondition()} throws {@code |
822 |
> |
* UnsupportedOperationException}. |
823 |
> |
* |
824 |
> |
* @return the lock |
825 |
> |
*/ |
826 |
> |
public Lock asWriteLock() { |
827 |
> |
WriteLockView v; |
828 |
> |
return ((v = writeLockView) != null ? v : |
829 |
> |
(writeLockView = new WriteLockView())); |
830 |
> |
} |
831 |
> |
|
832 |
> |
/** |
833 |
> |
* Returns a {@link ReadWriteLock} view of this StampedLock in |
834 |
> |
* which the {@link ReadWriteLock#readLock()} method is mapped to |
835 |
> |
* {@link #asReadLock()}, and {@link ReadWriteLock#writeLock()} to |
836 |
> |
* {@link #asWriteLock()}. |
837 |
> |
* |
838 |
> |
* @return the lock |
839 |
> |
*/ |
840 |
> |
public ReadWriteLock asReadWriteLock() { |
841 |
> |
ReadWriteLockView v; |
842 |
> |
return ((v = readWriteLockView) != null ? v : |
843 |
> |
(readWriteLockView = new ReadWriteLockView())); |
844 |
> |
} |
845 |
> |
|
846 |
> |
// view classes |
847 |
> |
|
848 |
> |
final class ReadLockView implements Lock { |
849 |
> |
public void lock() { readLock(); } |
850 |
> |
public void lockInterruptibly() throws InterruptedException { |
851 |
> |
readLockInterruptibly(); |
852 |
> |
} |
853 |
> |
public boolean tryLock() { return tryReadLock() != 0L; } |
854 |
> |
public boolean tryLock(long time, TimeUnit unit) |
855 |
> |
throws InterruptedException { |
856 |
> |
return tryReadLock(time, unit) != 0L; |
857 |
> |
} |
858 |
> |
public void unlock() { unstampedUnlockRead(); } |
859 |
> |
public Condition newCondition() { |
860 |
> |
throw new UnsupportedOperationException(); |
861 |
> |
} |
862 |
> |
} |
863 |
> |
|
864 |
> |
final class WriteLockView implements Lock { |
865 |
> |
public void lock() { writeLock(); } |
866 |
> |
public void lockInterruptibly() throws InterruptedException { |
867 |
> |
writeLockInterruptibly(); |
868 |
> |
} |
869 |
> |
public boolean tryLock() { return tryWriteLock() != 0L; } |
870 |
> |
public boolean tryLock(long time, TimeUnit unit) |
871 |
> |
throws InterruptedException { |
872 |
> |
return tryWriteLock(time, unit) != 0L; |
873 |
> |
} |
874 |
> |
public void unlock() { unstampedUnlockWrite(); } |
875 |
> |
public Condition newCondition() { |
876 |
> |
throw new UnsupportedOperationException(); |
877 |
> |
} |
878 |
> |
} |
879 |
> |
|
880 |
> |
final class ReadWriteLockView implements ReadWriteLock { |
881 |
> |
public Lock readLock() { return asReadLock(); } |
882 |
> |
public Lock writeLock() { return asWriteLock(); } |
883 |
> |
} |
884 |
> |
|
885 |
> |
// Unlock methods without stamp argument checks for view classes. |
886 |
> |
// Needed because view-class lock methods throw away stamps. |
887 |
> |
|
888 |
> |
final void unstampedUnlockWrite() { |
889 |
> |
WNode h; long s; |
890 |
> |
if (((s = state) & WBIT) == 0L) |
891 |
> |
throw new IllegalMonitorStateException(); |
892 |
> |
state = (s += WBIT) == 0L ? ORIGIN : s; |
893 |
> |
if ((h = whead) != null && h.status != 0) |
894 |
> |
release(h); |
895 |
> |
} |
896 |
> |
|
897 |
> |
final void unstampedUnlockRead() { |
898 |
> |
for (;;) { |
899 |
> |
long s, m; WNode h; |
900 |
> |
if ((m = (s = state) & ABITS) == 0L || m >= WBIT) |
901 |
> |
throw new IllegalMonitorStateException(); |
902 |
> |
else if (m < RFULL) { |
903 |
> |
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) { |
904 |
> |
if (m == RUNIT && (h = whead) != null && h.status != 0) |
905 |
> |
release(h); |
906 |
> |
break; |
907 |
> |
} |
908 |
> |
} |
909 |
> |
else if (tryDecReaderOverflow(s) != 0L) |
910 |
> |
break; |
911 |
> |
} |
912 |
|
} |
913 |
|
|
914 |
|
private void readObject(java.io.ObjectInputStream s) |
924 |
|
* access bits value to RBITS, indicating hold of spinlock, |
925 |
|
* then updating, then releasing. |
926 |
|
* |
927 |
< |
* @param stamp, assumed that (stamp & ABITS) >= RFULL |
927 |
> |
* @param s a reader overflow stamp: (s & ABITS) >= RFULL |
928 |
|
* @return new stamp on success, else zero |
929 |
|
*/ |
930 |
|
private long tryIncReaderOverflow(long s) { |
931 |
+ |
// assert (s & ABITS) >= RFULL; |
932 |
|
if ((s & ABITS) == RFULL) { |
933 |
|
if (U.compareAndSwapLong(this, STATE, s, s | RBITS)) { |
934 |
|
++readerOverflow; |
945 |
|
/** |
946 |
|
* Tries to decrement readerOverflow. |
947 |
|
* |
948 |
< |
* @param stamp, assumed that (stamp & ABITS) >= RFULL |
948 |
> |
* @param s a reader overflow stamp: (s & ABITS) >= RFULL |
949 |
|
* @return new stamp on success, else zero |
950 |
|
*/ |
951 |
|
private long tryDecReaderOverflow(long s) { |
952 |
+ |
// assert (s & ABITS) >= RFULL; |
953 |
|
if ((s & ABITS) == RFULL) { |
954 |
|
if (U.compareAndSwapLong(this, STATE, s, s | RBITS)) { |
955 |
|
int r; long next; |
969 |
|
return 0L; |
970 |
|
} |
971 |
|
|
972 |
< |
/* |
973 |
< |
* The two versions of signal implement the phase-fair policy. |
974 |
< |
* They include almost the same code, but repacked in different |
975 |
< |
* ways. Integrating the policy with the mechanics eliminates |
976 |
< |
* state rechecks that would be needed with separate reader and |
977 |
< |
* writer signal methods. Both methods assume that they are |
978 |
< |
* called when the lock is last known to be available, and |
979 |
< |
* continue until the lock is unavailable, or at least one thread |
980 |
< |
* is signalled, or there are no more waiting threads. Signalling |
981 |
< |
* a reader entails popping (CASing) from rhead and unparking |
982 |
< |
* unless the thread already cancelled (indicated by a null waiter |
834 |
< |
* field). Signalling a writer requires finding the first node, |
835 |
< |
* i.e., the successor of whead. This is normally just head.next, |
836 |
< |
* but may require traversal from wtail if next pointers are |
837 |
< |
* lagging. These methods may fail to wake up an acquiring thread |
838 |
< |
* when one or more have been cancelled, but the cancel methods |
839 |
< |
* themselves provide extra safeguards to ensure liveness. |
840 |
< |
*/ |
841 |
< |
|
842 |
< |
private void readerPrefSignal() { |
843 |
< |
boolean readers = false; |
844 |
< |
RNode p; WNode h, q; long s; Thread w; |
845 |
< |
while ((p = rhead) != null) { |
846 |
< |
if (((s = state) & WBIT) != 0L) |
847 |
< |
return; |
848 |
< |
if (p.seq == (s & SBITS)) |
849 |
< |
break; |
850 |
< |
readers = true; |
851 |
< |
if (U.compareAndSwapObject(this, RHEAD, p, p.next) && |
852 |
< |
(w = p.waiter) != null && |
853 |
< |
U.compareAndSwapObject(p, WAITER, w, null)) |
854 |
< |
U.unpark(w); |
855 |
< |
} |
856 |
< |
if (!readers && (state & ABITS) == 0L && |
857 |
< |
(h = whead) != null && h.status != 0) { |
858 |
< |
U.compareAndSwapInt(h, STATUS, WAITING, 0); |
859 |
< |
if ((q = h.next) == null || q.status == CANCELLED) { |
860 |
< |
q = null; |
861 |
< |
for (WNode t = wtail; t != null && t != h; t = t.prev) |
862 |
< |
if (t.status <= 0) |
863 |
< |
q = t; |
864 |
< |
} |
865 |
< |
if (q != null && (w = q.thread) != null) |
866 |
< |
U.unpark(w); |
867 |
< |
} |
868 |
< |
} |
869 |
< |
|
870 |
< |
private void writerPrefSignal() { |
871 |
< |
RNode p; WNode h, q; long s; Thread w; |
872 |
< |
if ((h = whead) != null && h.status != 0) { |
873 |
< |
U.compareAndSwapInt(h, STATUS, WAITING, 0); |
972 |
> |
/** |
973 |
> |
* Wakes up the successor of h (normally whead). This is normally |
974 |
> |
* just h.next, but may require traversal from wtail if next |
975 |
> |
* pointers are lagging. This may fail to wake up an acquiring |
976 |
> |
* thread when one or more have been cancelled, but the cancel |
977 |
> |
* methods themselves provide extra safeguards to ensure liveness. |
978 |
> |
*/ |
979 |
> |
private void release(WNode h) { |
980 |
> |
if (h != null) { |
981 |
> |
WNode q; Thread w; |
982 |
> |
U.compareAndSwapInt(h, WSTATUS, WAITING, 0); |
983 |
|
if ((q = h.next) == null || q.status == CANCELLED) { |
875 |
– |
q = null; |
984 |
|
for (WNode t = wtail; t != null && t != h; t = t.prev) |
985 |
|
if (t.status <= 0) |
986 |
|
q = t; |
987 |
|
} |
988 |
< |
if (q != null && (w = q.thread) != null) |
989 |
< |
U.unpark(w); |
990 |
< |
} |
991 |
< |
else { |
992 |
< |
while ((p = rhead) != null && ((s = state) & WBIT) == 0L && |
993 |
< |
p.seq != (s & SBITS)) { |
994 |
< |
if (U.compareAndSwapObject(this, RHEAD, p, p.next) && |
995 |
< |
(w = p.waiter) != null && |
996 |
< |
U.compareAndSwapObject(p, WAITER, w, null)) |
997 |
< |
U.unpark(w); |
988 |
> |
if (q != null) { |
989 |
> |
for (WNode r = q;;) { // release co-waiters too |
990 |
> |
if ((w = r.thread) != null) { |
991 |
> |
r.thread = null; |
992 |
> |
U.unpark(w); |
993 |
> |
} |
994 |
> |
if ((r = q.cowait) == null) |
995 |
> |
break; |
996 |
> |
U.compareAndSwapObject(q, WCOWAIT, r, r.cowait); |
997 |
> |
} |
998 |
|
} |
999 |
|
} |
1000 |
|
} |
1001 |
|
|
1002 |
|
/** |
1003 |
< |
* RNG for local spins. The first call from await{Read,Write} |
896 |
< |
* produces a thread-local value. Unless zero, subsequent calls |
897 |
< |
* use an xorShift to further reduce memory traffic. Both await |
898 |
< |
* methods use a similar spin strategy: If associated queue |
899 |
< |
* appears to be empty, then the thread spin-waits up to SPINS |
900 |
< |
* times before enqueing, and then, if the first thread to be |
901 |
< |
* enqueued, spins again up to SPINS times before blocking. If, |
902 |
< |
* upon wakening it fails to obtain lock, and is still (or |
903 |
< |
* becomes) the first waiting thread (which indicates that some |
904 |
< |
* other thread barged and obtained lock), it escalates spins (up |
905 |
< |
* to MAX_HEAD_SPINS) to reduce the likelihood of continually |
906 |
< |
* losing to barging threads. |
907 |
< |
*/ |
908 |
< |
private static int nextRandom(int r) { |
909 |
< |
if (r == 0) |
910 |
< |
return ThreadLocalRandom.current().nextInt(); |
911 |
< |
r ^= r << 1; // xorshift |
912 |
< |
r ^= r >>> 3; |
913 |
< |
r ^= r << 10; |
914 |
< |
return r; |
915 |
< |
} |
916 |
< |
|
917 |
< |
/** |
918 |
< |
* Possibly spins trying to obtain write lock, then enqueues and |
919 |
< |
* blocks while not head of write queue or cannot acquire lock, |
920 |
< |
* possibly spinning when at head; cancelling on timeout or |
921 |
< |
* interrupt. |
1003 |
> |
* See above for explanation. |
1004 |
|
* |
1005 |
|
* @param interruptible true if should check interrupts and if so |
1006 |
|
* return INTERRUPTED |
1007 |
|
* @param deadline if nonzero, the System.nanoTime value to timeout |
1008 |
|
* at (and return zero) |
1009 |
+ |
* @return next state, or INTERRUPTED |
1010 |
|
*/ |
1011 |
< |
private long awaitWrite(boolean interruptible, long deadline) { |
1012 |
< |
WNode node = null; |
1013 |
< |
for (int r = 0, spins = -1;;) { |
1014 |
< |
WNode p; long s, next; |
1011 |
> |
private long acquireWrite(boolean interruptible, long deadline) { |
1012 |
> |
WNode node = null, p; |
1013 |
> |
for (int spins = -1;;) { // spin while enqueuing |
1014 |
> |
long s, ns; |
1015 |
|
if (((s = state) & ABITS) == 0L) { |
1016 |
< |
if (U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) |
1017 |
< |
return next; |
1016 |
> |
if (U.compareAndSwapLong(this, STATE, s, ns = s + WBIT)) |
1017 |
> |
return ns; |
1018 |
|
} |
936 |
– |
else if (spins < 0) |
937 |
– |
spins = whead == wtail ? SPINS : 0; |
1019 |
|
else if (spins > 0) { |
1020 |
< |
if ((r = nextRandom(r)) >= 0) |
1020 |
> |
if (ThreadLocalRandom.current().nextInt() >= 0) |
1021 |
|
--spins; |
1022 |
|
} |
1023 |
|
else if ((p = wtail) == null) { // initialize queue |
1024 |
< |
if (U.compareAndSwapObject(this, WHEAD, null, |
1025 |
< |
new WNode(null, null))) |
1026 |
< |
wtail = whead; |
1024 |
> |
WNode h = new WNode(WMODE, null); |
1025 |
> |
if (U.compareAndSwapObject(this, WHEAD, null, h)) |
1026 |
> |
wtail = h; |
1027 |
|
} |
1028 |
+ |
else if (spins < 0) |
1029 |
+ |
spins = (p == whead) ? SPINS : 0; |
1030 |
|
else if (node == null) |
1031 |
< |
node = new WNode(Thread.currentThread(), p); |
1031 |
> |
node = new WNode(WMODE, p); |
1032 |
|
else if (node.prev != p) |
1033 |
|
node.prev = p; |
1034 |
|
else if (U.compareAndSwapObject(this, WTAIL, p, node)) { |
1035 |
|
p.next = node; |
1036 |
< |
for (int headSpins = SPINS;;) { |
1037 |
< |
WNode np; int ps; |
1038 |
< |
if ((np = node.prev) != p && np != null) |
1039 |
< |
(p = np).next = node; // stale |
1040 |
< |
if (p == whead) { |
1041 |
< |
for (int k = headSpins;;) { |
1042 |
< |
if (((s = state) & ABITS) == 0L) { |
1043 |
< |
if (U.compareAndSwapLong(this, STATE, |
1044 |
< |
s, next = s + WBIT)) { |
1045 |
< |
whead = node; |
1046 |
< |
node.thread = null; |
1047 |
< |
node.prev = null; |
1048 |
< |
return next; |
1049 |
< |
} |
1050 |
< |
break; |
1036 |
> |
break; |
1037 |
> |
} |
1038 |
> |
} |
1039 |
> |
|
1040 |
> |
for (int spins = SPINS;;) { |
1041 |
> |
WNode np, pp; int ps; long s, ns; Thread w; |
1042 |
> |
while ((np = node.prev) != p && np != null) |
1043 |
> |
(p = np).next = node; // stale |
1044 |
> |
if (whead == p) { |
1045 |
> |
for (int k = spins;;) { // spin at head |
1046 |
> |
if (((s = state) & ABITS) == 0L) { |
1047 |
> |
if (U.compareAndSwapLong(this, STATE, s, ns = s+WBIT)) { |
1048 |
> |
whead = node; |
1049 |
> |
node.prev = null; |
1050 |
> |
return ns; |
1051 |
> |
} |
1052 |
> |
} |
1053 |
> |
else if (ThreadLocalRandom.current().nextInt() >= 0 && |
1054 |
> |
--k <= 0) |
1055 |
> |
break; |
1056 |
> |
} |
1057 |
> |
if (spins < MAX_HEAD_SPINS) |
1058 |
> |
spins <<= 1; |
1059 |
> |
} |
1060 |
> |
if ((ps = p.status) == 0) |
1061 |
> |
U.compareAndSwapInt(p, WSTATUS, 0, WAITING); |
1062 |
> |
else if (ps == CANCELLED) { |
1063 |
> |
if ((pp = p.prev) != null) { |
1064 |
> |
node.prev = pp; |
1065 |
> |
pp.next = node; |
1066 |
> |
} |
1067 |
> |
} |
1068 |
> |
else { |
1069 |
> |
long time; // 0 argument to park means no timeout |
1070 |
> |
if (deadline == 0L) |
1071 |
> |
time = 0L; |
1072 |
> |
else if ((time = deadline - System.nanoTime()) <= 0L) |
1073 |
> |
return cancelWaiter(node, node, false); |
1074 |
> |
Thread wt = Thread.currentThread(); |
1075 |
> |
U.putObject(wt, PARKBLOCKER, this); // emulate LockSupport.park |
1076 |
> |
node.thread = wt; |
1077 |
> |
if (node.prev == p && p.status == WAITING && // recheck |
1078 |
> |
(p != whead || (state & ABITS) != 0L)) |
1079 |
> |
U.park(false, time); |
1080 |
> |
node.thread = null; |
1081 |
> |
U.putObject(wt, PARKBLOCKER, null); |
1082 |
> |
if (interruptible && Thread.interrupted()) |
1083 |
> |
return cancelWaiter(node, node, true); |
1084 |
> |
} |
1085 |
> |
} |
1086 |
> |
} |
1087 |
> |
|
1088 |
> |
/** |
1089 |
> |
* See above for explanation. |
1090 |
> |
* |
1091 |
> |
* @param interruptible true if should check interrupts and if so |
1092 |
> |
* return INTERRUPTED |
1093 |
> |
* @param deadline if nonzero, the System.nanoTime value to timeout |
1094 |
> |
* at (and return zero) |
1095 |
> |
* @return next state, or INTERRUPTED |
1096 |
> |
*/ |
1097 |
> |
private long acquireRead(boolean interruptible, long deadline) { |
1098 |
> |
WNode node = null, group = null, p; |
1099 |
> |
for (int spins = -1;;) { |
1100 |
> |
for (;;) { |
1101 |
> |
long s, m, ns; WNode h, q; Thread w; // anti-barging guard |
1102 |
> |
if (group == null && (h = whead) != null && |
1103 |
> |
(q = h.next) != null && q.mode != RMODE) |
1104 |
> |
break; |
1105 |
> |
if ((m = (s = state) & ABITS) < RFULL ? |
1106 |
> |
U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT) : |
1107 |
> |
(m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L)) { |
1108 |
> |
if (group != null) { // help release others |
1109 |
> |
for (WNode r = group;;) { |
1110 |
> |
if ((w = r.thread) != null) { |
1111 |
> |
r.thread = null; |
1112 |
> |
U.unpark(w); |
1113 |
|
} |
1114 |
< |
if ((r = nextRandom(r)) >= 0 && --k <= 0) |
1114 |
> |
if ((r = group.cowait) == null) |
1115 |
|
break; |
1116 |
+ |
U.compareAndSwapObject(group, WCOWAIT, r, r.cowait); |
1117 |
|
} |
972 |
– |
if (headSpins < MAX_HEAD_SPINS) |
973 |
– |
headSpins <<= 1; |
1118 |
|
} |
1119 |
< |
if ((ps = p.status) == 0) |
1120 |
< |
U.compareAndSwapInt(p, STATUS, 0, WAITING); |
1121 |
< |
else if (ps == CANCELLED) |
1122 |
< |
node.prev = p.prev; |
1123 |
< |
else { |
1124 |
< |
long time; // 0 argument to park means no timeout |
1119 |
> |
return ns; |
1120 |
> |
} |
1121 |
> |
if (m >= WBIT) |
1122 |
> |
break; |
1123 |
> |
} |
1124 |
> |
if (spins > 0) { |
1125 |
> |
if (ThreadLocalRandom.current().nextInt() >= 0) |
1126 |
> |
--spins; |
1127 |
> |
} |
1128 |
> |
else if ((p = wtail) == null) { |
1129 |
> |
WNode h = new WNode(WMODE, null); |
1130 |
> |
if (U.compareAndSwapObject(this, WHEAD, null, h)) |
1131 |
> |
wtail = h; |
1132 |
> |
} |
1133 |
> |
else if (spins < 0) |
1134 |
> |
spins = (p == whead) ? SPINS : 0; |
1135 |
> |
else if (node == null) |
1136 |
> |
node = new WNode(WMODE, p); |
1137 |
> |
else if (node.prev != p) |
1138 |
> |
node.prev = p; |
1139 |
> |
else if (p.mode == RMODE && p != whead) { |
1140 |
> |
WNode pp = p.prev; // become co-waiter with group p |
1141 |
> |
if (pp != null && p == wtail && |
1142 |
> |
U.compareAndSwapObject(p, WCOWAIT, |
1143 |
> |
node.cowait = p.cowait, node)) { |
1144 |
> |
node.thread = Thread.currentThread(); |
1145 |
> |
for (long time;;) { |
1146 |
|
if (deadline == 0L) |
1147 |
|
time = 0L; |
1148 |
|
else if ((time = deadline - System.nanoTime()) <= 0L) |
1149 |
< |
return cancelWriter(node, false); |
1150 |
< |
if (node.prev == p && p.status == WAITING && |
1151 |
< |
(p != whead || (state & WBIT) != 0L)) { // recheck |
1152 |
< |
U.park(false, time); |
1153 |
< |
if (interruptible && Thread.interrupted()) |
1154 |
< |
return cancelWriter(node, true); |
1149 |
> |
return cancelWaiter(node, p, false); |
1150 |
> |
if (node.thread == null) |
1151 |
> |
break; |
1152 |
> |
if (p.prev != pp || p.status == CANCELLED || |
1153 |
> |
p == whead || p.prev != pp) { |
1154 |
> |
node.thread = null; |
1155 |
> |
break; |
1156 |
|
} |
1157 |
+ |
Thread wt = Thread.currentThread(); |
1158 |
+ |
U.putObject(wt, PARKBLOCKER, this); |
1159 |
+ |
if (node.thread == null) // must recheck |
1160 |
+ |
break; |
1161 |
+ |
U.park(false, time); |
1162 |
+ |
U.putObject(wt, PARKBLOCKER, null); |
1163 |
+ |
if (interruptible && Thread.interrupted()) |
1164 |
+ |
return cancelWaiter(node, p, true); |
1165 |
|
} |
1166 |
+ |
group = p; |
1167 |
|
} |
1168 |
+ |
node = null; // throw away |
1169 |
|
} |
1170 |
< |
} |
1171 |
< |
} |
1172 |
< |
|
997 |
< |
/** |
998 |
< |
* If node non-null, forces cancel status and unsplices from queue |
999 |
< |
* if possible. This is a streamlined variant of cancellation |
1000 |
< |
* methods in AbstractQueuedSynchronizer that includes a detailed |
1001 |
< |
* explanation. |
1002 |
< |
*/ |
1003 |
< |
private long cancelWriter(WNode node, boolean interrupted) { |
1004 |
< |
WNode pred; |
1005 |
< |
if (node != null && (pred = node.prev) != null) { |
1006 |
< |
WNode pp; |
1007 |
< |
node.thread = null; |
1008 |
< |
while (pred.status == CANCELLED && (pp = pred.prev) != null) |
1009 |
< |
pred = node.prev = pp; |
1010 |
< |
WNode predNext = pred.next; |
1011 |
< |
node.status = CANCELLED; |
1012 |
< |
if (predNext != null) { |
1013 |
< |
Thread w = null; |
1014 |
< |
WNode succ = node.next; |
1015 |
< |
while (succ != null && succ.status == CANCELLED) |
1016 |
< |
succ = succ.next; |
1017 |
< |
if (succ != null) |
1018 |
< |
w = succ.thread; |
1019 |
< |
else if (node == wtail) |
1020 |
< |
U.compareAndSwapObject(this, WTAIL, node, pred); |
1021 |
< |
U.compareAndSwapObject(pred, WNEXT, predNext, succ); |
1022 |
< |
if (w != null) |
1023 |
< |
U.unpark(w); |
1170 |
> |
else if (U.compareAndSwapObject(this, WTAIL, p, node)) { |
1171 |
> |
p.next = node; |
1172 |
> |
break; |
1173 |
|
} |
1174 |
|
} |
1026 |
– |
writerPrefSignal(); |
1027 |
– |
return (interrupted || Thread.interrupted()) ? INTERRUPTED : 0L; |
1028 |
– |
} |
1175 |
|
|
1176 |
< |
/** |
1177 |
< |
* Waits for read lock or timeout or interrupt. The form of |
1178 |
< |
* awaitRead differs from awaitWrite mainly because it must |
1179 |
< |
* restart (with a new wait node) if the thread was unqueued and |
1180 |
< |
* unparked but could not the obtain lock. We also need to help |
1181 |
< |
* with preference rules by not trying to acquire the lock before |
1182 |
< |
* enqueuing if there is a known waiting writer, but also helping |
1183 |
< |
* to release those threads that are still queued from the last |
1184 |
< |
* release. |
1185 |
< |
*/ |
1186 |
< |
private long awaitRead(long stamp, boolean interruptible, long deadline) { |
1187 |
< |
long seq = stamp & SBITS; |
1188 |
< |
RNode node = null; |
1189 |
< |
boolean queued = false; |
1190 |
< |
for (int r = 0, headSpins = SPINS, spins = -1;;) { |
1191 |
< |
long s, m, next; RNode p; WNode wh; Thread w; |
1192 |
< |
if ((m = (s = state) & ABITS) != WBIT && |
1193 |
< |
((s & SBITS) != seq || (wh = whead) == null || |
1194 |
< |
wh.status == 0)) { |
1195 |
< |
if (m < RFULL ? |
1196 |
< |
U.compareAndSwapLong(this, STATE, s, next = s + RUNIT) : |
1197 |
< |
(next = tryIncReaderOverflow(s)) != 0L) { |
1198 |
< |
if (node != null && (w = node.waiter) != null) |
1199 |
< |
U.compareAndSwapObject(node, WAITER, w, null); |
1200 |
< |
if ((p = rhead) != null && (s & SBITS) != p.seq && |
1201 |
< |
U.compareAndSwapObject(this, RHEAD, p, p.next) && |
1056 |
< |
(w = p.waiter) != null && |
1057 |
< |
U.compareAndSwapObject(p, WAITER, w, null)) |
1058 |
< |
U.unpark(w); // help signal other waiters |
1059 |
< |
return next; |
1176 |
> |
for (int spins = SPINS;;) { |
1177 |
> |
WNode np, pp, r; int ps; long m, s, ns; Thread w; |
1178 |
> |
while ((np = node.prev) != p && np != null) |
1179 |
> |
(p = np).next = node; |
1180 |
> |
if (whead == p) { |
1181 |
> |
for (int k = spins;;) { |
1182 |
> |
if ((m = (s = state) & ABITS) != WBIT) { |
1183 |
> |
if (m < RFULL ? |
1184 |
> |
U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT): |
1185 |
> |
(ns = tryIncReaderOverflow(s)) != 0L) { |
1186 |
> |
whead = node; |
1187 |
> |
node.prev = null; |
1188 |
> |
while ((r = node.cowait) != null) { |
1189 |
> |
if (U.compareAndSwapObject(node, WCOWAIT, |
1190 |
> |
r, r.cowait) && |
1191 |
> |
(w = r.thread) != null) { |
1192 |
> |
r.thread = null; |
1193 |
> |
U.unpark(w); // release co-waiter |
1194 |
> |
} |
1195 |
> |
} |
1196 |
> |
return ns; |
1197 |
> |
} |
1198 |
> |
} |
1199 |
> |
else if (ThreadLocalRandom.current().nextInt() >= 0 && |
1200 |
> |
--k <= 0) |
1201 |
> |
break; |
1202 |
|
} |
1203 |
+ |
if (spins < MAX_HEAD_SPINS) |
1204 |
+ |
spins <<= 1; |
1205 |
|
} |
1206 |
< |
else if (m != WBIT && (p = rhead) != null && |
1207 |
< |
(s & SBITS) != p.seq) { // help release old readers |
1208 |
< |
if (U.compareAndSwapObject(this, RHEAD, p, p.next) && |
1209 |
< |
(w = p.waiter) != null && |
1210 |
< |
U.compareAndSwapObject(p, WAITER, w, null)) |
1211 |
< |
U.unpark(w); |
1212 |
< |
} |
1069 |
< |
else if (queued && node != null && node.waiter == null) { |
1070 |
< |
node = null; // restart |
1071 |
< |
queued = false; |
1072 |
< |
spins = -1; |
1073 |
< |
} |
1074 |
< |
else if (spins < 0) { |
1075 |
< |
if (rhead != node) |
1076 |
< |
spins = 0; |
1077 |
< |
else if ((spins = headSpins) < MAX_HEAD_SPINS && node != null) |
1078 |
< |
headSpins <<= 1; |
1079 |
< |
} |
1080 |
< |
else if (spins > 0) { |
1081 |
< |
if ((r = nextRandom(r)) >= 0) |
1082 |
< |
--spins; |
1083 |
< |
} |
1084 |
< |
else if (node == null) |
1085 |
< |
node = new RNode(seq, Thread.currentThread()); |
1086 |
< |
else if (!queued) { |
1087 |
< |
if (queued = U.compareAndSwapObject(this, RHEAD, |
1088 |
< |
node.next = rhead, node)) |
1089 |
< |
spins = -1; |
1206 |
> |
if ((ps = p.status) == 0) |
1207 |
> |
U.compareAndSwapInt(p, WSTATUS, 0, WAITING); |
1208 |
> |
else if (ps == CANCELLED) { |
1209 |
> |
if ((pp = p.prev) != null) { |
1210 |
> |
node.prev = pp; |
1211 |
> |
pp.next = node; |
1212 |
> |
} |
1213 |
|
} |
1214 |
|
else { |
1215 |
|
long time; |
1216 |
|
if (deadline == 0L) |
1217 |
|
time = 0L; |
1218 |
|
else if ((time = deadline - System.nanoTime()) <= 0L) |
1219 |
< |
return cancelReader(node, false); |
1220 |
< |
if ((state & WBIT) != 0L && node.waiter != null) { // recheck |
1219 |
> |
return cancelWaiter(node, node, false); |
1220 |
> |
Thread wt = Thread.currentThread(); |
1221 |
> |
U.putObject(wt, PARKBLOCKER, this); |
1222 |
> |
node.thread = wt; |
1223 |
> |
if (node.prev == p && p.status == WAITING && |
1224 |
> |
(p != whead || (state & ABITS) != WBIT)) |
1225 |
|
U.park(false, time); |
1226 |
< |
if (interruptible && Thread.interrupted()) |
1227 |
< |
return cancelReader(node, true); |
1228 |
< |
} |
1226 |
> |
node.thread = null; |
1227 |
> |
U.putObject(wt, PARKBLOCKER, null); |
1228 |
> |
if (interruptible && Thread.interrupted()) |
1229 |
> |
return cancelWaiter(node, node, true); |
1230 |
|
} |
1231 |
|
} |
1232 |
|
} |
1233 |
|
|
1234 |
|
/** |
1235 |
< |
* If node non-null, forces cancel status and unsplices from queue |
1236 |
< |
* if possible, by traversing entire queue looking for cancelled |
1237 |
< |
* nodes. |
1238 |
< |
*/ |
1239 |
< |
private long cancelReader(RNode node, boolean interrupted) { |
1240 |
< |
Thread w; |
1241 |
< |
if (node != null && (w = node.waiter) != null && |
1242 |
< |
U.compareAndSwapObject(node, WAITER, w, null)) { |
1243 |
< |
for (RNode pred = null, p = rhead; p != null;) { |
1244 |
< |
RNode q = p.next; |
1245 |
< |
if (p.waiter == null) { |
1246 |
< |
if (pred == null) { |
1247 |
< |
U.compareAndSwapObject(this, RHEAD, p, q); |
1248 |
< |
p = rhead; |
1249 |
< |
} |
1250 |
< |
else { |
1251 |
< |
U.compareAndSwapObject(pred, RNEXT, p, q); |
1252 |
< |
p = pred.next; |
1235 |
> |
* If node non-null, forces cancel status and unsplices it from |
1236 |
> |
* queue if possible and wakes up any cowaiters (of the node, or |
1237 |
> |
* group, as applicable), and in any case helps release current |
1238 |
> |
* first waiter if lock is free. (Calling with null arguments |
1239 |
> |
* serves as a conditional form of release, which is not currently |
1240 |
> |
* needed but may be needed under possible future cancellation |
1241 |
> |
* policies). This is a variant of cancellation methods in |
1242 |
> |
* AbstractQueuedSynchronizer (see its detailed explanation in AQS |
1243 |
> |
* internal documentation). |
1244 |
> |
* |
1245 |
> |
* @param node if nonnull, the waiter |
1246 |
> |
* @param group either node or the group node is cowaiting with |
1247 |
> |
* @param interrupted if already interrupted |
1248 |
> |
* @return INTERRUPTED if interrupted or Thread.interrupted, else zero |
1249 |
> |
*/ |
1250 |
> |
private long cancelWaiter(WNode node, WNode group, boolean interrupted) { |
1251 |
> |
if (node != null && group != null) { |
1252 |
> |
Thread w; |
1253 |
> |
node.status = CANCELLED; |
1254 |
> |
node.thread = null; |
1255 |
> |
// unsplice cancelled nodes from group |
1256 |
> |
for (WNode p = group, q; (q = p.cowait) != null;) { |
1257 |
> |
if (q.status == CANCELLED) |
1258 |
> |
U.compareAndSwapObject(p, WNEXT, q, q.next); |
1259 |
> |
else |
1260 |
> |
p = q; |
1261 |
> |
} |
1262 |
> |
if (group == node) { |
1263 |
> |
WNode r; // detach and wake up uncancelled co-waiters |
1264 |
> |
while ((r = node.cowait) != null) { |
1265 |
> |
if (U.compareAndSwapObject(node, WCOWAIT, r, r.cowait) && |
1266 |
> |
(w = r.thread) != null) { |
1267 |
> |
r.thread = null; |
1268 |
> |
U.unpark(w); |
1269 |
|
} |
1270 |
|
} |
1271 |
< |
else { |
1272 |
< |
pred = p; |
1273 |
< |
p = q; |
1271 |
> |
for (WNode pred = node.prev; pred != null; ) { // unsplice |
1272 |
> |
WNode succ, pp; // find valid successor |
1273 |
> |
while ((succ = node.next) == null || |
1274 |
> |
succ.status == CANCELLED) { |
1275 |
> |
WNode q = null; // find successor the slow way |
1276 |
> |
for (WNode t = wtail; t != null && t != node; t = t.prev) |
1277 |
> |
if (t.status != CANCELLED) |
1278 |
> |
q = t; // don't link if succ cancelled |
1279 |
> |
if (succ == q || // ensure accurate successor |
1280 |
> |
U.compareAndSwapObject(node, WNEXT, |
1281 |
> |
succ, succ = q)) { |
1282 |
> |
if (succ == null && node == wtail) |
1283 |
> |
U.compareAndSwapObject(this, WTAIL, node, pred); |
1284 |
> |
break; |
1285 |
> |
} |
1286 |
> |
} |
1287 |
> |
if (pred.next == node) // unsplice pred link |
1288 |
> |
U.compareAndSwapObject(pred, WNEXT, node, succ); |
1289 |
> |
if (succ != null && (w = succ.thread) != null) { |
1290 |
> |
succ.thread = null; |
1291 |
> |
U.unpark(w); // wake up succ to observe new pred |
1292 |
> |
} |
1293 |
> |
if (pred.status != CANCELLED || (pp = pred.prev) == null) |
1294 |
> |
break; |
1295 |
> |
node.prev = pp; // repeat if new pred wrong/cancelled |
1296 |
> |
U.compareAndSwapObject(pp, WNEXT, pred, succ); |
1297 |
> |
pred = pp; |
1298 |
|
} |
1299 |
|
} |
1300 |
|
} |
1301 |
< |
readerPrefSignal(); |
1301 |
> |
WNode h; // Possibly release first waiter |
1302 |
> |
while ((h = whead) != null) { |
1303 |
> |
long s; WNode q; // similar to release() but check eligibility |
1304 |
> |
if ((q = h.next) == null || q.status == CANCELLED) { |
1305 |
> |
for (WNode t = wtail; t != null && t != h; t = t.prev) |
1306 |
> |
if (t.status <= 0) |
1307 |
> |
q = t; |
1308 |
> |
} |
1309 |
> |
if (h == whead) { |
1310 |
> |
if (q != null && h.status == 0 && |
1311 |
> |
((s = state) & ABITS) != WBIT && // waiter is eligible |
1312 |
> |
(s == 0L || q.mode == RMODE)) |
1313 |
> |
release(h); |
1314 |
> |
break; |
1315 |
> |
} |
1316 |
> |
} |
1317 |
|
return (interrupted || Thread.interrupted()) ? INTERRUPTED : 0L; |
1318 |
|
} |
1319 |
|
|
1320 |
|
// Unsafe mechanics |
1321 |
|
private static final sun.misc.Unsafe U; |
1322 |
|
private static final long STATE; |
1140 |
– |
private static final long RHEAD; |
1323 |
|
private static final long WHEAD; |
1324 |
|
private static final long WTAIL; |
1143 |
– |
private static final long RNEXT; |
1325 |
|
private static final long WNEXT; |
1326 |
< |
private static final long WPREV; |
1327 |
< |
private static final long WAITER; |
1328 |
< |
private static final long STATUS; |
1326 |
> |
private static final long WSTATUS; |
1327 |
> |
private static final long WCOWAIT; |
1328 |
> |
private static final long PARKBLOCKER; |
1329 |
|
|
1330 |
|
static { |
1331 |
|
try { |
1332 |
|
U = getUnsafe(); |
1333 |
|
Class<?> k = StampedLock.class; |
1153 |
– |
Class<?> rk = RNode.class; |
1334 |
|
Class<?> wk = WNode.class; |
1335 |
|
STATE = U.objectFieldOffset |
1336 |
|
(k.getDeclaredField("state")); |
1157 |
– |
RHEAD = U.objectFieldOffset |
1158 |
– |
(k.getDeclaredField("rhead")); |
1337 |
|
WHEAD = U.objectFieldOffset |
1338 |
|
(k.getDeclaredField("whead")); |
1339 |
|
WTAIL = U.objectFieldOffset |
1340 |
|
(k.getDeclaredField("wtail")); |
1341 |
< |
RNEXT = U.objectFieldOffset |
1164 |
< |
(rk.getDeclaredField("next")); |
1165 |
< |
WAITER = U.objectFieldOffset |
1166 |
< |
(rk.getDeclaredField("waiter")); |
1167 |
< |
STATUS = U.objectFieldOffset |
1341 |
> |
WSTATUS = U.objectFieldOffset |
1342 |
|
(wk.getDeclaredField("status")); |
1343 |
|
WNEXT = U.objectFieldOffset |
1344 |
|
(wk.getDeclaredField("next")); |
1345 |
< |
WPREV = U.objectFieldOffset |
1346 |
< |
(wk.getDeclaredField("prev")); |
1345 |
> |
WCOWAIT = U.objectFieldOffset |
1346 |
> |
(wk.getDeclaredField("cowait")); |
1347 |
> |
Class<?> tk = Thread.class; |
1348 |
> |
PARKBLOCKER = U.objectFieldOffset |
1349 |
> |
(tk.getDeclaredField("parkBlocker")); |
1350 |
|
|
1351 |
|
} catch (Exception e) { |
1352 |
|
throw new Error(e); |
1363 |
|
private static sun.misc.Unsafe getUnsafe() { |
1364 |
|
try { |
1365 |
|
return sun.misc.Unsafe.getUnsafe(); |
1366 |
< |
} catch (SecurityException se) { |
1367 |
< |
try { |
1368 |
< |
return java.security.AccessController.doPrivileged |
1369 |
< |
(new java.security |
1370 |
< |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1371 |
< |
public sun.misc.Unsafe run() throws Exception { |
1372 |
< |
java.lang.reflect.Field f = sun.misc |
1373 |
< |
.Unsafe.class.getDeclaredField("theUnsafe"); |
1374 |
< |
f.setAccessible(true); |
1375 |
< |
return (sun.misc.Unsafe) f.get(null); |
1376 |
< |
}}); |
1377 |
< |
} catch (java.security.PrivilegedActionException e) { |
1378 |
< |
throw new RuntimeException("Could not initialize intrinsics", |
1379 |
< |
e.getCause()); |
1380 |
< |
} |
1366 |
> |
} catch (SecurityException tryReflectionInstead) {} |
1367 |
> |
try { |
1368 |
> |
return java.security.AccessController.doPrivileged |
1369 |
> |
(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1370 |
> |
public sun.misc.Unsafe run() throws Exception { |
1371 |
> |
Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class; |
1372 |
> |
for (java.lang.reflect.Field f : k.getDeclaredFields()) { |
1373 |
> |
f.setAccessible(true); |
1374 |
> |
Object x = f.get(null); |
1375 |
> |
if (k.isInstance(x)) |
1376 |
> |
return k.cast(x); |
1377 |
> |
} |
1378 |
> |
throw new NoSuchFieldError("the Unsafe"); |
1379 |
> |
}}); |
1380 |
> |
} catch (java.security.PrivilegedActionException e) { |
1381 |
> |
throw new RuntimeException("Could not initialize intrinsics", |
1382 |
> |
e.getCause()); |
1383 |
|
} |
1384 |
|
} |
1206 |
– |
|
1385 |
|
} |