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import java.util.concurrent.*; |
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import java.util.Random; |
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import java.util.Collection; |
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import java.util.concurrent.locks.LockSupport; |
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/** |
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* A thread managed by a {@link ForkJoinPool}. This class is |
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*/ |
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public class ForkJoinWorkerThread extends Thread { |
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/* |
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* Algorithm overview: |
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* Overview: |
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* |
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* 1. Work-Stealing: Work-stealing queues are special forms of |
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* Deques that support only three of the four possible |
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* end-operations -- push, pop, and deq (aka steal), and only do |
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* so under the constraints that push and pop are called only from |
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* the owning thread, while deq may be called from other threads. |
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* (If you are unfamiliar with them, you probably want to read |
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* Herlihy and Shavit's book "The Art of Multiprocessor |
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* programming", chapter 16 describing these in more detail before |
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* proceeding.) The main work-stealing queue design is roughly |
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* similar to "Dynamic Circular Work-Stealing Deque" by David |
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* Chase and Yossi Lev, SPAA 2005 |
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* (http://research.sun.com/scalable/pubs/index.html). The main |
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* difference ultimately stems from gc requirements that we null |
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* out taken slots as soon as we can, to maintain as small a |
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* footprint as possible even in programs generating huge numbers |
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* of tasks. To accomplish this, we shift the CAS arbitrating pop |
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* vs deq (steal) from being on the indices ("base" and "sp") to |
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* the slots themselves (mainly via method "casSlotNull()"). So, |
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* both a successful pop and deq mainly entail CAS'ing a non-null |
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* slot to null. Because we rely on CASes of references, we do |
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* not need tag bits on base or sp. They are simple ints as used |
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* in any circular array-based queue (see for example ArrayDeque). |
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* Updates to the indices must still be ordered in a way that |
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* guarantees that (sp - base) > 0 means the queue is empty, but |
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* otherwise may err on the side of possibly making the queue |
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* appear nonempty when a push, pop, or deq have not fully |
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* committed. Note that this means that the deq operation, |
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* considered individually, is not wait-free. One thief cannot |
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* successfully continue until another in-progress one (or, if |
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* previously empty, a push) completes. However, in the |
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* aggregate, we ensure at least probabilistic non-blockingness. If |
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* an attempted steal fails, a thief always chooses a different |
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* ForkJoinWorkerThreads are managed by ForkJoinPools and perform |
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* ForkJoinTasks. This class includes bookkeeping in support of |
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* worker activation, suspension, and lifecycle control described |
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* in more detail in the internal documentation of class |
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* ForkJoinPool. And as described further below, this class also |
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* includes special-cased support for some ForkJoinTask |
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* methods. But the main mechanics involve work-stealing: |
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* |
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* Work-stealing queues are special forms of Deques that support |
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* only three of the four possible end-operations -- push, pop, |
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* and deq (aka steal), under the further constraints that push |
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* and pop are called only from the owning thread, while deq may |
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* be called from other threads. (If you are unfamiliar with |
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* them, you probably want to read Herlihy and Shavit's book "The |
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* Art of Multiprocessor programming", chapter 16 describing these |
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* in more detail before proceeding.) The main work-stealing |
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* queue design is roughly similar to those in the papers "Dynamic |
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* Circular Work-Stealing Deque" by Chase and Lev, SPAA 2005 |
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* (http://research.sun.com/scalable/pubs/index.html) and |
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* "Idempotent work stealing" by Michael, Saraswat, and Vechev, |
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* PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186). |
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* The main differences ultimately stem from gc requirements that |
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* we null out taken slots as soon as we can, to maintain as small |
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* a footprint as possible even in programs generating huge |
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* numbers of tasks. To accomplish this, we shift the CAS |
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* arbitrating pop vs deq (steal) from being on the indices |
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* ("base" and "sp") to the slots themselves (mainly via method |
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* "casSlotNull()"). So, both a successful pop and deq mainly |
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* entail a CAS of a slot from non-null to null. Because we rely |
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* on CASes of references, we do not need tag bits on base or sp. |
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* They are simple ints as used in any circular array-based queue |
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* (see for example ArrayDeque). Updates to the indices must |
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* still be ordered in a way that guarantees that sp == base means |
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* the queue is empty, but otherwise may err on the side of |
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* possibly making the queue appear nonempty when a push, pop, or |
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* deq have not fully committed. Note that this means that the deq |
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* operation, considered individually, is not wait-free. One thief |
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* cannot successfully continue until another in-progress one (or, |
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* if previously empty, a push) completes. However, in the |
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* aggregate, we ensure at least probabilistic non-blockingness. |
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* If an attempted steal fails, a thief always chooses a different |
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* random victim target to try next. So, in order for one thief to |
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* progress, it suffices for any in-progress deq or new push on |
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* any empty queue to complete. One reason this works well here is |
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* that apparently-nonempty often means soon-to-be-stealable, |
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* which gives threads a chance to activate if necessary before |
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* stealing (see below). |
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* which gives threads a chance to set activation status if |
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* necessary before stealing. |
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* |
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* This approach also enables support for "async mode" where local |
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* task processing is in FIFO, not LIFO order; simply by using a |
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* by the ForkJoinPool). This allows use in message-passing |
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* frameworks in which tasks are never joined. |
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* |
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* Efficient implementation of this approach currently relies on |
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* an uncomfortable amount of "Unsafe" mechanics. To maintain |
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* When a worker would otherwise be blocked waiting to join a |
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* task, it first tries a form of linear helping: Each worker |
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* records (in field currentSteal) the most recent task it stole |
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* from some other worker. Plus, it records (in field currentJoin) |
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* the task it is currently actively joining. Method joinTask uses |
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* these markers to try to find a worker to help (i.e., steal back |
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* a task from and execute it) that could hasten completion of the |
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* actively joined task. In essence, the joiner executes a task |
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* that would be on its own local deque had the to-be-joined task |
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* not been stolen. This may be seen as a conservative variant of |
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* the approach in Wagner & Calder "Leapfrogging: a portable |
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* technique for implementing efficient futures" SIGPLAN Notices, |
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* 1993 (http://portal.acm.org/citation.cfm?id=155354). It differs |
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* in that: (1) We only maintain dependency links across workers |
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* upon steals, rather than use per-task bookkeeping. This may |
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* require a linear scan of workers array to locate stealers, but |
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* usually doesn't because stealers leave hints (that may become |
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* stale/wrong) of where to locate them. This isolates cost to |
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* when it is needed, rather than adding to per-task overhead. |
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* (2) It is "shallow", ignoring nesting and potentially cyclic |
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* mutual steals. (3) It is intentionally racy: field currentJoin |
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* is updated only while actively joining, which means that we |
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* miss links in the chain during long-lived tasks, GC stalls etc |
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* (which is OK since blocking in such cases is usually a good |
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* idea). (4) We bound the number of attempts to find work (see |
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* MAX_HELP_DEPTH) and fall back to suspending the worker and if |
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* necessary replacing it with a spare (see |
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* ForkJoinPool.tryAwaitJoin). |
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* |
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* Efficient implementation of these algorithms currently relies |
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* on an uncomfortable amount of "Unsafe" mechanics. To maintain |
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* correct orderings, reads and writes of variable base require |
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* volatile ordering. Variable sp does not require volatile write |
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* but needs cheaper store-ordering on writes. Because they are |
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* protected by volatile base reads, reads of the queue array and |
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* its slots do not need volatile load semantics, but writes (in |
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* push) require store order and CASes (in pop and deq) require |
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* (volatile) CAS semantics. Since these combinations aren't |
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* supported using ordinary volatiles, the only way to accomplish |
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* these efficiently is to use direct Unsafe calls. (Using external |
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* AtomicIntegers and AtomicReferenceArrays for the indices and |
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* array is significantly slower because of memory locality and |
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* indirection effects.) Further, performance on most platforms is |
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* very sensitive to placement and sizing of the (resizable) queue |
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* array. Even though these queues don't usually become all that |
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* big, the initial size must be large enough to counteract cache |
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* volatile ordering. Variable sp does not require volatile |
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* writes but still needs store-ordering, which we accomplish by |
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* pre-incrementing sp before filling the slot with an ordered |
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* store. (Pre-incrementing also enables backouts used in |
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* joinTask.) Because they are protected by volatile base reads, |
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* reads of the queue array and its slots by other threads do not |
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* need volatile load semantics, but writes (in push) require |
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* store order and CASes (in pop and deq) require (volatile) CAS |
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* semantics. (Michael, Saraswat, and Vechev's algorithm has |
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* similar properties, but without support for nulling slots.) |
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* Since these combinations aren't supported using ordinary |
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* volatiles, the only way to accomplish these efficiently is to |
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* use direct Unsafe calls. (Using external AtomicIntegers and |
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* AtomicReferenceArrays for the indices and array is |
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* significantly slower because of memory locality and indirection |
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* effects.) |
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* |
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* Further, performance on most platforms is very sensitive to |
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* placement and sizing of the (resizable) queue array. Even |
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* though these queues don't usually become all that big, the |
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* initial size must be large enough to counteract cache |
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* contention effects across multiple queues (especially in the |
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* presence of GC cardmarking). Also, to improve thread-locality, |
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* queues are currently initialized immediately after the thread |
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* gets the initial signal to start processing tasks. However, |
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* all queue-related methods except pushTask are written in a way |
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* that allows them to instead be lazily allocated and/or disposed |
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* of when empty. All together, these low-level implementation |
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* choices produce as much as a factor of 4 performance |
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* improvement compared to naive implementations, and enable the |
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* processing of billions of tasks per second, sometimes at the |
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* expense of ugliness. |
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* |
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* 2. Run control: The primary run control is based on a global |
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* counter (activeCount) held by the pool. It uses an algorithm |
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* similar to that in Herlihy and Shavit section 17.6 to cause |
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* threads to eventually block when all threads declare they are |
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* inactive. (See variable "scans".) For this to work, threads |
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* must be declared active when executing tasks, and before |
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* stealing a task. They must be inactive before blocking on the |
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* Pool Barrier (awaiting a new submission or other Pool |
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* event). In between, there is some free play which we take |
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* advantage of to avoid contention and rapid flickering of the |
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* global activeCount: If inactive, we activate only if a victim |
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* queue appears to be nonempty (see above). Similarly, a thread |
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* tries to inactivate only after a full scan of other threads. |
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* The net effect is that contention on activeCount is rarely a |
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* measurable performance issue. (There are also a few other cases |
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* where we scan for work rather than retry/block upon |
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* contention.) |
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* |
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* 3. Selection control. We maintain policy of always choosing to |
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* run local tasks rather than stealing, and always trying to |
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* steal tasks before trying to run a new submission. All steals |
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* are currently performed in randomly-chosen deq-order. It may be |
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* worthwhile to bias these with locality / anti-locality |
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* information, but doing this well probably requires more |
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* lower-level information from JVMs than currently provided. |
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* queues are initialized after starting. All together, these |
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* low-level implementation choices produce as much as a factor of |
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* 4 performance improvement compared to naive implementations, |
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* and enable the processing of billions of tasks per second, |
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* sometimes at the expense of ugliness. |
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*/ |
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|
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/** |
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* Generator for initial random seeds for random victim |
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* selection. This is used only to create initial seeds. Random |
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* steals use a cheaper xorshift generator per steal attempt. We |
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* expect only rare contention on seedGenerator, so just use a |
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* plain Random. |
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*/ |
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private static final Random seedGenerator = new Random(); |
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|
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/** |
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* The maximum stolen->joining link depth allowed in helpJoinTask. |
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* Depths for legitimate chains are unbounded, but we use a fixed |
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* constant to avoid (otherwise unchecked) cycles and bound |
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* staleness of traversal parameters at the expense of sometimes |
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* blocking when we could be helping. |
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*/ |
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private static final int MAX_HELP_DEPTH = 8; |
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|
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/** |
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* The wakeup interval (in nanoseconds) for the oldest worker |
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* suspended as spare. On each wakeup not signalled by a |
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* resumption, it may ask the pool to reduce the number of spares. |
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*/ |
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private static final long TRIM_RATE_NANOS = |
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5L * 1000L * 1000L * 1000L; // 5sec |
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|
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/** |
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* Capacity of work-stealing queue array upon initialization. |
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* Must be a power of two. Initial size must be at least 2, but is |
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* Must be a power of two. Initial size must be at least 4, but is |
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* padded to minimize cache effects. |
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*/ |
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private static final int INITIAL_QUEUE_CAPACITY = 1 << 13; |
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|
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/** |
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* The work-stealing queue array. Size must be a power of two. |
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* Initialized when thread starts, to improve memory locality. |
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* Initialized in onStart, to improve memory locality. |
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*/ |
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private ForkJoinTask<?>[] queue; |
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/** |
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* Index (mod queue.length) of next queue slot to push to or pop |
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* from. It is written only by owner thread, via ordered store. |
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* Both sp and base are allowed to wrap around on overflow, but |
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* (sp - base) still estimates size. |
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*/ |
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private volatile int sp; |
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|
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/** |
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* Index (mod queue.length) of least valid queue slot, which is |
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* always the next position to steal from if nonempty. |
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*/ |
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private volatile int base; |
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|
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/** |
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* Activity status. When true, this worker is considered active. |
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* Must be false upon construction. It must be true when executing |
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* tasks, and BEFORE stealing a task. It must be false before |
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* calling pool.sync. |
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* Index (mod queue.length) of next queue slot to push to or pop |
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* from. It is written only by owner thread, and accessed by other |
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* threads only after reading (volatile) base. Both sp and base |
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* are allowed to wrap around on overflow, but (sp - base) still |
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* estimates size. |
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*/ |
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private boolean active; |
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private int sp; |
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|
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/** |
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* Run state of this worker. Supports simple versions of the usual |
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* shutdown/shutdownNow control. |
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* The index of most recent stealer, used as a hint to avoid |
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* traversal in method helpJoinTask. This is only a hint because a |
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* worker might have had multiple steals and this only holds one |
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* of them (usually the most current). Declared non-volatile, |
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* relying on other prevailing sync to keep reasonably current. |
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*/ |
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private int stealHint; |
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|
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/** |
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* Run state of this worker. In addition to the usual run levels, |
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* tracks if this worker is suspended as a spare, and if it was |
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* killed (trimmed) while suspended. However, "active" status is |
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* maintained separately and modified only in conjunction with |
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* CASes of the pool's runState (which are currently sadly manually |
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* inlined for performance.) |
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*/ |
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private volatile int runState; |
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|
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private static final int TERMINATING = 0x01; |
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private static final int TERMINATED = 0x02; |
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private static final int SUSPENDED = 0x04; // inactive spare |
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private static final int TRIMMED = 0x08; // killed while suspended |
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|
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/** |
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* Number of steals, transferred and reset in pool callbacks pool |
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* when idle Accessed directly by pool. |
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*/ |
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int stealCount; |
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|
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/** |
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* Seed for random number generator for choosing steal victims. |
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* Uses Marsaglia xorshift. Must be nonzero upon initialization. |
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* Uses Marsaglia xorshift. Must be initialized as nonzero. |
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*/ |
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private int seed; |
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|
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/** |
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* Number of steals, transferred to pool when idle |
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* Activity status. When true, this worker is considered active. |
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* Accessed directly by pool. Must be false upon construction. |
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*/ |
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boolean active; |
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|
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/** |
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* True if use local fifo, not default lifo, for local polling. |
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* Shadows value from ForkJoinPool. |
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*/ |
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< |
private int stealCount; |
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> |
private final boolean locallyFifo; |
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|
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/** |
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* Index of this worker in pool array. Set once by pool before |
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* running, and accessed directly by pool during cleanup etc. |
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* running, and accessed directly by pool to locate this worker in |
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* its workers array. |
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*/ |
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int poolIndex; |
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|
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/** |
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* The last barrier event waited for. Accessed in pool callback |
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* methods, but only by current thread. |
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* The last pool event waited for. Accessed only by pool in |
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* callback methods invoked within this thread. |
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*/ |
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int lastEventCount; |
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|
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/** |
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* Encoded index and event count of next event waiter. Used only |
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* by ForkJoinPool for managing event waiters. |
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*/ |
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volatile long nextWaiter; |
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|
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/** |
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* Number of times this thread suspended as spare |
284 |
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*/ |
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> |
int spareCount; |
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|
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/** |
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* Encoded index and count of next spare waiter. Used only |
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* by ForkJoinPool for managing spares. |
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*/ |
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< |
long lastEventCount; |
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> |
volatile int nextSpare; |
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|
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/** |
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< |
* True if use local fifo, not default lifo, for local polling |
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> |
* The task currently being joined, set only when actively trying |
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> |
* to helpStealer. Written only by current thread, but read by |
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> |
* others. |
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*/ |
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< |
private boolean locallyFifo; |
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> |
private volatile ForkJoinTask<?> currentJoin; |
299 |
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|
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> |
/** |
301 |
> |
* The task most recently stolen from another worker (or |
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> |
* submission queue). Not volatile because always read/written in |
303 |
> |
* presence of related volatiles in those cases where it matters. |
304 |
> |
*/ |
305 |
> |
private ForkJoinTask<?> currentSteal; |
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|
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|
/** |
308 |
|
* Creates a ForkJoinWorkerThread operating in the given pool. |
311 |
|
* @throws NullPointerException if pool is null |
312 |
|
*/ |
313 |
|
protected ForkJoinWorkerThread(ForkJoinPool pool) { |
220 |
– |
if (pool == null) throw new NullPointerException(); |
314 |
|
this.pool = pool; |
315 |
< |
// Note: poolIndex is set by pool during construction |
316 |
< |
// Remaining initialization is deferred to onStart |
315 |
> |
this.locallyFifo = pool.locallyFifo; |
316 |
> |
setDaemon(true); |
317 |
> |
// To avoid exposing construction details to subclasses, |
318 |
> |
// remaining initialization is in start() and onStart() |
319 |
> |
} |
320 |
> |
|
321 |
> |
/** |
322 |
> |
* Performs additional initialization and starts this thread |
323 |
> |
*/ |
324 |
> |
final void start(int poolIndex, UncaughtExceptionHandler ueh) { |
325 |
> |
this.poolIndex = poolIndex; |
326 |
> |
if (ueh != null) |
327 |
> |
setUncaughtExceptionHandler(ueh); |
328 |
> |
start(); |
329 |
|
} |
330 |
|
|
331 |
< |
// Public access methods |
331 |
> |
// Public/protected methods |
332 |
|
|
333 |
|
/** |
334 |
|
* Returns the pool hosting this thread. |
353 |
|
} |
354 |
|
|
355 |
|
/** |
356 |
< |
* Establishes local first-in-first-out scheduling mode for forked |
357 |
< |
* tasks that are never joined. |
358 |
< |
* |
359 |
< |
* @param async if true, use locally FIFO scheduling |
356 |
> |
* Initializes internal state after construction but before |
357 |
> |
* processing any tasks. If you override this method, you must |
358 |
> |
* invoke super.onStart() at the beginning of the method. |
359 |
> |
* Initialization requires care: Most fields must have legal |
360 |
> |
* default values, to ensure that attempted accesses from other |
361 |
> |
* threads work correctly even before this thread starts |
362 |
> |
* processing tasks. |
363 |
|
*/ |
364 |
< |
void setAsyncMode(boolean async) { |
365 |
< |
locallyFifo = async; |
366 |
< |
} |
259 |
< |
|
260 |
< |
// Runstate management |
261 |
< |
|
262 |
< |
// Runstate values. Order matters |
263 |
< |
private static final int RUNNING = 0; |
264 |
< |
private static final int SHUTDOWN = 1; |
265 |
< |
private static final int TERMINATING = 2; |
266 |
< |
private static final int TERMINATED = 3; |
267 |
< |
|
268 |
< |
final boolean isShutdown() { return runState >= SHUTDOWN; } |
269 |
< |
final boolean isTerminating() { return runState >= TERMINATING; } |
270 |
< |
final boolean isTerminated() { return runState == TERMINATED; } |
271 |
< |
final boolean shutdown() { return transitionRunStateTo(SHUTDOWN); } |
272 |
< |
final boolean shutdownNow() { return transitionRunStateTo(TERMINATING); } |
364 |
> |
protected void onStart() { |
365 |
> |
int rs = seedGenerator.nextInt(); |
366 |
> |
seed = rs == 0? 1 : rs; // seed must be nonzero |
367 |
|
|
368 |
< |
/** |
369 |
< |
* Transitions to at least the given state. |
370 |
< |
* |
371 |
< |
* @return {@code true} if not already at least at given state |
278 |
< |
*/ |
279 |
< |
private boolean transitionRunStateTo(int state) { |
280 |
< |
for (;;) { |
281 |
< |
int s = runState; |
282 |
< |
if (s >= state) |
283 |
< |
return false; |
284 |
< |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, state)) |
285 |
< |
return true; |
286 |
< |
} |
287 |
< |
} |
368 |
> |
// Allocate name string and arrays in this thread |
369 |
> |
String pid = Integer.toString(pool.getPoolNumber()); |
370 |
> |
String wid = Integer.toString(poolIndex); |
371 |
> |
setName("ForkJoinPool-" + pid + "-worker-" + wid); |
372 |
|
|
373 |
< |
/** |
290 |
< |
* Tries to set status to active; fails on contention. |
291 |
< |
*/ |
292 |
< |
private boolean tryActivate() { |
293 |
< |
if (!active) { |
294 |
< |
if (!pool.tryIncrementActiveCount()) |
295 |
< |
return false; |
296 |
< |
active = true; |
297 |
< |
} |
298 |
< |
return true; |
373 |
> |
queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY]; |
374 |
|
} |
375 |
|
|
376 |
|
/** |
377 |
< |
* Tries to set status to inactive; fails on contention. |
377 |
> |
* Performs cleanup associated with termination of this worker |
378 |
> |
* thread. If you override this method, you must invoke |
379 |
> |
* {@code super.onTermination} at the end of the overridden method. |
380 |
> |
* |
381 |
> |
* @param exception the exception causing this thread to abort due |
382 |
> |
* to an unrecoverable error, or {@code null} if completed normally |
383 |
|
*/ |
384 |
< |
private boolean tryInactivate() { |
385 |
< |
if (active) { |
386 |
< |
if (!pool.tryDecrementActiveCount()) |
387 |
< |
return false; |
388 |
< |
active = false; |
384 |
> |
protected void onTermination(Throwable exception) { |
385 |
> |
try { |
386 |
> |
ForkJoinPool p = pool; |
387 |
> |
if (active) { |
388 |
> |
int a; // inline p.tryDecrementActiveCount |
389 |
> |
active = false; |
390 |
> |
do {} while(!UNSAFE.compareAndSwapInt |
391 |
> |
(p, poolRunStateOffset, a = p.runState, a - 1)); |
392 |
> |
} |
393 |
> |
cancelTasks(); |
394 |
> |
setTerminated(); |
395 |
> |
p.workerTerminated(this); |
396 |
> |
} catch (Throwable ex) { // Shouldn't ever happen |
397 |
> |
if (exception == null) // but if so, at least rethrown |
398 |
> |
exception = ex; |
399 |
> |
} finally { |
400 |
> |
if (exception != null) |
401 |
> |
UNSAFE.throwException(exception); |
402 |
|
} |
310 |
– |
return true; |
311 |
– |
} |
312 |
– |
|
313 |
– |
/** |
314 |
– |
* Computes next value for random victim probe. Scans don't |
315 |
– |
* require a very high quality generator, but also not a crummy |
316 |
– |
* one. Marsaglia xor-shift is cheap and works well. |
317 |
– |
*/ |
318 |
– |
private static int xorShift(int r) { |
319 |
– |
r ^= (r << 13); |
320 |
– |
r ^= (r >>> 17); |
321 |
– |
return r ^ (r << 5); |
403 |
|
} |
404 |
|
|
324 |
– |
// Lifecycle methods |
325 |
– |
|
405 |
|
/** |
406 |
|
* This method is required to be public, but should never be |
407 |
|
* called explicitly. It performs the main run loop to execute |
411 |
|
Throwable exception = null; |
412 |
|
try { |
413 |
|
onStart(); |
335 |
– |
pool.sync(this); // await first pool event |
414 |
|
mainLoop(); |
415 |
|
} catch (Throwable ex) { |
416 |
|
exception = ex; |
419 |
|
} |
420 |
|
} |
421 |
|
|
422 |
+ |
// helpers for run() |
423 |
+ |
|
424 |
|
/** |
425 |
< |
* Executes tasks until shut down. |
425 |
> |
* Find and execute tasks and check status while running |
426 |
|
*/ |
427 |
|
private void mainLoop() { |
428 |
< |
while (!isShutdown()) { |
429 |
< |
ForkJoinTask<?> t = pollTask(); |
430 |
< |
if (t != null || (t = pollSubmission()) != null) |
431 |
< |
t.quietlyExec(); |
432 |
< |
else if (tryInactivate()) |
433 |
< |
pool.sync(this); |
428 |
> |
int misses = 0; // track consecutive times failed to find work; max 2 |
429 |
> |
ForkJoinPool p = pool; |
430 |
> |
for (;;) { |
431 |
> |
p.preStep(this, misses); |
432 |
> |
if (runState != 0) |
433 |
> |
break; |
434 |
> |
misses = ((tryExecSteal() || tryExecSubmission()) ? 0 : |
435 |
> |
(misses < 2 ? misses + 1 : 2)); |
436 |
|
} |
437 |
|
} |
438 |
|
|
439 |
|
/** |
440 |
< |
* Initializes internal state after construction but before |
441 |
< |
* processing any tasks. If you override this method, you must |
442 |
< |
* invoke super.onStart() at the beginning of the method. |
361 |
< |
* Initialization requires care: Most fields must have legal |
362 |
< |
* default values, to ensure that attempted accesses from other |
363 |
< |
* threads work correctly even before this thread starts |
364 |
< |
* processing tasks. |
440 |
> |
* Try to steal a task and execute it |
441 |
> |
* |
442 |
> |
* @return true if ran a task |
443 |
|
*/ |
444 |
< |
protected void onStart() { |
445 |
< |
// Allocate while starting to improve chances of thread-local |
446 |
< |
// isolation |
447 |
< |
queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY]; |
448 |
< |
// Initial value of seed need not be especially random but |
449 |
< |
// should differ across workers and must be nonzero |
450 |
< |
int p = poolIndex + 1; |
451 |
< |
seed = p + (p << 8) + (p << 16) + (p << 24); // spread bits |
444 |
> |
private boolean tryExecSteal() { |
445 |
> |
ForkJoinTask<?> t; |
446 |
> |
if ((t = scan()) != null) { |
447 |
> |
t.quietlyExec(); |
448 |
> |
currentSteal = null; |
449 |
> |
if (sp != base) |
450 |
> |
execLocalTasks(); |
451 |
> |
return true; |
452 |
> |
} |
453 |
> |
return false; |
454 |
|
} |
455 |
|
|
456 |
|
/** |
457 |
< |
* Performs cleanup associated with termination of this worker |
378 |
< |
* thread. If you override this method, you must invoke |
379 |
< |
* {@code super.onTermination} at the end of the overridden method. |
457 |
> |
* If a submission exists, try to activate and run it; |
458 |
|
* |
459 |
< |
* @param exception the exception causing this thread to abort due |
382 |
< |
* to an unrecoverable error, or {@code null} if completed normally |
459 |
> |
* @return true if ran a task |
460 |
|
*/ |
461 |
< |
protected void onTermination(Throwable exception) { |
462 |
< |
// Execute remaining local tasks unless aborting or terminating |
463 |
< |
while (exception == null && pool.isProcessingTasks() && base != sp) { |
464 |
< |
try { |
465 |
< |
ForkJoinTask<?> t = popTask(); |
466 |
< |
if (t != null) |
461 |
> |
private boolean tryExecSubmission() { |
462 |
> |
ForkJoinPool p = pool; |
463 |
> |
while (p.hasQueuedSubmissions()) { |
464 |
> |
ForkJoinTask<?> t; int a; |
465 |
> |
if (active || // ugly/hacky: inline p.tryIncrementActiveCount |
466 |
> |
(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset, |
467 |
> |
a = p.runState, a + 1))) { |
468 |
> |
if ((t = p.pollSubmission()) != null) { |
469 |
> |
currentSteal = t; |
470 |
|
t.quietlyExec(); |
471 |
< |
} catch (Throwable ex) { |
472 |
< |
exception = ex; |
471 |
> |
currentSteal = null; |
472 |
> |
if (sp != base) |
473 |
> |
execLocalTasks(); |
474 |
> |
return true; |
475 |
> |
} |
476 |
|
} |
477 |
|
} |
478 |
< |
// Cancel other tasks, transition status, notify pool, and |
396 |
< |
// propagate exception to uncaught exception handler |
397 |
< |
try { |
398 |
< |
do {} while (!tryInactivate()); // ensure inactive |
399 |
< |
cancelTasks(); |
400 |
< |
runState = TERMINATED; |
401 |
< |
pool.workerTerminated(this); |
402 |
< |
} catch (Throwable ex) { // Shouldn't ever happen |
403 |
< |
if (exception == null) // but if so, at least rethrown |
404 |
< |
exception = ex; |
405 |
< |
} finally { |
406 |
< |
if (exception != null) |
407 |
< |
ForkJoinTask.rethrowException(exception); |
408 |
< |
} |
478 |
> |
return false; |
479 |
|
} |
480 |
|
|
411 |
– |
// Intrinsics-based support for queue operations. |
412 |
– |
|
481 |
|
/** |
482 |
< |
* Adds in store-order the given task at given slot of q to null. |
483 |
< |
* Caller must ensure q is non-null and index is in range. |
482 |
> |
* Runs local tasks until queue is empty or shut down. Call only |
483 |
> |
* while active. |
484 |
|
*/ |
485 |
< |
private static void setSlot(ForkJoinTask<?>[] q, int i, |
486 |
< |
ForkJoinTask<?> t) { |
487 |
< |
UNSAFE.putOrderedObject(q, (i << qShift) + qBase, t); |
485 |
> |
private void execLocalTasks() { |
486 |
> |
while (runState == 0) { |
487 |
> |
ForkJoinTask<?> t = locallyFifo? locallyDeqTask() : popTask(); |
488 |
> |
if (t != null) |
489 |
> |
t.quietlyExec(); |
490 |
> |
else if (sp == base) |
491 |
> |
break; |
492 |
> |
} |
493 |
|
} |
494 |
|
|
495 |
+ |
/* |
496 |
+ |
* Intrinsics-based atomic writes for queue slots. These are |
497 |
+ |
* basically the same as methods in AtomicObjectArray, but |
498 |
+ |
* specialized for (1) ForkJoinTask elements (2) requirement that |
499 |
+ |
* nullness and bounds checks have already been performed by |
500 |
+ |
* callers and (3) effective offsets are known not to overflow |
501 |
+ |
* from int to long (because of MAXIMUM_QUEUE_CAPACITY). We don't |
502 |
+ |
* need corresponding version for reads: plain array reads are OK |
503 |
+ |
* because they protected by other volatile reads and are |
504 |
+ |
* confirmed by CASes. |
505 |
+ |
* |
506 |
+ |
* Most uses don't actually call these methods, but instead contain |
507 |
+ |
* inlined forms that enable more predictable optimization. We |
508 |
+ |
* don't define the version of write used in pushTask at all, but |
509 |
+ |
* instead inline there a store-fenced array slot write. |
510 |
+ |
*/ |
511 |
+ |
|
512 |
|
/** |
513 |
< |
* CAS given slot of q to null. Caller must ensure q is non-null |
514 |
< |
* and index is in range. |
513 |
> |
* CASes slot i of array q from t to null. Caller must ensure q is |
514 |
> |
* non-null and index is in range. |
515 |
|
*/ |
516 |
< |
private static boolean casSlotNull(ForkJoinTask<?>[] q, int i, |
517 |
< |
ForkJoinTask<?> t) { |
516 |
> |
private static final boolean casSlotNull(ForkJoinTask<?>[] q, int i, |
517 |
> |
ForkJoinTask<?> t) { |
518 |
|
return UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null); |
519 |
|
} |
520 |
|
|
521 |
|
/** |
522 |
< |
* Sets sp in store-order. |
522 |
> |
* Performs a volatile write of the given task at given slot of |
523 |
> |
* array q. Caller must ensure q is non-null and index is in |
524 |
> |
* range. This method is used only during resets and backouts. |
525 |
|
*/ |
526 |
< |
private void storeSp(int s) { |
527 |
< |
UNSAFE.putOrderedInt(this, spOffset, s); |
526 |
> |
private static final void writeSlot(ForkJoinTask<?>[] q, int i, |
527 |
> |
ForkJoinTask<?> t) { |
528 |
> |
UNSAFE.putObjectVolatile(q, (i << qShift) + qBase, t); |
529 |
|
} |
530 |
|
|
531 |
< |
// Main queue methods |
531 |
> |
// queue methods |
532 |
|
|
533 |
|
/** |
534 |
< |
* Pushes a task. Called only by current thread. |
534 |
> |
* Pushes a task. Call only from this thread. |
535 |
|
* |
536 |
|
* @param t the task. Caller must ensure non-null. |
537 |
|
*/ |
538 |
|
final void pushTask(ForkJoinTask<?> t) { |
539 |
|
ForkJoinTask<?>[] q = queue; |
540 |
< |
int mask = q.length - 1; |
541 |
< |
int s = sp; |
542 |
< |
setSlot(q, s & mask, t); |
543 |
< |
storeSp(++s); |
544 |
< |
if ((s -= base) == 1) |
545 |
< |
pool.signalWork(); |
546 |
< |
else if (s >= mask) |
454 |
< |
growQueue(); |
540 |
> |
int mask = q.length - 1; // implicit assert q != null |
541 |
> |
int s = sp++; // ok to increment sp before slot write |
542 |
> |
UNSAFE.putOrderedObject(q, ((s & mask) << qShift) + qBase, t); |
543 |
> |
if ((s -= base) == 0) |
544 |
> |
pool.signalWork(); // was empty |
545 |
> |
else if (s == mask) |
546 |
> |
growQueue(); // is full |
547 |
|
} |
548 |
|
|
549 |
|
/** |
550 |
|
* Tries to take a task from the base of the queue, failing if |
551 |
< |
* either empty or contended. |
551 |
> |
* empty or contended. Note: Specializations of this code appear |
552 |
> |
* in locallyDeqTask and elsewhere. |
553 |
|
* |
554 |
|
* @return a task, or null if none or contended |
555 |
|
*/ |
556 |
|
final ForkJoinTask<?> deqTask() { |
557 |
|
ForkJoinTask<?> t; |
558 |
|
ForkJoinTask<?>[] q; |
559 |
< |
int i; |
467 |
< |
int b; |
559 |
> |
int b, i; |
560 |
|
if (sp != (b = base) && |
561 |
|
(q = queue) != null && // must read q after b |
562 |
< |
(t = q[i = (q.length - 1) & b]) != null && |
563 |
< |
casSlotNull(q, i, t)) { |
562 |
> |
(t = q[i = (q.length - 1) & b]) != null && base == b && |
563 |
> |
UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) { |
564 |
|
base = b + 1; |
565 |
|
return t; |
566 |
|
} |
568 |
|
} |
569 |
|
|
570 |
|
/** |
571 |
< |
* Tries to take a task from the base of own queue, activating if |
572 |
< |
* necessary, failing only if empty. Called only by current thread. |
571 |
> |
* Tries to take a task from the base of own queue. Assumes active |
572 |
> |
* status. Called only by current thread. |
573 |
|
* |
574 |
|
* @return a task, or null if none |
575 |
|
*/ |
576 |
|
final ForkJoinTask<?> locallyDeqTask() { |
577 |
< |
int b; |
578 |
< |
while (sp != (b = base)) { |
579 |
< |
if (tryActivate()) { |
580 |
< |
ForkJoinTask<?>[] q = queue; |
581 |
< |
int i = (q.length - 1) & b; |
582 |
< |
ForkJoinTask<?> t = q[i]; |
583 |
< |
if (t != null && casSlotNull(q, i, t)) { |
577 |
> |
ForkJoinTask<?>[] q = queue; |
578 |
> |
if (q != null) { |
579 |
> |
ForkJoinTask<?> t; |
580 |
> |
int b, i; |
581 |
> |
while (sp != (b = base)) { |
582 |
> |
if ((t = q[i = (q.length - 1) & b]) != null && base == b && |
583 |
> |
UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, |
584 |
> |
t, null)) { |
585 |
|
base = b + 1; |
586 |
|
return t; |
587 |
|
} |
591 |
|
} |
592 |
|
|
593 |
|
/** |
594 |
< |
* Returns a popped task, or null if empty. Ensures active status |
595 |
< |
* if non-null. Called only by current thread. |
594 |
> |
* Returns a popped task, or null if empty. Assumes active status. |
595 |
> |
* Called only by current thread. |
596 |
|
*/ |
597 |
< |
final ForkJoinTask<?> popTask() { |
598 |
< |
int s = sp; |
599 |
< |
while (s != base) { |
600 |
< |
if (tryActivate()) { |
601 |
< |
ForkJoinTask<?>[] q = queue; |
602 |
< |
int mask = q.length - 1; |
603 |
< |
int i = (s - 1) & mask; |
597 |
> |
private ForkJoinTask<?> popTask() { |
598 |
> |
ForkJoinTask<?>[] q = queue; |
599 |
> |
if (q != null) { |
600 |
> |
int s; |
601 |
> |
while ((s = sp) != base) { |
602 |
> |
int i = (q.length - 1) & --s; |
603 |
> |
long u = (i << qShift) + qBase; // raw offset |
604 |
|
ForkJoinTask<?> t = q[i]; |
605 |
< |
if (t == null || !casSlotNull(q, i, t)) |
605 |
> |
if (t == null) // lost to stealer |
606 |
|
break; |
607 |
< |
storeSp(s - 1); |
608 |
< |
return t; |
607 |
> |
if (UNSAFE.compareAndSwapObject(q, u, t, null)) { |
608 |
> |
sp = s; // putOrderedInt may encourage more timely write |
609 |
> |
// UNSAFE.putOrderedInt(this, spOffset, s); |
610 |
> |
return t; |
611 |
> |
} |
612 |
|
} |
613 |
|
} |
614 |
|
return null; |
615 |
|
} |
616 |
|
|
617 |
|
/** |
618 |
< |
* Specialized version of popTask to pop only if |
619 |
< |
* topmost element is the given task. Called only |
620 |
< |
* by current thread while active. |
618 |
> |
* Specialized version of popTask to pop only if topmost element |
619 |
> |
* is the given task. Called only by current thread while |
620 |
> |
* active. |
621 |
|
* |
622 |
|
* @param t the task. Caller must ensure non-null. |
623 |
|
*/ |
624 |
|
final boolean unpushTask(ForkJoinTask<?> t) { |
625 |
+ |
int s; |
626 |
|
ForkJoinTask<?>[] q = queue; |
627 |
< |
int mask = q.length - 1; |
628 |
< |
int s = sp - 1; |
629 |
< |
if (casSlotNull(q, s & mask, t)) { |
630 |
< |
storeSp(s); |
627 |
> |
if ((s = sp) != base && q != null && |
628 |
> |
UNSAFE.compareAndSwapObject |
629 |
> |
(q, (((q.length - 1) & --s) << qShift) + qBase, t, null)) { |
630 |
> |
sp = s; |
631 |
> |
// UNSAFE.putOrderedInt(this, spOffset, s); |
632 |
|
return true; |
633 |
|
} |
634 |
|
return false; |
668 |
|
ForkJoinTask<?> t = oldQ[oldIndex]; |
669 |
|
if (t != null && !casSlotNull(oldQ, oldIndex, t)) |
670 |
|
t = null; |
671 |
< |
setSlot(newQ, b & newMask, t); |
671 |
> |
writeSlot(newQ, b & newMask, t); |
672 |
|
} while (++b != bf); |
673 |
|
pool.signalWork(); |
674 |
|
} |
675 |
|
|
676 |
|
/** |
677 |
+ |
* Computes next value for random victim probe in scan(). Scans |
678 |
+ |
* don't require a very high quality generator, but also not a |
679 |
+ |
* crummy one. Marsaglia xor-shift is cheap and works well enough. |
680 |
+ |
* Note: This is manually inlined in scan() |
681 |
+ |
*/ |
682 |
+ |
private static final int xorShift(int r) { |
683 |
+ |
r ^= r << 13; |
684 |
+ |
r ^= r >>> 17; |
685 |
+ |
return r ^ (r << 5); |
686 |
+ |
} |
687 |
+ |
|
688 |
+ |
/** |
689 |
|
* Tries to steal a task from another worker. Starts at a random |
690 |
|
* index of workers array, and probes workers until finding one |
691 |
|
* with non-empty queue or finding that all are empty. It |
692 |
|
* randomly selects the first n probes. If these are empty, it |
693 |
< |
* resorts to a full circular traversal, which is necessary to |
694 |
< |
* accurately set active status by caller. Also restarts if pool |
695 |
< |
* events occurred since last scan, which forces refresh of |
696 |
< |
* workers array, in case barrier was associated with resize. |
693 |
> |
* resorts to a circular sweep, which is necessary to accurately |
694 |
> |
* set active status. (The circular sweep uses steps of |
695 |
> |
* approximately half the array size plus 1, to avoid bias |
696 |
> |
* stemming from leftmost packing of the array in ForkJoinPool.) |
697 |
|
* |
698 |
|
* This method must be both fast and quiet -- usually avoiding |
699 |
|
* memory accesses that could disrupt cache sharing etc other than |
700 |
< |
* those needed to check for and take tasks. This accounts for, |
701 |
< |
* among other things, updating random seed in place without |
702 |
< |
* storing it until exit. |
700 |
> |
* those needed to check for and take tasks (or to activate if not |
701 |
> |
* already active). This accounts for, among other things, |
702 |
> |
* updating random seed in place without storing it until exit. |
703 |
|
* |
704 |
|
* @return a task, or null if none found |
705 |
|
*/ |
706 |
|
private ForkJoinTask<?> scan() { |
707 |
< |
ForkJoinTask<?> t = null; |
708 |
< |
int r = seed; // extract once to keep scan quiet |
709 |
< |
ForkJoinWorkerThread[] ws; // refreshed on outer loop |
710 |
< |
int mask; // must be power 2 minus 1 and > 0 |
711 |
< |
outer:do { |
712 |
< |
if ((ws = pool.workers) != null && (mask = ws.length - 1) > 0) { |
713 |
< |
int idx = r; |
714 |
< |
int probes = ~mask; // use random index while negative |
715 |
< |
for (;;) { |
716 |
< |
r = xorShift(r); // update random seed |
717 |
< |
ForkJoinWorkerThread v = ws[mask & idx]; |
718 |
< |
if (v == null || v.sp == v.base) { |
719 |
< |
if (probes <= mask) |
720 |
< |
idx = (probes++ < 0) ? r : (idx + 1); |
721 |
< |
else |
722 |
< |
break; |
707 |
> |
ForkJoinPool p = pool; |
708 |
> |
ForkJoinWorkerThread[] ws; // worker array |
709 |
> |
int n; // upper bound of #workers |
710 |
> |
if ((ws = p.workers) != null && (n = ws.length) > 1) { |
711 |
> |
boolean canSteal = active; // shadow active status |
712 |
> |
int r = seed; // extract seed once |
713 |
> |
int mask = n - 1; |
714 |
> |
int j = -n; // loop counter |
715 |
> |
int k = r; // worker index, random if j < 0 |
716 |
> |
for (;;) { |
717 |
> |
ForkJoinWorkerThread v = ws[k & mask]; |
718 |
> |
r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // inline xorshift |
719 |
> |
if (v != null && v.base != v.sp) { |
720 |
> |
ForkJoinTask<?>[] q; int b, a; |
721 |
> |
if ((canSteal || // Ugly/hacky: inline |
722 |
> |
(canSteal = active = // p.tryIncrementActiveCount |
723 |
> |
UNSAFE.compareAndSwapInt(p, poolRunStateOffset, |
724 |
> |
a = p.runState, a + 1))) && |
725 |
> |
(q = v.queue) != null && (b = v.base) != v.sp) { |
726 |
> |
int i = (q.length - 1) & b; |
727 |
> |
long u = (i << qShift) + qBase; // raw offset |
728 |
> |
ForkJoinTask<?> t = q[i]; |
729 |
> |
if (v.base == b && t != null && |
730 |
> |
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
731 |
> |
int pid = poolIndex; |
732 |
> |
currentSteal = t; |
733 |
> |
v.stealHint = pid; |
734 |
> |
v.base = b + 1; |
735 |
> |
seed = r; |
736 |
> |
++stealCount; |
737 |
> |
return t; |
738 |
> |
} |
739 |
|
} |
740 |
< |
else if (!tryActivate() || (t = v.deqTask()) == null) |
741 |
< |
continue outer; // restart on contention |
616 |
< |
else |
617 |
< |
break outer; |
740 |
> |
j = -n; |
741 |
> |
k = r; // restart on contention |
742 |
|
} |
743 |
+ |
else if (++j <= 0) |
744 |
+ |
k = r; |
745 |
+ |
else if (j <= n) |
746 |
+ |
k += (n >>> 1) | 1; |
747 |
+ |
else |
748 |
+ |
break; |
749 |
|
} |
750 |
< |
} while (pool.hasNewSyncEvent(this)); // retry on pool events |
751 |
< |
seed = r; |
622 |
< |
return t; |
750 |
> |
} |
751 |
> |
return null; |
752 |
|
} |
753 |
|
|
754 |
+ |
// Run State management |
755 |
+ |
|
756 |
+ |
// status check methods used mainly by ForkJoinPool |
757 |
+ |
final boolean isRunning() { return runState == 0; } |
758 |
+ |
final boolean isTerminating() { return (runState & TERMINATING) != 0; } |
759 |
+ |
final boolean isTerminated() { return (runState & TERMINATED) != 0; } |
760 |
+ |
final boolean isSuspended() { return (runState & SUSPENDED) != 0; } |
761 |
+ |
final boolean isTrimmed() { return (runState & TRIMMED) != 0; } |
762 |
+ |
|
763 |
|
/** |
764 |
< |
* Gets and removes a local or stolen task. |
765 |
< |
* |
628 |
< |
* @return a task, if available |
764 |
> |
* Sets state to TERMINATING. Does NOT unpark or interrupt |
765 |
> |
* to wake up if currently blocked. |
766 |
|
*/ |
767 |
< |
final ForkJoinTask<?> pollTask() { |
768 |
< |
ForkJoinTask<?> t = locallyFifo ? locallyDeqTask() : popTask(); |
769 |
< |
if (t == null && (t = scan()) != null) |
770 |
< |
++stealCount; |
771 |
< |
return t; |
767 |
> |
final void shutdown() { |
768 |
> |
for (;;) { |
769 |
> |
int s = runState; |
770 |
> |
if ((s & (TERMINATING|TERMINATED)) != 0) |
771 |
> |
break; |
772 |
> |
if ((s & SUSPENDED) != 0) { // kill and wakeup if suspended |
773 |
> |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
774 |
> |
(s & ~SUSPENDED) | |
775 |
> |
(TRIMMED|TERMINATING))) |
776 |
> |
break; |
777 |
> |
} |
778 |
> |
else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
779 |
> |
s | TERMINATING)) |
780 |
> |
break; |
781 |
> |
} |
782 |
|
} |
783 |
|
|
784 |
|
/** |
785 |
< |
* Gets a local task. |
639 |
< |
* |
640 |
< |
* @return a task, if available |
785 |
> |
* Sets state to TERMINATED. Called only by onTermination() |
786 |
|
*/ |
787 |
< |
final ForkJoinTask<?> pollLocalTask() { |
788 |
< |
return locallyFifo ? locallyDeqTask() : popTask(); |
787 |
> |
private void setTerminated() { |
788 |
> |
int s; |
789 |
> |
do {} while (!UNSAFE.compareAndSwapInt(this, runStateOffset, |
790 |
> |
s = runState, |
791 |
> |
s | (TERMINATING|TERMINATED))); |
792 |
|
} |
793 |
|
|
794 |
|
/** |
795 |
< |
* Returns a pool submission, if one exists, activating first. |
795 |
> |
* If suspended, tries to set status to unsuspended. |
796 |
|
* |
797 |
< |
* @return a submission, if available |
797 |
> |
* @return true if successful |
798 |
> |
*/ |
799 |
> |
final boolean tryUnsuspend() { |
800 |
> |
int s; |
801 |
> |
while (((s = runState) & SUSPENDED) != 0) { |
802 |
> |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
803 |
> |
s & ~SUSPENDED)) |
804 |
> |
return true; |
805 |
> |
} |
806 |
> |
return false; |
807 |
> |
} |
808 |
> |
|
809 |
> |
/** |
810 |
> |
* Sets suspended status and blocks as spare until resumed |
811 |
> |
* or shutdown. |
812 |
|
*/ |
813 |
< |
private ForkJoinTask<?> pollSubmission() { |
813 |
> |
final void suspendAsSpare() { |
814 |
> |
for (;;) { // set suspended unless terminating |
815 |
> |
int s = runState; |
816 |
> |
if ((s & TERMINATING) != 0) { // must kill |
817 |
> |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
818 |
> |
s | (TRIMMED | TERMINATING))) |
819 |
> |
return; |
820 |
> |
} |
821 |
> |
else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
822 |
> |
s | SUSPENDED)) |
823 |
> |
break; |
824 |
> |
} |
825 |
|
ForkJoinPool p = pool; |
826 |
< |
while (p.hasQueuedSubmissions()) { |
827 |
< |
ForkJoinTask<?> t; |
828 |
< |
if (tryActivate() && (t = p.pollSubmission()) != null) |
829 |
< |
return t; |
826 |
> |
p.pushSpare(this); |
827 |
> |
lastEventCount = 0; // reset upon resume |
828 |
> |
while ((runState & SUSPENDED) != 0) { |
829 |
> |
if (p.tryAccumulateStealCount(this)) { |
830 |
> |
boolean untimed = nextSpare != 0; |
831 |
> |
long startTime = untimed? 0 : System.nanoTime(); |
832 |
> |
interrupted(); // clear/ignore interrupts |
833 |
> |
if ((runState & SUSPENDED) == 0) |
834 |
> |
break; |
835 |
> |
if (untimed) // untimed |
836 |
> |
LockSupport.park(this); |
837 |
> |
else { |
838 |
> |
LockSupport.parkNanos(this, TRIM_RATE_NANOS); |
839 |
> |
if ((runState & SUSPENDED) == 0) |
840 |
> |
break; |
841 |
> |
if (System.nanoTime() - startTime >= TRIM_RATE_NANOS) |
842 |
> |
p.tryShutdownSpare(); |
843 |
> |
} |
844 |
> |
} |
845 |
|
} |
658 |
– |
return null; |
846 |
|
} |
847 |
|
|
848 |
< |
// Methods accessed only by Pool |
848 |
> |
// Misc support methods for ForkJoinPool |
849 |
> |
|
850 |
> |
/** |
851 |
> |
* Returns an estimate of the number of tasks in the queue. Also |
852 |
> |
* used by ForkJoinTask. |
853 |
> |
*/ |
854 |
> |
final int getQueueSize() { |
855 |
> |
int n; // external calls must read base first |
856 |
> |
return (n = -base + sp) <= 0 ? 0 : n; |
857 |
> |
} |
858 |
|
|
859 |
|
/** |
860 |
|
* Removes and cancels all tasks in queue. Can be called from any |
861 |
|
* thread. |
862 |
|
*/ |
863 |
|
final void cancelTasks() { |
864 |
< |
ForkJoinTask<?> t; |
865 |
< |
while (base != sp && (t = deqTask()) != null) |
866 |
< |
t.cancelIgnoringExceptions(); |
864 |
> |
ForkJoinTask<?> cj = currentJoin; // try to cancel ongoing tasks |
865 |
> |
if (cj != null) { |
866 |
> |
currentJoin = null; |
867 |
> |
cj.cancelIgnoringExceptions(); |
868 |
> |
try { |
869 |
> |
this.interrupt(); // awaken wait |
870 |
> |
} catch (SecurityException ignore) { |
871 |
> |
} |
872 |
> |
} |
873 |
> |
ForkJoinTask<?> cs = currentSteal; |
874 |
> |
if (cs != null) { |
875 |
> |
currentSteal = null; |
876 |
> |
cs.cancelIgnoringExceptions(); |
877 |
> |
} |
878 |
> |
while (base != sp) { |
879 |
> |
ForkJoinTask<?> t = deqTask(); |
880 |
> |
if (t != null) |
881 |
> |
t.cancelIgnoringExceptions(); |
882 |
> |
} |
883 |
|
} |
884 |
|
|
885 |
|
/** |
889 |
|
*/ |
890 |
|
final int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
891 |
|
int n = 0; |
892 |
< |
ForkJoinTask<?> t; |
893 |
< |
while (base != sp && (t = deqTask()) != null) { |
894 |
< |
c.add(t); |
895 |
< |
++n; |
892 |
> |
while (base != sp) { |
893 |
> |
ForkJoinTask<?> t = deqTask(); |
894 |
> |
if (t != null) { |
895 |
> |
c.add(t); |
896 |
> |
++n; |
897 |
> |
} |
898 |
|
} |
899 |
|
return n; |
900 |
|
} |
901 |
|
|
902 |
+ |
// Support methods for ForkJoinTask |
903 |
+ |
|
904 |
|
/** |
905 |
< |
* Gets and clears steal count for accumulation by pool. Called |
906 |
< |
* only when known to be idle (in pool.sync and termination). |
905 |
> |
* Gets and removes a local task. |
906 |
> |
* |
907 |
> |
* @return a task, if available |
908 |
|
*/ |
909 |
< |
final int getAndClearStealCount() { |
910 |
< |
int sc = stealCount; |
911 |
< |
stealCount = 0; |
912 |
< |
return sc; |
909 |
> |
final ForkJoinTask<?> pollLocalTask() { |
910 |
> |
ForkJoinPool p = pool; |
911 |
> |
while (sp != base) { |
912 |
> |
int a; // inline p.tryIncrementActiveCount |
913 |
> |
if (active || |
914 |
> |
(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset, |
915 |
> |
a = p.runState, a + 1))) |
916 |
> |
return locallyFifo? locallyDeqTask() : popTask(); |
917 |
> |
} |
918 |
> |
return null; |
919 |
|
} |
920 |
|
|
921 |
|
/** |
922 |
< |
* Returns {@code true} if at least one worker in the given array |
700 |
< |
* appears to have at least one queued task. |
922 |
> |
* Gets and removes a local or stolen task. |
923 |
|
* |
924 |
< |
* @param ws array of workers |
924 |
> |
* @return a task, if available |
925 |
|
*/ |
926 |
< |
static boolean hasQueuedTasks(ForkJoinWorkerThread[] ws) { |
927 |
< |
if (ws != null) { |
928 |
< |
int len = ws.length; |
929 |
< |
for (int j = 0; j < 2; ++j) { // need two passes for clean sweep |
930 |
< |
for (int i = 0; i < len; ++i) { |
709 |
< |
ForkJoinWorkerThread w = ws[i]; |
710 |
< |
if (w != null && w.sp != w.base) |
711 |
< |
return true; |
712 |
< |
} |
713 |
< |
} |
926 |
> |
final ForkJoinTask<?> pollTask() { |
927 |
> |
ForkJoinTask<?> t = pollLocalTask(); |
928 |
> |
if (t == null) { |
929 |
> |
t = scan(); |
930 |
> |
currentSteal = null; // cannot retain/track/help |
931 |
|
} |
932 |
< |
return false; |
932 |
> |
return t; |
933 |
|
} |
934 |
|
|
718 |
– |
// Support methods for ForkJoinTask |
719 |
– |
|
935 |
|
/** |
936 |
< |
* Returns an estimate of the number of tasks in the queue. |
936 |
> |
* Possibly runs some tasks and/or blocks, until task is done. |
937 |
> |
* |
938 |
> |
* @param joinMe the task to join |
939 |
|
*/ |
940 |
< |
final int getQueueSize() { |
941 |
< |
// suppress momentarily negative values |
942 |
< |
return Math.max(0, sp - base); |
940 |
> |
final void joinTask(ForkJoinTask<?> joinMe) { |
941 |
> |
// currentJoin only written by this thread; only need ordered store |
942 |
> |
ForkJoinTask<?> prevJoin = currentJoin; |
943 |
> |
UNSAFE.putOrderedObject(this, currentJoinOffset, joinMe); |
944 |
> |
if (sp != base) |
945 |
> |
localHelpJoinTask(joinMe); |
946 |
> |
if (joinMe.status >= 0) |
947 |
> |
pool.awaitJoin(joinMe, this); |
948 |
> |
UNSAFE.putOrderedObject(this, currentJoinOffset, prevJoin); |
949 |
|
} |
950 |
|
|
951 |
|
/** |
952 |
< |
* Returns an estimate of the number of tasks, offset by a |
953 |
< |
* function of number of idle workers. |
952 |
> |
* Run tasks in local queue until given task is done. |
953 |
> |
* |
954 |
> |
* @param joinMe the task to join |
955 |
|
*/ |
956 |
< |
final int getEstimatedSurplusTaskCount() { |
957 |
< |
// The halving approximates weighting idle vs non-idle workers |
958 |
< |
return (sp - base) - (pool.getIdleThreadCount() >>> 1); |
956 |
> |
private void localHelpJoinTask(ForkJoinTask<?> joinMe) { |
957 |
> |
int s; |
958 |
> |
ForkJoinTask<?>[] q; |
959 |
> |
while (joinMe.status >= 0 && (s = sp) != base && (q = queue) != null) { |
960 |
> |
int i = (q.length - 1) & --s; |
961 |
> |
long u = (i << qShift) + qBase; // raw offset |
962 |
> |
ForkJoinTask<?> t = q[i]; |
963 |
> |
if (t == null) // lost to a stealer |
964 |
> |
break; |
965 |
> |
if (UNSAFE.compareAndSwapObject(q, u, t, null)) { |
966 |
> |
/* |
967 |
> |
* This recheck (and similarly in helpJoinTask) |
968 |
> |
* handles cases where joinMe is independently |
969 |
> |
* cancelled or forced even though there is other work |
970 |
> |
* available. Back out of the pop by putting t back |
971 |
> |
* into slot before we commit by writing sp. |
972 |
> |
*/ |
973 |
> |
if (joinMe.status < 0) { |
974 |
> |
UNSAFE.putObjectVolatile(q, u, t); |
975 |
> |
break; |
976 |
> |
} |
977 |
> |
sp = s; |
978 |
> |
// UNSAFE.putOrderedInt(this, spOffset, s); |
979 |
> |
t.quietlyExec(); |
980 |
> |
} |
981 |
> |
} |
982 |
|
} |
983 |
|
|
984 |
|
/** |
985 |
< |
* Scans, returning early if joinMe done. |
986 |
< |
*/ |
987 |
< |
final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) { |
988 |
< |
ForkJoinTask<?> t = pollTask(); |
989 |
< |
if (t != null && joinMe.status < 0 && sp == base) { |
990 |
< |
pushTask(t); // unsteal if done and this task would be stealable |
991 |
< |
t = null; |
985 |
> |
* Tries to locate and help perform tasks for a stealer of the |
986 |
> |
* given task, or in turn one of its stealers. Traces |
987 |
> |
* currentSteal->currentJoin links looking for a thread working on |
988 |
> |
* a descendant of the given task and with a non-empty queue to |
989 |
> |
* steal back and execute tasks from. |
990 |
> |
* |
991 |
> |
* The implementation is very branchy to cope with the potential |
992 |
> |
* inconsistencies or loops encountering chains that are stale, |
993 |
> |
* unknown, or of length greater than MAX_HELP_DEPTH links. All |
994 |
> |
* of these cases are dealt with by just returning back to the |
995 |
> |
* caller, who is expected to retry if other join mechanisms also |
996 |
> |
* don't work out. |
997 |
> |
* |
998 |
> |
* @param joinMe the task to join |
999 |
> |
*/ |
1000 |
> |
final void helpJoinTask(ForkJoinTask<?> joinMe) { |
1001 |
> |
ForkJoinWorkerThread[] ws = pool.workers; |
1002 |
> |
int n; // need at least 2 workers |
1003 |
> |
if (ws != null && (n = ws.length) > 1 && joinMe.status >= 0) { |
1004 |
> |
ForkJoinTask<?> task = joinMe; // base of chain |
1005 |
> |
ForkJoinWorkerThread thread = this; // thread with stolen task |
1006 |
> |
for (int d = 0; d < MAX_HELP_DEPTH; ++d) { // chain length |
1007 |
> |
// Try to find v, the stealer of task, by first using hint |
1008 |
> |
ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)]; |
1009 |
> |
if (v == null || v.currentSteal != task) { |
1010 |
> |
for (int j = 0; ; ++j) { // search array |
1011 |
> |
if (j < n) { |
1012 |
> |
if ((v = ws[j]) != null) { |
1013 |
> |
if (task.status < 0) |
1014 |
> |
return; // stale or done |
1015 |
> |
if (v.currentSteal == task) { |
1016 |
> |
thread.stealHint = j; |
1017 |
> |
break; // save hint for next time |
1018 |
> |
} |
1019 |
> |
} |
1020 |
> |
} |
1021 |
> |
else |
1022 |
> |
return; // no stealer |
1023 |
> |
} |
1024 |
> |
} |
1025 |
> |
// Try to help v, using specialized form of deqTask |
1026 |
> |
int b; |
1027 |
> |
ForkJoinTask<?>[] q; |
1028 |
> |
while ((b = v.base) != v.sp && (q = v.queue) != null) { |
1029 |
> |
int i = (q.length - 1) & b; |
1030 |
> |
long u = (i << qShift) + qBase; |
1031 |
> |
ForkJoinTask<?> t = q[i]; |
1032 |
> |
if (task.status < 0) |
1033 |
> |
return; // stale or done |
1034 |
> |
if (v.base == b) { |
1035 |
> |
if (t == null) |
1036 |
> |
return; // producer stalled |
1037 |
> |
if (UNSAFE.compareAndSwapObject(q, u, t, null)) { |
1038 |
> |
if (joinMe.status < 0) { |
1039 |
> |
UNSAFE.putObjectVolatile(q, u, t); |
1040 |
> |
return; // back out on cancel |
1041 |
> |
} |
1042 |
> |
int pid = poolIndex; |
1043 |
> |
ForkJoinTask<?> prevSteal = currentSteal; |
1044 |
> |
currentSteal = t; |
1045 |
> |
v.stealHint = pid; |
1046 |
> |
v.base = b + 1; |
1047 |
> |
t.quietlyExec(); |
1048 |
> |
currentSteal = prevSteal; |
1049 |
> |
} |
1050 |
> |
} |
1051 |
> |
if (joinMe.status < 0) |
1052 |
> |
return; |
1053 |
> |
} |
1054 |
> |
// Try to descend to find v's stealer |
1055 |
> |
ForkJoinTask<?> next = v.currentJoin; |
1056 |
> |
if (task.status < 0 || next == null || next == task || |
1057 |
> |
joinMe.status < 0) |
1058 |
> |
return; |
1059 |
> |
task = next; |
1060 |
> |
thread = v; |
1061 |
> |
} |
1062 |
|
} |
1063 |
< |
return t; |
1063 |
> |
} |
1064 |
> |
|
1065 |
> |
/** |
1066 |
> |
* Returns an estimate of the number of tasks, offset by a |
1067 |
> |
* function of number of idle workers. |
1068 |
> |
* |
1069 |
> |
* This method provides a cheap heuristic guide for task |
1070 |
> |
* partitioning when programmers, frameworks, tools, or languages |
1071 |
> |
* have little or no idea about task granularity. In essence by |
1072 |
> |
* offering this method, we ask users only about tradeoffs in |
1073 |
> |
* overhead vs expected throughput and its variance, rather than |
1074 |
> |
* how finely to partition tasks. |
1075 |
> |
* |
1076 |
> |
* In a steady state strict (tree-structured) computation, each |
1077 |
> |
* thread makes available for stealing enough tasks for other |
1078 |
> |
* threads to remain active. Inductively, if all threads play by |
1079 |
> |
* the same rules, each thread should make available only a |
1080 |
> |
* constant number of tasks. |
1081 |
> |
* |
1082 |
> |
* The minimum useful constant is just 1. But using a value of 1 |
1083 |
> |
* would require immediate replenishment upon each steal to |
1084 |
> |
* maintain enough tasks, which is infeasible. Further, |
1085 |
> |
* partitionings/granularities of offered tasks should minimize |
1086 |
> |
* steal rates, which in general means that threads nearer the top |
1087 |
> |
* of computation tree should generate more than those nearer the |
1088 |
> |
* bottom. In perfect steady state, each thread is at |
1089 |
> |
* approximately the same level of computation tree. However, |
1090 |
> |
* producing extra tasks amortizes the uncertainty of progress and |
1091 |
> |
* diffusion assumptions. |
1092 |
> |
* |
1093 |
> |
* So, users will want to use values larger, but not much larger |
1094 |
> |
* than 1 to both smooth over transient shortages and hedge |
1095 |
> |
* against uneven progress; as traded off against the cost of |
1096 |
> |
* extra task overhead. We leave the user to pick a threshold |
1097 |
> |
* value to compare with the results of this call to guide |
1098 |
> |
* decisions, but recommend values such as 3. |
1099 |
> |
* |
1100 |
> |
* When all threads are active, it is on average OK to estimate |
1101 |
> |
* surplus strictly locally. In steady-state, if one thread is |
1102 |
> |
* maintaining say 2 surplus tasks, then so are others. So we can |
1103 |
> |
* just use estimated queue length (although note that (sp - base) |
1104 |
> |
* can be an overestimate because of stealers lagging increments |
1105 |
> |
* of base). However, this strategy alone leads to serious |
1106 |
> |
* mis-estimates in some non-steady-state conditions (ramp-up, |
1107 |
> |
* ramp-down, other stalls). We can detect many of these by |
1108 |
> |
* further considering the number of "idle" threads, that are |
1109 |
> |
* known to have zero queued tasks, so compensate by a factor of |
1110 |
> |
* (#idle/#active) threads. |
1111 |
> |
*/ |
1112 |
> |
final int getEstimatedSurplusTaskCount() { |
1113 |
> |
return sp - base - pool.idlePerActive(); |
1114 |
|
} |
1115 |
|
|
1116 |
|
/** |
1118 |
|
*/ |
1119 |
|
final void helpQuiescePool() { |
1120 |
|
for (;;) { |
1121 |
< |
ForkJoinTask<?> t = pollTask(); |
1122 |
< |
if (t != null) |
1121 |
> |
ForkJoinTask<?> t = pollLocalTask(); |
1122 |
> |
if (t != null || (t = scan()) != null) { |
1123 |
|
t.quietlyExec(); |
1124 |
< |
else if (tryInactivate() && pool.isQuiescent()) |
1125 |
< |
break; |
1124 |
> |
currentSteal = null; |
1125 |
> |
} |
1126 |
> |
else { |
1127 |
> |
ForkJoinPool p = pool; |
1128 |
> |
int a; // to inline CASes |
1129 |
> |
if (active) { |
1130 |
> |
if (!UNSAFE.compareAndSwapInt |
1131 |
> |
(p, poolRunStateOffset, a = p.runState, a - 1)) |
1132 |
> |
continue; // retry later |
1133 |
> |
active = false; // inactivate |
1134 |
> |
} |
1135 |
> |
if (p.isQuiescent()) { |
1136 |
> |
active = true; // re-activate |
1137 |
> |
do {} while(!UNSAFE.compareAndSwapInt |
1138 |
> |
(p, poolRunStateOffset, a = p.runState, a+1)); |
1139 |
> |
return; |
1140 |
> |
} |
1141 |
> |
} |
1142 |
|
} |
760 |
– |
do {} while (!tryActivate()); // re-activate on exit |
1143 |
|
} |
1144 |
|
|
1145 |
|
// Unsafe mechanics |
1149 |
|
objectFieldOffset("sp", ForkJoinWorkerThread.class); |
1150 |
|
private static final long runStateOffset = |
1151 |
|
objectFieldOffset("runState", ForkJoinWorkerThread.class); |
1152 |
< |
private static final long qBase; |
1152 |
> |
private static final long currentJoinOffset = |
1153 |
> |
objectFieldOffset("currentJoin", ForkJoinWorkerThread.class); |
1154 |
> |
private static final long currentStealOffset = |
1155 |
> |
objectFieldOffset("currentSteal", ForkJoinWorkerThread.class); |
1156 |
> |
private static final long qBase = |
1157 |
> |
UNSAFE.arrayBaseOffset(ForkJoinTask[].class); |
1158 |
> |
private static final long poolRunStateOffset = // to inline CAS |
1159 |
> |
objectFieldOffset("runState", ForkJoinPool.class); |
1160 |
> |
|
1161 |
|
private static final int qShift; |
1162 |
|
|
1163 |
|
static { |
774 |
– |
qBase = UNSAFE.arrayBaseOffset(ForkJoinTask[].class); |
1164 |
|
int s = UNSAFE.arrayIndexScale(ForkJoinTask[].class); |
1165 |
|
if ((s & (s-1)) != 0) |
1166 |
|
throw new Error("data type scale not a power of two"); |