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public class Exchanger<V> { |
| 77 |
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|
| 78 |
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/* |
| 79 |
< |
* Oveview: The core algorithm is, for an exchange "slot", |
| 79 |
> |
* Overview: The core algorithm is, for an exchange "slot", |
| 80 |
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* and a participant (caller) with an item: |
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* |
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* for (;;) { |
| 114 |
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* and related bookkeeping state. (We can safely reuse per-thread |
| 115 |
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* nodes rather than creating them fresh each time because slots |
| 116 |
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* alternate between pointing to a node vs null, so cannot |
| 117 |
< |
* encounter ABA problems. However, we do need som care in |
| 117 |
> |
* encounter ABA problems. However, we do need some care in |
| 118 |
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* resetting them between uses.) |
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* |
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* Implementing an effective arena requires allocating a bunch of |
| 203 |
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* both methods may be called. This is done by using null return |
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* as a sentinel to recheck interrupt status.) |
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* |
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< |
* As is too common in this sort of code, methods are monolothic |
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> |
* As is too common in this sort of code, methods are monolithic |
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* because most of the logic relies on reads of fields that are |
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* maintained as local variables so can't be nicely factored -- |
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* mainly, here, bulky spin->yield->block/cancel code), and |
| 210 |
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* heavily dependent on intrinsics (Unsafe) to use inlined |
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< |
* embedded CAS and related mameory access operations (that tend |
| 211 |
> |
* embedded CAS and related memory access operations (that tend |
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* not to be as readily inlined by dynamic compilers when they are |
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* hidden behind other methods that would more nicely name and |
| 214 |
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* encapsulate the intended effects). This includes the use of |
| 215 |
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* putOrderedX to clear fields of the per-thread Nodes between |
| 216 |
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* uses. Note that field Node.item is not declared as volatile |
| 217 |
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* even though it is read by releasing threads, because they only |
| 218 |
< |
* do so after CAS operations that must preceed access, and all |
| 218 |
> |
* do so after CAS operations that must precede access, and all |
| 219 |
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* uses by the owning thread are otherwise acceptably ordered by |
| 220 |
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* other operations. (Because the actual points of atomicity are |
| 221 |
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* slot CASes, it would also be legal for the write to Node.match |
