com.bigdata.relation.accesspath.BlockingBuffer Maven / Gradle / Ivy
/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
[email protected]
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Created on Nov 11, 2007
*/
package com.bigdata.relation.accesspath;
import java.nio.channels.ClosedByInterruptException;
import java.nio.channels.FileChannel;
import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingDeque;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.ReentrantLock;
import org.apache.log4j.Logger;
import cern.colt.Arrays;
import com.bigdata.bop.engine.QueryTimeoutException;
import com.bigdata.rdf.store.BigdataSolutionResolverator;
import com.bigdata.rdf.store.BigdataStatementIteratorImpl;
import com.bigdata.relation.rule.IQueryOptions;
import com.bigdata.relation.rule.IRule;
import com.bigdata.util.InnerCause;
import cutthecrap.utils.striterators.ICloseableIterator;
/**
*
* A buffer that will block when it is full. You write elements on the buffer
* and they can be read using {@link #iterator()}. This class is safe for
* concurrent writes (multiple threads can use {@link #add(Object)}) but the
* {@link #iterator()} is not thread-safe (it assumes a single reader).
*
*
* You MUST make sure that the thread that sets up the
* {@link BlockingBuffer} and which submits a task that writes on the buffer
* also sets the {@link Future} on the {@link BlockingBuffer} so that the
* iterator can monitor the {@link Future}, detect if it has been canceled, and
* throw out the exception from the {@link Future} back to the client. Failure
* to do this can lead to the iterator not terminating!
*
*
* Note: {@link BlockingBuffer} is used (a) for {@link IAccessPath} iterators
* that exceed the fully-buffered read threshold; (b) for high-level query with
* at least one join; (c) by the {@link BigdataStatementIteratorImpl}, which is
* used by the RDF DB for high-level query with no joins; and by the
* {@link BigdataSolutionResolverator}, which is used by the RDF DB high-level
* query that produces binding sets.
*
*
* @author Bryan Thompson
* @version $Id$
*
* @todo This class has internal complexities which arise from the need to
* coordinate elements being added to the buffer with elements being
* drained by the iterator without access to the internal lock of the
* backing queue. If we could use that internal lock then we could get rid
* of the spin loops and related cruft.
*/
public class BlockingBuffer implements IBlockingBuffer {
/**
* Warning messages are emitted if either the producer or the consumer is
* stalled. When {@link Logger#isInfoEnabled()} is true,
* those log messages will be include stack traces which can help to
* identify the the consumer or producer.
*/
protected static final Logger log = Logger.getLogger(BlockingBuffer.class);
/**
* The initial delay before we will log a warning for {@link #add(Object)}
* and {@link BlockingBuffer.BlockingIterator#hasNext(long, TimeUnit)}.
*/
private static final long initialLogTimeout = TimeUnit.NANOSECONDS.convert(
2000L, TimeUnit.MILLISECONDS);
/**
* The maximum timeout before we log the next warning for
* {@link #add(Object)} and
* {@link BlockingBuffer.BlockingIterator#hasNext(long, TimeUnit)}.
* The log timeout will double after each warning logged up to this maximum.
*/
private static final long maxLogTimeout = TimeUnit.NANOSECONDS
.convert(10000L, TimeUnit.MILLISECONDS);
/**
* The #of times that we will use {@link BlockingQueue#offer(Object)} or
* before converting to the variant of that method which accept a timeout.
* The timeouts are used to reduce the contention for the queue if either
* the consumer is lagging.
*/
private static final int NSPIN_ADD = Integer.valueOf(System.getProperty(
BlockingBuffer.class.getName() + ".NSPIN.ADD", "100"));
/**
* The #of times that we will use {@link Queue#poll()} before converting to
* the variant of that method which accept a timeout. The timeouts are used
* to reduce the contention for the queue if either the producer is lagging.
*/
private static final int NSPIN_READ = Integer.valueOf(System.getProperty(
BlockingBuffer.class.getName() + ".NSPIN.READ", "100"));
/**
* The timeout for offer() or poll() as a function of the #of tries that
* have already been made to {@link #add(Object)} or read a chunk.
*
* @param ntries
* The #of tries.
*
* @return The timeout (milliseconds).
*/
private static final long getTimeoutMillis(final int ntries) {
return ntries < 500 ? 10L : ntries < 1000 ? 100L : 250L;
}
/**
* true until the buffer is {@link #close()}ed.
*/
private volatile boolean open = true;
/**
* Lock used to make {@link BlockingIterator#_hasNext(long)} atomic with
* respect to {@link #add(Object, long, TimeUnit)} when the buffer has been
* closed.
*/
private final ReentrantLock lock = new ReentrantLock();
/**
* The exception (if any) which caused the buffer to be closed.
*/
private volatile Throwable cause = null;
/**
* Used to coordinate the reader and the writer.
*/
private final BlockingQueue queue;
/**
* The singleton for the iterator used to read from this buffer.
*/
private final IAsynchronousIterator iterator;
/**
* The default capacity for the internal {@link Queue} on which elements (or
* chunks of elements) are buffered.
*/
public static transient final int DEFAULT_PRODUCER_QUEUE_CAPACITY = 100;//5000;
/**
* The default minimum chunk size for the chunk combiner.
*/
public static transient final int DEFAULT_MINIMUM_CHUNK_SIZE = 100;//10000;
/**
* The default timeout in milliseconds during which chunks of elements may
* be combined in order to satisfy the desired minimum chunk size.
*/
public static transient final long DEFAULT_CONSUMER_CHUNK_TIMEOUT = 20;
/**
* The unit in which {@link #DEFAULT_CONSUMER_CHUNK_TIMEOUT} is expressed
* (milliseconds).
*/
public static transient final TimeUnit DEFAULT_CONSUMER_CHUNK_TIMEOUT_UNIT = TimeUnit.MILLISECONDS;
/**
* The desired minimum chunk size for the chunk combiner.
*
* @see #DEFAULT_MINIMUM_CHUNK_SIZE
*/
private final int minimumChunkSize;
/**
* The desired minimum chunk size for the chunk combiner.
*
* @see #DEFAULT_MINIMUM_CHUNK_SIZE
*/
public final int getMinimumChunkSize() {
return minimumChunkSize;
}
/**
* The maximum time to wait in nanoseconds for another chunk to come along
* so that we can combine it with the current chunk for {@link #next()}. A
* value of ZERO(0) disables chunk combiner.
*
* @see #DEFAULT_CONSUMER_CHUNK_TIMEOUT
*/
private final long chunkTimeout;
/**
* The maximum time to wait in nanoseconds for another chunk to come along
* so that we can combine it with the current chunk for {@link #next()}. A
* value of ZERO(0) disables chunk combiner.
*
* @see #DEFAULT_CONSUMER_CHUNK_TIMEOUT
*/
public final long getChunkTimeout() {
return chunkTimeout;
}
/**
* true iff the data in the buffered are chunks of elements
* presented in their natural sort order. When true, the
* {@link BlockingIterator} will apply a merge sort if it combines chunks so
* that the combined chunk remains in the natural order for the element
* type.
*/
private final boolean ordered;
/**
* The future of the producer.
*/
private volatile Future future;
/**
* Set the future of the producer feeding the {@link BlockingBuffer}.
*/
public void setFuture(final Future future) {
synchronized (this) {
if (future == null)
throw new IllegalArgumentException();
if (this.future != null)
throw new IllegalStateException();
this.future = future;
}
}
/**
* The {@link Future} of the producer feeding the {@link BlockingBuffer}.
*
* @return The {@link Future} -or- null if no {@link Future}
* has been set.
*
* @todo There should be a generic type for this.
*/
public Future getFuture() {
/*
* Note: [future] is volatile so we do not need to be synchronized to
* read the reference (changes to the reference will be visible anyway).
*/
return future;
}
/**
*
*/
public BlockingBuffer() {
this(DEFAULT_PRODUCER_QUEUE_CAPACITY);
}
/**
* Ctor automatically provisions an appropriate {@link BlockingQueue}.
*
* @param capacity
* The capacity of the buffer. When the generic type <E>
* is an array type, then this is the chunkOfChunksCapacity
* and small chunks will be automatically combined based on
* availability and latency. When zero (0) a
* {@link SynchronousQueue} will be used. Otherwise an
* {@link ArrayBlockingQueue} of the given capacity is used.
*/
public BlockingBuffer(final int capacity) {
this(capacity,
DEFAULT_MINIMUM_CHUNK_SIZE,
DEFAULT_CONSUMER_CHUNK_TIMEOUT,
DEFAULT_CONSUMER_CHUNK_TIMEOUT_UNIT
);
}
/**
*
* @param capacity
* The capacity of the buffer. When the generic type
* <E> is an array type, then this is the
* chunkOfChunksCapacity and small chunks will be
* automatically combined based on availability and latency. When
* zero (0) a {@link SynchronousQueue} will be used. Otherwise an
* {@link LinkedBlockingDeque} of the given capacity is used.
* @param minimumChunkSize
* The desired minimum chunk size. When the elements stored in
* the buffer are chunks (i.e., arrays of some component type),
* elements will be combined together to form larger chunks until
* this minimumChunkSize is satisfied, the {@link #iterator()} is
* exhausted, or the chunkTimeout is reached.
* @param chunkTimeout
* The maximum time to wait in nanoseconds for another chunk to
* come along so that we can combine it with the current chunk
* for {@link #next()}. A value of ZERO(0) disables chunk
* combiner.
* @param chunkTimeoutUnit
* The units in which the chunkTimeout is expressed.
*
* @todo There has been little to no testing of {@link BlockingBuffer} in
* combination with a {@link SynchronousQueue}.
*/
public BlockingBuffer(final int capacity, final int minimumChunkSize,
final long chunkTimeout, final TimeUnit chunkTimeoutUnit) {
this(capacity == 0 ? new SynchronousQueue()
: new LinkedBlockingDeque(capacity),//
// new ArrayBlockingQueue(capacity), //
minimumChunkSize,//
chunkTimeout,//
chunkTimeoutUnit,//
false// ordered
);
}
/**
* Core ctor.
*
* @param queue
* The queue on which elements will be buffered. Elements will be
* {@link #add(Object) added} to the queue and drained by the
* {@link #iterator()}. When this is a {@link BlockingDeque}
* array element types will be combined by
* {@link #add(Object, long, TimeUnit)} until the
* minimumChunkSize is satisfied.
* @param minimumChunkSize
* The desired minimum chunk size. When the elements stored in
* the buffer are chunks (i.e., arrays of some component type),
* elements will be combined together to form larger chunks until
* this chunkSize is satisfied, the {@link #iterator()} is
* exhausted, or the chunkTimeout is reached.
* @param chunkTimeout
* The maximum time to wait in nanoseconds for another chunk to
* come along so that we can combine it with the current chunk
* for {@link #next()}. A value of ZERO(0) disables chunk
* combiner.
* @param chunkTimeoutUnit
* The units in which the chunkTimeout is expressed.
* @param ordered
* When true the data are asserted to be ordered and
* a merge sort will be applied if chunks are combined such that
* the combined chunks will also be ordered (this has no effect
* unless the generic type of the buffer is an array type).
*/
public BlockingBuffer(final BlockingQueue queue,
final int minimumChunkSize, final long chunkTimeout,
final TimeUnit chunkTimeoutUnit, final boolean ordered) {
// if (minimumChunkSize >= 1000 || queue.remainingCapacity() >= 1000)
// log.fatal(new RuntimeException("queueCapacity="
// + queue.remainingCapacity() + ", minimumChunkSize="
// + minimumChunkSize));
if (queue == null)
throw new IllegalArgumentException();
if (minimumChunkSize < 0) {
/*
* Note: zero is allowed since the buffer may store individual
* elements depending on the generic type , not just chunks of
* elements.
*/
throw new IllegalArgumentException();
}
if (chunkTimeout < 0L) {
/*
* Note: zero is allowed and will disable the chunk combiner.
*/
throw new IllegalArgumentException();
}
if (chunkTimeoutUnit == null)
throw new IllegalArgumentException();
this.queue = queue;
this.minimumChunkSize = minimumChunkSize;
// convert to nanoseconds.
this.chunkTimeout = TimeUnit.NANOSECONDS.convert(chunkTimeout,
chunkTimeoutUnit);
this.ordered = ordered;
this.iterator = new BlockingIterator();
/*
* The stack frame in which the buffer was allocated. This gives you a
* clue about who is the producer that will write on the buffer.
*
* Note: This is only allocated for debugging purposes. Otherwise the
* stack frame should not be taken.
*/
if (log.isInfoEnabled()) {
this.openStackFrame = new RuntimeException(
MSG_ALLOCATION_STACK_FRAME);
}
}
/**
* When true, this will issue some annoying warnings that can
* be used to identify slow consumers or fast producers.
*
* @see LOG
* BlockingBuffer not progressing at INFO or lower level
*/
private static final boolean producerConsumerWarnings = false;
/**
* Label for messages displaying the stack frame within which the
* {@link BlockingBuffer} was allocated.
*
* @see #openStackFrame
*/
private static transient final String MSG_ALLOCATION_STACK_FRAME = "Buffer Allocation Stack Frame";
/**
* Label for messages displaying the stack frame within which the
* {@link BlockingBuffer} was {@link #close() closed}.
*
* @see #closeStackFrame
*/
private static transient final String MSG_CLOSED_STACK_FRAME = "Buffer Closed Stack Frame";
/**
* Label for messages displaying the stack frame of the producer writing on
* the {@link BlockingBuffer} using {@link #add(Object)}.
*/
private static transient final String MSG_PRODUCER_STACK_FRAME = "Buffer Producer Stack Frame";
/**
* Label for messages displaying the stack frame of the consumer draining
* the {@link BlockingBuffer} using the {@link BlockingIterator}.
*/
private static transient final String MSG_CONSUMER_STACK_FRAME = "Buffer Consumer Stack Frame";
/**
* Stack frame where the buffer was allocated. This is allocated iff
* {@link Logger#isInfoEnabled()} is true for {@link #log}.
*/
private RuntimeException openStackFrame;
/**
* Stack frame where the buffer was closed. This is allocated iff
* {@link Logger#isInfoEnabled()} is true for {@link #log}.
*/
private RuntimeException closeStackFrame;
public String toString() {
final StringBuilder sb = new StringBuilder();
sb.append(super.toString());
// sb.append("BlockingBuffer");
sb.append("{ open=" + open);
sb.append(", hasFuture=" + (future != null));
sb.append(", elementsAddedCount=" + elementsAddedCount);
sb.append(", chunksAddedCount=" + chunksAddedCount);
sb.append(", chunksDrainedCount=" + chunksDrainedCount);
sb.append(", elementsDrainedCount=" + elementsDrainedCount);
if (true || log.isInfoEnabled()) {
/*
* Note: These data are only approximate and most BlockingQueue
* implementations will obtain a when when you call size() or
* remainingCapacity().
*/
sb.append(", size~=" + queue.size());
sb.append(", remainingCapacity~=" + queue.remainingCapacity());
}
if (cause != null)
sb.append(", cause=" + cause);
sb.append("}");
return sb.toString();
}
/**
* @throws BufferClosedException
* if the buffer is not open. The cause will be set if
* {@link #abort(Throwable)} was used.
*/
private void assertOpen() {
if(!open) {
if (openStackFrame != null) {
/*
* Purely for debugging.
*/
log.warn(openStackFrame);
}
if (closeStackFrame != null) {
/*
* Purely for debugging.
*/
log.warn(closeStackFrame);
}
if (cause != null) {
throw new BufferClosedException(cause);
}
throw new BufferClosedException();
}
}
public boolean isEmpty() {
return queue.isEmpty();
}
/**
* This reports the #of items in the queue.
*
* @see #getElementsOnQueueCount()
*/
public int size() {
return queue.size();
}
public boolean isOpen() {
return open;
}
public boolean isOrdered() {
return ordered;
}
/**
* Closes the {@link BlockingBuffer} such that it will not accept new
* elements (this is a NOP if unless the buffer is open). Once the buffer is
* closed, the {@link BlockingIterator} will drain any elements remaining in
* the {@link BlockingBuffer} and then report false for
* {@link BlockingIterator#hasNext()) (this does NOT close the
* {@link BlockingIterator}).
*/
synchronized public void close() {
if (open) {
try {
// if (log.isInfoEnabled()) {
//
// // Note: Stack trace is to show WHO closed the buffer
// log.info("Closing buffer: ", new RuntimeException(
// "Closing buffer."));
//
// }
if (log.isInfoEnabled()) {
this.closeStackFrame = new RuntimeException(
MSG_CLOSED_STACK_FRAME);
}
// if (openStackFrame != null) {
//
// /*
// * Purely for debugging.
// */
//
//// log.warn("closing buffer at", new RuntimeException());
//
// log.warn("buffer allocated at", openStackFrame);
//
// }
} finally {
this.open = false;
}
}
}
/**
* Clear the backing queue.
*
* @throws IllegalStateException
* If the buffer is open.
*/
public void clear() throws IllegalStateException {
if(open)
throw new IllegalStateException();
if (log.isInfoEnabled())
log.info("");
queue.clear();
}
public void abort(final Throwable cause) {
if (cause == null)
throw new IllegalArgumentException();
if (log.isInfoEnabled())
log.info("cause=" + cause, cause);
synchronized (this) {
if (this.cause != null) {
log.warn("Already aborted with cause=" + this.cause);
return;
}
// set the cause.
this.cause = cause;
// mark as closed.
this.open = false;
}
}
/**
* The #of chunks {@link #add(Object)ed} to the buffer. This will be ZERO
* unless the generic type of the buffer is an array type.
*/
private long chunksAddedCount = 0L;
/**
* The #of elements {@link #add(Object)ed} to the buffer. When the generic
* type of the buffer is an array type, this will be the sum of the length
* of the arrays {@link #add(Object)ed} to the buffer.
*/
private long elementsAddedCount = 0L;
/**
* The #of elements on the queue. When the queue uses a scalar element
* type this will track the {@link #size()} very closely. However, when
* the queue uses an array element type, this will be the sum of the #of
* elements across all arrays on the queue.
*/
private AtomicLong elementsOnQueueCount = new AtomicLong(0L);
/**
* The #of chunks read so far from the iterator (aka drained from the
* buffer).
*/
private long chunksDrainedCount = 0L;
/**
* The #of elements read so far from the iterator (aka drained from the
* buffer).
*/
private long elementsDrainedCount = 0L;
/**
* The #of chunks {@link #add(Object)ed} to the buffer. This will be ZERO
* unless the generic type of the buffer is an array type.
*/
public long getChunksAddedCount() {
return chunksAddedCount;
}
/**
* The #of elements {@link #add(Object)ed} to the buffer. When the generic
* type of the buffer is an array type, this will be the sum of the length
* of the arrays {@link #add(Object)ed} to the buffer.
*/
public long getElementsAddedCount() {
return elementsAddedCount;
}
/**
* The #of elements on the queue. When the queue uses a scalar element
* type this will track the {@link #size()} very closely. However, when
* the queue uses an array element type, this will be the sum of the #of
* elements across all arrays on the queue.
*/
public long getElementsOnQueueCount() {
return elementsOnQueueCount.get();
}
/**
* @throws BufferClosedException
* if the buffer has been {@link #close()}d.
* @throws RuntimeException
* if the caller's {@link Thread} is interrupted. The
* {@link RuntimeException} will wrap the
* {@link InterruptedException} as its cause.
*/
public void add(final E e) {
try {
if (!add(e, Long.MAX_VALUE, TimeUnit.NANOSECONDS)) {
/*
* Note: with an infinite timeout, the add should always
* succeed. A false return indicates a problem.
*/
throw new AssertionError();
}
} catch(InterruptedException ex) {
throw new RuntimeException(ex);
}
}
/**
* This method provides a non-blocking feature to combine chunks when they
* are added to an internal {@link BlockingDeque}. The feature is enabled
* iff the elements are an array type (chunks) and a {@link BlockingDeque}
* was specified via the constructor. The purpose of this is to keep the
* size of the queue down when it is common that (a) the chunks being added
* to the queue are small; and (b) the consumer is slower than the producer
* (so combining chunks when the queue is drained by the iterator will not
* keep the queue size down).
*
* Approach: While holding the lock in add(e,timeout) and when offering a
* chunk which is LTE the desired chunkSize, do Dequeue()#peekLast() and
* verify that the last chunk could be combined with the current chunk. If
* so, then do Dequeue#pollLast() to remove the last chunk from the queue
* [if pollLast() returns non-null it will return the same chunk as
* peekLast() since no other thread is draining from this end of the
* dequeue].
*
* If pollLast() returns an chunk which be combined with the chunk to be
* offered, then combine the chunks, apply a mergeSort if they are ordered,
* and add(E) the combined chunk [this should succeed immediately since we
* are holding the lock, so no other thread can be adding to the queue
* concurrently and we have just drained something from the queue so it can
* not be full.]
*
* Otherwise, add(E) the chunk returned by pollLast() [again, this should
* succeed immediately since we are holding the lock and no other thread can
* cause the size of the queue to increase] and then then offer(E) the
* original chunk [but do not retry the chunk combination logic.]
*
* Note: if no other thread is dequeuing elements from the last position
* then we do not need to iteratively dequeue successive elements since any
* successive element already has either a sufficient chunk size or can not
* be combined with the current element.]
*
* @todo review performance impact. do we need head combining and tail
* combining? tail combining is more efficient in that it does one
* merge sort no matter how many chunks were combined. head combining
* handles the special case where the queue is being run up to its
* capacity because a lot of small chunks are being added to the
* queue. This sometimes can cause a problem. For example, in the
* asynchronous write API, if ANY sink queue fills up then the master
* will block and progress will halt until the sink queue is no longer
* full.
*/
private boolean combineChunkOnAdd(final E e) {
/*
* Note: the caller must verify that the element is an array type and
* that the internal queue is a BlockingDeque.
*/
/*
* Note: the caller MUST be holding the lock. That is how we achieve
* our non-blocking guarantee.
*/
assert lock.isHeldByCurrentThread();
final BlockingDeque deque = (BlockingDeque) queue; //
// examine the last chunk in the dequeue.
E t = deque.peekLast();
if (t != null
&& ((Object[]) t).length + ((Object[]) e).length <= minimumChunkSize) {
/*
* Take the last chunk from the dequeue.
*
* Note: Since we are holding the lock, and since the lock is
* required to add a chunk to the internal queue, we are guaranteed
* that we can return a chunk to the queue without blocking. That
* will either be the chunk that we get from pollLast() or a new
* chunk we obtain by combining the caller's chunk with the chunk
* from pollLast().
*/
t = deque.pollLast();
if (t != null) {
if (((Object[]) t).length + ((Object[]) e).length <= minimumChunkSize) {
/*
* Combine chunks.
*
* Note: The order of the elements in the resulting array
* maintains their queuing order. Since [t] was on the
* queue, it comes first in the combined chunk.
*/
t = combineChunks(t, e);
if(ordered) {
/*
* Maintain the natural order within the
* combined chunk using an in place merge
* sort.
*/
ChunkMergeSortHelper.mergeSort((Object[]) t);
}
// add combined chunk (will not block).
deque.add(t);
chunksAddedCount++;
elementsAddedCount += ((Object[]) e).length;
elementsOnQueueCount.addAndGet(((Object[]) e).length);
if (log.isDebugEnabled())
log.debug("add/combined chunk: len="
+ ((Object[]) e).length + ", combined length="
+ ((Object[]) t).length);
// done : must exit : @todo count #of head combined chunks.
return true;
}
// return chunk to dequeue (will not block)
deque.add(t);
// fall through (caller's chunk was not queued).
}
}
/*
* Fall through - either the dequeue is empty or last chunk
* plus this chunk exceeds the target chunkCapacity.
*/
return false;
}
/**
* Add element to the buffer.
*
* @param e
* The element.
* @param timeout
* The timeout.
* @param unit
* The unit in which the timeout is expressed.
*
* @return true iff the element was added to the buffer (
* false indicates that the timeout expired before the
* element could be added to the buffer).
*
* @throws InterruptedException
* if interrupted
*/
public boolean add(final E e, final long timeout, final TimeUnit unit)
throws InterruptedException {
if (e == null)
throw new IllegalArgumentException();
if (e.getClass().getComponentType() != null) {
if (((Object[]) e).length == 0) {
if(log.isInfoEnabled())
log.info("Empty chunk.");
// empty chunk.
return true;
}
}
final long begin = System.nanoTime();
// wait if the queue is full.
int ntries = 0;
// initial delay before the 1st log message.
long logTimeout = initialLogTimeout;
// false unless we attempt to combine the chunk with the last chunk on the deque.
boolean didCombine = false;
// nanoseconds remaining until the timeout.
long nanos = unit.toNanos(timeout);
long lastTime = begin;
while (true) {
{
final long now = System.nanoTime();
nanos -= now - lastTime;
lastTime = now;
if (nanos <= 0) {
// timeout.
return false;
}
}
if (/* lock.tryLock()|| */lock.tryLock(nanos, TimeUnit.NANOSECONDS)) {
try {
/*
* Note: This is done inside of the loop so that we will
* notice if the buffer is closed asynchronously. Otherwise
* we would just spin forever once we made it past the guard
* the first time.
*/
assertOpen();
/*
* Consider combining with the last element on the queue
* only the first time through. If it does not work, then
* trying again will only waste CPU.
*/
if (!didCombine && minimumChunkSize > 0
&& queue instanceof BlockingDeque
&& e.getClass().getComponentType() != null) {
if (combineChunkOnAdd(e)) {
// done (was able to combine the chunks on add).
return true;
}
didCombine = true;
} // not a dequeue or not an array type (fall through).
/*
* Note: This is basically a spin lock, though offer(e) does
* acquire a lock internally. If we have spun enough times,
* then we will use staged timeouts for subsequent offer()s.
* This allows the consumer to catch up with less contention
* for the queue. [@todo complexity imposed by non-access to queue's internal lock.]
*/
final boolean added;
if (ntries < NSPIN_ADD) {
// offer (non-blocking).
added = queue.offer(e);
} else {
// update in case we waited a while for the lock.
final long now = System.nanoTime();
nanos -= now - lastTime;
lastTime = now;
final long offerTimeoutNanos = Math.min(nanos,
TimeUnit.MILLISECONDS
.toNanos(getTimeoutMillis(ntries)));
try {
// offer (staged timeout, not to exceed the time
// remaining).
added = queue.offer(e, offerTimeoutNanos,
TimeUnit.NANOSECONDS);
} catch (InterruptedException ex) {
abort(ex);
throw new RuntimeException(
"Buffer closed by interrupt", ex);
}
}
if (!added) {
ntries++;
final long elapsed = System.nanoTime() - begin;
if (elapsed >= logTimeout) {
logTimeout += Math.min(maxLogTimeout, logTimeout);
if(producerConsumerWarnings && log.isInfoEnabled()) {
final String msg = "blocked: ntries="
+ ntries
+ ", elapsed="
+ TimeUnit.MILLISECONDS.convert(elapsed,
TimeUnit.NANOSECONDS)
+ ", timeout="
+ TimeUnit.MILLISECONDS.convert(logTimeout,
TimeUnit.NANOSECONDS) + "ms : "
+ this;
if (log.isInfoEnabled()
&& logTimeout > maxLogTimeout) {
/*
* Issue warning with stack trace showing who is
* blocked.
*/
log.warn(msg, new RuntimeException(
MSG_PRODUCER_STACK_FRAME));
} else {
// issue warning.
log.warn(msg);
}
}
}
// try to add the element again.
continue;
} // if (!added)
// item now on the queue.
if (e.getClass().getComponentType() != null) {
chunksAddedCount++;
elementsAddedCount += ((Object[]) e).length;
elementsOnQueueCount.addAndGet(((Object[]) e).length);
if (log.isDebugEnabled())
log.debug("added chunk: len="
+ ((Object[]) e).length);
} else {
elementsAddedCount++;
elementsOnQueueCount.incrementAndGet();
if (log.isDebugEnabled())
log.debug("added: " + e.toString());
}
// success.
return true;
} finally {
lock.unlock();
}
} // if(tryLock())
} // while
}
public long flush() {
return 0L;
}
public void reset() {
queue.clear();
// clear nextE on the inner class?
}
/**
* The iterator is NOT thread-safe and does NOT support remove().
*
* Note: If the {@link IAsynchronousIterator} is
* {@link ICloseableIterator#close()}d before the {@link Future} of the
* process writing on the {@link BlockingBuffer} is done, then the
* {@link Future} will be canceled using {@link Thread#interrupt()}. Owing
* to a feature of {@link FileChannel}, this will cause the backing store to
* be asynchronously closed if the interrupt is detected during an IO. The
* backing store will be re-opened transparently, but there is overhead
* associated with that (locks to be re-acquired, etc).
*
* The most common reason to close an iterator early are that you want to
* only visit a limited #of elements. However, if you use either
* {@link IAccessPath#iterator(long,long, int)} or {@link IRule} with an
* {@link IQueryOptions} to impose that limit, then most processes that
* produce {@link IAsynchronousIterator}s will automatically terminate when
* they reach the desired limit, thereby avoiding issuing interrupts. Those
* processes include {@link IAccessPath} scans where the #of elements to be
* visited exceeds the fully materialized chunk threshold and {@link IRule}
* evaluation.
*
* @return The iterator (this is a singleton).
*
* @see BlockingIterator#close()
*/
public IAsynchronousIterator iterator() {
return iterator;
}
/**
* An inner class that reads from the buffer. This is not thread-safe - it
* makes no attempt to be atomic in its operations in {@link #hasNext()} or
* {@link #next()}.
*
* @author Bryan Thompson
* @version $Id$
*/
protected class BlockingIterator implements IAsynchronousIterator {
/**
* true iff this iterator is open - it is closed when the
* thread consuming the iterator decides that it is done with the
* iterator.
*
* Note: {@link BlockingBuffer#open} is true until the
* thread WRITING on the buffer decides that it has nothing further to
* write. Once {@link BlockingBuffer#open} becomes false
* and there are no more elements in the buffer then the iterator is
* exhausted since there is nothing left that it can visit and nothing
* new will enter into the buffer.
*
* Note: This is NOT volatile since it is set by the
* consumer using {@link #close()} and the consumer is supposed to be
* single-threaded. However, this means that invoking {@link #toString()}
* from another thread can show the old state of the field.
*/
private boolean open = true;
/**
* The next element to be returned (from the head of the queue).
*
* Note: We use {@link #nextE} because {@link BlockingQueue} does not
* offer a method in which we peek with a timeout, only in which we poll
* with a timeout. Therefore we poll with a timeout and if poll()
* returns an element, then we set it on {@link #nextE}.
*/
private E nextE = null;
/**
* Safe non-blocking representation of the iterator state.
*/
public String toString() {
final StringBuilder sb = new StringBuilder();
sb.append("BlockingIterator");
sb.append("{ open=" + open);
sb.append(", futureIsDone=" + futureIsDone);
sb.append(", bufferIsOpen=" + BlockingBuffer.this.open);
sb.append(", nextE=" + (nextE != null));
sb.append("}");
return sb.toString();
}
/**
* Create an iterator that reads from the buffer.
*/
private BlockingIterator() {
if (log.isInfoEnabled())
log.info("Starting iterator.");
}
// /**
// * @throws IllegalStateException
// * if the {@link BlockingBuffer#abort(Throwable)} was
// * invoked asynchronously.
// */
// final private void assertNotAborted() {
//
// if (cause != null) {
//
// throw new IllegalStateException(cause);
//
// }
//
// }
/**
* Mark the iterator as being closed but DO NOT cancel the
* {@link Future}.
*/
private void _close() {
if (log.isDebugEnabled())
log.debug("");
if (!open)
return;
open = false;
}
/**
* {@inheritDoc}
*
* @see BlockingBuffer#iterator()
*/
public void close() {
_close();
if (future == null) {
/*
* Note: The future is not always set. For example, when a Join
* Task creates a BlockingBuffer for each sink there is an
* inversion of control. The JoinTask is populating the
* BlockingBuffer in its own thread(s) while the sink is
* draining the BlockingBuffer independently. However, the more
* common case has a task that is created to write on the
* BlockingBuffer and the iterator is then consumed by the
* caller (Query works this way).
*/
if (log.isInfoEnabled()) {
/*
* Purely for debugging.
*/
final String msg = "Future not set: " + this;
log.warn(msg, new RuntimeException());
if (openStackFrame != null) {
log.warn(msg, openStackFrame);
}
}
} else if (!future.isDone()) {
if (log.isInfoEnabled()) {
/*
* Log @ WARN with a stack trace so that you can see who
* closed the iterator.
*/
log.warn(this, new RuntimeException("Cancelling future: "
+ future));
/*
* Note: I have taken out this warning message since it is a
* common enough event and nothing to be concerned about. It
* is just the relative timing and source of the buffer
* close event. If the Iterator (consumer) is closed first,
* then this code path is not taken. It is common that the
* iterator is closed first, but a common counter example is
* when a join breaks in a manner which throus an exception
* which we are willing to mask and we interrupt the
* downstream join tasks. If the BlockingBuffer (producer)
* is closed first, then this code path is token. Since this
* is not a difference which makes a difference there is no
* point issuing a warning for it.
*/
// } else {
//
// /*
// * Otherwise log @ WARN w/o a stack trace.
// */
// log.warn("Cancelling future: " + future);
}
/*
* Note: Cancelling the Future may cause a
* ClosedByInterruptException to be thrown. That will be noticed
* by checkFuture(), which logs this @ INFO..
*/
future.cancel(true/* mayInterruptIfRunning */);
}
}
// /**
// * true iff the {@link Future} has been set and
// * {@link Future#isDone()} returns true.
// */
// public boolean isFutureDone() {
//
// return futureIsDone;
//
// }
/**
* Checks the {@link BlockingBuffer#future} to see if it (a) is done;
* and (b) has completed successfully. The first time this method checks
* the {@link Future} and discovers that {@link Future#isDone()} returns
* true it {@link BlockingBuffer#close()}s the
* {@link BlockingBuffer}. This is done in case the producer fails to
* close the {@link BlockingBuffer} themselves. If this method tests the
* {@link Future} and discovers an exception, then it will wrap and
* re-throw that exception such that it becomes visible to the consumer.
*
* Note: {@link #hasNext()} WILL NOT return false until
* the {@link BlockingBuffer} is closed. Therefore, this method MUST be
* invoked MUST be invoked periodically. We do this if the iterator
* appears to not be progressing since failure by the producer to close
* the {@link BlockingBuffer} will lead to an iterator that appears to
* be stalled. However, we also must invoke {@link #checkFuture()} no
* later than when {@link #hasNext(long, TimeUnit)} returns
* false in order for the consumer to be guaranteed to
* see any exception thrown by the producer.
*
* Note: Once the {@link BlockingBuffer} is closed (except for aborts),
* the consumer still needs to drain the {@link BlockingBuffer#queue}.
*/
private final void checkFuture() {
if (!futureIsDone && future != null && future.isDone()) {
if (log.isInfoEnabled())
log.info("Future is done");
// don't re-execute this code.
futureIsDone = true;
/*
* Make sure the buffer is closed. In fact, the caller probably
* does not need to close the buffer since we do it here when
* their task completes.
*/
BlockingBuffer.this.close();
try {
// look for an error from the Future.
future.get();
} catch (InterruptedException e) {
if (log.isInfoEnabled())
log.info(e.getMessage());
// itr will not deliver any more elements.
_close();
} catch (ExecutionException e) {
if(InnerCause.isInnerCause(e,
QueryTimeoutException.class)) {
/**
* Closed by query deadline expiration.
*
* @see
* Query timeout only checked at operator
* start/stop.
*/
if (log.isInfoEnabled())
log.info(e.getMessage());
// itr will not deliver any more elements.
_close();
// need to rethrow to convert to openrdf query interrupted exception.
throw new RuntimeException(e);
}
if (InnerCause.isInnerCause(e,
ClosedByInterruptException.class)||
InnerCause.isInnerCause(e,
InterruptedException.class)) {
/*
* Note: ClosedByInterruptException indicates that the
* producer was interrupted. This occurs any time the
* iterator is closed prematurely. For example, if there
* is a LIMIT on a query then the join will be broken
* when the limit is satisfied. That causes the
* producer's Future to be cancelled, which means that
* it gets interrupted. This is not an error.
*
* Note: a wrapped InterruptedException is handled the
* same as an plain InterruptedException (above) or the
* ClosedByInterruptException (here).
*/
if (log.isInfoEnabled())
log.info(e.getMessage());
// itr will not deliver any more elements.
_close();
return;
}
log.error(e, e);
// itr will not deliver any more elements.
_close();
// rethrow exception.
throw new RuntimeException(e);
}
}
}
private boolean futureIsDone = false;
public boolean isExhausted() {
if (!BlockingBuffer.this.open && nextE == null && queue.isEmpty()) {
// iterator is known to be exhausted.
return true;
}
// iterator might visit more elements (might not also).
return false;
}
/**
* Return true iff there is at least one element that can
* be visited (blocking). If the buffer is empty then this will block
* until: (a) an element appears in the buffer; or (b) the buffer is
* {@link BlockingBuffer#close()}ed.
*/
public boolean hasNext() {
/*
* Note: We can safely interpret a [false] return as an indication
* that the iterator is exhausted since we have set an infinite
* timeout.
*/
try {
// Note: This shaves off the conversion to nanoseconds.
return _hasNext(Long.MAX_VALUE);//, TimeUnit.SECONDS);
} catch (InterruptedException ex) {
// itr will not deliver any more elements.
_close();
// strong false (interrupted, so itr is closed).
checkFuture();
if (log.isDebugEnabled())
log.info("Interrupted: " + this, ex);
else if (log.isInfoEnabled())
log.info("Interrupted: " + this);
/**
* Note: Propagating the interrupt appears to be necessary here
* in order to have timely termination of nested subqueries.
*
* @see https://sourceforge.net/apps/trac/bigdata/ticket/707
* (BlockingBuffer.close() does not unblock threads)
* @see https://sourceforge.net/apps/trac/bigdata/ticket/716
* (Verify that IRunningQuery instances (and nested
* queries) are correctly cancelled when interrupted)
*/
Thread.currentThread().interrupt();
return false;
}
}
public boolean hasNext(final long timeout, final TimeUnit unit)
throws InterruptedException {
// if (nextE != null) {
//
// // we already have the next element on hand.
// return true;
//
// }
//
// /*
// * core impl.
// */
final long nanos = unit.toNanos(timeout);
// final boolean hasNext = _hasNext(nanos);
//
// if(!hasNext) {
//
// /*
// * Note: We call checkFuture() no later than when hasNext()
// * would return false so that the consumer will see any
// * exception thrown by the producer's Future.
// */
//
// checkFuture();
//
// }
return _hasNext(nanos);
}
/**
*
* @param nanos
* The number of nanoseconds remaining until timeout. This
* value is decremented until LTE ZERO (0L), at which point
* {@link #_hasNext(long)} will timeout.
*
* @return iff an element is available before the timeout has expired.
*
* @throws InterruptedException
*/
private boolean _hasNext(long nanos) throws InterruptedException {
if (nextE != null) {
// we already have the next element on hand.
return true;
}
// set to true to log stack traces at most once per request.
final boolean logOnce = !log.isDebugEnabled();
/*
* This false until the producer/consumer stack traces have been
* logged. The flag is used to prevent repeated logging of those
* stack traces while the iterator is blocked in this method. The
* traces will be logged at most once per invocation of this method.
*/
boolean loggedStackTraces = false;
final long begin = System.nanoTime();
long lastTime = begin;
// #of times that we poll() the queue.
int ntries = 0;
// the timeout until the next log message.
long logTimeout = initialLogTimeout;
/*
* Loop while the BlockingBuffer is open -or- there is an element
* available.
*
* Note: hasNext() must wait until the buffer is closed and all
* elements in the queue (and nextE) have been consumed before it
* can conclude that there will be nothing more that it can visit.
* This re-tests whether or not the buffer is open after a timeout
* and continues to loop until the buffer is closed AND there are no
* more elements in the queue.
*
* Note: These tests are in order of _speed_. poll() and isEmpty()
* both acquire a lock, so they are the slowest. BlockingBuffer.open
* is volatile. nextE is just a local field.
*/
// while (nextE != null || BlockingBuffer.this.open
// || ((nextE = queue.poll()) != null)) {
while (true) {
if (nextE == null && !BlockingBuffer.this.open) {
/*
* Note: The lock is used to make the decision that the
* buffer is exhausted atomic with respect to the close of
* the buffer and add(E,timeout). Without the lock it is
* possible that add(E,timeout) passed the assertOpen()
* guard but has not yet offered the element to the queue.
* With the lock, this becomes atomic.
*/
// Wait a bit for the lock, but not more time than remains.
final long lockTimeout = Math.min(nanos,
TimeUnit.MILLISECONDS.toNanos(5));
if (lock.tryLock(lockTimeout, TimeUnit.NANOSECONDS)) {
try {
if (((nextE = queue.poll()) == null)) {
if (log.isInfoEnabled())
log.info("Exhausted");
assert isExhausted();
// strong false - the iterator is exhausted.
checkFuture();
return false;
}
} finally {
lock.unlock();
}
} else { // else tryLock()
final long now = System.nanoTime();
// decrement time remaining.
nanos -= now - lastTime;
lastTime = now;
if (nanos <= 0) {
if (log.isDebugEnabled())
log.debug("Timeout");
// weak false (timeout).
return false;
}
if(log.isDebugEnabled())
log.debug("Lock timeout - will retry.");
// try again for the lock.
continue;
}// end if(tryLock)
}
if (nextE == null) {
/*
* Non-blocking test. This covers the case when the buffer
* is still open so we would not have polled the queue in
* the while() condition above. Since we did not poll above
* we will do it now before testing against the timeout. If
* we don't poll the queue before we examine the timeout
* then hasNext(timeout) will return false when there is
* something already buffered and the timeout is short
* (1ns).
*/
nextE = queue.poll();
}
if (nextE != null) {
/*
* Either nextE was already bound or the queue was not empty
* and we took the head of the queue using the non-blocking
* poll().
*
* Note: poll() is no more expensive than size(). However,
* it both tests whether or not the queue is empty and takes
* the head of the queue iff it is not empty. Note that we
* DO NOT poll unless [nextE] is [null] since that would
* cause us to loose the value in [nextE].
*/
return true;
}
/*
* Perform some checks to decide whether the iterator is still
* valid.
*/
if(!open) {
if (log.isDebugEnabled())
log.debug("iterator is closed");
// check before returning a strong [false] (vs timeout).
checkFuture();
return false;
}
// Note: tests volatile field.
if (cause != null)
throw new IllegalStateException(cause);
/*
* Now that we have those checks out of the way, update the time
* remaining and see if we have a timeout.
*/
final long now = System.nanoTime();
// decrement time remaining.
nanos -= now - lastTime;
lastTime = now;
if (nanos <= 0) {
if (log.isDebugEnabled())
log.debug("Timeout");
// weak false (timeout).
return false;
}
/*
* Poll the queue.
*
* Note: DO NOT sleep() here. Polling will use a Condition to
* wake up when there is something in the queue. If you sleep()
* here then ANY timeout can introduce an unacceptable latency
* since many queries can be evaluated in LT 10ms !
*
* Note: Even with poll(timeout,unit), a modest timeout will
* result in the thread yielding and a dramatic performance
* hit. We are better off using a short timeout so that we can
* continue to test the other conditions, specifically whether
* the buffer was closed asynchronously. Otherwise a client that
* writes nothing on the buffer will wind up hitting the timeout
* inside of poll(timeout,unit) [@todo This could be fixed by a poison pill.]
*/
if (ntries < NSPIN_READ) {
/*
* This is basically a spin lock (it can spin without
* yielding if there is no contention for the queue because
* the producer is lagging).
*/
if ((nextE = queue.poll()) != null) {
if (log.isDebugEnabled())
log.debug("next: " + nextE);
return true;
}
} else {
/*
* Here we are willing to be put to sleep for a bit. This
* can free a CPU that was otherwise caught in a spin on
* poll() to run the producer so that we have something to
* read.
*/
// try {
// final long timeout = getTimeoutMillis(ntries);
final long timeout = Math.min(nanos, TimeUnit.MILLISECONDS
.toNanos(getTimeoutMillis(ntries)));
if ((nextE = queue.poll(timeout, TimeUnit.NANOSECONDS)) != null) {
if (log.isDebugEnabled())
log
.debug("next: "
+ (nextE.getClass()
.getComponentType() != null ? Arrays
.toString((Object[]) nextE)
: nextE));
return true;
}
// } catch (InterruptedException ex) {
//
// // itr will not deliver any more elements.
// _close();
//
// // strong false (interrupted, so itr is closed).
// checkFuture();
//
// if (log.isDebugEnabled())
// log.info("Interrupted: " + this, ex);
// else if (log.isInfoEnabled())
// log.info("Interrupted: " + this);
//
// return false;
//
// }
}
/*
* Nothing available yet on the queue.
*/
assert nextE == null;
ntries++;
final long elapsedNanos = (now - begin);
if (elapsedNanos >= logTimeout) {
/*
* This could be a variety of things such as waiting on a
* mutex that is already held, e.g., an index lock, that
* results in a deadlock between the process writing on the
* buffer and the process reading from the buffer. If you
* are careful with who gets the unisolated view then this
* should not be a problem.
*/
// increase timeout until the next log message.
logTimeout += Math.min(maxLogTimeout, logTimeout);
if (future == null) {
/*
* This can arise if you fail to set the future on the
* buffer such that the iterator can not monitor it. If
* the future completes (esp. with an error) then the
* iterator can keep looking for another element but the
* source is no longer writing on the buffer and nothing
* will show up.
*
* Whether or not this is an error depends on whether or
* not you are intending to chain together producers and
* consumers using blocking buffers or if the output of
* the producer will be collected and then passed onto
* another process (perhaps on another node) once the
* producer is done.
*/
if (log.isInfoEnabled())
log.info("Future not set on buffer.");
} else {
/*
* check future : if there is an error in the producer
* task and the producer fails to close() the blocking
* buffer then the iterator will appear to be stalled.
*/
checkFuture();
if(producerConsumerWarnings) {
final String msg = "Iterator is not progressing: ntries="
+ ntries
+ ", elapsed="
+ TimeUnit.MILLISECONDS.convert(elapsedNanos,
TimeUnit.NANOSECONDS) + "ms : " + this;
if (log.isInfoEnabled() && !loggedStackTraces) {
// shows stack trace of the consumer.
log.warn(msg, new RuntimeException(
MSG_CONSUMER_STACK_FRAME));
if (openStackFrame != null) {
// shows stack trace where allocated.
log.warn(msg, openStackFrame);
}
if (logOnce) {
/*
* Do not log the stack traces again during this
* invocation.
*/
loggedStackTraces = true;
}
} else {
// log a warning w/o stack trace.
log.warn(msg);
}
}// if(producerConsumerWarnings)
}
}
// loop again.
continue;
}
// if (log.isInfoEnabled())
// log.info("Exhausted");
//
// assert isExhausted();
//
// // strong false - the iterator is exhausted.
// checkFuture();
//
// return false;
}
public E next(long timeout, final TimeUnit unit) throws InterruptedException {
// elapsed is measured against this timestamp.
final long startTime = System.nanoTime();
long lastTime = startTime;
/*
* [nanos] is the time remaining in nanoseconds.
*
* Note: we convert [timeout] to nanoseconds on entry since it is
* passed into combineChunks() as nanoseconds.
*/
long nanos = timeout = TimeUnit.NANOSECONDS.convert(timeout, unit);
if (!hasNext(nanos, TimeUnit.NANOSECONDS)) {
final long now = System.nanoTime();
nanos -= now - lastTime;
lastTime = now;
if (nanos <= 0) {
/*
* Since the timeout was exceeded we can not know whether
* or not the buffer was exhausted,
*/
return null;
}
throw new NoSuchElementException();
}
final E e = _next();
if (e.getClass().getComponentType() != null) {
/*
* Combine chunk(s)?
*/
final long now = System.nanoTime();
nanos = now - startTime;
if (nanos > 0) {
// combine chunks.
return combineChunks(e, 1/* nchunks */, startTime, timeout);
}
}
return e;
}
/**
* Return the next element. If the element is an array type, then the
* optional chunk combiner may be applied to aggregate chunks. When the
* chunk combiner is applied, this method will block until either a
* chunk of sufficient size has been accumulated -or- the chunk combiner
* timeout has been exceeded. In either case, it will then return the
* chunk which was accumulated.
*/
public E next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
final E e = _next();
if (chunkTimeout > 0 && e.getClass().getComponentType() != null) {
/*
* Combine chunk(s).
*/
final E chunk = combineChunks(e, 1/* nchunks */, System
.nanoTime(), chunkTimeout);
if (ordered) {
/*
* The data in the source chunk(s) are ordered so we apply a
* merge sort IFF two or more chunks were combined together
* such that the resulting chunk will remain ordered.
*
* @todo Verify that this provides us with an efficient
* sort. We are merging N arrays of sorted elements.
* However, this merge sort does not directly take advantage
* of the source chunk boundaries. It would be easy enough
* to consider the current element for each source chunk in
* turn and take the smallest, writing it onto an output
* array. Since we know that we need to combine the chunks
* anyway, this might be faster. However, the
* combineChunks() method would have to be written
* differently so that it returned an array of chunks to
* which we could then apply the merge sort IFF the array
* had more than one element and the data were known to be
* ordered.
*/
final int len0 = ((Object[]) e).length;
final int len1 = ((Object[]) chunk).length;
if (len1 != len0) {
// in place merge sort.
ChunkMergeSortHelper.mergeSort((Object[]) chunk);
}
}
return chunk;
}
return e;
}
/**
* Returns the next element (non-blocking).
*
* @throws NoSuchElementException
* if {@link #nextE} is null (there is no
* element waiting for us).
*/
private E _next() {
if (nextE == null)
throw new NoSuchElementException();
// we already have the next element.
final E e = nextE;
nextE = null;
if (e.getClass().getComponentType() != null) {
chunksDrainedCount++;
elementsDrainedCount += ((Object[]) e).length;
elementsOnQueueCount.addAndGet(-((Object[]) e).length);
} else {
elementsDrainedCount++;
elementsOnQueueCount.decrementAndGet();
}
return e;
}
/**
* Method is invoked IFF E is an array type (a chunk).
* The method examines the size of E compared to a desired minimum chunk
* size. If we would rather have a larger chunk and the buffer is not
* empty, then we immediately take the next chunk and combine it with
* the current chunk. This proceeds recursively until either we have a
* suitable chunk size or the queue is empty.
*
* This method is intended to optimize cases where multiple threads
* produce small chunks that were flushed onto the buffer. By combining
* those chunks we can improve throughput.
*
* @param e
* A chunk.
* @param nchunks
* The #of chunks that have already been consumed. This is
* ONE (1) the first time this method is invoked by
* {@link #next()}.
* @param startTime
* The start time in nanoseconds of the depth==1
* request.
* @param timeout
* The timeout in nanoseconds.
*
* @return Either the same chunk or another chunk with additional
* elements.
*/
private E combineChunks(final E e, final int nchunks,
final long startTime, final long timeout) {
final Object[] chunk = (Object[]) e;
final long elapsed = System.nanoTime() - startTime;
final boolean isTimeout = elapsed >= timeout;
boolean isInterrupt = false;
// remaining nanos until timeout.
final long nanos = chunkTimeout - elapsed;
if (chunk.length < minimumChunkSize && !isTimeout) {
try {
if (hasNext(nanos, TimeUnit.NANOSECONDS)) {
/*
* Note: hasNext() will block until either (a) we have
* another chunk; (b) the timeout has expired; (c) until
* the iterator is known to be exhausted; or (d) the
* current thread is interrupted.
*/
return combineChunks(combineNextChunk(e), nchunks + 1,
startTime, timeout);
}
} catch (InterruptedException ex) {
// Note: we treat an interrupt as if it forced a timeout.
isInterrupt = true;
}
}
if (chunk.length < minimumChunkSize && !isTimeout && !isInterrupt
&& !queue.isEmpty()) {
/*
* Non-blocking case. Once we have satisfied the minimum chunk
* size we will only combine chunks that are already waiting in
* the queue.
*
* Note: hasNext() is invoked here to make sure that _nextE is
* bound. This is non-blocking since we already know that the
* queue is not empty.
*/
hasNext();
return combineChunks(combineNextChunk(e), nchunks + 1,
startTime, timeout);
}
// Done.
if (log.isInfoEnabled())
log.info("done:\n" + ">>> #combined=" + nchunks + ", #elements="
+ chunk.length + ", minimumChunkCapacity=" + minimumChunkSize
+ ", elapsed=" + elapsed + "ns, isTimeout=" + isTimeout
+ ", queueEmpty=" + queue.isEmpty() + ", open="
+ BlockingBuffer.this.open);
return e;
}
/**
* Combines this chunk with the {@link #_next()} one.
*
* @param e
* A chunk that we already have on hand.
*
* @return The given chunk combined with the {@link #_next()} chunk.
*/
// @SuppressWarnings("unchecked")
private E combineNextChunk(final E e) {
return BlockingBuffer.this.combineChunks(e, _next());
// final Object[] e1 = (Object[]) e;
//
// final Object[] e2 = (Object[]) _next();
//
// if (e2.length == 0) {
//
// // empty chunk.
// return e;
//
// }
//
// final int chunkSize = e1.length + e2.length;
//
// // Dynamic instantiation of array of the same component type.
// final Object[] a = (E[]) java.lang.reflect.Array.newInstance(e1[0]
// .getClass(), chunkSize);
//
// // copy first chunk onto the new array.
// System.arraycopy(e, 0, a, 0, e1.length);
//
// // copy second chunk onto the new array.
// System.arraycopy(e2, 0, a, e1.length, e2.length);
//
// // return the combined chunk.
// return (E) a;
}
/**
* The operation is not supported.
*/
public void remove() {
throw new UnsupportedOperationException();
}
}
/**
* Combines two chunks in the order given (DOES NOT apply a merge sort).
*
* @param chunk1
* The first chunk.
* @param chunk2
* The second chunk.
*
* @return The combined chunks.
*/
public static E combineChunks(final E chunk1, final E chunk2) {
final Object[] e1 = (Object[]) chunk1;
if (e1.length == 0) {
// empty chunk - return the other argument.
return chunk2;
}
final Object[] e2 = (Object[]) chunk2;
if (e2.length == 0) {
// empty chunk - return the other argument.
return chunk1;
}
assert e1[0] != null;
assert e2[0] != null;
if (log.isDebugEnabled()) {
log.debug("Combining chunks: e.length=" + e1.length + ", t.length="
+ e2.length);
}
final int chunkSize = e1.length + e2.length;
// Dynamic instantiation of array of the same component type.
final Object[] a = (Object[]) java.lang.reflect.Array.newInstance(//
// e1[0].getClass(),
e1.getClass().getComponentType(),//
chunkSize);
// copy first chunk onto the new array.
System.arraycopy(e1, 0, a, 0, e1.length);
// copy second chunk onto the new array.
System.arraycopy(e2, 0, a, e1.length, e2.length);
assert a[0] != null;
// return the combined chunk.
return (E) a;
}
}