11 |
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|
12 |
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/** |
13 |
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* A capability-based lock with three modes for controlling read/write |
14 |
< |
* access. The state of a StampedLock consists of a version and |
15 |
< |
* mode. Lock acquisition methods return a stamp that represents and |
14 |
> |
* access. The state of a StampedLock consists of a version and mode. |
15 |
> |
* Lock acquisition methods return a stamp that represents and |
16 |
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* controls access with respect to a lock state; "try" versions of |
17 |
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* these methods may instead return the special value zero to |
18 |
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* represent failure to acquire access. Lock release and conversion |
55 |
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* <p>This class also supports methods that conditionally provide |
56 |
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* conversions across the three modes. For example, method {@link |
57 |
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* #tryConvertToWriteLock} attempts to "upgrade" a mode, returning |
58 |
< |
* valid write stamp if (1) already in writing mode (2) in reading |
58 |
> |
* a valid write stamp if (1) already in writing mode (2) in reading |
59 |
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* mode and there are no other readers or (3) in optimistic mode and |
60 |
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* the lock is available. The forms of these methods are designed to |
61 |
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* help reduce some of the code bloat that otherwise occurs in |
261 |
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private static final int OVERFLOW_YIELD_RATE = 7; // must be power 2 - 1 |
262 |
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|
263 |
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/** The number of bits to use for reader count before overflowing */ |
264 |
< |
private static final int LG_READERS = 7; |
264 |
> |
private static final int LG_READERS = 7; |
265 |
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|
266 |
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// Values for lock state and stamp operations |
267 |
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private static final long RUNIT = 1L; |
334 |
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* Exclusively acquires the lock if it is immediately available. |
335 |
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* |
336 |
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* @return a stamp that can be used to unlock or convert mode, |
337 |
< |
* or zero if the lock is not available. |
337 |
> |
* or zero if the lock is not available |
338 |
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*/ |
339 |
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public long tryWriteLock() { |
340 |
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long s, next; |
539 |
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} |
540 |
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|
541 |
|
/** |
542 |
< |
* If the lock state matches the given stamp, releases |
542 |
> |
* If the lock state matches the given stamp, releases the |
543 |
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* non-exclusive lock. |
544 |
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* |
545 |
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* @param stamp a stamp returned by a read-lock operation |
606 |
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/** |
607 |
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* If the lock state matches the given stamp then performs one of |
608 |
|
* the following actions. If the stamp represents holding a write |
609 |
< |
* lock, returns it. Or, if a read lock, if the write lock is |
610 |
< |
* available, releases the read and returns a write stamp. Or, if |
611 |
< |
* an optimistic read, returns a write stamp only if immediately |
612 |
< |
* available. This method returns zero in all other cases. |
609 |
> |
* lock, returns it. Or, if a read lock, if the write lock is |
610 |
> |
* available, releases the read lock and returns a write stamp. |
611 |
> |
* Or, if an optimistic read, returns a write stamp only if |
612 |
> |
* immediately available. This method returns zero in all other |
613 |
> |
* cases. |
614 |
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* |
615 |
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* @param stamp a stamp |
616 |
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* @return a valid write stamp, or zero on failure |