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8019481: Sync misc j.u.c classes from 166 to tl

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Reviewed-by: martin
This commit is contained in:
Doug Lea 2013-07-03 11:58:10 +02:00 committed by Paul Sandoz
parent efb561f632
commit 1001452ba9
8 changed files with 600 additions and 612 deletions
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4
jdk/src/share/classes/java/util/concurrent/BrokenBarrierException.java
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@ -49,13 +49,13 @@ public class BrokenBarrierException extends Exception {
private static final long serialVersionUID = 7117394618823254244L;
/**
* Constructs a <tt>BrokenBarrierException</tt> with no specified detail
* Constructs a {@code BrokenBarrierException} with no specified detail
* message.
*/
public BrokenBarrierException() {}
/**
* Constructs a <tt>BrokenBarrierException</tt> with the specified
* Constructs a {@code BrokenBarrierException} with the specified
* detail message.
*
* @param message the detail message

26
jdk/src/share/classes/java/util/concurrent/CountDownLatch.java
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@ -92,15 +92,15 @@ import java.util.concurrent.locks.AbstractQueuedSynchronizer;
* private final CountDownLatch startSignal;
* private final CountDownLatch doneSignal;
* Worker(CountDownLatch startSignal, CountDownLatch doneSignal) {
* this.startSignal = startSignal;
* this.doneSignal = doneSignal;
* this.startSignal = startSignal;
* this.doneSignal = doneSignal;
* }
* public void run() {
* try {
* startSignal.await();
* doWork();
* doneSignal.countDown();
* } catch (InterruptedException ex) {} // return;
* try {
* startSignal.await();
* doWork();
* doneSignal.countDown();
* } catch (InterruptedException ex) {} // return;
* }
*
* void doWork() { ... }
@ -130,14 +130,14 @@ import java.util.concurrent.locks.AbstractQueuedSynchronizer;
* private final CountDownLatch doneSignal;
* private final int i;
* WorkerRunnable(CountDownLatch doneSignal, int i) {
* this.doneSignal = doneSignal;
* this.i = i;
* this.doneSignal = doneSignal;
* this.i = i;
* }
* public void run() {
* try {
* doWork(i);
* doneSignal.countDown();
* } catch (InterruptedException ex) {} // return;
* try {
* doWork(i);
* doneSignal.countDown();
* } catch (InterruptedException ex) {} // return;
* }
*
* void doWork() { ... }

59
jdk/src/share/classes/java/util/concurrent/CyclicBarrier.java
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@ -45,14 +45,14 @@ import java.util.concurrent.locks.ReentrantLock;
* <em>cyclic</em> because it can be re-used after the waiting threads
* are released.
*
* <p>A <tt>CyclicBarrier</tt> supports an optional {@link Runnable} command
* <p>A {@code CyclicBarrier} supports an optional {@link Runnable} command
* that is run once per barrier point, after the last thread in the party
* arrives, but before any threads are released.
* This <em>barrier action</em> is useful
* for updating shared-state before any of the parties continue.
*
* <p><b>Sample usage:</b> Here is an example of
* using a barrier in a parallel decomposition design:
* <p><b>Sample usage:</b> Here is an example of using a barrier in a
* parallel decomposition design:
*
* <pre> {@code
* class Solver {
@ -81,16 +81,20 @@ import java.util.concurrent.locks.ReentrantLock;
* public Solver(float[][] matrix) {
* data = matrix;
* N = matrix.length;
* barrier = new CyclicBarrier(N,
* new Runnable() {
* public void run() {
* mergeRows(...);
* }
* });
* for (int i = 0; i < N; ++i)
* new Thread(new Worker(i)).start();
* Runnable barrierAction =
* new Runnable() { public void run() { mergeRows(...); }};
* barrier = new CyclicBarrier(N, barrierAction);
*
* waitUntilDone();
* List<Thread> threads = new ArrayList<Thread>(N);
* for (int i = 0; i < N; i++) {
* Thread thread = new Thread(new Worker(i));
* threads.add(thread);
* thread.start();
* }
*
* // wait until done
* for (Thread thread : threads)
* thread.join();
* }
* }}</pre>
*
@ -98,8 +102,8 @@ import java.util.concurrent.locks.ReentrantLock;
* barrier until all rows have been processed. When all rows are processed
* the supplied {@link Runnable} barrier action is executed and merges the
* rows. If the merger
* determines that a solution has been found then <tt>done()</tt> will return
* <tt>true</tt> and each worker will terminate.
* determines that a solution has been found then {@code done()} will return
* {@code true} and each worker will terminate.
*
* <p>If the barrier action does not rely on the parties being suspended when
* it is executed, then any of the threads in the party could execute that
@ -112,7 +116,7 @@ import java.util.concurrent.locks.ReentrantLock;
* // log the completion of this iteration
* }}</pre>
*
* <p>The <tt>CyclicBarrier</tt> uses an all-or-none breakage model
* <p>The {@code CyclicBarrier} uses an all-or-none breakage model
* for failed synchronization attempts: If a thread leaves a barrier
* point prematurely because of interruption, failure, or timeout, all
* other threads waiting at that barrier point will also leave
@ -139,7 +143,7 @@ public class CyclicBarrier {
* is reset. There can be many generations associated with threads
* using the barrier - due to the non-deterministic way the lock
* may be allocated to waiting threads - but only one of these
* can be active at a time (the one to which <tt>count</tt> applies)
* can be active at a time (the one to which {@code count} applies)
* and all the rest are either broken or tripped.
* There need not be an active generation if there has been a break
* but no subsequent reset.
@ -259,7 +263,7 @@ public class CyclicBarrier {
}
/**
* Creates a new <tt>CyclicBarrier</tt> that will trip when the
* Creates a new {@code CyclicBarrier} that will trip when the
* given number of parties (threads) are waiting upon it, and which
* will execute the given barrier action when the barrier is tripped,
* performed by the last thread entering the barrier.
@ -278,7 +282,7 @@ public class CyclicBarrier {
}
/**
* Creates a new <tt>CyclicBarrier</tt> that will trip when the
* Creates a new {@code CyclicBarrier} that will trip when the
* given number of parties (threads) are waiting upon it, and
* does not perform a predefined action when the barrier is tripped.
*
@ -301,7 +305,7 @@ public class CyclicBarrier {
/**
* Waits until all {@linkplain #getParties parties} have invoked
* <tt>await</tt> on this barrier.
* {@code await} on this barrier.
*
* <p>If the current thread is not the last to arrive then it is
* disabled for thread scheduling purposes and lies dormant until
@ -326,7 +330,7 @@ public class CyclicBarrier {
*
* <p>If the barrier is {@link #reset} while any thread is waiting,
* or if the barrier {@linkplain #isBroken is broken} when
* <tt>await</tt> is invoked, or while any thread is waiting, then
* {@code await} is invoked, or while any thread is waiting, then
* {@link BrokenBarrierException} is thrown.
*
* <p>If any thread is {@linkplain Thread#interrupt interrupted} while waiting,
@ -343,7 +347,7 @@ public class CyclicBarrier {
* the broken state.
*
* @return the arrival index of the current thread, where index
* <tt>{@link #getParties()} - 1</tt> indicates the first
* {@code getParties() - 1} indicates the first
* to arrive and zero indicates the last to arrive
* @throws InterruptedException if the current thread was interrupted
* while waiting
@ -351,7 +355,7 @@ public class CyclicBarrier {
* interrupted or timed out while the current thread was
* waiting, or the barrier was reset, or the barrier was
* broken when {@code await} was called, or the barrier
* action (if present) failed due an exception.
* action (if present) failed due to an exception
*/
public int await() throws InterruptedException, BrokenBarrierException {
try {
@ -363,7 +367,7 @@ public class CyclicBarrier {
/**
* Waits until all {@linkplain #getParties parties} have invoked
* <tt>await</tt> on this barrier, or the specified waiting time elapses.
* {@code await} on this barrier, or the specified waiting time elapses.
*
* <p>If the current thread is not the last to arrive then it is
* disabled for thread scheduling purposes and lies dormant until
@ -393,7 +397,7 @@ public class CyclicBarrier {
*
* <p>If the barrier is {@link #reset} while any thread is waiting,
* or if the barrier {@linkplain #isBroken is broken} when
* <tt>await</tt> is invoked, or while any thread is waiting, then
* {@code await} is invoked, or while any thread is waiting, then
* {@link BrokenBarrierException} is thrown.
*
* <p>If any thread is {@linkplain Thread#interrupt interrupted} while
@ -412,16 +416,17 @@ public class CyclicBarrier {
* @param timeout the time to wait for the barrier
* @param unit the time unit of the timeout parameter
* @return the arrival index of the current thread, where index
* <tt>{@link #getParties()} - 1</tt> indicates the first
* {@code getParties() - 1} indicates the first
* to arrive and zero indicates the last to arrive
* @throws InterruptedException if the current thread was interrupted
* while waiting
* @throws TimeoutException if the specified timeout elapses
* @throws TimeoutException if the specified timeout elapses.
* In this case the barrier will be broken.
* @throws BrokenBarrierException if <em>another</em> thread was
* interrupted or timed out while the current thread was
* waiting, or the barrier was reset, or the barrier was broken
* when {@code await} was called, or the barrier action (if
* present) failed due an exception
* present) failed due to an exception
*/
public int await(long timeout, TimeUnit unit)
throws InterruptedException,

867
jdk/src/share/classes/java/util/concurrent/Exchanger.java
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@ -35,7 +35,8 @@
*/
package java.util.concurrent;
import java.util.concurrent.atomic.*;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.LockSupport;
/**
@ -52,7 +53,7 @@ import java.util.concurrent.locks.LockSupport;
* to swap buffers between threads so that the thread filling the
* buffer gets a freshly emptied one when it needs it, handing off the
* filled one to the thread emptying the buffer.
* <pre>{@code
* <pre> {@code
* class FillAndEmpty {
* Exchanger<DataBuffer> exchanger = new Exchanger<DataBuffer>();
* DataBuffer initialEmptyBuffer = ... a made-up type
@ -88,8 +89,7 @@ import java.util.concurrent.locks.LockSupport;
* new Thread(new FillingLoop()).start();
* new Thread(new EmptyingLoop()).start();
* }
* }
* }</pre>
* }}</pre>
*
* <p>Memory consistency effects: For each pair of threads that
* successfully exchange objects via an {@code Exchanger}, actions
@ -103,486 +103,425 @@ import java.util.concurrent.locks.LockSupport;
* @param <V> The type of objects that may be exchanged
*/
public class Exchanger<V> {
/*
* Algorithm Description:
* Overview: The core algorithm is, for an exchange "slot",
* and a participant (caller) with an item:
*
* The basic idea is to maintain a "slot", which is a reference to
* a Node containing both an Item to offer and a "hole" waiting to
* get filled in. If an incoming "occupying" thread sees that the
* slot is null, it CAS'es (compareAndSets) a Node there and waits
* for another to invoke exchange. That second "fulfilling" thread
* sees that the slot is non-null, and so CASes it back to null,
* also exchanging items by CASing the hole, plus waking up the
* occupying thread if it is blocked. In each case CAS'es may
* fail because a slot at first appears non-null but is null upon
* CAS, or vice-versa. So threads may need to retry these
* actions.
* for (;;) {
* if (slot is empty) { // offer
* place item in a Node;
* if (can CAS slot from empty to node) {
* wait for release;
* return matching item in node;
* }
* }
* else if (can CAS slot from node to empty) { // release
* get the item in node;
* set matching item in node;
* release waiting thread;
* }
* // else retry on CAS failure
* }
*
* This simple approach works great when there are only a few
* threads using an Exchanger, but performance rapidly
* deteriorates due to CAS contention on the single slot when
* there are lots of threads using an exchanger. So instead we use
* an "arena"; basically a kind of hash table with a dynamically
* varying number of slots, any one of which can be used by
* threads performing an exchange. Incoming threads pick slots
* based on a hash of their Thread ids. If an incoming thread
* fails to CAS in its chosen slot, it picks an alternative slot
* instead. And similarly from there. If a thread successfully
* CASes into a slot but no other thread arrives, it tries
* another, heading toward the zero slot, which always exists even
* if the table shrinks. The particular mechanics controlling this
* are as follows:
* This is among the simplest forms of a "dual data structure" --
* see Scott and Scherer's DISC 04 paper and
* http://www.cs.rochester.edu/research/synchronization/pseudocode/duals.html
*
* Waiting: Slot zero is special in that it is the only slot that
* exists when there is no contention. A thread occupying slot
* zero will block if no thread fulfills it after a short spin.
* In other cases, occupying threads eventually give up and try
* another slot. Waiting threads spin for a while (a period that
* should be a little less than a typical context-switch time)
* before either blocking (if slot zero) or giving up (if other
* slots) and restarting. There is no reason for threads to block
* unless there are unlikely to be any other threads present.
* Occupants are mainly avoiding memory contention so sit there
* quietly polling for a shorter period than it would take to
* block and then unblock them. Non-slot-zero waits that elapse
* because of lack of other threads waste around one extra
* context-switch time per try, which is still on average much
* faster than alternative approaches.
* This works great in principle. But in practice, like many
* algorithms centered on atomic updates to a single location, it
* scales horribly when there are more than a few participants
* using the same Exchanger. So the implementation instead uses a
* form of elimination arena, that spreads out this contention by
* arranging that some threads typically use different slots,
* while still ensuring that eventually, any two parties will be
* able to exchange items. That is, we cannot completely partition
* across threads, but instead give threads arena indices that
* will on average grow under contention and shrink under lack of
* contention. We approach this by defining the Nodes that we need
* anyway as ThreadLocals, and include in them per-thread index
* and related bookkeeping state. (We can safely reuse per-thread
* nodes rather than creating them fresh each time because slots
* alternate between pointing to a node vs null, so cannot
* encounter ABA problems. However, we do need some care in
* resetting them between uses.)
*
* Sizing: Usually, using only a few slots suffices to reduce
* contention. Especially with small numbers of threads, using
* too many slots can lead to just as poor performance as using
* too few of them, and there's not much room for error. The
* variable "max" maintains the number of slots actually in
* use. It is increased when a thread sees too many CAS
* failures. (This is analogous to resizing a regular hash table
* based on a target load factor, except here, growth steps are
* just one-by-one rather than proportional.) Growth requires
* contention failures in each of three tried slots. Requiring
* multiple failures for expansion copes with the fact that some
* failed CASes are not due to contention but instead to simple
* races between two threads or thread pre-emptions occurring
* between reading and CASing. Also, very transient peak
* contention can be much higher than the average sustainable
* levels. An attempt to decrease the max limit is usually made
* when a non-slot-zero wait elapses without being fulfilled.
* Threads experiencing elapsed waits move closer to zero, so
* eventually find existing (or future) threads even if the table
* has been shrunk due to inactivity. The chosen mechanics and
* thresholds for growing and shrinking are intrinsically
* entangled with indexing and hashing inside the exchange code,
* and can't be nicely abstracted out.
* Implementing an effective arena requires allocating a bunch of
* space, so we only do so upon detecting contention (except on
* uniprocessors, where they wouldn't help, so aren't used).
* Otherwise, exchanges use the single-slot slotExchange method.
* On contention, not only must the slots be in different
* locations, but the locations must not encounter memory
* contention due to being on the same cache line (or more
* generally, the same coherence unit). Because, as of this
* writing, there is no way to determine cacheline size, we define
* a value that is enough for common platforms. Additionally,
* extra care elsewhere is taken to avoid other false/unintended
* sharing and to enhance locality, including adding padding (via
* sun.misc.Contended) to Nodes, embedding "bound" as an Exchanger
* field, and reworking some park/unpark mechanics compared to
* LockSupport versions.
*
* Hashing: Each thread picks its initial slot to use in accord
* with a simple hashcode. The sequence is the same on each
* encounter by any given thread, but effectively random across
* threads. Using arenas encounters the classic cost vs quality
* tradeoffs of all hash tables. Here, we use a one-step FNV-1a
* hash code based on the current thread's Thread.getId(), along
* with a cheap approximation to a mod operation to select an
* index. The downside of optimizing index selection in this way
* is that the code is hardwired to use a maximum table size of
* 32. But this value more than suffices for known platforms and
* applications.
* The arena starts out with only one used slot. We expand the
* effective arena size by tracking collisions; i.e., failed CASes
* while trying to exchange. By nature of the above algorithm, the
* only kinds of collision that reliably indicate contention are
* when two attempted releases collide -- one of two attempted
* offers can legitimately fail to CAS without indicating
* contention by more than one other thread. (Note: it is possible
* but not worthwhile to more precisely detect contention by
* reading slot values after CAS failures.) When a thread has
* collided at each slot within the current arena bound, it tries
* to expand the arena size by one. We track collisions within
* bounds by using a version (sequence) number on the "bound"
* field, and conservatively reset collision counts when a
* participant notices that bound has been updated (in either
* direction).
*
* Probing: On sensed contention of a selected slot, we probe
* sequentially through the table, analogously to linear probing
* after collision in a hash table. (We move circularly, in
* reverse order, to mesh best with table growth and shrinkage
* rules.) Except that to minimize the effects of false-alarms
* and cache thrashing, we try the first selected slot twice
* before moving.
* The effective arena size is reduced (when there is more than
* one slot) by giving up on waiting after a while and trying to
* decrement the arena size on expiration. The value of "a while"
* is an empirical matter. We implement by piggybacking on the
* use of spin->yield->block that is essential for reasonable
* waiting performance anyway -- in a busy exchanger, offers are
* usually almost immediately released, in which case context
* switching on multiprocessors is extremely slow/wasteful. Arena
* waits just omit the blocking part, and instead cancel. The spin
* count is empirically chosen to be a value that avoids blocking
* 99% of the time under maximum sustained exchange rates on a
* range of test machines. Spins and yields entail some limited
* randomness (using a cheap xorshift) to avoid regular patterns
* that can induce unproductive grow/shrink cycles. (Using a
* pseudorandom also helps regularize spin cycle duration by
* making branches unpredictable.) Also, during an offer, a
* waiter can "know" that it will be released when its slot has
* changed, but cannot yet proceed until match is set. In the
* mean time it cannot cancel the offer, so instead spins/yields.
* Note: It is possible to avoid this secondary check by changing
* the linearization point to be a CAS of the match field (as done
* in one case in the Scott & Scherer DISC paper), which also
* increases asynchrony a bit, at the expense of poorer collision
* detection and inability to always reuse per-thread nodes. So
* the current scheme is typically a better tradeoff.
*
* Padding: Even with contention management, slots are heavily
* contended, so use cache-padding to avoid poor memory
* performance. Because of this, slots are lazily constructed
* only when used, to avoid wasting this space unnecessarily.
* While isolation of locations is not much of an issue at first
* in an application, as time goes on and garbage-collectors
* perform compaction, slots are very likely to be moved adjacent
* to each other, which can cause much thrashing of cache lines on
* MPs unless padding is employed.
* On collisions, indices traverse the arena cyclically in reverse
* order, restarting at the maximum index (which will tend to be
* sparsest) when bounds change. (On expirations, indices instead
* are halved until reaching 0.) It is possible (and has been
* tried) to use randomized, prime-value-stepped, or double-hash
* style traversal instead of simple cyclic traversal to reduce
* bunching. But empirically, whatever benefits these may have
* don't overcome their added overhead: We are managing operations
* that occur very quickly unless there is sustained contention,
* so simpler/faster control policies work better than more
* accurate but slower ones.
*
* This is an improvement of the algorithm described in the paper
* "A Scalable Elimination-based Exchange Channel" by William
* Scherer, Doug Lea, and Michael Scott in Proceedings of SCOOL05
* workshop. Available at: http://hdl.handle.net/1802/2104
* Because we use expiration for arena size control, we cannot
* throw TimeoutExceptions in the timed version of the public
* exchange method until the arena size has shrunken to zero (or
* the arena isn't enabled). This may delay response to timeout
* but is still within spec.
*
* Essentially all of the implementation is in methods
* slotExchange and arenaExchange. These have similar overall
* structure, but differ in too many details to combine. The
* slotExchange method uses the single Exchanger field "slot"
* rather than arena array elements. However, it still needs
* minimal collision detection to trigger arena construction.
* (The messiest part is making sure interrupt status and
* InterruptedExceptions come out right during transitions when
* both methods may be called. This is done by using null return
* as a sentinel to recheck interrupt status.)
*
* As is too common in this sort of code, methods are monolithic
* because most of the logic relies on reads of fields that are
* maintained as local variables so can't be nicely factored --
* mainly, here, bulky spin->yield->block/cancel code), and
* heavily dependent on intrinsics (Unsafe) to use inlined
* embedded CAS and related memory access operations (that tend
* not to be as readily inlined by dynamic compilers when they are
* hidden behind other methods that would more nicely name and
* encapsulate the intended effects). This includes the use of
* putOrderedX to clear fields of the per-thread Nodes between
* uses. Note that field Node.item is not declared as volatile
* even though it is read by releasing threads, because they only
* do so after CAS operations that must precede access, and all
* uses by the owning thread are otherwise acceptably ordered by
* other operations. (Because the actual points of atomicity are
* slot CASes, it would also be legal for the write to Node.match
* in a release to be weaker than a full volatile write. However,
* this is not done because it could allow further postponement of
* the write, delaying progress.)
*/
/**
* The byte distance (as a shift value) between any two used slots
* in the arena. 1 << ASHIFT should be at least cacheline size.
*/
private static final int ASHIFT = 7;
/**
* The maximum supported arena index. The maximum allocatable
* arena size is MMASK + 1. Must be a power of two minus one, less
* than (1<<(31-ASHIFT)). The cap of 255 (0xff) more than suffices
* for the expected scaling limits of the main algorithms.
*/
private static final int MMASK = 0xff;
/**
* Unit for sequence/version bits of bound field. Each successful
* change to the bound also adds SEQ.
*/
private static final int SEQ = MMASK + 1;
/** The number of CPUs, for sizing and spin control */
private static final int NCPU = Runtime.getRuntime().availableProcessors();
/**
* The capacity of the arena. Set to a value that provides more
* than enough space to handle contention. On small machines
* most slots won't be used, but it is still not wasted because
* the extra space provides some machine-level address padding
* to minimize interference with heavily CAS'ed Slot locations.
* And on very large machines, performance eventually becomes
* bounded by memory bandwidth, not numbers of threads/CPUs.
* This constant cannot be changed without also modifying
* indexing and hashing algorithms.
* The maximum slot index of the arena: The number of slots that
* can in principle hold all threads without contention, or at
* most the maximum indexable value.
*/
private static final int CAPACITY = 32;
static final int FULL = (NCPU >= (MMASK << 1)) ? MMASK : NCPU >>> 1;
/**
* The value of "max" that will hold all threads without
* contention. When this value is less than CAPACITY, some
* otherwise wasted expansion can be avoided.
* The bound for spins while waiting for a match. The actual
* number of iterations will on average be about twice this value
* due to randomization. Note: Spinning is disabled when NCPU==1.
*/
private static final int FULL =
Math.max(0, Math.min(CAPACITY, NCPU / 2) - 1);
/**
* The number of times to spin (doing nothing except polling a
* memory location) before blocking or giving up while waiting to
* be fulfilled. Should be zero on uniprocessors. On
* multiprocessors, this value should be large enough so that two
* threads exchanging items as fast as possible block only when
* one of them is stalled (due to GC or preemption), but not much
* longer, to avoid wasting CPU resources. Seen differently, this
* value is a little over half the number of cycles of an average
* context switch time on most systems. The value here is
* approximately the average of those across a range of tested
* systems.
*/
private static final int SPINS = (NCPU == 1) ? 0 : 2000;
/**
* The number of times to spin before blocking in timed waits.
* Timed waits spin more slowly because checking the time takes
* time. The best value relies mainly on the relative rate of
* System.nanoTime vs memory accesses. The value is empirically
* derived to work well across a variety of systems.
*/
private static final int TIMED_SPINS = SPINS / 20;
/**
* Sentinel item representing cancellation of a wait due to
* interruption, timeout, or elapsed spin-waits. This value is
* placed in holes on cancellation, and used as a return value
* from waiting methods to indicate failure to set or get hole.
*/
private static final Object CANCEL = new Object();
private static final int SPINS = 1 << 10;
/**
* Value representing null arguments/returns from public
* methods. This disambiguates from internal requirement that
* holes start out as null to mean they are not yet set.
* methods. Needed because the API originally didn't disallow null
* arguments, which it should have.
*/
private static final Object NULL_ITEM = new Object();
/**
* Nodes hold partially exchanged data. This class
* opportunistically subclasses AtomicReference to represent the
* hole. So get() returns hole, and compareAndSet CAS'es value
* into hole. This class cannot be parameterized as "V" because
* of the use of non-V CANCEL sentinels.
* Sentinel value returned by internal exchange methods upon
* timeout, to avoid need for separate timed versions of these
* methods.
*/
@SuppressWarnings("serial")
private static final class Node extends AtomicReference<Object> {
/** The element offered by the Thread creating this node. */
public final Object item;
private static final Object TIMED_OUT = new Object();
/** The Thread waiting to be signalled; null until waiting. */
public volatile Thread waiter;
/**
* Nodes hold partially exchanged data, plus other per-thread
* bookkeeping. Padded via @sun.misc.Contended to reduce memory
* contention.
*/
@sun.misc.Contended static final class Node {
int index; // Arena index
int bound; // Last recorded value of Exchanger.bound
int collides; // Number of CAS failures at current bound
int hash; // Pseudo-random for spins
Object item; // This thread's current item
volatile Object match; // Item provided by releasing thread
volatile Thread parked; // Set to this thread when parked, else null
}
/**
* Creates node with given item and empty hole.
* @param item the item
*/
public Node(Object item) {
this.item = item;
}
/** The corresponding thread local class */
static final class Participant extends ThreadLocal<Node> {
public Node initialValue() { return new Node(); }
}
/**
* A Slot is an AtomicReference with heuristic padding to lessen
* cache effects of this heavily CAS'ed location. While the
* padding adds noticeable space, all slots are created only on
* demand, and there will be more than one of them only when it
* would improve throughput more than enough to outweigh using
* extra space.
* Per-thread state
*/
@SuppressWarnings("serial")
private static final class Slot extends AtomicReference<Object> {
// Improve likelihood of isolation on <= 64 byte cache lines
long q0, q1, q2, q3, q4, q5, q6, q7, q8, q9, qa, qb, qc, qd, qe;
}
private final Participant participant;
/**
* Slot array. Elements are lazily initialized when needed.
* Declared volatile to enable double-checked lazy construction.
* Elimination array; null until enabled (within slotExchange).
* Element accesses use emulation of volatile gets and CAS.
*/
private volatile Slot[] arena = new Slot[CAPACITY];
private volatile Node[] arena;
/**
* The maximum slot index being used. The value sometimes
* increases when a thread experiences too many CAS contentions,
* and sometimes decreases when a spin-wait elapses. Changes
* are performed only via compareAndSet, to avoid stale values
* when a thread happens to stall right before setting.
* Slot used until contention detected.
*/
private final AtomicInteger max = new AtomicInteger();
private volatile Node slot;
/**
* Main exchange function, handling the different policy variants.
* Uses Object, not "V" as argument and return value to simplify
* handling of sentinel values. Callers from public methods decode
* and cast accordingly.
* The index of the largest valid arena position, OR'ed with SEQ
* number in high bits, incremented on each update. The initial
* update from 0 to SEQ is used to ensure that the arena array is
* constructed only once.
*/
private volatile int bound;
/**
* Exchange function when arenas enabled. See above for explanation.
*
* @param item the (non-null) item to exchange
* @param timed true if the wait is timed
* @param nanos if timed, the maximum wait time
* @return the other thread's item, or CANCEL if interrupted or timed out
* @param ns if timed, the maximum wait time, else 0L
* @return the other thread's item; or null if interrupted; or
* TIMED_OUT if timed and timed out
*/
private Object doExchange(Object item, boolean timed, long nanos) {
Node me = new Node(item); // Create in case occupying
int index = hashIndex(); // Index of current slot
int fails = 0; // Number of CAS failures
for (;;) {
Object y; // Contents of current slot
Slot slot = arena[index];
if (slot == null) // Lazily initialize slots
createSlot(index); // Continue loop to reread
else if ((y = slot.get()) != null && // Try to fulfill
slot.compareAndSet(y, null)) {
Node you = (Node)y; // Transfer item
if (you.compareAndSet(null, item)) {
LockSupport.unpark(you.waiter);
return you.item;
} // Else cancelled; continue
}
else if (y == null && // Try to occupy
slot.compareAndSet(null, me)) {
if (index == 0) // Blocking wait for slot 0
return timed ?
awaitNanos(me, slot, nanos) :
await(me, slot);
Object v = spinWait(me, slot); // Spin wait for non-0
if (v != CANCEL)
return v;
me = new Node(item); // Throw away cancelled node
int m = max.get();
if (m > (index >>>= 1)) // Decrease index
max.compareAndSet(m, m - 1); // Maybe shrink table
}
else if (++fails > 1) { // Allow 2 fails on 1st slot
int m = max.get();
if (fails > 3 && m < FULL && max.compareAndSet(m, m + 1))
index = m + 1; // Grow on 3rd failed slot
else if (--index < 0)
index = m; // Circularly traverse
}
}
}
/**
* Returns a hash index for the current thread. Uses a one-step
* FNV-1a hash code (http://www.isthe.com/chongo/tech/comp/fnv/)
* based on the current thread's Thread.getId(). These hash codes
* have more uniform distribution properties with respect to small
* moduli (here 1-31) than do other simple hashing functions.
*
* <p>To return an index between 0 and max, we use a cheap
* approximation to a mod operation, that also corrects for bias
* due to non-power-of-2 remaindering (see {@link
* java.util.Random#nextInt}). Bits of the hashcode are masked
* with "nbits", the ceiling power of two of table size (looked up
* in a table packed into three ints). If too large, this is
* retried after rotating the hash by nbits bits, while forcing new
* top bit to 0, which guarantees eventual termination (although
* with a non-random-bias). This requires an average of less than
* 2 tries for all table sizes, and has a maximum 2% difference
* from perfectly uniform slot probabilities when applied to all
* possible hash codes for sizes less than 32.
*
* @return a per-thread-random index, 0 <= index < max
*/
private final int hashIndex() {
long id = Thread.currentThread().getId();
int hash = (((int)(id ^ (id >>> 32))) ^ 0x811c9dc5) * 0x01000193;
int m = max.get();
int nbits = (((0xfffffc00 >> m) & 4) | // Compute ceil(log2(m+1))
((0x000001f8 >>> m) & 2) | // The constants hold
((0xffff00f2 >>> m) & 1)); // a lookup table
int index;
while ((index = hash & ((1 << nbits) - 1)) > m) // May retry on
hash = (hash >>> nbits) | (hash << (33 - nbits)); // non-power-2 m
return index;
}
/**
* Creates a new slot at given index. Called only when the slot
* appears to be null. Relies on double-check using builtin
* locks, since they rarely contend. This in turn relies on the
* arena array being declared volatile.
*
* @param index the index to add slot at
*/
private void createSlot(int index) {
// Create slot outside of lock to narrow sync region
Slot newSlot = new Slot();
Slot[] a = arena;
synchronized (a) {
if (a[index] == null)
a[index] = newSlot;
}
}
/**
* Tries to cancel a wait for the given node waiting in the given
* slot, if so, helping clear the node from its slot to avoid
* garbage retention.
*
* @param node the waiting node
* @param the slot it is waiting in
* @return true if successfully cancelled
*/
private static boolean tryCancel(Node node, Slot slot) {
if (!node.compareAndSet(null, CANCEL))
return false;
if (slot.get() == node) // pre-check to minimize contention
slot.compareAndSet(node, null);
return true;
}
// Three forms of waiting. Each just different enough not to merge
// code with others.
/**
* Spin-waits for hole for a non-0 slot. Fails if spin elapses
* before hole filled. Does not check interrupt, relying on check
* in public exchange method to abort if interrupted on entry.
*
* @param node the waiting node
* @return on success, the hole; on failure, CANCEL
*/
private static Object spinWait(Node node, Slot slot) {
int spins = SPINS;
for (;;) {
Object v = node.get();
if (v != null)
private final Object arenaExchange(Object item, boolean timed, long ns) {
Node[] a = arena;
Node p = participant.get();
for (int i = p.index;;) { // access slot at i
int b, m, c; long j; // j is raw array offset
Node q = (Node)U.getObjectVolatile(a, j = (i << ASHIFT) + ABASE);
if (q != null && U.compareAndSwapObject(a, j, q, null)) {
Object v = q.item; // release
q.match = item;
Thread w = q.parked;
if (w != null)
U.unpark(w);
return v;
else if (spins > 0)
--spins;
else
tryCancel(node, slot);
}
}
/**
* Waits for (by spinning and/or blocking) and gets the hole
* filled in by another thread. Fails if interrupted before
* hole filled.
*
* When a node/thread is about to block, it sets its waiter field
* and then rechecks state at least one more time before actually
* parking, thus covering race vs fulfiller noticing that waiter
* is non-null so should be woken.
*
* Thread interruption status is checked only surrounding calls to
* park. The caller is assumed to have checked interrupt status
* on entry.
*
* @param node the waiting node
* @return on success, the hole; on failure, CANCEL
*/
private static Object await(Node node, Slot slot) {
Thread w = Thread.currentThread();
int spins = SPINS;
for (;;) {
Object v = node.get();
if (v != null)
return v;
else if (spins > 0) // Spin-wait phase
--spins;
else if (node.waiter == null) // Set up to block next
node.waiter = w;
else if (w.isInterrupted()) // Abort on interrupt
tryCancel(node, slot);
else // Block
LockSupport.park(node);
}
}
/**
* Waits for (at index 0) and gets the hole filled in by another
* thread. Fails if timed out or interrupted before hole filled.
* Same basic logic as untimed version, but a bit messier.
*
* @param node the waiting node
* @param nanos the wait time
* @return on success, the hole; on failure, CANCEL
*/
private Object awaitNanos(Node node, Slot slot, long nanos) {
int spins = TIMED_SPINS;
long lastTime = 0;
Thread w = null;
for (;;) {
Object v = node.get();
if (v != null)
return v;
long now = System.nanoTime();
if (w == null)
w = Thread.currentThread();
else
nanos -= now - lastTime;
lastTime = now;
if (nanos > 0) {
if (spins > 0)
--spins;
else if (node.waiter == null)
node.waiter = w;
else if (w.isInterrupted())
tryCancel(node, slot);
else
LockSupport.parkNanos(node, nanos);
}
else if (tryCancel(node, slot) && !w.isInterrupted())
return scanOnTimeout(node);
}
}
/**
* Sweeps through arena checking for any waiting threads. Called
* only upon return from timeout while waiting in slot 0. When a
* thread gives up on a timed wait, it is possible that a
* previously-entered thread is still waiting in some other
* slot. So we scan to check for any. This is almost always
* overkill, but decreases the likelihood of timeouts when there
* are other threads present to far less than that in lock-based
* exchangers in which earlier-arriving threads may still be
* waiting on entry locks.
*
* @param node the waiting node
* @return another thread's item, or CANCEL
*/
private Object scanOnTimeout(Node node) {
Object y;
for (int j = arena.length - 1; j >= 0; --j) {
Slot slot = arena[j];
if (slot != null) {
while ((y = slot.get()) != null) {
if (slot.compareAndSet(y, null)) {
Node you = (Node)y;
if (you.compareAndSet(null, node.item)) {
LockSupport.unpark(you.waiter);
return you.item;
else if (i <= (m = (b = bound) & MMASK) && q == null) {
p.item = item; // offer
if (U.compareAndSwapObject(a, j, null, p)) {
long end = (timed && m == 0) ? System.nanoTime() + ns : 0L;
Thread t = Thread.currentThread(); // wait
for (int h = p.hash, spins = SPINS;;) {
Object v = p.match;
if (v != null) {
U.putOrderedObject(p, MATCH, null);
p.item = null; // clear for next use
p.hash = h;
return v;
}
else if (spins > 0) {
h ^= h << 1; h ^= h >>> 3; h ^= h << 10; // xorshift
if (h == 0) // initialize hash
h = SPINS | (int)t.getId();
else if (h < 0 && // approx 50% true
(--spins & ((SPINS >>> 1) - 1)) == 0)
Thread.yield(); // two yields per wait
}
else if (U.getObjectVolatile(a, j) != p)
spins = SPINS; // releaser hasn't set match yet
else if (!t.isInterrupted() && m == 0 &&
(!timed ||
(ns = end - System.nanoTime()) > 0L)) {
U.putObject(t, BLOCKER, this); // emulate LockSupport
p.parked = t; // minimize window
if (U.getObjectVolatile(a, j) == p)
U.park(false, ns);
p.parked = null;
U.putObject(t, BLOCKER, null);
}
else if (U.getObjectVolatile(a, j) == p &&
U.compareAndSwapObject(a, j, p, null)) {
if (m != 0) // try to shrink
U.compareAndSwapInt(this, BOUND, b, b + SEQ - 1);
p.item = null;
p.hash = h;
i = p.index >>>= 1; // descend
if (Thread.interrupted())
return null;
if (timed && m == 0 && ns <= 0L)
return TIMED_OUT;
break; // expired; restart
}
}
}
else
p.item = null; // clear offer
}
else {
if (p.bound != b) { // stale; reset
p.bound = b;
p.collides = 0;
i = (i != m || m == 0) ? m : m - 1;
}
else if ((c = p.collides) < m || m == FULL ||
!U.compareAndSwapInt(this, BOUND, b, b + SEQ + 1)) {
p.collides = c + 1;
i = (i == 0) ? m : i - 1; // cyclically traverse
}
else
i = m + 1; // grow
p.index = i;
}
}
return CANCEL;
}
/**
* Exchange function used until arenas enabled. See above for explanation.
*
* @param item the item to exchange
* @param timed true if the wait is timed
* @param ns if timed, the maximum wait time, else 0L
* @return the other thread's item; or null if either the arena
* was enabled or the thread was interrupted before completion; or
* TIMED_OUT if timed and timed out
*/
private final Object slotExchange(Object item, boolean timed, long ns) {
Node p = participant.get();
Thread t = Thread.currentThread();
if (t.isInterrupted()) // preserve interrupt status so caller can recheck
return null;
for (Node q;;) {
if ((q = slot) != null) {
if (U.compareAndSwapObject(this, SLOT, q, null)) {
Object v = q.item;
q.match = item;
Thread w = q.parked;
if (w != null)
U.unpark(w);
return v;
}
// create arena on contention, but continue until slot null
if (NCPU > 1 && bound == 0 &&
U.compareAndSwapInt(this, BOUND, 0, SEQ))
arena = new Node[(FULL + 2) << ASHIFT];
}
else if (arena != null)
return null; // caller must reroute to arenaExchange
else {
p.item = item;
if (U.compareAndSwapObject(this, SLOT, null, p))
break;
p.item = null;
}
}
// await release
int h = p.hash;
long end = timed ? System.nanoTime() + ns : 0L;
int spins = (NCPU > 1) ? SPINS : 1;
Object v;
while ((v = p.match) == null) {
if (spins > 0) {
h ^= h << 1; h ^= h >>> 3; h ^= h << 10;
if (h == 0)
h = SPINS | (int)t.getId();
else if (h < 0 && (--spins & ((SPINS >>> 1) - 1)) == 0)
Thread.yield();
}
else if (slot != p)
spins = SPINS;
else if (!t.isInterrupted() && arena == null &&
(!timed || (ns = end - System.nanoTime()) > 0L)) {
U.putObject(t, BLOCKER, this);
p.parked = t;
if (slot == p)
U.park(false, ns);
p.parked = null;
U.putObject(t, BLOCKER, null);
}
else if (U.compareAndSwapObject(this, SLOT, p, null)) {
v = timed && ns <= 0L && !t.isInterrupted() ? TIMED_OUT : null;
break;
}
}
U.putOrderedObject(p, MATCH, null);
p.item = null;
p.hash = h;
return v;
}
/**
* Creates a new Exchanger.
*/
public Exchanger() {
participant = new Participant();
}
/**
@ -620,15 +559,14 @@ public class Exchanger<V> {
*/
@SuppressWarnings("unchecked")
public V exchange(V x) throws InterruptedException {
if (!Thread.interrupted()) {
Object o = doExchange((x == null) ? NULL_ITEM : x, false, 0);
if (o == NULL_ITEM)
return null;
if (o != CANCEL)
return (V)o;
Thread.interrupted(); // Clear interrupt status on IE throw
}
throw new InterruptedException();
Object v;
Object item = (x == null) ? NULL_ITEM : x; // translate null args
if ((arena != null ||
(v = slotExchange(item, false, 0L)) == null) &&
((Thread.interrupted() || // disambiguates null return
(v = arenaExchange(item, false, 0L)) == null)))
throw new InterruptedException();
return (v == NULL_ITEM) ? null : (V)v;
}
/**
@ -666,7 +604,7 @@ public class Exchanger<V> {
*
* @param x the object to exchange
* @param timeout the maximum time to wait
* @param unit the time unit of the <tt>timeout</tt> argument
* @param unit the time unit of the {@code timeout} argument
* @return the object provided by the other thread
* @throws InterruptedException if the current thread was
* interrupted while waiting
@ -676,16 +614,51 @@ public class Exchanger<V> {
@SuppressWarnings("unchecked")
public V exchange(V x, long timeout, TimeUnit unit)
throws InterruptedException, TimeoutException {
if (!Thread.interrupted()) {
Object o = doExchange((x == null) ? NULL_ITEM : x,
true, unit.toNanos(timeout));
if (o == NULL_ITEM)
return null;
if (o != CANCEL)
return (V)o;
if (!Thread.interrupted())
throw new TimeoutException();
}
throw new InterruptedException();
Object v;
Object item = (x == null) ? NULL_ITEM : x;
long ns = unit.toNanos(timeout);
if ((arena != null ||
(v = slotExchange(item, true, ns)) == null) &&
((Thread.interrupted() ||
(v = arenaExchange(item, true, ns)) == null)))
throw new InterruptedException();
if (v == TIMED_OUT)
throw new TimeoutException();
return (v == NULL_ITEM) ? null : (V)v;
}
// Unsafe mechanics
private static final sun.misc.Unsafe U;
private static final long BOUND;
private static final long SLOT;
private static final long MATCH;
private static final long BLOCKER;
private static final int ABASE;
static {
int s;
try {
U = sun.misc.Unsafe.getUnsafe();
Class<?> ek = Exchanger.class;
Class<?> nk = Node.class;
Class<?> ak = Node[].class;
Class<?> tk = Thread.class;
BOUND = U.objectFieldOffset
(ek.getDeclaredField("bound"));
SLOT = U.objectFieldOffset
(ek.getDeclaredField("slot"));
MATCH = U.objectFieldOffset
(nk.getDeclaredField("match"));
BLOCKER = U.objectFieldOffset
(tk.getDeclaredField("parkBlocker"));
s = U.arrayIndexScale(ak);
// ABASE absorbs padding in front of element 0
ABASE = U.arrayBaseOffset(ak) + (1 << ASHIFT);
} catch (Exception e) {
throw new Error(e);
}
if ((s & (s-1)) != 0 || s > (1 << ASHIFT))
throw new Error("Unsupported array scale");
}
}

143
jdk/src/share/classes/java/util/concurrent/Phaser.java
View File

@ -46,7 +46,7 @@ import java.util.concurrent.locks.LockSupport;
* {@link java.util.concurrent.CountDownLatch CountDownLatch}
* but supporting more flexible usage.
*
* <p> <b>Registration.</b> Unlike the case for other barriers, the
* <p><b>Registration.</b> Unlike the case for other barriers, the
* number of parties <em>registered</em> to synchronize on a phaser
* may vary over time. Tasks may be registered at any time (using
* methods {@link #register}, {@link #bulkRegister}, or forms of
@ -59,7 +59,7 @@ import java.util.concurrent.locks.LockSupport;
* (However, you can introduce such bookkeeping by subclassing this
* class.)
*
* <p> <b>Synchronization.</b> Like a {@code CyclicBarrier}, a {@code
* <p><b>Synchronization.</b> Like a {@code CyclicBarrier}, a {@code
* Phaser} may be repeatedly awaited. Method {@link
* #arriveAndAwaitAdvance} has effect analogous to {@link
* java.util.concurrent.CyclicBarrier#await CyclicBarrier.await}. Each
@ -103,7 +103,7 @@ import java.util.concurrent.locks.LockSupport;
*
* </ul>
*
* <p> <b>Termination.</b> A phaser may enter a <em>termination</em>
* <p><b>Termination.</b> A phaser may enter a <em>termination</em>
* state, that may be checked using method {@link #isTerminated}. Upon
* termination, all synchronization methods immediately return without
* waiting for advance, as indicated by a negative return value.
@ -118,7 +118,7 @@ import java.util.concurrent.locks.LockSupport;
* also available to abruptly release waiting threads and allow them
* to terminate.
*
* <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e.,
* <p><b>Tiering.</b> Phasers may be <em>tiered</em> (i.e.,
* constructed in tree structures) to reduce contention. Phasers with
* large numbers of parties that would otherwise experience heavy
* synchronization contention costs may instead be set up so that
@ -300,18 +300,20 @@ public class Phaser {
private static final int PHASE_SHIFT = 32;
private static final int UNARRIVED_MASK = 0xffff; // to mask ints
private static final long PARTIES_MASK = 0xffff0000L; // to mask longs
private static final long COUNTS_MASK = 0xffffffffL;
private static final long TERMINATION_BIT = 1L << 63;
// some special values
private static final int ONE_ARRIVAL = 1;
private static final int ONE_PARTY = 1 << PARTIES_SHIFT;
private static final int ONE_DEREGISTER = ONE_ARRIVAL|ONE_PARTY;
private static final int EMPTY = 1;
// The following unpacking methods are usually manually inlined
private static int unarrivedOf(long s) {
int counts = (int)s;
return (counts == EMPTY) ? 0 : counts & UNARRIVED_MASK;
return (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK);
}
private static int partiesOf(long s) {
@ -372,37 +374,44 @@ public class Phaser {
* Manually tuned to speed up and minimize race windows for the
* common case of just decrementing unarrived field.
*
* @param deregister false for arrive, true for arriveAndDeregister
* @param adjust value to subtract from state;
* ONE_ARRIVAL for arrive,
* ONE_DEREGISTER for arriveAndDeregister
*/
private int doArrive(boolean deregister) {
int adj = deregister ? ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL;
private int doArrive(int adjust) {
final Phaser root = this.root;
for (;;) {
long s = (root == this) ? state : reconcileState();
int phase = (int)(s >>> PHASE_SHIFT);
int counts = (int)s;
int unarrived = (counts & UNARRIVED_MASK) - 1;
if (phase < 0)
return phase;
else if (counts == EMPTY || unarrived < 0) {
if (root == this || reconcileState() == s)
throw new IllegalStateException(badArrive(s));
}
else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) {
if (unarrived == 0) {
int counts = (int)s;
int unarrived = (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK);
if (unarrived <= 0)
throw new IllegalStateException(badArrive(s));
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adjust)) {
if (unarrived == 1) {
long n = s & PARTIES_MASK; // base of next state
int nextUnarrived = (int)n >>> PARTIES_SHIFT;
if (root != this)
return parent.doArrive(nextUnarrived == 0);
if (onAdvance(phase, nextUnarrived))
n |= TERMINATION_BIT;
else if (nextUnarrived == 0)
n |= EMPTY;
if (root == this) {
if (onAdvance(phase, nextUnarrived))
n |= TERMINATION_BIT;
else if (nextUnarrived == 0)
n |= EMPTY;
else
n |= nextUnarrived;
int nextPhase = (phase + 1) & MAX_PHASE;
n |= (long)nextPhase << PHASE_SHIFT;
UNSAFE.compareAndSwapLong(this, stateOffset, s, n);
releaseWaiters(phase);
}
else if (nextUnarrived == 0) { // propagate deregistration
phase = parent.doArrive(ONE_DEREGISTER);
UNSAFE.compareAndSwapLong(this, stateOffset,
s, s | EMPTY);
}
else
n |= nextUnarrived;
n |= (long)((phase + 1) & MAX_PHASE) << PHASE_SHIFT;
UNSAFE.compareAndSwapLong(this, stateOffset, s, n);
releaseWaiters(phase);
phase = parent.doArrive(ONE_ARRIVAL);
}
return phase;
}
@ -417,42 +426,49 @@ public class Phaser {
*/
private int doRegister(int registrations) {
// adjustment to state
long adj = ((long)registrations << PARTIES_SHIFT) | registrations;
long adjust = ((long)registrations << PARTIES_SHIFT) | registrations;
final Phaser parent = this.parent;
int phase;
for (;;) {
long s = state;
long s = (parent == null) ? state : reconcileState();
int counts = (int)s;
int parties = counts >>> PARTIES_SHIFT;
int unarrived = counts & UNARRIVED_MASK;
if (registrations > MAX_PARTIES - parties)
throw new IllegalStateException(badRegister(s));
else if ((phase = (int)(s >>> PHASE_SHIFT)) < 0)
phase = (int)(s >>> PHASE_SHIFT);
if (phase < 0)
break;
else if (counts != EMPTY) { // not 1st registration
if (counts != EMPTY) { // not 1st registration
if (parent == null || reconcileState() == s) {
if (unarrived == 0) // wait out advance
root.internalAwaitAdvance(phase, null);
else if (UNSAFE.compareAndSwapLong(this, stateOffset,
s, s + adj))
s, s + adjust))
break;
}
}
else if (parent == null) { // 1st root registration
long next = ((long)phase << PHASE_SHIFT) | adj;
long next = ((long)phase << PHASE_SHIFT) | adjust;
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next))
break;
}
else {
synchronized (this) { // 1st sub registration
if (state == s) { // recheck under lock
parent.doRegister(1);
do { // force current phase
phase = parent.doRegister(1);
if (phase < 0)
break;
// finish registration whenever parent registration
// succeeded, even when racing with termination,
// since these are part of the same "transaction".
while (!UNSAFE.compareAndSwapLong
(this, stateOffset, s,
((long)phase << PHASE_SHIFT) | adjust)) {
s = state;
phase = (int)(root.state >>> PHASE_SHIFT);
// assert phase < 0 || (int)state == EMPTY;
} while (!UNSAFE.compareAndSwapLong
(this, stateOffset, state,
((long)phase << PHASE_SHIFT) | adj));
// assert (int)s == EMPTY;
}
break;
}
}
@ -467,10 +483,6 @@ public class Phaser {
* subphasers have not yet done so, in which case they must finish
* their own advance by setting unarrived to parties (or if
* parties is zero, resetting to unregistered EMPTY state).
* However, this method may also be called when "floating"
* subphasers with possibly some unarrived parties are merely
* catching up to current phase, in which case counts are
* unaffected.
*
* @return reconciled state
*/
@ -478,16 +490,16 @@ public class Phaser {
final Phaser root = this.root;
long s = state;
if (root != this) {
int phase, u, p;
// CAS root phase with current parties; possibly trip unarrived
int phase, p;
// CAS to root phase with current parties, tripping unarrived
while ((phase = (int)(root.state >>> PHASE_SHIFT)) !=
(int)(s >>> PHASE_SHIFT) &&
!UNSAFE.compareAndSwapLong
(this, stateOffset, s,
s = (((long)phase << PHASE_SHIFT) |
(s & PARTIES_MASK) |
((p = (int)s >>> PARTIES_SHIFT) == 0 ? EMPTY :
(u = (int)s & UNARRIVED_MASK) == 0 ? p : u))))
((phase < 0) ? (s & COUNTS_MASK) :
(((p = (int)s >>> PARTIES_SHIFT) == 0) ? EMPTY :
((s & PARTIES_MASK) | p))))))
s = state;
}
return s;
@ -619,7 +631,7 @@ public class Phaser {
* of unarrived parties would become negative
*/
public int arrive() {
return doArrive(false);
return doArrive(ONE_ARRIVAL);
}
/**
@ -639,7 +651,7 @@ public class Phaser {
* of registered or unarrived parties would become negative
*/
public int arriveAndDeregister() {
return doArrive(true);
return doArrive(ONE_DEREGISTER);
}
/**
@ -666,17 +678,15 @@ public class Phaser {
for (;;) {
long s = (root == this) ? state : reconcileState();
int phase = (int)(s >>> PHASE_SHIFT);
int counts = (int)s;
int unarrived = (counts & UNARRIVED_MASK) - 1;
if (phase < 0)
return phase;
else if (counts == EMPTY || unarrived < 0) {
if (reconcileState() == s)
throw new IllegalStateException(badArrive(s));
}
else if (UNSAFE.compareAndSwapLong(this, stateOffset, s,
s -= ONE_ARRIVAL)) {
if (unarrived != 0)
int counts = (int)s;
int unarrived = (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK);
if (unarrived <= 0)
throw new IllegalStateException(badArrive(s));
if (UNSAFE.compareAndSwapLong(this, stateOffset, s,
s -= ONE_ARRIVAL)) {
if (unarrived > 1)
return root.internalAwaitAdvance(phase, null);
if (root != this)
return parent.arriveAndAwaitAdvance();
@ -809,8 +819,8 @@ public class Phaser {
if (UNSAFE.compareAndSwapLong(root, stateOffset,
s, s | TERMINATION_BIT)) {
// signal all threads
releaseWaiters(0);
releaseWaiters(1);
releaseWaiters(0); // Waiters on evenQ
releaseWaiters(1); // Waiters on oddQ
return;
}
}
@ -1016,7 +1026,7 @@ public class Phaser {
/**
* Possibly blocks and waits for phase to advance unless aborted.
* Call only from root node.
* Call only on root phaser.
*
* @param phase current phase
* @param node if non-null, the wait node to track interrupt and timeout;
@ -1024,6 +1034,7 @@ public class Phaser {
* @return current phase
*/
private int internalAwaitAdvance(int phase, QNode node) {
// assert root == this;
releaseWaiters(phase-1); // ensure old queue clean
boolean queued = false; // true when node is enqueued
int lastUnarrived = 0; // to increase spins upon change
@ -1082,7 +1093,7 @@ public class Phaser {
final boolean timed;
boolean wasInterrupted;
long nanos;
long lastTime;
final long deadline;
volatile Thread thread; // nulled to cancel wait
QNode next;
@ -1093,7 +1104,7 @@ public class Phaser {
this.interruptible = interruptible;
this.nanos = nanos;
this.timed = timed;
this.lastTime = timed ? System.nanoTime() : 0L;
this.deadline = timed ? System.nanoTime() + nanos : 0L;
thread = Thread.currentThread();
}
@ -1112,9 +1123,7 @@ public class Phaser {
}
if (timed) {
if (nanos > 0L) {
long now = System.nanoTime();
nanos -= now - lastTime;
lastTime = now;
nanos = deadline - System.nanoTime();
}
if (nanos <= 0L) {
thread = null;
@ -1129,7 +1138,7 @@ public class Phaser {
return true;
else if (!timed)
LockSupport.park(this);
else if (nanos > 0)
else if (nanos > 0L)
LockSupport.parkNanos(this, nanos);
return isReleasable();
}

93
jdk/src/share/classes/java/util/concurrent/TimeUnit.java
View File

@ -36,10 +36,10 @@
package java.util.concurrent;
/**
* A <tt>TimeUnit</tt> represents time durations at a given unit of
* A {@code TimeUnit} represents time durations at a given unit of
* granularity and provides utility methods to convert across units,
* and to perform timing and delay operations in these units. A
* <tt>TimeUnit</tt> does not maintain time information, but only
* {@code TimeUnit} does not maintain time information, but only
* helps organize and use time representations that may be maintained
* separately across various contexts. A nanosecond is defined as one
* thousandth of a microsecond, a microsecond as one thousandth of a
@ -47,7 +47,7 @@ package java.util.concurrent;
* as sixty seconds, an hour as sixty minutes, and a day as twenty four
* hours.
*
* <p>A <tt>TimeUnit</tt> is mainly used to inform time-based methods
* <p>A {@code TimeUnit} is mainly used to inform time-based methods
* how a given timing parameter should be interpreted. For example,
* the following code will timeout in 50 milliseconds if the {@link
* java.util.concurrent.locks.Lock lock} is not available:
@ -63,7 +63,7 @@ package java.util.concurrent;
*
* Note however, that there is no guarantee that a particular timeout
* implementation will be able to notice the passage of time at the
* same granularity as the given <tt>TimeUnit</tt>.
* same granularity as the given {@code TimeUnit}.
*
* @since 1.5
* @author Doug Lea
@ -174,83 +174,82 @@ public enum TimeUnit {
// etc. are not declared abstract but otherwise act as abstract methods.
/**
* Convert the given time duration in the given unit to this
* unit. Conversions from finer to coarser granularities
* truncate, so lose precision. For example converting
* <tt>999</tt> milliseconds to seconds results in
* <tt>0</tt>. Conversions from coarser to finer granularities
* with arguments that would numerically overflow saturate to
* <tt>Long.MIN_VALUE</tt> if negative or <tt>Long.MAX_VALUE</tt>
* if positive.
* Converts the given time duration in the given unit to this unit.
* Conversions from finer to coarser granularities truncate, so
* lose precision. For example, converting {@code 999} milliseconds
* to seconds results in {@code 0}. Conversions from coarser to
* finer granularities with arguments that would numerically
* overflow saturate to {@code Long.MIN_VALUE} if negative or
* {@code Long.MAX_VALUE} if positive.
*
* <p>For example, to convert 10 minutes to milliseconds, use:
* <tt>TimeUnit.MILLISECONDS.convert(10L, TimeUnit.MINUTES)</tt>
* {@code TimeUnit.MILLISECONDS.convert(10L, TimeUnit.MINUTES)}
*
* @param sourceDuration the time duration in the given <tt>sourceUnit</tt>
* @param sourceUnit the unit of the <tt>sourceDuration</tt> argument
* @param sourceDuration the time duration in the given {@code sourceUnit}
* @param sourceUnit the unit of the {@code sourceDuration} argument
* @return the converted duration in this unit,
* or <tt>Long.MIN_VALUE</tt> if conversion would negatively
* overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
* or {@code Long.MIN_VALUE} if conversion would negatively
* overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
*/
public long convert(long sourceDuration, TimeUnit sourceUnit) {
throw new AbstractMethodError();
}
/**
* Equivalent to <tt>NANOSECONDS.convert(duration, this)</tt>.
* Equivalent to
* {@link #convert(long, TimeUnit) NANOSECONDS.convert(duration, this)}.
* @param duration the duration
* @return the converted duration,
* or <tt>Long.MIN_VALUE</tt> if conversion would negatively
* overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
* @see #convert
* or {@code Long.MIN_VALUE} if conversion would negatively
* overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
*/
public long toNanos(long duration) {
throw new AbstractMethodError();
}
/**
* Equivalent to <tt>MICROSECONDS.convert(duration, this)</tt>.
* Equivalent to
* {@link #convert(long, TimeUnit) MICROSECONDS.convert(duration, this)}.
* @param duration the duration
* @return the converted duration,
* or <tt>Long.MIN_VALUE</tt> if conversion would negatively
* overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
* @see #convert
* or {@code Long.MIN_VALUE} if conversion would negatively
* overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
*/
public long toMicros(long duration) {
throw new AbstractMethodError();
}
/**
* Equivalent to <tt>MILLISECONDS.convert(duration, this)</tt>.
* Equivalent to
* {@link #convert(long, TimeUnit) MILLISECONDS.convert(duration, this)}.
* @param duration the duration
* @return the converted duration,
* or <tt>Long.MIN_VALUE</tt> if conversion would negatively
* overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
* @see #convert
* or {@code Long.MIN_VALUE} if conversion would negatively
* overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
*/
public long toMillis(long duration) {
throw new AbstractMethodError();
}
/**
* Equivalent to <tt>SECONDS.convert(duration, this)</tt>.
* Equivalent to
* {@link #convert(long, TimeUnit) SECONDS.convert(duration, this)}.
* @param duration the duration
* @return the converted duration,
* or <tt>Long.MIN_VALUE</tt> if conversion would negatively
* overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
* @see #convert
* or {@code Long.MIN_VALUE} if conversion would negatively
* overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
*/
public long toSeconds(long duration) {
throw new AbstractMethodError();
}
/**
* Equivalent to <tt>MINUTES.convert(duration, this)</tt>.
* Equivalent to
* {@link #convert(long, TimeUnit) MINUTES.convert(duration, this)}.
* @param duration the duration
* @return the converted duration,
* or <tt>Long.MIN_VALUE</tt> if conversion would negatively
* overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
* @see #convert
* or {@code Long.MIN_VALUE} if conversion would negatively
* overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
* @since 1.6
*/
public long toMinutes(long duration) {
@ -258,12 +257,12 @@ public enum TimeUnit {
}
/**
* Equivalent to <tt>HOURS.convert(duration, this)</tt>.
* Equivalent to
* {@link #convert(long, TimeUnit) HOURS.convert(duration, this)}.
* @param duration the duration
* @return the converted duration,
* or <tt>Long.MIN_VALUE</tt> if conversion would negatively
* overflow, or <tt>Long.MAX_VALUE</tt> if it would positively overflow.
* @see #convert
* or {@code Long.MIN_VALUE} if conversion would negatively
* overflow, or {@code Long.MAX_VALUE} if it would positively overflow.
* @since 1.6
*/
public long toHours(long duration) {
@ -271,10 +270,10 @@ public enum TimeUnit {
}
/**
* Equivalent to <tt>DAYS.convert(duration, this)</tt>.
* Equivalent to
* {@link #convert(long, TimeUnit) DAYS.convert(duration, this)}.
* @param duration the duration
* @return the converted duration
* @see #convert
* @since 1.6
*/
public long toDays(long duration) {
@ -294,9 +293,9 @@ public enum TimeUnit {
* Performs a timed {@link Object#wait(long, int) Object.wait}
* using this time unit.
* This is a convenience method that converts timeout arguments
* into the form required by the <tt>Object.wait</tt> method.
* into the form required by the {@code Object.wait} method.
*
* <p>For example, you could implement a blocking <tt>poll</tt>
* <p>For example, you could implement a blocking {@code poll}
* method (see {@link BlockingQueue#poll BlockingQueue.poll})
* using:
*
@ -327,7 +326,7 @@ public enum TimeUnit {
* Performs a timed {@link Thread#join(long, int) Thread.join}
* using this time unit.
* This is a convenience method that converts time arguments into the
* form required by the <tt>Thread.join</tt> method.
* form required by the {@code Thread.join} method.
*
* @param thread the thread to wait for
* @param timeout the maximum time to wait. If less than
@ -347,7 +346,7 @@ public enum TimeUnit {
* Performs a {@link Thread#sleep(long, int) Thread.sleep} using
* this time unit.
* This is a convenience method that converts time arguments into the
* form required by the <tt>Thread.sleep</tt> method.
* form required by the {@code Thread.sleep} method.
*
* @param timeout the minimum time to sleep. If less than
* or equal to zero, do not sleep at all.

6
jdk/src/share/classes/java/util/concurrent/TimeoutException.java
View File

@ -40,7 +40,7 @@ package java.util.concurrent;
* operations for which a timeout is specified need a means to
* indicate that the timeout has occurred. For many such operations it
* is possible to return a value that indicates timeout; when that is
* not possible or desirable then <tt>TimeoutException</tt> should be
* not possible or desirable then {@code TimeoutException} should be
* declared and thrown.
*
* @since 1.5
@ -50,13 +50,13 @@ public class TimeoutException extends Exception {
private static final long serialVersionUID = 1900926677490660714L;
/**
* Constructs a <tt>TimeoutException</tt> with no specified detail
* Constructs a {@code TimeoutException} with no specified detail
* message.
*/
public TimeoutException() {}
/**
* Constructs a <tt>TimeoutException</tt> with the specified detail
* Constructs a {@code TimeoutException} with the specified detail
* message.
*
* @param message the detail message

14
jdk/src/share/classes/java/util/concurrent/package-info.java
View File

@ -48,7 +48,7 @@
*
* {@link java.util.concurrent.Executor} is a simple standardized
* interface for defining custom thread-like subsystems, including
* thread pools, asynchronous IO, and lightweight task frameworks.
* thread pools, asynchronous I/O, and lightweight task frameworks.
* Depending on which concrete Executor class is being used, tasks may
* execute in a newly created thread, an existing task-execution thread,
* or the thread calling {@link java.util.concurrent.Executor#execute
@ -102,8 +102,10 @@
* <h2>Queues</h2>
*
* The {@link java.util.concurrent.ConcurrentLinkedQueue} class
* supplies an efficient scalable thread-safe non-blocking FIFO
* queue.
* supplies an efficient scalable thread-safe non-blocking FIFO queue.
* The {@link java.util.concurrent.ConcurrentLinkedDeque} class is
* similar, but additionally supports the {@link java.util.Deque}
* interface.
*
* <p>Five implementations in {@code java.util.concurrent} support
* the extended {@link java.util.concurrent.BlockingQueue}
@ -117,7 +119,7 @@
* for producer-consumer, messaging, parallel tasking, and
* related concurrent designs.
*
* <p> Extended interface {@link java.util.concurrent.TransferQueue},
* <p>Extended interface {@link java.util.concurrent.TransferQueue},
* and implementation {@link java.util.concurrent.LinkedTransferQueue}
* introduce a synchronous {@code transfer} method (along with related
* features) in which a producer may optionally block awaiting its
@ -216,9 +218,9 @@
* it may (or may not) reflect any updates since the iterator was
* created.
*
* <h2><a name="MemoryVisibility">Memory Consistency Properties</a></h2>
* <h2 id="MemoryVisibility">Memory Consistency Properties</h2>
*
* <a href="http://docs.oracle.com/javase/specs/jls/se7/html/index.html">
* <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-17.html#jls-17.4.5">
* Chapter 17 of the Java Language Specification</a> defines the
* <i>happens-before</i> relation on memory operations such as reads and
* writes of shared variables. The results of a write by one thread are