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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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*/ |
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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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* A thread that is internally managed by a ForkJoinPool to execute |
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* ForkJoinTasks. This class additionally provides public |
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* <tt>static</tt> methods accessing some basic scheduling and |
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* execution mechanics for the <em>current</em> |
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* ForkJoinWorkerThread. These methods may be invoked only from within |
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* other ForkJoinTask computations. Attempts to invoke in other |
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* contexts result in exceptions or errors including |
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* ClassCastException. These methods enable construction of |
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* special-purpose task classes, as well as specialized idioms |
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* occasionally useful in ForkJoinTask processing. |
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* |
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* <p>The form of supported static methods reflects the fact that |
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* worker threads may access and process tasks obtained in any of |
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* three ways. In preference order: <em>Local</em> tasks are processed |
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* in LIFO (newest first) order. <em>Stolen</em> tasks are obtained |
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* from other threads in FIFO (oldest first) order, only if there are |
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* no local tasks to run. <em>Submissions</em> form a FIFO queue |
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* common to the entire pool, and are started only if no other |
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* work is available. |
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* |
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* <p> 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 cleanup methods surrounding the main task |
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* processing loop. If you do create such a subclass, you will also |
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* need to supply a custom ForkJoinWorkerThreadFactory to use it in a |
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* ForkJoinPool. |
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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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* 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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* 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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* 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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* 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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* 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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* 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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* 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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* 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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* 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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// 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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* 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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*/ |
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private boolean active; |
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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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/** |
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* Seed for random number generator for choosing steal victims |
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*/ |
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private int randomVictimSeed; |
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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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* The last barrier event waited for |
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*/ |
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private long eventCount; |
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/** |
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* Creates a ForkJoinWorkerThread operating in the given pool. |
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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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this.pool = pool; |
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// remaining initialization deferred to onStart |
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} |
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// Access methods used by Pool |
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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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* 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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// 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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* 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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* 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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* 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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// Main queue methods |
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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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* 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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* 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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* 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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* Returns next task to pop. |
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*/ |
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private 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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} |
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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() { |
380 |
|
|
ForkJoinTask<?>[] oldQ = queue; |
381 |
|
|
int oldSize = oldQ.length; |
382 |
|
|
int newSize = oldSize << 1; |
383 |
|
|
if (newSize > MAXIMUM_QUEUE_CAPACITY) |
384 |
|
|
throw new RejectedExecutionException("Queue capacity exceeded"); |
385 |
|
|
ForkJoinTask<?>[] newQ = queue = new ForkJoinTask<?>[newSize]; |
386 |
|
|
|
387 |
|
|
int b = base; |
388 |
|
|
int bf = b + oldSize; |
389 |
|
|
int oldMask = oldSize - 1; |
390 |
|
|
int newMask = newSize - 1; |
391 |
|
|
do { |
392 |
|
|
int oldIndex = b & oldMask; |
393 |
|
|
ForkJoinTask<?> t = oldQ[oldIndex]; |
394 |
|
|
if (t != null && !casSlotNull(oldQ, oldIndex, t)) |
395 |
|
|
t = null; |
396 |
|
|
setSlot(newQ, b & newMask, t); |
397 |
|
|
} while (++b != bf); |
398 |
|
|
pool.signalIdleWorkers(false); |
399 |
|
|
} |
400 |
|
|
|
401 |
|
|
// Runstate management |
402 |
|
|
|
403 |
|
|
final boolean isShutdown() { return runState >= SHUTDOWN; } |
404 |
|
|
final boolean isTerminating() { return runState >= TERMINATING; } |
405 |
|
|
final boolean isTerminated() { return runState == TERMINATED; } |
406 |
|
|
final boolean shutdown() { return transitionRunStateTo(SHUTDOWN); } |
407 |
|
|
final boolean shutdownNow() { return transitionRunStateTo(TERMINATING); } |
408 |
|
|
|
409 |
|
|
/** |
410 |
|
|
* Transition to at least the given state. Return true if not |
411 |
|
|
* already at least given state. |
412 |
|
|
*/ |
413 |
|
|
private boolean transitionRunStateTo(int state) { |
414 |
|
|
for (;;) { |
415 |
|
|
int s = runState; |
416 |
|
|
if (s >= state) |
417 |
|
|
return false; |
418 |
|
|
if (_unsafe.compareAndSwapInt(this, runStateOffset, s, state)) |
419 |
|
|
return true; |
420 |
|
|
} |
421 |
|
|
} |
422 |
|
|
|
423 |
|
|
/** |
424 |
|
|
* Ensure status is active and if necessary adjust pool active count |
425 |
|
|
*/ |
426 |
|
|
final void activate() { |
427 |
|
|
if (!active) { |
428 |
|
|
active = true; |
429 |
|
|
pool.incrementActiveCount(); |
430 |
|
|
} |
431 |
|
|
} |
432 |
|
|
|
433 |
|
|
/** |
434 |
|
|
* Ensure status is inactive and if necessary adjust pool active count |
435 |
|
|
*/ |
436 |
|
|
final void inactivate() { |
437 |
|
|
if (active) { |
438 |
|
|
active = false; |
439 |
|
|
pool.decrementActiveCount(); |
440 |
|
|
} |
441 |
|
|
} |
442 |
|
|
|
443 |
|
|
// Lifecycle methods |
444 |
|
|
|
445 |
|
|
/** |
446 |
|
|
* Initializes internal state after construction but before |
447 |
|
|
* processing any tasks. If you override this method, you must |
448 |
|
|
* invoke super.onStart() at the beginning of the method. |
449 |
|
|
* Initialization requires care: Most fields must have legal |
450 |
|
|
* default values, to ensure that attempted accesses from other |
451 |
|
|
* threads work correctly even before this thread starts |
452 |
|
|
* processing tasks. |
453 |
|
|
*/ |
454 |
|
|
protected void onStart() { |
455 |
|
|
juRandomSeed = randomSeedGenerator.nextLong(); |
456 |
|
|
do;while((randomVictimSeed = nextRandomInt()) == 0); // must be nonzero |
457 |
|
|
if (queue == null) |
458 |
|
|
queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY]; |
459 |
|
|
|
460 |
|
|
// Heuristically allow one initial thread to warm up; others wait |
461 |
|
|
if (poolIndex < pool.getParallelism() - 1) { |
462 |
|
|
eventCount = pool.sync(this, 0); |
463 |
|
|
activate(); |
464 |
|
|
} |
465 |
|
|
} |
466 |
|
|
|
467 |
|
|
/** |
468 |
|
|
* Perform cleanup associated with termination of this worker |
469 |
|
|
* thread. If you override this method, you must invoke |
470 |
|
|
* super.onTermination at the end of the overridden method. |
471 |
|
|
* |
472 |
|
|
* @param exception the exception causing this thread to abort due |
473 |
|
|
* to an unrecoverable error, or null if completed normally. |
474 |
|
|
*/ |
475 |
|
|
protected void onTermination(Throwable exception) { |
476 |
|
|
try { |
477 |
|
|
clearLocalTasks(); |
478 |
|
|
inactivate(); |
479 |
|
|
cancelTasks(); |
480 |
|
|
} finally { |
481 |
|
|
terminate(exception); |
482 |
|
|
} |
483 |
|
|
} |
484 |
|
|
|
485 |
|
|
/** |
486 |
|
|
* Notify pool of termination and, if exception is nonnull, |
487 |
|
|
* rethrow it to trigger this thread's uncaughtExceptionHandler |
488 |
|
|
*/ |
489 |
|
|
private void terminate(Throwable exception) { |
490 |
|
|
transitionRunStateTo(TERMINATED); |
491 |
|
|
try { |
492 |
|
|
pool.workerTerminated(this); |
493 |
|
|
} finally { |
494 |
|
|
if (exception != null) |
495 |
|
|
ForkJoinTask.rethrowException(exception); |
496 |
|
|
} |
497 |
|
|
} |
498 |
|
|
|
499 |
|
|
/** |
500 |
|
|
* Run local tasks on exit from main. |
501 |
|
|
*/ |
502 |
|
|
private void clearLocalTasks() { |
503 |
|
|
while (base != sp && !pool.isTerminating()) { |
504 |
|
|
ForkJoinTask<?> t = popTask(); |
505 |
|
|
if (t != null) { |
506 |
|
|
activate(); // ensure active status |
507 |
|
|
t.quietlyExec(); |
508 |
|
|
} |
509 |
|
|
} |
510 |
|
|
} |
511 |
|
|
|
512 |
|
|
/** |
513 |
|
|
* Removes and cancels all tasks in queue. Can be called from any |
514 |
|
|
* thread. |
515 |
|
|
*/ |
516 |
|
|
final void cancelTasks() { |
517 |
|
|
while (base != sp) { |
518 |
|
|
ForkJoinTask<?> t = deqTask(); |
519 |
|
|
if (t != null) |
520 |
|
|
t.cancelIgnoreExceptions(); |
521 |
|
|
} |
522 |
|
|
} |
523 |
|
|
|
524 |
|
|
/** |
525 |
|
|
* This method is required to be public, but should never be |
526 |
|
|
* called explicitly. It performs the main run loop to execute |
527 |
|
|
* ForkJoinTasks. |
528 |
|
|
*/ |
529 |
|
|
public void run() { |
530 |
|
|
Throwable exception = null; |
531 |
|
|
try { |
532 |
|
|
onStart(); |
533 |
|
|
while (!isShutdown()) |
534 |
|
|
step(); |
535 |
|
|
} catch (Throwable ex) { |
536 |
|
|
exception = ex; |
537 |
|
|
} finally { |
538 |
|
|
onTermination(exception); |
539 |
|
|
} |
540 |
|
|
} |
541 |
|
|
|
542 |
|
|
/** |
543 |
|
|
* Main top-level action. |
544 |
|
|
*/ |
545 |
|
|
private void step() { |
546 |
|
|
ForkJoinTask<?> t = sp != base? popTask() : null; |
547 |
|
|
if (t != null || (t = scan(null, true)) != null) { |
548 |
|
|
activate(); |
549 |
|
|
t.quietlyExec(); |
550 |
|
|
} |
551 |
|
|
else { |
552 |
|
|
inactivate(); |
553 |
|
|
eventCount = pool.sync(this, eventCount); |
554 |
|
|
} |
555 |
|
|
} |
556 |
|
|
|
557 |
|
|
// scanning for and stealing tasks |
558 |
|
|
|
559 |
|
|
/** |
560 |
|
|
* Computes next value for random victim probe. Scans don't |
561 |
|
|
* require a very high quality generator, but also not a crummy |
562 |
|
|
* one. Marsaglia xor-shift is cheap and works well. |
563 |
|
|
* |
564 |
|
|
* This is currently unused, and manually inlined |
565 |
|
|
*/ |
566 |
|
|
private static int xorShift(int r) { |
567 |
|
|
r ^= r << 1; |
568 |
|
|
r ^= r >>> 3; |
569 |
|
|
r ^= r << 10; |
570 |
|
|
return r; |
571 |
|
|
} |
572 |
|
|
|
573 |
|
|
/** |
574 |
|
|
* Tries to steal a task from another worker and/or, if enabled, |
575 |
|
|
* submission queue. Starts at a random index of workers array, |
576 |
|
|
* and probes workers until finding one with non-empty queue or |
577 |
|
|
* finding that all are empty. It randomly selects the first n-1 |
578 |
|
|
* probes. If these are empty, it resorts to full circular |
579 |
|
|
* traversal, which is necessary to accurately set active status |
580 |
|
|
* by caller. Also restarts if pool barrier has tripped since last |
581 |
|
|
* scan, which forces refresh of workers array, in case barrier |
582 |
|
|
* was associated with resize. |
583 |
|
|
* |
584 |
|
|
* This method must be both fast and quiet -- usually avoiding |
585 |
|
|
* memory accesses that could disrupt cache sharing etc other than |
586 |
|
|
* those needed to check for and take tasks. This accounts for, |
587 |
|
|
* among other things, updating random seed in place without |
588 |
|
|
* storing it until exit. (Note that we only need to store it if |
589 |
|
|
* we found a task; otherwise it doesn't matter if we start at the |
590 |
|
|
* same place next time.) |
591 |
|
|
* |
592 |
|
|
* @param joinMe if non null; exit early if done |
593 |
|
|
* @param checkSubmissions true if OK to take submissions |
594 |
|
|
* @return a task, or null if none found |
595 |
|
|
*/ |
596 |
|
|
private ForkJoinTask<?> scan(ForkJoinTask<?> joinMe, |
597 |
|
|
boolean checkSubmissions) { |
598 |
|
|
ForkJoinPool p = pool; |
599 |
|
|
if (p == null) // Never null, but avoids |
600 |
|
|
return null; // implicit nullchecks below |
601 |
|
|
int r = randomVictimSeed; // extract once to keep scan quiet |
602 |
|
|
restart: // outer loop refreshes ws array |
603 |
|
|
while (joinMe == null || joinMe.status >= 0) { |
604 |
|
|
int mask; |
605 |
|
|
ForkJoinWorkerThread[] ws = p.workers; |
606 |
|
|
if (ws != null && (mask = ws.length - 1) > 0) { |
607 |
|
|
int probes = -mask; // use random index while negative |
608 |
|
|
int idx = r; |
609 |
|
|
for (;;) { |
610 |
|
|
ForkJoinWorkerThread v; |
611 |
|
|
// inlined xorshift to update seed |
612 |
|
|
r ^= r << 1; r ^= r >>> 3; r ^= r << 10; |
613 |
|
|
if ((v = ws[mask & idx]) != null && v.sp != v.base) { |
614 |
|
|
ForkJoinTask<?> t; |
615 |
|
|
activate(); |
616 |
|
|
if ((joinMe == null || joinMe.status >= 0) && |
617 |
|
|
(t = v.deqTask()) != null) { |
618 |
|
|
randomVictimSeed = r; |
619 |
|
|
++stealCount; |
620 |
|
|
return t; |
621 |
|
|
} |
622 |
|
|
continue restart; // restart on contention |
623 |
|
|
} |
624 |
|
|
if ((probes >> 1) <= mask) // n-1 random then circular |
625 |
|
|
idx = (probes++ < 0)? r : (idx + 1); |
626 |
|
|
else |
627 |
|
|
break; |
628 |
|
|
} |
629 |
|
|
} |
630 |
|
|
if (checkSubmissions && p.hasQueuedSubmissions()) { |
631 |
|
|
activate(); |
632 |
|
|
ForkJoinTask<?> t = p.pollSubmission(); |
633 |
|
|
if (t != null) |
634 |
|
|
return t; |
635 |
|
|
} |
636 |
|
|
else { |
637 |
|
|
long ec = eventCount; // restart on pool event |
638 |
|
|
if ((eventCount = p.getEventCount()) == ec) |
639 |
|
|
break; |
640 |
|
|
} |
641 |
|
|
} |
642 |
|
|
return null; |
643 |
|
|
} |
644 |
|
|
|
645 |
|
|
/** |
646 |
|
|
* Callback from pool.sync to rescan before blocking. If a |
647 |
|
|
* task is found, it is pushed so it can be executed upon return. |
648 |
|
|
* @return true if found and pushed a task |
649 |
|
|
*/ |
650 |
|
|
final boolean prescan() { |
651 |
|
|
ForkJoinTask<?> t = scan(null, true); |
652 |
|
|
if (t != null) { |
653 |
|
|
pushTask(t); |
654 |
|
|
return true; |
655 |
|
|
} |
656 |
|
|
else { |
657 |
|
|
inactivate(); |
658 |
|
|
return false; |
659 |
|
|
} |
660 |
|
|
} |
661 |
|
|
|
662 |
|
|
/** |
663 |
|
|
* Implements ForkJoinTask.helpJoin |
664 |
|
|
*/ |
665 |
|
|
final int helpJoinTask(ForkJoinTask<?> joinMe) { |
666 |
|
|
ForkJoinTask<?> t = null; |
667 |
|
|
int s; |
668 |
|
|
while ((s = joinMe.status) >= 0) { |
669 |
|
|
if (t == null) { |
670 |
|
|
if ((t = scan(joinMe, false)) == null) // block if no work |
671 |
|
|
return joinMe.awaitDone(this, false); |
672 |
|
|
// else recheck status before exec |
673 |
|
|
} |
674 |
|
|
else { |
675 |
|
|
t.quietlyExec(); |
676 |
|
|
t = null; |
677 |
|
|
} |
678 |
|
|
} |
679 |
|
|
if (t != null) // unsteal |
680 |
|
|
pushTask(t); |
681 |
|
|
return s; |
682 |
|
|
} |
683 |
|
|
|
684 |
|
|
// Support for public static and/or ForkJoinTask methods |
685 |
|
|
|
686 |
|
|
/** |
687 |
|
|
* Returns an estimate of the number of tasks in the queue. |
688 |
|
|
*/ |
689 |
|
|
final int getQueueSize() { |
690 |
|
|
int b = base; |
691 |
|
|
int n = sp - b; |
692 |
|
|
return n <= 0? 0 : n; // suppress momentarily negative values |
693 |
|
|
} |
694 |
|
|
|
695 |
|
|
/** |
696 |
|
|
* Runs one popped task, if available |
697 |
|
|
* @return true if ran a task |
698 |
|
|
*/ |
699 |
|
|
private boolean runLocalTask() { |
700 |
|
|
ForkJoinTask<?> t = popTask(); |
701 |
|
|
if (t == null) |
702 |
|
|
return false; |
703 |
|
|
t.quietlyExec(); |
704 |
|
|
return true; |
705 |
|
|
} |
706 |
|
|
|
707 |
|
|
/** |
708 |
|
|
* Pops or steals a task |
709 |
|
|
* @return task, or null if none available |
710 |
|
|
*/ |
711 |
|
|
private ForkJoinTask<?> getLocalOrStolenTask() { |
712 |
|
|
ForkJoinTask<?> t = popTask(); |
713 |
|
|
return t != null? t : scan(null, false); |
714 |
|
|
} |
715 |
|
|
|
716 |
|
|
/** |
717 |
|
|
* Runs a popped or stolen task, if available |
718 |
|
|
* @return true if ran a task |
719 |
|
|
*/ |
720 |
|
|
private boolean runLocalOrStolenTask() { |
721 |
|
|
ForkJoinTask<?> t = getLocalOrStolenTask(); |
722 |
|
|
if (t == null) |
723 |
|
|
return false; |
724 |
|
|
t.quietlyExec(); |
725 |
|
|
return true; |
726 |
|
|
} |
727 |
|
|
|
728 |
|
|
/** |
729 |
|
|
* Runs tasks until pool isQuiescent |
730 |
|
|
*/ |
731 |
|
|
final void helpQuiescePool() { |
732 |
|
|
activate(); |
733 |
|
|
for (;;) { |
734 |
|
|
if (!runLocalOrStolenTask()) { |
735 |
|
|
inactivate(); |
736 |
|
|
if (pool.isQuiescent()) { |
737 |
|
|
activate(); // re-activate on exit |
738 |
|
|
break; |
739 |
|
|
} |
740 |
|
|
} |
741 |
|
|
} |
742 |
|
|
} |
743 |
|
|
|
744 |
|
|
/** |
745 |
|
|
* Returns an estimate of the number of tasks, offset by a |
746 |
|
|
* function of number of idle workers. |
747 |
|
|
*/ |
748 |
|
|
final int getEstimatedSurplusTaskCount() { |
749 |
|
|
return (sp - base) - (pool.getIdleThreadCount() >>> 1); |
750 |
|
|
} |
751 |
|
|
|
752 |
|
|
// Public methods on current thread |
753 |
|
|
|
754 |
|
|
/** |
755 |
|
|
* Returns the pool hosting the current task execution. |
756 |
|
|
* @return the pool |
757 |
|
|
*/ |
758 |
|
|
public static ForkJoinPool getPool() { |
759 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())).pool; |
760 |
|
|
} |
761 |
|
|
|
762 |
|
|
/** |
763 |
|
|
* Returns the index number of the current worker thread in its |
764 |
|
|
* pool. The returned value ranges from zero to the maximum |
765 |
|
|
* number of threads (minus one) that have ever been created in |
766 |
|
|
* the pool. This method may be useful for applications that |
767 |
|
|
* track status or collect results per-worker rather than |
768 |
|
|
* per-task. |
769 |
|
|
* @return the index number. |
770 |
|
|
*/ |
771 |
|
|
public static int getPoolIndex() { |
772 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())).poolIndex; |
773 |
|
|
} |
774 |
|
|
|
775 |
|
|
/** |
776 |
|
|
* Returns an estimate of the number of tasks waiting to be run by |
777 |
|
|
* the current worker thread. This value may be useful for |
778 |
|
|
* heuristic decisions about whether to fork other tasks. |
779 |
|
|
* @return the number of tasks |
780 |
|
|
*/ |
781 |
|
|
public static int getLocalQueueSize() { |
782 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
783 |
|
|
getQueueSize(); |
784 |
|
|
} |
785 |
|
|
|
786 |
|
|
/** |
787 |
|
|
* Returns, but does not remove or execute, the next task locally |
788 |
|
|
* queued for execution by the current worker thread. There is no |
789 |
|
|
* guarantee that this task will be the next one actually returned |
790 |
|
|
* or executed from other polling or execution methods. |
791 |
|
|
* @return the next task or null if none |
792 |
|
|
*/ |
793 |
|
|
public static ForkJoinTask<?> peekLocalTask() { |
794 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())).peekTask(); |
795 |
|
|
} |
796 |
|
|
|
797 |
|
|
/** |
798 |
|
|
* Removes and returns, without executing, the next task queued |
799 |
|
|
* for execution in the current worker thread's local queue. |
800 |
|
|
* @return the next task to execute, or null if none |
801 |
|
|
*/ |
802 |
|
|
public static ForkJoinTask<?> pollLocalTask() { |
803 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())).popTask(); |
804 |
|
|
} |
805 |
|
|
|
806 |
|
|
/** |
807 |
|
|
* Execute the next task locally queued by the current worker, if |
808 |
|
|
* one is available. |
809 |
|
|
* @return true if a task was run; a false return indicates |
810 |
|
|
* that no task was available. |
811 |
|
|
*/ |
812 |
|
|
public static boolean executeLocalTask() { |
813 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
814 |
|
|
runLocalTask(); |
815 |
|
|
} |
816 |
|
|
|
817 |
|
|
/** |
818 |
|
|
* Removes and returns, without executing, the next task queued |
819 |
|
|
* for execution in the current worker thread's local queue or if |
820 |
|
|
* none, a task stolen from another worker, if one is available. |
821 |
|
|
* A null return does not necessarily imply that all tasks are |
822 |
|
|
* completed, only that there are currently none available. |
823 |
|
|
* @return the next task to execute, or null if none |
824 |
|
|
*/ |
825 |
|
|
public static ForkJoinTask<?> pollTask() { |
826 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
827 |
|
|
getLocalOrStolenTask(); |
828 |
|
|
} |
829 |
|
|
|
830 |
|
|
/** |
831 |
|
|
* Helps this program complete by processing a local or stolen |
832 |
|
|
* task, if one is available. This method may be useful when |
833 |
|
|
* several tasks are forked, and only one of them must be joined, |
834 |
|
|
* as in: |
835 |
|
|
* |
836 |
|
|
* <pre> |
837 |
|
|
* while (!t1.isDone() && !t2.isDone()) |
838 |
|
|
* ForkJoinWorkerThread.executeTask(); |
839 |
|
|
* </pre> |
840 |
|
|
* |
841 |
|
|
* @return true if a task was run; a false return indicates |
842 |
|
|
* that no task was available. |
843 |
|
|
*/ |
844 |
|
|
public static boolean executeTask() { |
845 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
846 |
|
|
runLocalOrStolenTask(); |
847 |
|
|
} |
848 |
|
|
|
849 |
|
|
// Per-worker exported random numbers |
850 |
|
|
|
851 |
|
|
// Same constants as java.util.Random |
852 |
|
|
final static long JURandomMultiplier = 0x5DEECE66DL; |
853 |
|
|
final static long JURandomAddend = 0xBL; |
854 |
|
|
final static long JURandomMask = (1L << 48) - 1; |
855 |
|
|
|
856 |
|
|
private final int nextJURandom(int bits) { |
857 |
|
|
long next = (juRandomSeed * JURandomMultiplier + JURandomAddend) & |
858 |
|
|
JURandomMask; |
859 |
|
|
juRandomSeed = next; |
860 |
|
|
return (int)(next >>> (48 - bits)); |
861 |
|
|
} |
862 |
|
|
|
863 |
|
|
private final int nextJURandomInt(int n) { |
864 |
|
|
if (n <= 0) |
865 |
|
|
throw new IllegalArgumentException("n must be positive"); |
866 |
|
|
int bits = nextJURandom(31); |
867 |
|
|
if ((n & -n) == n) |
868 |
|
|
return (int)((n * (long)bits) >> 31); |
869 |
|
|
|
870 |
|
|
for (;;) { |
871 |
|
|
int val = bits % n; |
872 |
|
|
if (bits - val + (n-1) >= 0) |
873 |
|
|
return val; |
874 |
|
|
bits = nextJURandom(31); |
875 |
|
|
} |
876 |
|
|
} |
877 |
|
|
|
878 |
|
|
private final long nextJURandomLong() { |
879 |
|
|
return ((long)(nextJURandom(32)) << 32) + nextJURandom(32); |
880 |
|
|
} |
881 |
|
|
|
882 |
|
|
private final long nextJURandomLong(long n) { |
883 |
|
|
if (n <= 0) |
884 |
|
|
throw new IllegalArgumentException("n must be positive"); |
885 |
|
|
long offset = 0; |
886 |
|
|
while (n >= Integer.MAX_VALUE) { // randomly pick half range |
887 |
|
|
int bits = nextJURandom(2); // 2nd bit for odd vs even split |
888 |
|
|
long half = n >>> 1; |
889 |
|
|
long nextn = ((bits & 2) == 0)? half : n - half; |
890 |
|
|
if ((bits & 1) == 0) |
891 |
|
|
offset += n - nextn; |
892 |
|
|
n = nextn; |
893 |
|
|
} |
894 |
|
|
return offset + nextJURandomInt((int)n); |
895 |
|
|
} |
896 |
|
|
|
897 |
|
|
private final double nextJURandomDouble() { |
898 |
|
|
return (((long)(nextJURandom(26)) << 27) + nextJURandom(27)) |
899 |
|
|
/ (double)(1L << 53); |
900 |
|
|
} |
901 |
|
|
|
902 |
|
|
/** |
903 |
|
|
* Returns a random integer using a per-worker random |
904 |
|
|
* number generator with the same properties as |
905 |
|
|
* {@link java.util.Random#nextInt} |
906 |
|
|
* @return the next pseudorandom, uniformly distributed {@code int} |
907 |
|
|
* value from this worker's random number generator's sequence |
908 |
|
|
*/ |
909 |
|
|
public static int nextRandomInt() { |
910 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
911 |
|
|
nextJURandom(32); |
912 |
|
|
} |
913 |
|
|
|
914 |
|
|
/** |
915 |
|
|
* Returns a random integer using a per-worker random |
916 |
|
|
* number generator with the same properties as |
917 |
|
|
* {@link java.util.Random#nextInt(int)} |
918 |
|
|
* @param n the bound on the random number to be returned. Must be |
919 |
|
|
* positive. |
920 |
|
|
* @return the next pseudorandom, uniformly distributed {@code int} |
921 |
|
|
* value between {@code 0} (inclusive) and {@code n} (exclusive) |
922 |
|
|
* from this worker's random number generator's sequence |
923 |
|
|
* @throws IllegalArgumentException if n is not positive |
924 |
|
|
*/ |
925 |
|
|
public static int nextRandomInt(int n) { |
926 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
927 |
|
|
nextJURandomInt(n); |
928 |
|
|
} |
929 |
|
|
|
930 |
|
|
/** |
931 |
|
|
* Returns a random long using a per-worker random |
932 |
|
|
* number generator with the same properties as |
933 |
|
|
* {@link java.util.Random#nextLong} |
934 |
|
|
* @return the next pseudorandom, uniformly distributed {@code long} |
935 |
|
|
* value from this worker's random number generator's sequence |
936 |
|
|
*/ |
937 |
|
|
public static long nextRandomLong() { |
938 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
939 |
|
|
nextJURandomLong(); |
940 |
|
|
} |
941 |
|
|
|
942 |
|
|
/** |
943 |
|
|
* Returns a random integer using a per-worker random |
944 |
|
|
* number generator with the same properties as |
945 |
|
|
* {@link java.util.Random#nextInt(int)} |
946 |
|
|
* @param n the bound on the random number to be returned. Must be |
947 |
|
|
* positive. |
948 |
|
|
* @return the next pseudorandom, uniformly distributed {@code int} |
949 |
|
|
* value between {@code 0} (inclusive) and {@code n} (exclusive) |
950 |
|
|
* from this worker's random number generator's sequence |
951 |
|
|
* @throws IllegalArgumentException if n is not positive |
952 |
|
|
*/ |
953 |
|
|
public static long nextRandomLong(long n) { |
954 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
955 |
|
|
nextJURandomLong(n); |
956 |
|
|
} |
957 |
|
|
|
958 |
|
|
/** |
959 |
|
|
* Returns a random double using a per-worker random |
960 |
|
|
* number generator with the same properties as |
961 |
|
|
* {@link java.util.Random#nextDouble} |
962 |
|
|
* @return the next pseudorandom, uniformly distributed {@code double} |
963 |
|
|
* value between {@code 0.0} and {@code 1.0} from this |
964 |
|
|
* worker's random number generator's sequence |
965 |
|
|
*/ |
966 |
|
|
public static double nextRandomDouble() { |
967 |
|
|
return ((ForkJoinWorkerThread)(Thread.currentThread())). |
968 |
|
|
nextJURandomDouble(); |
969 |
|
|
} |
970 |
|
|
|
971 |
|
|
// Temporary Unsafe mechanics for preliminary release |
972 |
|
|
|
973 |
|
|
static final Unsafe _unsafe; |
974 |
|
|
static final long baseOffset; |
975 |
|
|
static final long spOffset; |
976 |
|
|
static final long qBase; |
977 |
|
|
static final int qShift; |
978 |
|
|
static final long runStateOffset; |
979 |
|
|
static { |
980 |
|
|
try { |
981 |
|
|
if (ForkJoinWorkerThread.class.getClassLoader() != null) { |
982 |
|
|
Field f = Unsafe.class.getDeclaredField("theUnsafe"); |
983 |
|
|
f.setAccessible(true); |
984 |
|
|
_unsafe = (Unsafe)f.get(null); |
985 |
|
|
} |
986 |
|
|
else |
987 |
|
|
_unsafe = Unsafe.getUnsafe(); |
988 |
|
|
baseOffset = _unsafe.objectFieldOffset |
989 |
|
|
(ForkJoinWorkerThread.class.getDeclaredField("base")); |
990 |
|
|
spOffset = _unsafe.objectFieldOffset |
991 |
|
|
(ForkJoinWorkerThread.class.getDeclaredField("sp")); |
992 |
|
|
runStateOffset = _unsafe.objectFieldOffset |
993 |
|
|
(ForkJoinWorkerThread.class.getDeclaredField("runState")); |
994 |
|
|
qBase = _unsafe.arrayBaseOffset(ForkJoinTask[].class); |
995 |
|
|
int s = _unsafe.arrayIndexScale(ForkJoinTask[].class); |
996 |
|
|
if ((s & (s-1)) != 0) |
997 |
|
|
throw new Error("data type scale not a power of two"); |
998 |
|
|
qShift = 31 - Integer.numberOfLeadingZeros(s); |
999 |
|
|
} catch (Exception e) { |
1000 |
|
|
throw new RuntimeException("Could not initialize intrinsics", e); |
1001 |
|
|
} |
1002 |
|
|
} |
1003 |
|
|
} |