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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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package jsr166y; |
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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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import java.util.concurrent.RejectedExecutionException; |
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/** |
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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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* ("queueBase" and "queueTop") to the slots themselves (mainly |
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* via method "casSlotNull()"). So, both a successful pop and deq |
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* mainly entail a CAS of a slot from non-null to null. Because |
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* we rely on CASes of references, we do not need tag bits on |
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* queueBase or queueTop. They are simple ints as used in any |
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* 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 queueTop == queueBase means the queue is empty, |
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* but 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. |
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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 set activation status if |
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* necessary before stealing. |
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* any empty queue to complete. |
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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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* version of deq rather than pop when locallyFifo is true (as set |
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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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* frameworks in which tasks are never joined. However neither |
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* mode considers affinities, loads, cache localities, etc, so |
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* rarely provide the best possible performance on a given |
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* machine, but portably provide good throughput by averaging over |
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* these factors. (Further, even if we did try to use such |
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* information, we do not usually have a basis for exploiting |
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* it. For example, some sets of tasks profit from cache |
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* affinities, but others are harmed by cache pollution effects.) |
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* |
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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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* 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.awaitJoin). |
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* MAX_HELP) and fall back to suspending the worker and if |
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* necessary replacing it with another. |
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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 |
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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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* correct orderings, reads and writes of variable queueBase |
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* require volatile ordering. Variable queueTop need not be |
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* volatile because non-local reads always follow those of |
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* queueBase. Similarly, because they are protected by volatile |
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* queueBase reads, reads of the queue array and its slots by |
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* other threads do not need volatile load semantics, but writes |
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* (in push) require store order and CASes (in pop and deq) |
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* require (volatile) CAS semantics. (Michael, Saraswat, and |
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* Vechev's algorithm has similar properties, but without support |
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* for nulling slots.) Since these combinations aren't supported |
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* using ordinary volatiles, the only way to accomplish these |
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* 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.) |
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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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* 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 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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* queues are initialized after starting. |
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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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* Mask for pool indices encoded as shorts |
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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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private static final int SMASK = 0xffff; |
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/** |
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* Capacity of work-stealing queue array upon initialization. |
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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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* Maximum work-stealing queue array size. Must be less than or |
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* equal to 1 << (31 - width of array entry) to ensure lack of |
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* index wraparound. The value is set in the static block |
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* at the end of this file after obtaining width. |
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* Maximum size for queue array. Must be a power of two |
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* less than or equal to 1 << (31 - width of array entry) to |
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* ensure lack of index wraparound, but is capped at a lower |
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* value to help users trap runaway computations. |
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*/ |
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private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M |
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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 started (as opposed to when constructed), to |
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* improve memory locality. |
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*/ |
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private static final int MAXIMUM_QUEUE_CAPACITY; |
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ForkJoinTask<?>[] queue; |
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/** |
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* The pool this thread works in. Accessed directly by ForkJoinTask. |
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final ForkJoinPool pool; |
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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 in onStart, to improve memory locality. |
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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) queueBase. Both queueTop |
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* and queueBase are allowed to wrap around on overflow, but |
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* (queueTop - queueBase) still estimates size. |
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*/ |
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private ForkJoinTask<?>[] queue; |
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int queueTop; |
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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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* 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 int sp; |
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volatile int queueBase; |
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|
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/** |
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* The index of most recent stealer, used as a hint to avoid |
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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 |
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* manually inlined for performance.) Accessed directly by pool |
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* to simplify checks for normal (zero) status. |
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*/ |
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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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int stealHint; |
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/** |
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* Number of steals. Directly accessed (and reset) by |
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* pool.tryAccumulateStealCount when idle. |
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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 to locate this worker in |
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* its workers array. |
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*/ |
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int stealCount; |
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final int poolIndex; |
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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 initialized as nonzero. |
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* Encoded record for pool task waits. Usages are always |
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* surrounded by volatile reads/writes |
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*/ |
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private int seed; |
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int nextWait; |
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/** |
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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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* Complement of poolIndex, offset by count of entries of task |
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* waits. Accessed by ForkJoinPool to manage event waiters. |
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*/ |
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boolean active; |
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volatile int eventCount; |
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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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* Seed for random number generator for choosing steal victims. |
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* Uses Marsaglia xorshift. Must be initialized as nonzero. |
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*/ |
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private final boolean locallyFifo; |
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int seed; |
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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 to locate this worker in |
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* its workers array. |
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* Number of steals. Directly accessed (and reset) by pool when |
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* idle. |
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*/ |
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int poolIndex; |
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int stealCount; |
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/** |
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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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* True if this worker should or did terminate |
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*/ |
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int lastEventCount; |
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volatile boolean terminate; |
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|
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/** |
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* Encoded index and event count of next event waiter. Accessed |
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* only by ForkJoinPool for managing event waiters. |
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* Set to true before LockSupport.park; false on return |
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*/ |
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volatile long nextWaiter; |
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volatile boolean parked; |
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|
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/** |
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* Number of times this thread suspended as spare. Accessed only |
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* by pool. |
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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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int spareCount; |
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final boolean locallyFifo; |
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|
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/** |
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* Encoded index and count of next spare waiter. Accessed only |
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* by ForkJoinPool for managing spares. |
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> |
* The task most recently stolen from another worker (or |
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> |
* submission queue). All uses are surrounded by enough volatile |
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> |
* reads/writes to maintain as non-volatile. |
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*/ |
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volatile int nextSpare; |
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> |
ForkJoinTask<?> currentSteal; |
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|
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/** |
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* The task currently being joined, set only when actively trying |
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< |
* to help other stealers in helpJoinTask. Written only by this |
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* thread, but read by others. |
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< |
*/ |
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private volatile ForkJoinTask<?> currentJoin; |
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|
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/** |
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* The task most recently stolen from another worker (or |
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< |
* submission queue). Written only by this thread, but read by |
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* others. |
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> |
* to help other stealers in helpJoinTask. All uses are surrounded |
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* by enough volatile reads/writes to maintain as non-volatile. |
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*/ |
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private volatile ForkJoinTask<?> currentSteal; |
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> |
ForkJoinTask<?> currentJoin; |
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|
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/** |
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* Creates a ForkJoinWorkerThread operating in the given pool. |
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* @throws NullPointerException if pool is null |
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*/ |
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protected ForkJoinWorkerThread(ForkJoinPool pool) { |
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+ |
super(pool.nextWorkerName()); |
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this.pool = pool; |
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< |
this.locallyFifo = pool.locallyFifo; |
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setDaemon(true); |
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// To avoid exposing construction details to subclasses, |
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// remaining initialization is in start() and onStart() |
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} |
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|
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/** |
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* Performs additional initialization and starts this thread. |
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*/ |
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final void start(int poolIndex, UncaughtExceptionHandler ueh) { |
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< |
this.poolIndex = poolIndex; |
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> |
int k = pool.registerWorker(this); |
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> |
poolIndex = k; |
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> |
eventCount = ~k & SMASK; // clear wait count |
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> |
locallyFifo = pool.locallyFifo; |
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> |
Thread.UncaughtExceptionHandler ueh = pool.ueh; |
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if (ueh != null) |
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setUncaughtExceptionHandler(ueh); |
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< |
start(); |
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> |
setDaemon(true); |
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} |
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|
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< |
// Public/protected methods |
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> |
// Public methods |
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|
282 |
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/** |
283 |
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* Returns the pool hosting this thread. |
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|
return poolIndex; |
302 |
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} |
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|
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+ |
// Randomization |
305 |
+ |
|
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+ |
/** |
307 |
+ |
* Computes next value for random victim probes and backoffs. |
308 |
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* Scans don't require a very high quality generator, but also not |
309 |
+ |
* a crummy one. Marsaglia xor-shift is cheap and works well |
310 |
+ |
* enough. Note: This is manually inlined in FJP.scan() to avoid |
311 |
+ |
* writes inside busy loops. |
312 |
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*/ |
313 |
+ |
private int nextSeed() { |
314 |
+ |
int r = seed; |
315 |
+ |
r ^= r << 13; |
316 |
+ |
r ^= r >>> 17; |
317 |
+ |
r ^= r << 5; |
318 |
+ |
return seed = r; |
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+ |
} |
320 |
+ |
|
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+ |
// Run State management |
322 |
+ |
|
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/** |
324 |
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* Initializes internal state after construction but before |
325 |
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* processing any tasks. If you override this method, you must |
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* processing tasks. |
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*/ |
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|
protected void onStart() { |
359 |
– |
int rs = seedGenerator.nextInt(); |
360 |
– |
seed = rs == 0? 1 : rs; // seed must be nonzero |
361 |
– |
|
362 |
– |
// Allocate name string and arrays in this thread |
363 |
– |
String pid = Integer.toString(pool.getPoolNumber()); |
364 |
– |
String wid = Integer.toString(poolIndex); |
365 |
– |
setName("ForkJoinPool-" + pid + "-worker-" + wid); |
366 |
– |
|
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queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY]; |
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+ |
int r = ForkJoinPool.workerSeedGenerator.nextInt(); |
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+ |
seed = (r == 0) ? 1 : r; // must be nonzero |
336 |
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} |
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|
338 |
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/** |
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|
*/ |
346 |
|
protected void onTermination(Throwable exception) { |
347 |
|
try { |
348 |
< |
ForkJoinPool p = pool; |
381 |
< |
if (active) { |
382 |
< |
int a; // inline p.tryDecrementActiveCount |
383 |
< |
active = false; |
384 |
< |
do {} while (!UNSAFE.compareAndSwapInt |
385 |
< |
(p, poolRunStateOffset, a = p.runState, a - 1)); |
386 |
< |
} |
348 |
> |
terminate = true; |
349 |
|
cancelTasks(); |
350 |
< |
setTerminated(); |
389 |
< |
p.workerTerminated(this); |
350 |
> |
pool.deregisterWorker(this, exception); |
351 |
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} catch (Throwable ex) { // Shouldn't ever happen |
352 |
|
if (exception == null) // but if so, at least rethrown |
353 |
|
exception = ex; |
366 |
|
Throwable exception = null; |
367 |
|
try { |
368 |
|
onStart(); |
369 |
< |
mainLoop(); |
369 |
> |
pool.work(this); |
370 |
|
} catch (Throwable ex) { |
371 |
|
exception = ex; |
372 |
|
} finally { |
374 |
|
} |
375 |
|
} |
376 |
|
|
416 |
– |
// helpers for run() |
417 |
– |
|
418 |
– |
/** |
419 |
– |
* Finds and executes tasks, and checks status while running. |
420 |
– |
*/ |
421 |
– |
private void mainLoop() { |
422 |
– |
boolean ran = false; // true if ran a task on last step |
423 |
– |
ForkJoinPool p = pool; |
424 |
– |
for (;;) { |
425 |
– |
p.preStep(this, ran); |
426 |
– |
if (runState != 0) |
427 |
– |
break; |
428 |
– |
ran = tryExecSteal() || tryExecSubmission(); |
429 |
– |
} |
430 |
– |
} |
431 |
– |
|
432 |
– |
/** |
433 |
– |
* Tries to steal a task and execute it. |
434 |
– |
* |
435 |
– |
* @return true if ran a task |
436 |
– |
*/ |
437 |
– |
private boolean tryExecSteal() { |
438 |
– |
ForkJoinTask<?> t; |
439 |
– |
if ((t = scan()) != null) { |
440 |
– |
t.quietlyExec(); |
441 |
– |
UNSAFE.putOrderedObject(this, currentStealOffset, null); |
442 |
– |
if (sp != base) |
443 |
– |
execLocalTasks(); |
444 |
– |
return true; |
445 |
– |
} |
446 |
– |
return false; |
447 |
– |
} |
448 |
– |
|
449 |
– |
/** |
450 |
– |
* If a submission exists, try to activate and run it. |
451 |
– |
* |
452 |
– |
* @return true if ran a task |
453 |
– |
*/ |
454 |
– |
private boolean tryExecSubmission() { |
455 |
– |
ForkJoinPool p = pool; |
456 |
– |
// This loop is needed in case attempt to activate fails, in |
457 |
– |
// which case we only retry if there still appears to be a |
458 |
– |
// submission. |
459 |
– |
while (p.hasQueuedSubmissions()) { |
460 |
– |
ForkJoinTask<?> t; int a; |
461 |
– |
if (active || // inline p.tryIncrementActiveCount |
462 |
– |
(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset, |
463 |
– |
a = p.runState, a + 1))) { |
464 |
– |
if ((t = p.pollSubmission()) != null) { |
465 |
– |
UNSAFE.putOrderedObject(this, currentStealOffset, t); |
466 |
– |
t.quietlyExec(); |
467 |
– |
UNSAFE.putOrderedObject(this, currentStealOffset, null); |
468 |
– |
if (sp != base) |
469 |
– |
execLocalTasks(); |
470 |
– |
return true; |
471 |
– |
} |
472 |
– |
} |
473 |
– |
} |
474 |
– |
return false; |
475 |
– |
} |
476 |
– |
|
477 |
– |
/** |
478 |
– |
* Runs local tasks until queue is empty or shut down. Call only |
479 |
– |
* while active. |
480 |
– |
*/ |
481 |
– |
private void execLocalTasks() { |
482 |
– |
while (runState == 0) { |
483 |
– |
ForkJoinTask<?> t = locallyFifo ? locallyDeqTask() : popTask(); |
484 |
– |
if (t != null) |
485 |
– |
t.quietlyExec(); |
486 |
– |
else if (sp == base) |
487 |
– |
break; |
488 |
– |
} |
489 |
– |
} |
490 |
– |
|
377 |
|
/* |
378 |
|
* Intrinsics-based atomic writes for queue slots. These are |
379 |
|
* basically the same as methods in AtomicReferenceArray, but |
385 |
|
* because they are protected by other volatile reads and are |
386 |
|
* confirmed by CASes. |
387 |
|
* |
388 |
< |
* Most uses don't actually call these methods, but instead contain |
389 |
< |
* inlined forms that enable more predictable optimization. We |
390 |
< |
* don't define the version of write used in pushTask at all, but |
391 |
< |
* instead inline there a store-fenced array slot write. |
388 |
> |
* Most uses don't actually call these methods, but instead |
389 |
> |
* contain inlined forms that enable more predictable |
390 |
> |
* optimization. We don't define the version of write used in |
391 |
> |
* pushTask at all, but instead inline there a store-fenced array |
392 |
> |
* slot write. |
393 |
> |
* |
394 |
> |
* Also in most methods, as a performance (not correctness) issue, |
395 |
> |
* we'd like to encourage compilers not to arbitrarily postpone |
396 |
> |
* setting queueTop after writing slot. Currently there is no |
397 |
> |
* intrinsic for arranging this, but using Unsafe putOrderedInt |
398 |
> |
* may be a preferable strategy on some compilers even though its |
399 |
> |
* main effect is a pre-, not post- fence. To simplify possible |
400 |
> |
* changes, the option is left in comments next to the associated |
401 |
> |
* assignments. |
402 |
|
*/ |
403 |
|
|
404 |
|
/** |
407 |
|
*/ |
408 |
|
private static final boolean casSlotNull(ForkJoinTask<?>[] q, int i, |
409 |
|
ForkJoinTask<?> t) { |
410 |
< |
return UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null); |
410 |
> |
return UNSAFE.compareAndSwapObject(q, (i << ASHIFT) + ABASE, t, null); |
411 |
|
} |
412 |
|
|
413 |
|
/** |
417 |
|
*/ |
418 |
|
private static final void writeSlot(ForkJoinTask<?>[] q, int i, |
419 |
|
ForkJoinTask<?> t) { |
420 |
< |
UNSAFE.putObjectVolatile(q, (i << qShift) + qBase, t); |
420 |
> |
UNSAFE.putObjectVolatile(q, (i << ASHIFT) + ABASE, t); |
421 |
|
} |
422 |
|
|
423 |
|
// queue methods |
428 |
|
* @param t the task. Caller must ensure non-null. |
429 |
|
*/ |
430 |
|
final void pushTask(ForkJoinTask<?> t) { |
431 |
< |
ForkJoinTask<?>[] q = queue; |
432 |
< |
int mask = q.length - 1; // implicit assert q != null |
433 |
< |
int s = sp++; // ok to increment sp before slot write |
434 |
< |
UNSAFE.putOrderedObject(q, ((s & mask) << qShift) + qBase, t); |
435 |
< |
if ((s -= base) == 0) |
436 |
< |
pool.signalWork(); // was empty |
437 |
< |
else if (s == mask) |
438 |
< |
growQueue(); // is full |
431 |
> |
ForkJoinTask<?>[] q; int s, m; |
432 |
> |
if ((q = queue) != null) { // ignore if queue removed |
433 |
> |
long u = (((s = queueTop) & (m = q.length - 1)) << ASHIFT) + ABASE; |
434 |
> |
UNSAFE.putOrderedObject(q, u, t); |
435 |
> |
queueTop = s + 1; // or use putOrderedInt |
436 |
> |
if ((s -= queueBase) <= 2) |
437 |
> |
pool.signalWork(); |
438 |
> |
else if (s == m) |
439 |
> |
growQueue(); |
440 |
> |
} |
441 |
> |
} |
442 |
> |
|
443 |
> |
/** |
444 |
> |
* Creates or doubles queue array. Transfers elements by |
445 |
> |
* emulating steals (deqs) from old array and placing, oldest |
446 |
> |
* first, into new array. |
447 |
> |
*/ |
448 |
> |
private void growQueue() { |
449 |
> |
ForkJoinTask<?>[] oldQ = queue; |
450 |
> |
int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY; |
451 |
> |
if (size > MAXIMUM_QUEUE_CAPACITY) |
452 |
> |
throw new RejectedExecutionException("Queue capacity exceeded"); |
453 |
> |
if (size < INITIAL_QUEUE_CAPACITY) |
454 |
> |
size = INITIAL_QUEUE_CAPACITY; |
455 |
> |
ForkJoinTask<?>[] q = queue = new ForkJoinTask<?>[size]; |
456 |
> |
int mask = size - 1; |
457 |
> |
int top = queueTop; |
458 |
> |
int oldMask; |
459 |
> |
if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) { |
460 |
> |
for (int b = queueBase; b != top; ++b) { |
461 |
> |
long u = ((b & oldMask) << ASHIFT) + ABASE; |
462 |
> |
Object x = UNSAFE.getObjectVolatile(oldQ, u); |
463 |
> |
if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null)) |
464 |
> |
UNSAFE.putObjectVolatile |
465 |
> |
(q, ((b & mask) << ASHIFT) + ABASE, x); |
466 |
> |
} |
467 |
> |
} |
468 |
|
} |
469 |
|
|
470 |
|
/** |
475 |
|
* @return a task, or null if none or contended |
476 |
|
*/ |
477 |
|
final ForkJoinTask<?> deqTask() { |
478 |
< |
ForkJoinTask<?> t; |
479 |
< |
ForkJoinTask<?>[] q; |
555 |
< |
int b, i; |
556 |
< |
if (sp != (b = base) && |
478 |
> |
ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i; |
479 |
> |
if (queueTop != (b = queueBase) && |
480 |
|
(q = queue) != null && // must read q after b |
481 |
< |
(t = q[i = (q.length - 1) & b]) != null && base == b && |
482 |
< |
UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) { |
483 |
< |
base = b + 1; |
481 |
> |
(i = (q.length - 1) & b) >= 0 && |
482 |
> |
(t = q[i]) != null && queueBase == b && |
483 |
> |
UNSAFE.compareAndSwapObject(q, (i << ASHIFT) + ABASE, t, null)) { |
484 |
> |
queueBase = b + 1; |
485 |
|
return t; |
486 |
|
} |
487 |
|
return null; |
488 |
|
} |
489 |
|
|
490 |
|
/** |
491 |
< |
* Tries to take a task from the base of own queue. Assumes active |
492 |
< |
* status. Called only by this thread. |
491 |
> |
* Tries to take a task from the base of own queue. Called only |
492 |
> |
* by this thread. |
493 |
|
* |
494 |
|
* @return a task, or null if none |
495 |
|
*/ |
496 |
|
final ForkJoinTask<?> locallyDeqTask() { |
497 |
+ |
ForkJoinTask<?> t; int m, b, i; |
498 |
|
ForkJoinTask<?>[] q = queue; |
499 |
< |
if (q != null) { |
500 |
< |
ForkJoinTask<?> t; |
501 |
< |
int b, i; |
502 |
< |
while (sp != (b = base)) { |
503 |
< |
if ((t = q[i = (q.length - 1) & b]) != null && base == b && |
579 |
< |
UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, |
499 |
> |
if (q != null && (m = q.length - 1) >= 0) { |
500 |
> |
while (queueTop != (b = queueBase)) { |
501 |
> |
if ((t = q[i = m & b]) != null && |
502 |
> |
queueBase == b && |
503 |
> |
UNSAFE.compareAndSwapObject(q, (i << ASHIFT) + ABASE, |
504 |
|
t, null)) { |
505 |
< |
base = b + 1; |
505 |
> |
queueBase = b + 1; |
506 |
|
return t; |
507 |
|
} |
508 |
|
} |
511 |
|
} |
512 |
|
|
513 |
|
/** |
514 |
< |
* Returns a popped task, or null if empty. Assumes active status. |
514 |
> |
* Returns a popped task, or null if empty. |
515 |
|
* Called only by this thread. |
516 |
|
*/ |
517 |
|
private ForkJoinTask<?> popTask() { |
518 |
+ |
int m; |
519 |
|
ForkJoinTask<?>[] q = queue; |
520 |
< |
if (q != null) { |
521 |
< |
int s; |
522 |
< |
while ((s = sp) != base) { |
523 |
< |
int i = (q.length - 1) & --s; |
599 |
< |
long u = (i << qShift) + qBase; // raw offset |
520 |
> |
if (q != null && (m = q.length - 1) >= 0) { |
521 |
> |
for (int s; (s = queueTop) != queueBase;) { |
522 |
> |
int i = m & --s; |
523 |
> |
long u = (i << ASHIFT) + ABASE; // raw offset |
524 |
|
ForkJoinTask<?> t = q[i]; |
525 |
|
if (t == null) // lost to stealer |
526 |
|
break; |
527 |
|
if (UNSAFE.compareAndSwapObject(q, u, t, null)) { |
528 |
< |
/* |
605 |
< |
* Note: here and in related methods, as a |
606 |
< |
* performance (not correctness) issue, we'd like |
607 |
< |
* to encourage compiler not to arbitrarily |
608 |
< |
* postpone setting sp after successful CAS. |
609 |
< |
* Currently there is no intrinsic for arranging |
610 |
< |
* this, but using Unsafe putOrderedInt may be a |
611 |
< |
* preferable strategy on some compilers even |
612 |
< |
* though its main effect is a pre-, not post- |
613 |
< |
* fence. To simplify possible changes, the option |
614 |
< |
* is left in comments next to the associated |
615 |
< |
* assignments. |
616 |
< |
*/ |
617 |
< |
sp = s; // putOrderedInt may encourage more timely write |
618 |
< |
// UNSAFE.putOrderedInt(this, spOffset, s); |
528 |
> |
queueTop = s; // or putOrderedInt |
529 |
|
return t; |
530 |
|
} |
531 |
|
} |
535 |
|
|
536 |
|
/** |
537 |
|
* Specialized version of popTask to pop only if topmost element |
538 |
< |
* is the given task. Called only by this thread while active. |
538 |
> |
* is the given task. Called only by this thread. |
539 |
|
* |
540 |
|
* @param t the task. Caller must ensure non-null. |
541 |
|
*/ |
542 |
|
final boolean unpushTask(ForkJoinTask<?> t) { |
543 |
+ |
ForkJoinTask<?>[] q; |
544 |
|
int s; |
545 |
< |
ForkJoinTask<?>[] q = queue; |
635 |
< |
if ((s = sp) != base && q != null && |
545 |
> |
if ((q = queue) != null && (s = queueTop) != queueBase && |
546 |
|
UNSAFE.compareAndSwapObject |
547 |
< |
(q, (((q.length - 1) & --s) << qShift) + qBase, t, null)) { |
548 |
< |
sp = s; // putOrderedInt may encourage more timely write |
639 |
< |
// UNSAFE.putOrderedInt(this, spOffset, s); |
547 |
> |
(q, (((q.length - 1) & --s) << ASHIFT) + ABASE, t, null)) { |
548 |
> |
queueTop = s; // or putOrderedInt |
549 |
|
return true; |
550 |
|
} |
551 |
|
return false; |
555 |
|
* Returns next task, or null if empty or contended. |
556 |
|
*/ |
557 |
|
final ForkJoinTask<?> peekTask() { |
558 |
+ |
int m; |
559 |
|
ForkJoinTask<?>[] q = queue; |
560 |
< |
if (q == null) |
560 |
> |
if (q == null || (m = q.length - 1) < 0) |
561 |
|
return null; |
562 |
< |
int mask = q.length - 1; |
563 |
< |
int i = locallyFifo ? base : (sp - 1); |
654 |
< |
return q[i & mask]; |
655 |
< |
} |
656 |
< |
|
657 |
< |
/** |
658 |
< |
* Doubles queue array size. Transfers elements by emulating |
659 |
< |
* steals (deqs) from old array and placing, oldest first, into |
660 |
< |
* new array. |
661 |
< |
*/ |
662 |
< |
private void growQueue() { |
663 |
< |
ForkJoinTask<?>[] oldQ = queue; |
664 |
< |
int oldSize = oldQ.length; |
665 |
< |
int newSize = oldSize << 1; |
666 |
< |
if (newSize > MAXIMUM_QUEUE_CAPACITY) |
667 |
< |
throw new RejectedExecutionException("Queue capacity exceeded"); |
668 |
< |
ForkJoinTask<?>[] newQ = queue = new ForkJoinTask<?>[newSize]; |
669 |
< |
|
670 |
< |
int b = base; |
671 |
< |
int bf = b + oldSize; |
672 |
< |
int oldMask = oldSize - 1; |
673 |
< |
int newMask = newSize - 1; |
674 |
< |
do { |
675 |
< |
int oldIndex = b & oldMask; |
676 |
< |
ForkJoinTask<?> t = oldQ[oldIndex]; |
677 |
< |
if (t != null && !casSlotNull(oldQ, oldIndex, t)) |
678 |
< |
t = null; |
679 |
< |
writeSlot(newQ, b & newMask, t); |
680 |
< |
} while (++b != bf); |
681 |
< |
pool.signalWork(); |
562 |
> |
int i = locallyFifo ? queueBase : (queueTop - 1); |
563 |
> |
return q[i & m]; |
564 |
|
} |
565 |
|
|
566 |
< |
/** |
685 |
< |
* Computes next value for random victim probe in scan(). Scans |
686 |
< |
* don't require a very high quality generator, but also not a |
687 |
< |
* crummy one. Marsaglia xor-shift is cheap and works well enough. |
688 |
< |
* Note: This is manually inlined in scan(). |
689 |
< |
*/ |
690 |
< |
private static final int xorShift(int r) { |
691 |
< |
r ^= r << 13; |
692 |
< |
r ^= r >>> 17; |
693 |
< |
return r ^ (r << 5); |
694 |
< |
} |
566 |
> |
// Support methods for ForkJoinPool |
567 |
|
|
568 |
|
/** |
569 |
< |
* Tries to steal a task from another worker. Starts at a random |
698 |
< |
* index of workers array, and probes workers until finding one |
699 |
< |
* with non-empty queue or finding that all are empty. It |
700 |
< |
* randomly selects the first n probes. If these are empty, it |
701 |
< |
* resorts to a circular sweep, which is necessary to accurately |
702 |
< |
* set active status. (The circular sweep uses steps of |
703 |
< |
* approximately half the array size plus 1, to avoid bias |
704 |
< |
* stemming from leftmost packing of the array in ForkJoinPool.) |
705 |
< |
* |
706 |
< |
* This method must be both fast and quiet -- usually avoiding |
707 |
< |
* memory accesses that could disrupt cache sharing etc other than |
708 |
< |
* those needed to check for and take tasks (or to activate if not |
709 |
< |
* already active). This accounts for, among other things, |
710 |
< |
* updating random seed in place without storing it until exit. |
711 |
< |
* |
712 |
< |
* @return a task, or null if none found |
569 |
> |
* Runs the given task, plus any local tasks until queue is empty |
570 |
|
*/ |
571 |
< |
private ForkJoinTask<?> scan() { |
572 |
< |
ForkJoinPool p = pool; |
716 |
< |
ForkJoinWorkerThread[] ws; // worker array |
717 |
< |
int n; // upper bound of #workers |
718 |
< |
if ((ws = p.workers) != null && (n = ws.length) > 1) { |
719 |
< |
boolean canSteal = active; // shadow active status |
720 |
< |
int r = seed; // extract seed once |
721 |
< |
int mask = n - 1; |
722 |
< |
int j = -n; // loop counter |
723 |
< |
int k = r; // worker index, random if j < 0 |
724 |
< |
for (;;) { |
725 |
< |
ForkJoinWorkerThread v = ws[k & mask]; |
726 |
< |
r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // inline xorshift |
727 |
< |
ForkJoinTask<?>[] q; ForkJoinTask<?> t; int b, a; |
728 |
< |
if (v != null && (b = v.base) != v.sp && |
729 |
< |
(q = v.queue) != null) { |
730 |
< |
int i = (q.length - 1) & b; |
731 |
< |
long u = (i << qShift) + qBase; // raw offset |
732 |
< |
int pid = poolIndex; |
733 |
< |
if ((t = q[i]) != null) { |
734 |
< |
if (!canSteal && // inline p.tryIncrementActiveCount |
735 |
< |
UNSAFE.compareAndSwapInt(p, poolRunStateOffset, |
736 |
< |
a = p.runState, a + 1)) |
737 |
< |
canSteal = active = true; |
738 |
< |
if (canSteal && v.base == b++ && |
739 |
< |
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
740 |
< |
v.base = b; |
741 |
< |
v.stealHint = pid; |
742 |
< |
UNSAFE.putOrderedObject(this, |
743 |
< |
currentStealOffset, t); |
744 |
< |
seed = r; |
745 |
< |
++stealCount; |
746 |
< |
return t; |
747 |
< |
} |
748 |
< |
} |
749 |
< |
j = -n; |
750 |
< |
k = r; // restart on contention |
751 |
< |
} |
752 |
< |
else if (++j <= 0) |
753 |
< |
k = r; |
754 |
< |
else if (j <= n) |
755 |
< |
k += (n >>> 1) | 1; |
756 |
< |
else |
757 |
< |
break; |
758 |
< |
} |
759 |
< |
} |
760 |
< |
return null; |
761 |
< |
} |
762 |
< |
|
763 |
< |
// Run State management |
764 |
< |
|
765 |
< |
// status check methods used mainly by ForkJoinPool |
766 |
< |
final boolean isRunning() { return runState == 0; } |
767 |
< |
final boolean isTerminated() { return (runState & TERMINATED) != 0; } |
768 |
< |
final boolean isSuspended() { return (runState & SUSPENDED) != 0; } |
769 |
< |
final boolean isTrimmed() { return (runState & TRIMMED) != 0; } |
770 |
< |
|
771 |
< |
final boolean isTerminating() { |
772 |
< |
if ((runState & TERMINATING) != 0) |
773 |
< |
return true; |
774 |
< |
if (pool.isAtLeastTerminating()) { // propagate pool state |
775 |
< |
shutdown(); |
776 |
< |
return true; |
777 |
< |
} |
778 |
< |
return false; |
779 |
< |
} |
780 |
< |
|
781 |
< |
/** |
782 |
< |
* Sets state to TERMINATING. Does NOT unpark or interrupt |
783 |
< |
* to wake up if currently blocked. Callers must do so if desired. |
784 |
< |
*/ |
785 |
< |
final void shutdown() { |
571 |
> |
final void execTask(ForkJoinTask<?> t) { |
572 |
> |
currentSteal = t; |
573 |
|
for (;;) { |
574 |
< |
int s = runState; |
575 |
< |
if ((s & (TERMINATING|TERMINATED)) != 0) |
576 |
< |
break; |
790 |
< |
if ((s & SUSPENDED) != 0) { // kill and wakeup if suspended |
791 |
< |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
792 |
< |
(s & ~SUSPENDED) | |
793 |
< |
(TRIMMED|TERMINATING))) |
794 |
< |
break; |
795 |
< |
} |
796 |
< |
else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
797 |
< |
s | TERMINATING)) |
798 |
< |
break; |
799 |
< |
} |
800 |
< |
} |
801 |
< |
|
802 |
< |
/** |
803 |
< |
* Sets state to TERMINATED. Called only by onTermination(). |
804 |
< |
*/ |
805 |
< |
private void setTerminated() { |
806 |
< |
int s; |
807 |
< |
do {} while (!UNSAFE.compareAndSwapInt(this, runStateOffset, |
808 |
< |
s = runState, |
809 |
< |
s | (TERMINATING|TERMINATED))); |
810 |
< |
} |
811 |
< |
|
812 |
< |
/** |
813 |
< |
* If suspended, tries to set status to unsuspended. |
814 |
< |
* Does NOT wake up if blocked. |
815 |
< |
* |
816 |
< |
* @return true if successful |
817 |
< |
*/ |
818 |
< |
final boolean tryUnsuspend() { |
819 |
< |
int s; |
820 |
< |
while (((s = runState) & SUSPENDED) != 0) { |
821 |
< |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
822 |
< |
s & ~SUSPENDED)) |
823 |
< |
return true; |
824 |
< |
} |
825 |
< |
return false; |
826 |
< |
} |
827 |
< |
|
828 |
< |
/** |
829 |
< |
* Sets suspended status and blocks as spare until resumed |
830 |
< |
* or shutdown. |
831 |
< |
*/ |
832 |
< |
final void suspendAsSpare() { |
833 |
< |
for (;;) { // set suspended unless terminating |
834 |
< |
int s = runState; |
835 |
< |
if ((s & TERMINATING) != 0) { // must kill |
836 |
< |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
837 |
< |
s | (TRIMMED | TERMINATING))) |
838 |
< |
return; |
839 |
< |
} |
840 |
< |
else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, |
841 |
< |
s | SUSPENDED)) |
574 |
> |
if (t != null) |
575 |
> |
t.doExec(); |
576 |
> |
if (queueTop == queueBase) |
577 |
|
break; |
578 |
+ |
t = locallyFifo ? locallyDeqTask() : popTask(); |
579 |
|
} |
580 |
< |
ForkJoinPool p = pool; |
581 |
< |
p.pushSpare(this); |
846 |
< |
while ((runState & SUSPENDED) != 0) { |
847 |
< |
if (p.tryAccumulateStealCount(this)) { |
848 |
< |
interrupted(); // clear/ignore interrupts |
849 |
< |
if ((runState & SUSPENDED) == 0) |
850 |
< |
break; |
851 |
< |
LockSupport.park(this); |
852 |
< |
} |
853 |
< |
} |
854 |
< |
} |
855 |
< |
|
856 |
< |
// Misc support methods for ForkJoinPool |
857 |
< |
|
858 |
< |
/** |
859 |
< |
* Returns an estimate of the number of tasks in the queue. Also |
860 |
< |
* used by ForkJoinTask. |
861 |
< |
*/ |
862 |
< |
final int getQueueSize() { |
863 |
< |
int n; // external calls must read base first |
864 |
< |
return (n = -base + sp) <= 0 ? 0 : n; |
580 |
> |
++stealCount; |
581 |
> |
currentSteal = null; |
582 |
|
} |
583 |
|
|
584 |
|
/** |
587 |
|
*/ |
588 |
|
final void cancelTasks() { |
589 |
|
ForkJoinTask<?> cj = currentJoin; // try to cancel ongoing tasks |
590 |
< |
if (cj != null && cj.status >= 0) { |
590 |
> |
if (cj != null && cj.status >= 0) |
591 |
|
cj.cancelIgnoringExceptions(); |
875 |
– |
try { |
876 |
– |
this.interrupt(); // awaken wait |
877 |
– |
} catch (SecurityException ignore) { |
878 |
– |
} |
879 |
– |
} |
592 |
|
ForkJoinTask<?> cs = currentSteal; |
593 |
|
if (cs != null && cs.status >= 0) |
594 |
|
cs.cancelIgnoringExceptions(); |
595 |
< |
while (base != sp) { |
595 |
> |
while (queueBase != queueTop) { |
596 |
|
ForkJoinTask<?> t = deqTask(); |
597 |
|
if (t != null) |
598 |
|
t.cancelIgnoringExceptions(); |
606 |
|
*/ |
607 |
|
final int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
608 |
|
int n = 0; |
609 |
< |
while (base != sp) { |
609 |
> |
while (queueBase != queueTop) { |
610 |
|
ForkJoinTask<?> t = deqTask(); |
611 |
|
if (t != null) { |
612 |
|
c.add(t); |
619 |
|
// Support methods for ForkJoinTask |
620 |
|
|
621 |
|
/** |
622 |
+ |
* Returns an estimate of the number of tasks in the queue. |
623 |
+ |
*/ |
624 |
+ |
final int getQueueSize() { |
625 |
+ |
return queueTop - queueBase; |
626 |
+ |
} |
627 |
+ |
|
628 |
+ |
/** |
629 |
|
* Gets and removes a local task. |
630 |
|
* |
631 |
|
* @return a task, if available |
632 |
|
*/ |
633 |
|
final ForkJoinTask<?> pollLocalTask() { |
634 |
< |
ForkJoinPool p = pool; |
916 |
< |
while (sp != base) { |
917 |
< |
int a; // inline p.tryIncrementActiveCount |
918 |
< |
if (active || |
919 |
< |
(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset, |
920 |
< |
a = p.runState, a + 1))) |
921 |
< |
return locallyFifo ? locallyDeqTask() : popTask(); |
922 |
< |
} |
923 |
< |
return null; |
634 |
> |
return locallyFifo ? locallyDeqTask() : popTask(); |
635 |
|
} |
636 |
|
|
637 |
|
/** |
640 |
|
* @return a task, if available |
641 |
|
*/ |
642 |
|
final ForkJoinTask<?> pollTask() { |
643 |
+ |
ForkJoinWorkerThread[] ws; |
644 |
|
ForkJoinTask<?> t = pollLocalTask(); |
645 |
< |
if (t == null) { |
646 |
< |
t = scan(); |
647 |
< |
// cannot retain/track/help steal |
648 |
< |
UNSAFE.putOrderedObject(this, currentStealOffset, null); |
645 |
> |
if (t != null || (ws = pool.workers) == null) |
646 |
> |
return t; |
647 |
> |
int n = ws.length; // cheap version of FJP.scan |
648 |
> |
int steps = n << 1; |
649 |
> |
int r = nextSeed(); |
650 |
> |
int i = 0; |
651 |
> |
while (i < steps) { |
652 |
> |
ForkJoinWorkerThread w = ws[(i++ + r) & (n - 1)]; |
653 |
> |
if (w != null && w.queueBase != w.queueTop && w.queue != null) { |
654 |
> |
if ((t = w.deqTask()) != null) |
655 |
> |
return t; |
656 |
> |
i = 0; |
657 |
> |
} |
658 |
|
} |
659 |
< |
return t; |
659 |
> |
return null; |
660 |
|
} |
661 |
|
|
662 |
|
/** |
663 |
< |
* Possibly runs some tasks and/or blocks, until task is done. |
663 |
> |
* The maximum stolen->joining link depth allowed in helpJoinTask, |
664 |
> |
* as well as the maximum number of retries (allowing on average |
665 |
> |
* one staleness retry per level) per attempt to instead try |
666 |
> |
* compensation. Depths for legitimate chains are unbounded, but |
667 |
> |
* we use a fixed constant to avoid (otherwise unchecked) cycles |
668 |
> |
* and bound staleness of traversal parameters at the expense of |
669 |
> |
* sometimes blocking when we could be helping. |
670 |
> |
*/ |
671 |
> |
private static final int MAX_HELP = 16; |
672 |
> |
|
673 |
> |
/** |
674 |
> |
* Possibly runs some tasks and/or blocks, until joinMe is done. |
675 |
|
* |
676 |
|
* @param joinMe the task to join |
677 |
< |
* @param timed true if use timed wait |
946 |
< |
* @param nanos wait time if timed |
677 |
> |
* @return completion status on exit |
678 |
|
*/ |
679 |
< |
final void joinTask(ForkJoinTask<?> joinMe, boolean timed, long nanos) { |
949 |
< |
// currentJoin only written by this thread; only need ordered store |
679 |
> |
final int joinTask(ForkJoinTask<?> joinMe) { |
680 |
|
ForkJoinTask<?> prevJoin = currentJoin; |
681 |
< |
UNSAFE.putOrderedObject(this, currentJoinOffset, joinMe); |
682 |
< |
pool.awaitJoin(joinMe, this, timed, nanos); |
683 |
< |
UNSAFE.putOrderedObject(this, currentJoinOffset, prevJoin); |
681 |
> |
currentJoin = joinMe; |
682 |
> |
for (int s, retries = MAX_HELP;;) { |
683 |
> |
if ((s = joinMe.status) < 0) { |
684 |
> |
currentJoin = prevJoin; |
685 |
> |
return s; |
686 |
> |
} |
687 |
> |
if (retries > 0) { |
688 |
> |
if (queueTop != queueBase) { |
689 |
> |
if (!localHelpJoinTask(joinMe)) |
690 |
> |
retries = 0; // cannot help |
691 |
> |
} |
692 |
> |
else if (retries == MAX_HELP >>> 1) { |
693 |
> |
--retries; // check uncommon case |
694 |
> |
if (tryDeqAndExec(joinMe) >= 0) |
695 |
> |
Thread.yield(); // for politeness |
696 |
> |
} |
697 |
> |
else |
698 |
> |
retries = helpJoinTask(joinMe) ? MAX_HELP : retries - 1; |
699 |
> |
} |
700 |
> |
else { |
701 |
> |
retries = MAX_HELP; // restart if not done |
702 |
> |
pool.tryAwaitJoin(joinMe); |
703 |
> |
} |
704 |
> |
} |
705 |
|
} |
706 |
|
|
707 |
|
/** |
708 |
< |
* Tries to locate and help perform tasks for a stealer of the |
709 |
< |
* given task, or in turn one of its stealers. Traces |
959 |
< |
* currentSteal->currentJoin links looking for a thread working on |
960 |
< |
* a descendant of the given task and with a non-empty queue to |
961 |
< |
* steal back and execute tasks from. |
962 |
< |
* |
963 |
< |
* The implementation is very branchy to cope with potential |
964 |
< |
* inconsistencies or loops encountering chains that are stale, |
965 |
< |
* unknown, or of length greater than MAX_HELP_DEPTH links. All |
966 |
< |
* of these cases are dealt with by just returning back to the |
967 |
< |
* caller, who is expected to retry if other join mechanisms also |
968 |
< |
* don't work out. |
708 |
> |
* If present, pops and executes the given task, or any other |
709 |
> |
* cancelled task |
710 |
|
* |
711 |
< |
* @param joinMe the task to join |
712 |
< |
* @param running if false, then must update pool count upon |
713 |
< |
* running a task |
714 |
< |
* @return value of running on exit |
715 |
< |
*/ |
716 |
< |
final boolean helpJoinTask(ForkJoinTask<?> joinMe, boolean running) { |
717 |
< |
/* |
718 |
< |
* Initial checks to (1) abort if terminating; (2) clean out |
719 |
< |
* old cancelled tasks from local queue; (3) if joinMe is next |
720 |
< |
* task, run it; (4) omit scan if local queue nonempty (since |
721 |
< |
* it may contain non-descendents of joinMe). |
722 |
< |
*/ |
723 |
< |
ForkJoinPool p = pool; |
983 |
< |
for (;;) { |
984 |
< |
ForkJoinTask<?>[] q; |
985 |
< |
int s; |
986 |
< |
if (joinMe.status < 0) |
987 |
< |
return running; |
988 |
< |
else if ((runState & TERMINATING) != 0) |
989 |
< |
joinMe.cancelIgnoringExceptions(); |
990 |
< |
else if ((s = sp) == base || (q = queue) == null) |
991 |
< |
break; // queue empty |
992 |
< |
else { |
993 |
< |
int i = (q.length - 1) & --s; |
994 |
< |
long u = (i << qShift) + qBase; // raw offset |
995 |
< |
ForkJoinTask<?> t = q[i]; |
996 |
< |
if (t == null) |
997 |
< |
break; // lost to a stealer |
998 |
< |
else if (t != joinMe && t.status >= 0) |
999 |
< |
return running; // cannot safely help |
1000 |
< |
else if ((running || |
1001 |
< |
(running = p.tryIncrementRunningCount())) && |
1002 |
< |
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
1003 |
< |
sp = s; // putOrderedInt may encourage more timely write |
1004 |
< |
// UNSAFE.putOrderedInt(this, spOffset, s); |
1005 |
< |
if (t.status >= 0) |
1006 |
< |
t.quietlyExec(); |
1007 |
< |
} |
711 |
> |
* @return false if any other non-cancelled task exists in local queue |
712 |
> |
*/ |
713 |
> |
private boolean localHelpJoinTask(ForkJoinTask<?> joinMe) { |
714 |
> |
int s, i; ForkJoinTask<?>[] q; ForkJoinTask<?> t; |
715 |
> |
if ((s = queueTop) != queueBase && (q = queue) != null && |
716 |
> |
(i = (q.length - 1) & --s) >= 0 && |
717 |
> |
(t = q[i]) != null) { |
718 |
> |
if (t != joinMe && t.status >= 0) |
719 |
> |
return false; |
720 |
> |
if (UNSAFE.compareAndSwapObject |
721 |
> |
(q, (i << ASHIFT) + ABASE, t, null)) { |
722 |
> |
queueTop = s; // or putOrderedInt |
723 |
> |
t.doExec(); |
724 |
|
} |
725 |
|
} |
726 |
+ |
return true; |
727 |
+ |
} |
728 |
|
|
729 |
< |
int n; // worker array size |
730 |
< |
ForkJoinWorkerThread[] ws = p.workers; |
731 |
< |
if (ws != null && (n = ws.length) > 1) { // need at least 2 workers |
732 |
< |
ForkJoinTask<?> task = joinMe; // base of chain |
733 |
< |
ForkJoinWorkerThread thread = this; // thread with stolen task |
734 |
< |
|
735 |
< |
outer:for (int d = 0; d < MAX_HELP_DEPTH; ++d) { // chain length |
729 |
> |
/** |
730 |
> |
* Tries to locate and execute tasks for a stealer of the given |
731 |
> |
* task, or in turn one of its stealers, Traces |
732 |
> |
* currentSteal->currentJoin links looking for a thread working on |
733 |
> |
* a descendant of the given task and with a non-empty queue to |
734 |
> |
* steal back and execute tasks from. The implementation is very |
735 |
> |
* branchy to cope with potential inconsistencies or loops |
736 |
> |
* encountering chains that are stale, unknown, or of length |
737 |
> |
* greater than MAX_HELP links. All of these cases are dealt with |
738 |
> |
* by just retrying by caller. |
739 |
> |
* |
740 |
> |
* @param joinMe the task to join |
741 |
> |
* @param canSteal true if local queue is empty |
742 |
> |
* @return true if ran a task |
743 |
> |
*/ |
744 |
> |
private boolean helpJoinTask(ForkJoinTask<?> joinMe) { |
745 |
> |
boolean helped = false; |
746 |
> |
int m = pool.scanGuard & SMASK; |
747 |
> |
ForkJoinWorkerThread[] ws = pool.workers; |
748 |
> |
if (ws != null && ws.length > m && joinMe.status >= 0) { |
749 |
> |
int levels = MAX_HELP; // remaining chain length |
750 |
> |
ForkJoinTask<?> task = joinMe; // base of chain |
751 |
> |
outer:for (ForkJoinWorkerThread thread = this;;) { |
752 |
|
// Try to find v, the stealer of task, by first using hint |
753 |
< |
ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)]; |
753 |
> |
ForkJoinWorkerThread v = ws[thread.stealHint & m]; |
754 |
|
if (v == null || v.currentSteal != task) { |
755 |
< |
for (int j = 0; ; ++j) { // search array |
756 |
< |
if (j < n) { |
757 |
< |
ForkJoinTask<?> vs; |
758 |
< |
if ((v = ws[j]) != null && |
1025 |
< |
(vs = v.currentSteal) != null) { |
1026 |
< |
if (joinMe.status < 0) |
1027 |
< |
break outer; |
1028 |
< |
if (vs == task) { |
1029 |
< |
if (task.status < 0) |
1030 |
< |
break outer; // stale |
1031 |
< |
thread.stealHint = j; |
1032 |
< |
break; // save hint for next time |
1033 |
< |
} |
1034 |
< |
} |
755 |
> |
for (int j = 0; ;) { // search array |
756 |
> |
if ((v = ws[j]) != null && v.currentSteal == task) { |
757 |
> |
thread.stealHint = j; |
758 |
> |
break; // save hint for next time |
759 |
|
} |
760 |
< |
else |
761 |
< |
break outer; // no stealer |
760 |
> |
if (++j > m) |
761 |
> |
break outer; // can't find stealer |
762 |
|
} |
763 |
|
} |
1040 |
– |
|
764 |
|
// Try to help v, using specialized form of deqTask |
765 |
|
for (;;) { |
766 |
+ |
ForkJoinTask<?>[] q; int b, i; |
767 |
|
if (joinMe.status < 0) |
768 |
|
break outer; |
769 |
< |
int b = v.base; |
770 |
< |
ForkJoinTask<?>[] q = v.queue; |
771 |
< |
if (b == v.sp || q == null) |
772 |
< |
break; // empty |
773 |
< |
int i = (q.length - 1) & b; |
1050 |
< |
long u = (i << qShift) + qBase; |
769 |
> |
if ((b = v.queueBase) == v.queueTop || |
770 |
> |
(q = v.queue) == null || |
771 |
> |
(i = (q.length-1) & b) < 0) |
772 |
> |
break; // empty |
773 |
> |
long u = (i << ASHIFT) + ABASE; |
774 |
|
ForkJoinTask<?> t = q[i]; |
775 |
|
if (task.status < 0) |
776 |
< |
break outer; // stale |
777 |
< |
if (t != null && |
1055 |
< |
(running || |
1056 |
< |
(running = p.tryIncrementRunningCount())) && |
1057 |
< |
v.base == b++ && |
776 |
> |
break outer; // stale |
777 |
> |
if (t != null && v.queueBase == b && |
778 |
|
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
779 |
< |
if (t != joinMe && joinMe.status < 0) { |
780 |
< |
UNSAFE.putObjectVolatile(q, u, t); |
781 |
< |
break outer; // joinMe cancelled; back out |
782 |
< |
} |
783 |
< |
v.base = b; |
784 |
< |
if (t.status >= 0) { |
785 |
< |
ForkJoinTask<?> ps = currentSteal; |
1066 |
< |
int pid = poolIndex; |
1067 |
< |
v.stealHint = pid; |
1068 |
< |
UNSAFE.putOrderedObject(this, |
1069 |
< |
currentStealOffset, t); |
1070 |
< |
t.quietlyExec(); |
1071 |
< |
UNSAFE.putOrderedObject(this, |
1072 |
< |
currentStealOffset, ps); |
1073 |
< |
} |
779 |
> |
v.queueBase = b + 1; |
780 |
> |
v.stealHint = poolIndex; |
781 |
> |
ForkJoinTask<?> ps = currentSteal; |
782 |
> |
currentSteal = t; |
783 |
> |
t.doExec(); |
784 |
> |
currentSteal = ps; |
785 |
> |
helped = true; |
786 |
|
} |
787 |
|
} |
1076 |
– |
|
788 |
|
// Try to descend to find v's stealer |
789 |
|
ForkJoinTask<?> next = v.currentJoin; |
790 |
< |
if (task.status < 0 || next == null || next == task) |
791 |
< |
break; // stale, dead-end, or cyclic |
792 |
< |
if ((runState & TERMINATING) != 0) |
793 |
< |
joinMe.cancelIgnoringExceptions(); |
794 |
< |
if (joinMe.status < 0) |
790 |
> |
if (--levels > 0 && task.status >= 0 && |
791 |
> |
next != null && next != task) { |
792 |
> |
task = next; |
793 |
> |
thread = v; |
794 |
> |
} |
795 |
> |
else |
796 |
> |
break; // max levels, stale, dead-end, or cyclic |
797 |
> |
} |
798 |
> |
} |
799 |
> |
return helped; |
800 |
> |
} |
801 |
> |
|
802 |
> |
/** |
803 |
> |
* Performs an uncommon case for joinTask: If task t is at base of |
804 |
> |
* some workers queue, steals and executes it. |
805 |
> |
* |
806 |
> |
* @param t the task |
807 |
> |
* @return t's status |
808 |
> |
*/ |
809 |
> |
private int tryDeqAndExec(ForkJoinTask<?> t) { |
810 |
> |
int m = pool.scanGuard & SMASK; |
811 |
> |
ForkJoinWorkerThread[] ws = pool.workers; |
812 |
> |
if (ws != null && ws.length > m && t.status >= 0) { |
813 |
> |
for (int j = 0; j <= m; ++j) { |
814 |
> |
ForkJoinTask<?>[] q; int b, i; |
815 |
> |
ForkJoinWorkerThread v = ws[j]; |
816 |
> |
if (v != null && |
817 |
> |
(b = v.queueBase) != v.queueTop && |
818 |
> |
(q = v.queue) != null && |
819 |
> |
(i = (q.length - 1) & b) >= 0 && |
820 |
> |
q[i] == t) { |
821 |
> |
long u = (i << ASHIFT) + ABASE; |
822 |
> |
if (v.queueBase == b && |
823 |
> |
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
824 |
> |
v.queueBase = b + 1; |
825 |
> |
v.stealHint = poolIndex; |
826 |
> |
ForkJoinTask<?> ps = currentSteal; |
827 |
> |
currentSteal = t; |
828 |
> |
t.doExec(); |
829 |
> |
currentSteal = ps; |
830 |
> |
} |
831 |
|
break; |
832 |
< |
task = next; |
1086 |
< |
thread = v; |
832 |
> |
} |
833 |
|
} |
834 |
|
} |
835 |
< |
return running; |
835 |
> |
return t.status; |
836 |
|
} |
837 |
|
|
838 |
|
/** |
839 |
< |
* Implements ForkJoinTask.getSurplusQueuedTaskCount(). |
840 |
< |
* Returns an estimate of the number of tasks, offset by a |
841 |
< |
* function of number of idle workers. |
839 |
> |
* Implements ForkJoinTask.getSurplusQueuedTaskCount(). Returns |
840 |
> |
* an estimate of the number of tasks, offset by a function of |
841 |
> |
* number of idle workers. |
842 |
|
* |
843 |
|
* This method provides a cheap heuristic guide for task |
844 |
|
* partitioning when programmers, frameworks, tools, or languages |
874 |
|
* When all threads are active, it is on average OK to estimate |
875 |
|
* surplus strictly locally. In steady-state, if one thread is |
876 |
|
* maintaining say 2 surplus tasks, then so are others. So we can |
877 |
< |
* just use estimated queue length (although note that (sp - base) |
878 |
< |
* can be an overestimate because of stealers lagging increments |
879 |
< |
* of base). However, this strategy alone leads to serious |
880 |
< |
* mis-estimates in some non-steady-state conditions (ramp-up, |
881 |
< |
* ramp-down, other stalls). We can detect many of these by |
882 |
< |
* further considering the number of "idle" threads, that are |
877 |
> |
* just use estimated queue length (although note that (queueTop - |
878 |
> |
* queueBase) can be an overestimate because of stealers lagging |
879 |
> |
* increments of queueBase). However, this strategy alone leads |
880 |
> |
* to serious mis-estimates in some non-steady-state conditions |
881 |
> |
* (ramp-up, ramp-down, other stalls). We can detect many of these |
882 |
> |
* by further considering the number of "idle" threads, that are |
883 |
|
* known to have zero queued tasks, so compensate by a factor of |
884 |
|
* (#idle/#active) threads. |
885 |
|
*/ |
886 |
|
final int getEstimatedSurplusTaskCount() { |
887 |
< |
return sp - base - pool.idlePerActive(); |
887 |
> |
return queueTop - queueBase - pool.idlePerActive(); |
888 |
|
} |
889 |
|
|
890 |
|
/** |
891 |
< |
* Runs tasks until {@code pool.isQuiescent()}. |
891 |
> |
* Runs tasks until {@code pool.isQuiescent()}. We piggyback on |
892 |
> |
* pool's active count ctl maintenance, but rather than blocking |
893 |
> |
* when tasks cannot be found, we rescan until all others cannot |
894 |
> |
* find tasks either. The bracketing by pool quiescerCounts |
895 |
> |
* updates suppresses pool auto-shutdown mechanics that could |
896 |
> |
* otherwise prematurely terminate the pool because all threads |
897 |
> |
* appear to be inactive. |
898 |
|
*/ |
899 |
|
final void helpQuiescePool() { |
900 |
+ |
boolean active = true; |
901 |
|
ForkJoinTask<?> ps = currentSteal; // to restore below |
902 |
+ |
ForkJoinPool p = pool; |
903 |
+ |
p.addQuiescerCount(1); |
904 |
|
for (;;) { |
905 |
< |
ForkJoinTask<?> t = pollLocalTask(); |
906 |
< |
if (t != null || (t = scan()) != null) |
907 |
< |
t.quietlyExec(); |
905 |
> |
ForkJoinWorkerThread[] ws = p.workers; |
906 |
> |
ForkJoinWorkerThread v = null; |
907 |
> |
int n; |
908 |
> |
if (queueTop != queueBase) |
909 |
> |
v = this; |
910 |
> |
else if (ws != null && (n = ws.length) > 1) { |
911 |
> |
ForkJoinWorkerThread w; |
912 |
> |
int r = nextSeed(); // cheap version of FJP.scan |
913 |
> |
int steps = n << 1; |
914 |
> |
for (int i = 0; i < steps; ++i) { |
915 |
> |
if ((w = ws[(i + r) & (n - 1)]) != null && |
916 |
> |
w.queueBase != w.queueTop) { |
917 |
> |
v = w; |
918 |
> |
break; |
919 |
> |
} |
920 |
> |
} |
921 |
> |
} |
922 |
> |
if (v != null) { |
923 |
> |
ForkJoinTask<?> t; |
924 |
> |
if (!active) { |
925 |
> |
active = true; |
926 |
> |
p.addActiveCount(1); |
927 |
> |
} |
928 |
> |
if ((t = (v != this) ? v.deqTask() : |
929 |
> |
locallyFifo ? locallyDeqTask() : popTask()) != null) { |
930 |
> |
currentSteal = t; |
931 |
> |
t.doExec(); |
932 |
> |
currentSteal = ps; |
933 |
> |
} |
934 |
> |
} |
935 |
|
else { |
1154 |
– |
ForkJoinPool p = pool; |
1155 |
– |
int a; // to inline CASes |
936 |
|
if (active) { |
937 |
< |
if (!UNSAFE.compareAndSwapInt |
938 |
< |
(p, poolRunStateOffset, a = p.runState, a - 1)) |
1159 |
< |
continue; // retry later |
1160 |
< |
active = false; // inactivate |
1161 |
< |
UNSAFE.putOrderedObject(this, currentStealOffset, ps); |
937 |
> |
active = false; |
938 |
> |
p.addActiveCount(-1); |
939 |
|
} |
940 |
|
if (p.isQuiescent()) { |
941 |
< |
active = true; // re-activate |
942 |
< |
do {} while (!UNSAFE.compareAndSwapInt |
943 |
< |
(p, poolRunStateOffset, a = p.runState, a+1)); |
1167 |
< |
return; |
941 |
> |
p.addActiveCount(1); |
942 |
> |
p.addQuiescerCount(-1); |
943 |
> |
break; |
944 |
|
} |
945 |
|
} |
946 |
|
} |
947 |
|
} |
948 |
|
|
949 |
|
// Unsafe mechanics |
950 |
< |
|
951 |
< |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
952 |
< |
private static final long spOffset = |
1177 |
< |
objectFieldOffset("sp", ForkJoinWorkerThread.class); |
1178 |
< |
private static final long runStateOffset = |
1179 |
< |
objectFieldOffset("runState", ForkJoinWorkerThread.class); |
1180 |
< |
private static final long currentJoinOffset = |
1181 |
< |
objectFieldOffset("currentJoin", ForkJoinWorkerThread.class); |
1182 |
< |
private static final long currentStealOffset = |
1183 |
< |
objectFieldOffset("currentSteal", ForkJoinWorkerThread.class); |
1184 |
< |
private static final long qBase = |
1185 |
< |
UNSAFE.arrayBaseOffset(ForkJoinTask[].class); |
1186 |
< |
private static final long poolRunStateOffset = // to inline CAS |
1187 |
< |
objectFieldOffset("runState", ForkJoinPool.class); |
1188 |
< |
|
1189 |
< |
private static final int qShift; |
950 |
> |
private static final sun.misc.Unsafe UNSAFE; |
951 |
> |
private static final long ABASE; |
952 |
> |
private static final int ASHIFT; |
953 |
|
|
954 |
|
static { |
955 |
< |
int s = UNSAFE.arrayIndexScale(ForkJoinTask[].class); |
1193 |
< |
if ((s & (s-1)) != 0) |
1194 |
< |
throw new Error("data type scale not a power of two"); |
1195 |
< |
qShift = 31 - Integer.numberOfLeadingZeros(s); |
1196 |
< |
MAXIMUM_QUEUE_CAPACITY = 1 << (31 - qShift); |
1197 |
< |
} |
1198 |
< |
|
1199 |
< |
private static long objectFieldOffset(String field, Class<?> klazz) { |
955 |
> |
int s; |
956 |
|
try { |
957 |
< |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
958 |
< |
} catch (NoSuchFieldException e) { |
959 |
< |
// Convert Exception to corresponding Error |
960 |
< |
NoSuchFieldError error = new NoSuchFieldError(field); |
961 |
< |
error.initCause(e); |
962 |
< |
throw error; |
957 |
> |
UNSAFE = getUnsafe(); |
958 |
> |
Class<?> a = ForkJoinTask[].class; |
959 |
> |
ABASE = UNSAFE.arrayBaseOffset(a); |
960 |
> |
s = UNSAFE.arrayIndexScale(a); |
961 |
> |
} catch (Exception e) { |
962 |
> |
throw new Error(e); |
963 |
|
} |
964 |
+ |
if ((s & (s-1)) != 0) |
965 |
+ |
throw new Error("data type scale not a power of two"); |
966 |
+ |
ASHIFT = 31 - Integer.numberOfLeadingZeros(s); |
967 |
|
} |
968 |
|
|
969 |
|
/** |