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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.*; |
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import java.util.concurrent.*; |
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import java.util.concurrent.atomic.*; |
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import java.util.concurrent.locks.*; |
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import sun.misc.Unsafe; |
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import java.lang.reflect.*; |
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|
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/** |
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* A thread managed by a {@link ForkJoinPool}. This class is |
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* subclassable solely for the sake of adding functionality -- there |
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* are no overridable methods dealing with scheduling or |
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* execution. However, you can override initialization and termination |
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* cleanup methods surrounding the main task processing loop. If you |
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* do create such a subclass, you will also need to supply a custom |
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* ForkJoinWorkerThreadFactory to use it in a ForkJoinPool. |
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* |
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* <p>This class also provides methods for generating per-thread |
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* random numbers, with the same properties as {@link |
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* java.util.Random} but with each generator isolated from those of |
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* other threads. |
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* A thread managed by a {@link ForkJoinPool}, which executes |
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* {@link ForkJoinTask}s. |
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* This class is subclassable solely for the sake of adding |
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* functionality -- there are no overridable methods dealing with |
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* scheduling or execution. However, you can override initialization |
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* and termination methods surrounding the main task processing loop. |
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* If you do create such a subclass, you will also need to supply a |
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* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to use it |
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* in a {@code ForkJoinPool}. |
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* |
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* @since 1.7 |
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* @author Doug Lea |
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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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* |
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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 nonnull |
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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 probablistic non-blockingness. If |
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* 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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* |
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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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* 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 effciently 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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* 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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*/ |
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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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* 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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* Maximum work-stealing queue array size. Must be less than or |
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* equal to 1 << 30 to ensure lack of index wraparound. |
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*/ |
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private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 30; |
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|
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/** |
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* Generator of seeds for per-thread random numbers. |
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*/ |
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private static final Random randomSeedGenerator = new Random(); |
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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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*/ |
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private ForkJoinTask<?>[] queue; |
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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, 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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* The pool this thread works in. |
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*/ |
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final ForkJoinPool pool; |
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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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*/ |
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int poolIndex; |
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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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*/ |
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private volatile int runState; |
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|
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// Runstate values. Order matters |
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private static final int RUNNING = 0; |
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private static final int SHUTDOWN = 1; |
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private static final int TERMINATING = 2; |
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private static final int TERMINATED = 3; |
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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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* blocking on the Pool Barrier. |
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* ForkJoinWorkerThreads are managed by ForkJoinPools and perform |
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* ForkJoinTasks. For explanation, see the internal documentation |
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* of class ForkJoinPool. |
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*/ |
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private boolean active; |
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|
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/** |
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* Number of steals, transferred to pool when idle |
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*/ |
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private int stealCount; |
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final ForkJoinPool.WorkQueue workQueue; // Work-stealing mechanics |
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final ForkJoinPool pool; // the pool this thread works in |
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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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* An initial name for a newly constructed worker, used until |
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* onStart can establish a useful name. This removes need to |
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* establish a name from worker startup path. |
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*/ |
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private int randomVictimSeed; |
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|
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/** |
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* Seed for embedded Jurandom |
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*/ |
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private long juRandomSeed; |
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|
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/** |
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* The last barrier event waited for |
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*/ |
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private long eventCount; |
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static final String provisionalName = "aForkJoinWorkerThread"; |
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|
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/** |
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* Creates a ForkJoinWorkerThread operating in the given pool. |
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* |
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* @param pool the pool this thread works in |
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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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if (pool == null) throw new NullPointerException(); |
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super(provisionalName); // bootstrap name |
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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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setDaemon(true); |
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this.pool = pool; |
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// remaining initialization deferred to onStart |
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pool.registerWorker(this.workQueue = new ForkJoinPool.WorkQueue |
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(pool, this, pool.localMode)); |
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} |
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|
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// public access methods |
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|
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/** |
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* Returns the pool hosting this thread |
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* Returns the pool hosting this thread. |
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* |
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* @return the pool |
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*/ |
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public ForkJoinPool getPool() { |
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* returned value ranges from zero to the maximum number of |
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* threads (minus one) that have ever been created in the pool. |
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* This method may be useful for applications that track status or |
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* collect results on a per-worker basis. |
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* @return the index number. |
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* collect results per-worker rather than per-task. |
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* |
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* @return the index number |
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*/ |
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public int getPoolIndex() { |
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return poolIndex; |
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} |
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|
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// Access methods used by Pool |
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|
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/** |
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* Get and clear steal count for accumulation by pool. Called |
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* only when known to be idle (in pool.sync and termination). |
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*/ |
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final int getAndClearStealCount() { |
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int sc = stealCount; |
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stealCount = 0; |
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return sc; |
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} |
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|
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/** |
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* Returns estimate of the number of tasks in the queue, without |
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* correcting for transient negative values |
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*/ |
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final int getRawQueueSize() { |
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return sp - base; |
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} |
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|
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// Intrinsics-based support for queue operations. |
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// Currently these three (setSp, setSlot, casSlotNull) are |
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// usually manually inlined to improve performance |
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|
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/** |
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* Sets sp in store-order. |
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*/ |
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private void setSp(int s) { |
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_unsafe.putOrderedInt(this, spOffset, s); |
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} |
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|
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/** |
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* Add in store-order the given task at given slot of q to |
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* null. Caller must ensure q is nonnull and index is in range. |
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*/ |
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private static void setSlot(ForkJoinTask<?>[] q, int i, |
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ForkJoinTask<?> t){ |
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_unsafe.putOrderedObject(q, (i << qShift) + qBase, t); |
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} |
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|
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/** |
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* CAS given slot of q to null. Caller must ensure q is nonnull |
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* and index is in range. |
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*/ |
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private static boolean casSlotNull(ForkJoinTask<?>[] q, int i, |
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ForkJoinTask<?> t) { |
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return _unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null); |
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} |
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|
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// Main queue methods |
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|
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/** |
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* Pushes a task. Called only by current thread. |
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* @param t the task. Caller must ensure nonnull |
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*/ |
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final void pushTask(ForkJoinTask<?> t) { |
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ForkJoinTask<?>[] q = queue; |
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int mask = q.length - 1; |
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int s = sp; |
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_unsafe.putOrderedObject(q, ((s & mask) << qShift) + qBase, t); |
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_unsafe.putOrderedInt(this, spOffset, ++s); |
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if ((s -= base) == 1) |
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pool.signalNonEmptyWorkerQueue(); |
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else if (s >= mask) |
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growQueue(); |
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} |
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|
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/** |
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* Tries to take a task from the base of the queue, failing if |
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* either empty or contended. |
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* @return a task, or null if none or contended. |
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*/ |
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private ForkJoinTask<?> deqTask() { |
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ForkJoinTask<?>[] q; |
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ForkJoinTask<?> t; |
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int i; |
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int b; |
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if (sp != (b = base) && |
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(q = queue) != null && // must read q after b |
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(t = q[i = (q.length - 1) & b]) != null && |
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_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) { |
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base = b + 1; |
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return t; |
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} |
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return null; |
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} |
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|
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/** |
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* Returns a popped task, or null if empty. Called only by |
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* current thread. |
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*/ |
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final ForkJoinTask<?> popTask() { |
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ForkJoinTask<?> t; |
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int i; |
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ForkJoinTask<?>[] q = queue; |
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int mask = q.length - 1; |
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int s = sp; |
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if (s != base && |
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(t = q[i = (s - 1) & mask]) != null && |
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_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) { |
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_unsafe.putOrderedInt(this, spOffset, s - 1); |
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return t; |
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} |
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return null; |
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} |
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|
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/** |
356 |
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* Specialized version of popTask to pop only if |
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* topmost element is the given task. Called only |
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* by current thread. |
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* @param t the task. Caller must ensure nonnull |
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*/ |
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final boolean unpushTask(ForkJoinTask<?> t) { |
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ForkJoinTask<?>[] q = queue; |
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int mask = q.length - 1; |
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int s = sp - 1; |
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if (_unsafe.compareAndSwapObject(q, ((s & mask) << qShift) + qBase, |
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t, null)) { |
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_unsafe.putOrderedInt(this, spOffset, s); |
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return true; |
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} |
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return false; |
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} |
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|
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/** |
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* Returns next task to pop. |
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*/ |
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final ForkJoinTask<?> peekTask() { |
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ForkJoinTask<?>[] q = queue; |
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return q == null? null : q[(sp - 1) & (q.length - 1)]; |
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return workQueue.poolIndex; |
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} |
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|
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/** |
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* Doubles queue array size. Transfers elements by emulating |
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* steals (deqs) from old array and placing, oldest first, into |
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* new array. |
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*/ |
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private void growQueue() { |
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ForkJoinTask<?>[] oldQ = queue; |
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int oldSize = oldQ.length; |
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int newSize = oldSize << 1; |
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if (newSize > MAXIMUM_QUEUE_CAPACITY) |
391 |
– |
throw new RejectedExecutionException("Queue capacity exceeded"); |
392 |
– |
ForkJoinTask<?>[] newQ = queue = new ForkJoinTask<?>[newSize]; |
393 |
– |
|
394 |
– |
int b = base; |
395 |
– |
int bf = b + oldSize; |
396 |
– |
int oldMask = oldSize - 1; |
397 |
– |
int newMask = newSize - 1; |
398 |
– |
do { |
399 |
– |
int oldIndex = b & oldMask; |
400 |
– |
ForkJoinTask<?> t = oldQ[oldIndex]; |
401 |
– |
if (t != null && !casSlotNull(oldQ, oldIndex, t)) |
402 |
– |
t = null; |
403 |
– |
setSlot(newQ, b & newMask, t); |
404 |
– |
} while (++b != bf); |
405 |
– |
pool.signalIdleWorkers(false); |
406 |
– |
} |
407 |
– |
|
408 |
– |
// Runstate management |
409 |
– |
|
410 |
– |
final boolean isShutdown() { return runState >= SHUTDOWN; } |
411 |
– |
final boolean isTerminating() { return runState >= TERMINATING; } |
412 |
– |
final boolean isTerminated() { return runState == TERMINATED; } |
413 |
– |
final boolean shutdown() { return transitionRunStateTo(SHUTDOWN); } |
414 |
– |
final boolean shutdownNow() { return transitionRunStateTo(TERMINATING); } |
415 |
– |
|
416 |
– |
/** |
417 |
– |
* Transition to at least the given state. Return true if not |
418 |
– |
* already at least given state. |
419 |
– |
*/ |
420 |
– |
private boolean transitionRunStateTo(int state) { |
421 |
– |
for (;;) { |
422 |
– |
int s = runState; |
423 |
– |
if (s >= state) |
424 |
– |
return false; |
425 |
– |
if (_unsafe.compareAndSwapInt(this, runStateOffset, s, state)) |
426 |
– |
return true; |
427 |
– |
} |
428 |
– |
} |
429 |
– |
|
430 |
– |
/** |
431 |
– |
* Ensure status is active and if necessary adjust pool active count |
432 |
– |
*/ |
433 |
– |
final void activate() { |
434 |
– |
if (!active) { |
435 |
– |
active = true; |
436 |
– |
pool.incrementActiveCount(); |
437 |
– |
} |
438 |
– |
} |
439 |
– |
|
440 |
– |
/** |
441 |
– |
* Ensure status is inactive and if necessary adjust pool active count |
442 |
– |
*/ |
443 |
– |
final void inactivate() { |
444 |
– |
if (active) { |
445 |
– |
active = false; |
446 |
– |
pool.decrementActiveCount(); |
447 |
– |
} |
448 |
– |
} |
449 |
– |
|
450 |
– |
// Lifecycle methods |
451 |
– |
|
452 |
– |
/** |
80 |
|
* Initializes internal state after construction but before |
81 |
|
* processing any tasks. If you override this method, you must |
82 |
< |
* invoke super.onStart() at the beginning of the method. |
82 |
> |
* invoke {@code super.onStart()} at the beginning of the method. |
83 |
|
* Initialization requires care: Most fields must have legal |
84 |
|
* default values, to ensure that attempted accesses from other |
85 |
|
* threads work correctly even before this thread starts |
86 |
|
* processing tasks. |
87 |
|
*/ |
88 |
|
protected void onStart() { |
89 |
< |
juRandomSeed = randomSeedGenerator.nextLong(); |
90 |
< |
do;while((randomVictimSeed = nextRandomInt()) == 0); // must be nonzero |
91 |
< |
if (queue == null) |
92 |
< |
queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY]; |
466 |
< |
|
467 |
< |
// Heuristically allow one initial thread to warm up; others wait |
468 |
< |
if (poolIndex < pool.getParallelism() - 1) { |
469 |
< |
eventCount = pool.sync(this, 0); |
470 |
< |
activate(); |
471 |
< |
} |
89 |
> |
String pref; // replace bootstrap name |
90 |
> |
if (provisionalName.equals(getName()) && |
91 |
> |
(pref = pool.workerNamePrefix) != null) |
92 |
> |
setName(pref.concat(Long.toString(getId()))); |
93 |
|
} |
94 |
|
|
95 |
|
/** |
96 |
< |
* Perform cleanup associated with termination of this worker |
96 |
> |
* Performs cleanup associated with termination of this worker |
97 |
|
* thread. If you override this method, you must invoke |
98 |
< |
* super.onTermination at the end of the overridden method. |
98 |
> |
* {@code super.onTermination} at the end of the overridden method. |
99 |
|
* |
100 |
|
* @param exception the exception causing this thread to abort due |
101 |
< |
* to an unrecoverable error, or null if completed normally. |
101 |
> |
* to an unrecoverable error, or {@code null} if completed normally |
102 |
|
*/ |
103 |
|
protected void onTermination(Throwable exception) { |
483 |
– |
try { |
484 |
– |
clearLocalTasks(); |
485 |
– |
inactivate(); |
486 |
– |
cancelTasks(); |
487 |
– |
} finally { |
488 |
– |
terminate(exception); |
489 |
– |
} |
490 |
– |
} |
491 |
– |
|
492 |
– |
/** |
493 |
– |
* Notify pool of termination and, if exception is nonnull, |
494 |
– |
* rethrow it to trigger this thread's uncaughtExceptionHandler |
495 |
– |
*/ |
496 |
– |
private void terminate(Throwable exception) { |
497 |
– |
transitionRunStateTo(TERMINATED); |
498 |
– |
try { |
499 |
– |
pool.workerTerminated(this); |
500 |
– |
} finally { |
501 |
– |
if (exception != null) |
502 |
– |
ForkJoinTask.rethrowException(exception); |
503 |
– |
} |
504 |
– |
} |
505 |
– |
|
506 |
– |
/** |
507 |
– |
* Run local tasks on exit from main. |
508 |
– |
*/ |
509 |
– |
private void clearLocalTasks() { |
510 |
– |
while (base != sp && !pool.isTerminating()) { |
511 |
– |
ForkJoinTask<?> t = popTask(); |
512 |
– |
if (t != null) { |
513 |
– |
activate(); // ensure active status |
514 |
– |
t.quietlyExec(); |
515 |
– |
} |
516 |
– |
} |
517 |
– |
} |
518 |
– |
|
519 |
– |
/** |
520 |
– |
* Removes and cancels all tasks in queue. Can be called from any |
521 |
– |
* thread. |
522 |
– |
*/ |
523 |
– |
final void cancelTasks() { |
524 |
– |
while (base != sp) { |
525 |
– |
ForkJoinTask<?> t = deqTask(); |
526 |
– |
if (t != null) |
527 |
– |
t.cancelIgnoringExceptions(); |
528 |
– |
} |
104 |
|
} |
105 |
|
|
106 |
|
/** |
107 |
|
* This method is required to be public, but should never be |
108 |
|
* called explicitly. It performs the main run loop to execute |
109 |
< |
* ForkJoinTasks. |
109 |
> |
* {@link ForkJoinTask}s. |
110 |
|
*/ |
111 |
|
public void run() { |
112 |
|
Throwable exception = null; |
113 |
|
try { |
114 |
|
onStart(); |
115 |
< |
while (!isShutdown()) |
541 |
< |
step(); |
115 |
> |
pool.runWorker(workQueue); |
116 |
|
} catch (Throwable ex) { |
117 |
|
exception = ex; |
118 |
|
} finally { |
119 |
< |
onTermination(exception); |
120 |
< |
} |
121 |
< |
} |
122 |
< |
|
123 |
< |
/** |
124 |
< |
* Main top-level action. |
125 |
< |
*/ |
552 |
< |
private void step() { |
553 |
< |
ForkJoinTask<?> t = sp != base? popTask() : null; |
554 |
< |
if (t != null || (t = scan(null, true)) != null) { |
555 |
< |
activate(); |
556 |
< |
t.quietlyExec(); |
557 |
< |
} |
558 |
< |
else { |
559 |
< |
inactivate(); |
560 |
< |
eventCount = pool.sync(this, eventCount); |
561 |
< |
} |
562 |
< |
} |
563 |
< |
|
564 |
< |
// scanning for and stealing tasks |
565 |
< |
|
566 |
< |
/** |
567 |
< |
* Computes next value for random victim probe. Scans don't |
568 |
< |
* require a very high quality generator, but also not a crummy |
569 |
< |
* one. Marsaglia xor-shift is cheap and works well. |
570 |
< |
* |
571 |
< |
* This is currently unused, and manually inlined |
572 |
< |
*/ |
573 |
< |
private static int xorShift(int r) { |
574 |
< |
r ^= r << 1; |
575 |
< |
r ^= r >>> 3; |
576 |
< |
r ^= r << 10; |
577 |
< |
return r; |
578 |
< |
} |
579 |
< |
|
580 |
< |
/** |
581 |
< |
* Tries to steal a task from another worker and/or, if enabled, |
582 |
< |
* submission queue. Starts at a random index of workers array, |
583 |
< |
* and probes workers until finding one with non-empty queue or |
584 |
< |
* finding that all are empty. It randomly selects the first n-1 |
585 |
< |
* probes. If these are empty, it resorts to full circular |
586 |
< |
* traversal, which is necessary to accurately set active status |
587 |
< |
* by caller. Also restarts if pool barrier has tripped since last |
588 |
< |
* scan, which forces refresh of workers array, in case barrier |
589 |
< |
* was associated with resize. |
590 |
< |
* |
591 |
< |
* This method must be both fast and quiet -- usually avoiding |
592 |
< |
* memory accesses that could disrupt cache sharing etc other than |
593 |
< |
* those needed to check for and take tasks. This accounts for, |
594 |
< |
* among other things, updating random seed in place without |
595 |
< |
* storing it until exit. (Note that we only need to store it if |
596 |
< |
* we found a task; otherwise it doesn't matter if we start at the |
597 |
< |
* same place next time.) |
598 |
< |
* |
599 |
< |
* @param joinMe if non null; exit early if done |
600 |
< |
* @param checkSubmissions true if OK to take submissions |
601 |
< |
* @return a task, or null if none found |
602 |
< |
*/ |
603 |
< |
private ForkJoinTask<?> scan(ForkJoinTask<?> joinMe, |
604 |
< |
boolean checkSubmissions) { |
605 |
< |
ForkJoinPool p = pool; |
606 |
< |
if (p == null) // Never null, but avoids |
607 |
< |
return null; // implicit nullchecks below |
608 |
< |
int r = randomVictimSeed; // extract once to keep scan quiet |
609 |
< |
restart: // outer loop refreshes ws array |
610 |
< |
while (joinMe == null || joinMe.status >= 0) { |
611 |
< |
int mask; |
612 |
< |
ForkJoinWorkerThread[] ws = p.workers; |
613 |
< |
if (ws != null && (mask = ws.length - 1) > 0) { |
614 |
< |
int probes = -mask; // use random index while negative |
615 |
< |
int idx = r; |
616 |
< |
for (;;) { |
617 |
< |
ForkJoinWorkerThread v; |
618 |
< |
// inlined xorshift to update seed |
619 |
< |
r ^= r << 1; r ^= r >>> 3; r ^= r << 10; |
620 |
< |
if ((v = ws[mask & idx]) != null && v.sp != v.base) { |
621 |
< |
ForkJoinTask<?> t; |
622 |
< |
activate(); |
623 |
< |
if ((joinMe == null || joinMe.status >= 0) && |
624 |
< |
(t = v.deqTask()) != null) { |
625 |
< |
randomVictimSeed = r; |
626 |
< |
++stealCount; |
627 |
< |
return t; |
628 |
< |
} |
629 |
< |
continue restart; // restart on contention |
630 |
< |
} |
631 |
< |
if ((probes >> 1) <= mask) // n-1 random then circular |
632 |
< |
idx = (probes++ < 0)? r : (idx + 1); |
633 |
< |
else |
634 |
< |
break; |
635 |
< |
} |
636 |
< |
} |
637 |
< |
if (checkSubmissions && p.hasQueuedSubmissions()) { |
638 |
< |
activate(); |
639 |
< |
ForkJoinTask<?> t = p.pollSubmission(); |
640 |
< |
if (t != null) |
641 |
< |
return t; |
642 |
< |
} |
643 |
< |
else { |
644 |
< |
long ec = eventCount; // restart on pool event |
645 |
< |
if ((eventCount = p.getEventCount()) == ec) |
646 |
< |
break; |
647 |
< |
} |
648 |
< |
} |
649 |
< |
return null; |
650 |
< |
} |
651 |
< |
|
652 |
< |
/** |
653 |
< |
* Callback from pool.sync to rescan before blocking. If a |
654 |
< |
* task is found, it is pushed so it can be executed upon return. |
655 |
< |
* @return true if found and pushed a task |
656 |
< |
*/ |
657 |
< |
final boolean prescan() { |
658 |
< |
ForkJoinTask<?> t = scan(null, true); |
659 |
< |
if (t != null) { |
660 |
< |
pushTask(t); |
661 |
< |
return true; |
662 |
< |
} |
663 |
< |
else { |
664 |
< |
inactivate(); |
665 |
< |
return false; |
666 |
< |
} |
667 |
< |
} |
668 |
< |
|
669 |
< |
// Support for ForkJoinTask methods |
670 |
< |
|
671 |
< |
/** |
672 |
< |
* Scan, returning early if joinMe done |
673 |
< |
*/ |
674 |
< |
final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) { |
675 |
< |
ForkJoinTask<?> t = scan(joinMe, false); |
676 |
< |
if (t != null && joinMe.status < 0 && sp == base) { |
677 |
< |
pushTask(t); // unsteal if done and this task would be stealable |
678 |
< |
t = null; |
679 |
< |
} |
680 |
< |
return t; |
681 |
< |
} |
682 |
< |
|
683 |
< |
/** |
684 |
< |
* Pops or steals a task |
685 |
< |
* @return task, or null if none available |
686 |
< |
*/ |
687 |
< |
final ForkJoinTask<?> pollLocalOrStolenTask() { |
688 |
< |
ForkJoinTask<?> t; |
689 |
< |
return (t = popTask()) == null? scan(null, false) : t; |
690 |
< |
} |
691 |
< |
|
692 |
< |
/** |
693 |
< |
* Runs tasks until pool isQuiescent |
694 |
< |
*/ |
695 |
< |
final void helpQuiescePool() { |
696 |
< |
for (;;) { |
697 |
< |
ForkJoinTask<?> t = pollLocalOrStolenTask(); |
698 |
< |
if (t != null) { |
699 |
< |
activate(); |
700 |
< |
t.quietlyExec(); |
701 |
< |
} |
702 |
< |
else { |
703 |
< |
inactivate(); |
704 |
< |
if (pool.isQuiescent()) { |
705 |
< |
activate(); // re-activate on exit |
706 |
< |
break; |
707 |
< |
} |
708 |
< |
} |
709 |
< |
} |
710 |
< |
} |
711 |
< |
|
712 |
< |
/** |
713 |
< |
* Returns an estimate of the number of tasks in the queue. |
714 |
< |
*/ |
715 |
< |
final int getQueueSize() { |
716 |
< |
int n = sp - base; |
717 |
< |
return n <= 0? 0 : n; // suppress momentarily negative values |
718 |
< |
} |
719 |
< |
|
720 |
< |
/** |
721 |
< |
* Returns an estimate of the number of tasks, offset by a |
722 |
< |
* function of number of idle workers. |
723 |
< |
*/ |
724 |
< |
final int getEstimatedSurplusTaskCount() { |
725 |
< |
// The halving approximates weighting idle vs non-idle workers |
726 |
< |
return (sp - base) - (pool.getIdleThreadCount() >>> 1); |
727 |
< |
} |
728 |
< |
|
729 |
< |
// Per-worker exported random numbers |
730 |
< |
|
731 |
< |
// Same constants as java.util.Random |
732 |
< |
final static long JURandomMultiplier = 0x5DEECE66DL; |
733 |
< |
final static long JURandomAddend = 0xBL; |
734 |
< |
final static long JURandomMask = (1L << 48) - 1; |
735 |
< |
|
736 |
< |
private final int nextJURandom(int bits) { |
737 |
< |
long next = (juRandomSeed * JURandomMultiplier + JURandomAddend) & |
738 |
< |
JURandomMask; |
739 |
< |
juRandomSeed = next; |
740 |
< |
return (int)(next >>> (48 - bits)); |
741 |
< |
} |
742 |
< |
|
743 |
< |
private final int nextJURandomInt(int n) { |
744 |
< |
if (n <= 0) |
745 |
< |
throw new IllegalArgumentException("n must be positive"); |
746 |
< |
int bits = nextJURandom(31); |
747 |
< |
if ((n & -n) == n) |
748 |
< |
return (int)((n * (long)bits) >> 31); |
749 |
< |
|
750 |
< |
for (;;) { |
751 |
< |
int val = bits % n; |
752 |
< |
if (bits - val + (n-1) >= 0) |
753 |
< |
return val; |
754 |
< |
bits = nextJURandom(31); |
755 |
< |
} |
756 |
< |
} |
757 |
< |
|
758 |
< |
private final long nextJURandomLong() { |
759 |
< |
return ((long)(nextJURandom(32)) << 32) + nextJURandom(32); |
760 |
< |
} |
761 |
< |
|
762 |
< |
private final long nextJURandomLong(long n) { |
763 |
< |
if (n <= 0) |
764 |
< |
throw new IllegalArgumentException("n must be positive"); |
765 |
< |
long offset = 0; |
766 |
< |
while (n >= Integer.MAX_VALUE) { // randomly pick half range |
767 |
< |
int bits = nextJURandom(2); // 2nd bit for odd vs even split |
768 |
< |
long half = n >>> 1; |
769 |
< |
long nextn = ((bits & 2) == 0)? half : n - half; |
770 |
< |
if ((bits & 1) == 0) |
771 |
< |
offset += n - nextn; |
772 |
< |
n = nextn; |
773 |
< |
} |
774 |
< |
return offset + nextJURandomInt((int)n); |
775 |
< |
} |
776 |
< |
|
777 |
< |
private final double nextJURandomDouble() { |
778 |
< |
return (((long)(nextJURandom(26)) << 27) + nextJURandom(27)) |
779 |
< |
/ (double)(1L << 53); |
780 |
< |
} |
781 |
< |
|
782 |
< |
/** |
783 |
< |
* Returns a random integer using a per-worker random |
784 |
< |
* number generator with the same properties as |
785 |
< |
* {@link java.util.Random#nextInt} |
786 |
< |
* @return the next pseudorandom, uniformly distributed {@code int} |
787 |
< |
* value from this worker's random number generator's sequence |
788 |
< |
*/ |
789 |
< |
public static int nextRandomInt() { |
790 |
< |
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
791 |
< |
nextJURandom(32); |
792 |
< |
} |
793 |
< |
|
794 |
< |
/** |
795 |
< |
* Returns a random integer using a per-worker random |
796 |
< |
* number generator with the same properties as |
797 |
< |
* {@link java.util.Random#nextInt(int)} |
798 |
< |
* @param n the bound on the random number to be returned. Must be |
799 |
< |
* positive. |
800 |
< |
* @return the next pseudorandom, uniformly distributed {@code int} |
801 |
< |
* value between {@code 0} (inclusive) and {@code n} (exclusive) |
802 |
< |
* from this worker's random number generator's sequence |
803 |
< |
* @throws IllegalArgumentException if n is not positive |
804 |
< |
*/ |
805 |
< |
public static int nextRandomInt(int n) { |
806 |
< |
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
807 |
< |
nextJURandomInt(n); |
808 |
< |
} |
809 |
< |
|
810 |
< |
/** |
811 |
< |
* Returns a random long using a per-worker random |
812 |
< |
* number generator with the same properties as |
813 |
< |
* {@link java.util.Random#nextLong} |
814 |
< |
* @return the next pseudorandom, uniformly distributed {@code long} |
815 |
< |
* value from this worker's random number generator's sequence |
816 |
< |
*/ |
817 |
< |
public static long nextRandomLong() { |
818 |
< |
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
819 |
< |
nextJURandomLong(); |
820 |
< |
} |
821 |
< |
|
822 |
< |
/** |
823 |
< |
* Returns a random integer using a per-worker random |
824 |
< |
* number generator with the same properties as |
825 |
< |
* {@link java.util.Random#nextInt(int)} |
826 |
< |
* @param n the bound on the random number to be returned. Must be |
827 |
< |
* positive. |
828 |
< |
* @return the next pseudorandom, uniformly distributed {@code int} |
829 |
< |
* value between {@code 0} (inclusive) and {@code n} (exclusive) |
830 |
< |
* from this worker's random number generator's sequence |
831 |
< |
* @throws IllegalArgumentException if n is not positive |
832 |
< |
*/ |
833 |
< |
public static long nextRandomLong(long n) { |
834 |
< |
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
835 |
< |
nextJURandomLong(n); |
836 |
< |
} |
837 |
< |
|
838 |
< |
/** |
839 |
< |
* Returns a random double using a per-worker random |
840 |
< |
* number generator with the same properties as |
841 |
< |
* {@link java.util.Random#nextDouble} |
842 |
< |
* @return the next pseudorandom, uniformly distributed {@code double} |
843 |
< |
* value between {@code 0.0} and {@code 1.0} from this |
844 |
< |
* worker's random number generator's sequence |
845 |
< |
*/ |
846 |
< |
public static double nextRandomDouble() { |
847 |
< |
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
848 |
< |
nextJURandomDouble(); |
849 |
< |
} |
850 |
< |
|
851 |
< |
// Temporary Unsafe mechanics for preliminary release |
852 |
< |
|
853 |
< |
static final Unsafe _unsafe; |
854 |
< |
static final long baseOffset; |
855 |
< |
static final long spOffset; |
856 |
< |
static final long qBase; |
857 |
< |
static final int qShift; |
858 |
< |
static final long runStateOffset; |
859 |
< |
static { |
860 |
< |
try { |
861 |
< |
if (ForkJoinWorkerThread.class.getClassLoader() != null) { |
862 |
< |
Field f = Unsafe.class.getDeclaredField("theUnsafe"); |
863 |
< |
f.setAccessible(true); |
864 |
< |
_unsafe = (Unsafe)f.get(null); |
119 |
> |
try { |
120 |
> |
onTermination(exception); |
121 |
> |
} catch (Throwable ex) { |
122 |
> |
if (exception == null) |
123 |
> |
exception = ex; |
124 |
> |
} finally { |
125 |
> |
pool.deregisterWorker(this, exception); |
126 |
|
} |
866 |
– |
else |
867 |
– |
_unsafe = Unsafe.getUnsafe(); |
868 |
– |
baseOffset = _unsafe.objectFieldOffset |
869 |
– |
(ForkJoinWorkerThread.class.getDeclaredField("base")); |
870 |
– |
spOffset = _unsafe.objectFieldOffset |
871 |
– |
(ForkJoinWorkerThread.class.getDeclaredField("sp")); |
872 |
– |
runStateOffset = _unsafe.objectFieldOffset |
873 |
– |
(ForkJoinWorkerThread.class.getDeclaredField("runState")); |
874 |
– |
qBase = _unsafe.arrayBaseOffset(ForkJoinTask[].class); |
875 |
– |
int s = _unsafe.arrayIndexScale(ForkJoinTask[].class); |
876 |
– |
if ((s & (s-1)) != 0) |
877 |
– |
throw new Error("data type scale not a power of two"); |
878 |
– |
qShift = 31 - Integer.numberOfLeadingZeros(s); |
879 |
– |
} catch (Exception e) { |
880 |
– |
throw new RuntimeException("Could not initialize intrinsics", e); |
127 |
|
} |
128 |
|
} |
129 |
|
} |