Пример #1
0
 /**
  * If the lock state matches the given stamp then, if the stamp represents holding a lock,
  * releases it and returns an observation stamp. Or, if an optimistic read, returns it if
  * validated. This method returns zero in all other cases, and so may be useful as a form of
  * "tryUnlock".
  *
  * @param stamp a stamp
  * @return a valid optimistic read stamp, or zero on failure
  */
 public long tryConvertToOptimisticRead(long stamp) {
   long a = stamp & ABITS, m, s, next;
   WNode h;
   U.loadFence();
   for (; ; ) {
     if (((s = state) & SBITS) != (stamp & SBITS)) break;
     if ((m = s & ABITS) == 0L) {
       if (a != 0L) break;
       return s;
     } else if (m == WBIT) {
       if (a != m) break;
       state = next = (s += WBIT) == 0L ? ORIGIN : s;
       if ((h = whead) != null && h.status != 0) release(h);
       return next;
     } else if (a == 0L || a >= WBIT) break;
     else if (m < RFULL) {
       if (U.compareAndSwapLong(this, STATE, s, next = s - RUNIT)) {
         if (m == RUNIT && (h = whead) != null && h.status != 0) release(h);
         return next & SBITS;
       }
     } else if ((next = tryDecReaderOverflow(s)) != 0L) return next & SBITS;
   }
   return 0L;
 }
Пример #2
0
 /**
  * Returns true if the lock has not been exclusively acquired since issuance of the given stamp.
  * Always returns false if the stamp is zero. Always returns true if the stamp represents a
  * currently held lock. Invoking this method with a value not obtained from {@link
  * #tryOptimisticRead} or a locking method for this lock has no defined effect or result.
  *
  * @param stamp a stamp
  * @return {@code true} if the lock has not been exclusively acquired since issuance of the given
  *     stamp; else false
  */
 public boolean validate(long stamp) {
   U.loadFence();
   return (stamp & SBITS) == (state & SBITS);
 }