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The SliceOps.java Java example source code
/*
* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code 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
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.util.stream;
import java.util.Spliterator;
import java.util.concurrent.CountedCompleter;
import java.util.function.IntFunction;
/**
* Factory for instances of a short-circuiting stateful intermediate operations
* that produce subsequences of their input stream.
*
* @since 1.8
*/
final class SliceOps {
// No instances
private SliceOps() { }
/**
* Calculates the sliced size given the current size, number of elements
* skip, and the number of elements to limit.
*
* @param size the current size
* @param skip the number of elements to skip, assumed to be >= 0
* @param limit the number of elements to limit, assumed to be >= 0, with
* a value of {@code Long.MAX_VALUE} if there is no limit
* @return the sliced size
*/
private static long calcSize(long size, long skip, long limit) {
return size >= 0 ? Math.max(-1, Math.min(size - skip, limit)) : -1;
}
/**
* Calculates the slice fence, which is one past the index of the slice
* range
* @param skip the number of elements to skip, assumed to be >= 0
* @param limit the number of elements to limit, assumed to be >= 0, with
* a value of {@code Long.MAX_VALUE} if there is no limit
* @return the slice fence.
*/
private static long calcSliceFence(long skip, long limit) {
long sliceFence = limit >= 0 ? skip + limit : Long.MAX_VALUE;
// Check for overflow
return (sliceFence >= 0) ? sliceFence : Long.MAX_VALUE;
}
/**
* Creates a slice spliterator given a stream shape governing the
* spliterator type. Requires that the underlying Spliterator
* be SUBSIZED.
*/
@SuppressWarnings("unchecked")
private static <P_IN> Spliterator sliceSpliterator(StreamShape shape,
Spliterator<P_IN> s,
long skip, long limit) {
assert s.hasCharacteristics(Spliterator.SUBSIZED);
long sliceFence = calcSliceFence(skip, limit);
switch (shape) {
case REFERENCE:
return new StreamSpliterators
.SliceSpliterator.OfRef<>(s, skip, sliceFence);
case INT_VALUE:
return (Spliterator<P_IN>) new StreamSpliterators
.SliceSpliterator.OfInt((Spliterator.OfInt) s, skip, sliceFence);
case LONG_VALUE:
return (Spliterator<P_IN>) new StreamSpliterators
.SliceSpliterator.OfLong((Spliterator.OfLong) s, skip, sliceFence);
case DOUBLE_VALUE:
return (Spliterator<P_IN>) new StreamSpliterators
.SliceSpliterator.OfDouble((Spliterator.OfDouble) s, skip, sliceFence);
default:
throw new IllegalStateException("Unknown shape " + shape);
}
}
@SuppressWarnings("unchecked")
private static <T> IntFunction castingArray() {
return size -> (T[]) new Object[size];
}
/**
* Appends a "slice" operation to the provided stream. The slice operation
* may be may be skip-only, limit-only, or skip-and-limit.
*
* @param <T> the type of both input and output elements
* @param upstream a reference stream with element type T
* @param skip the number of elements to skip. Must be >= 0.
* @param limit the maximum size of the resulting stream, or -1 if no limit
* is to be imposed
*/
public static <T> Stream makeRef(AbstractPipeline upstream,
long skip, long limit) {
if (skip < 0)
throw new IllegalArgumentException("Skip must be non-negative: " + skip);
return new ReferencePipeline.StatefulOp<T, T>(upstream, StreamShape.REFERENCE,
flags(limit)) {
Spliterator<T> unorderedSkipLimitSpliterator(Spliterator s,
long skip, long limit, long sizeIfKnown) {
if (skip <= sizeIfKnown) {
// Use just the limit if the number of elements
// to skip is <= the known pipeline size
limit = limit >= 0 ? Math.min(limit, sizeIfKnown - skip) : sizeIfKnown - skip;
skip = 0;
}
return new StreamSpliterators.UnorderedSliceSpliterator.OfRef<>(s, skip, limit);
}
@Override
<P_IN> Spliterator opEvaluateParallelLazy(PipelineHelper helper, Spliterator spliterator) {
long size = helper.exactOutputSizeIfKnown(spliterator);
if (size > 0 && spliterator.hasCharacteristics(Spliterator.SUBSIZED)) {
return new StreamSpliterators.SliceSpliterator.OfRef<>(
helper.wrapSpliterator(spliterator),
skip,
calcSliceFence(skip, limit));
} else if (!StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
return unorderedSkipLimitSpliterator(
helper.wrapSpliterator(spliterator),
skip, limit, size);
}
else {
// @@@ OOMEs will occur for LongStream.longs().filter(i -> true).limit(n)
// regardless of the value of n
// Need to adjust the target size of splitting for the
// SliceTask from say (size / k) to say min(size / k, 1 << 14)
// This will limit the size of the buffers created at the leaf nodes
// cancellation will be more aggressive cancelling later tasks
// if the target slice size has been reached from a given task,
// cancellation should also clear local results if any
return new SliceTask<>(this, helper, spliterator, castingArray(), skip, limit).
invoke().spliterator();
}
}
@Override
<P_IN> Node opEvaluateParallel(PipelineHelper helper,
Spliterator<P_IN> spliterator,
IntFunction<T[]> generator) {
long size = helper.exactOutputSizeIfKnown(spliterator);
if (size > 0 && spliterator.hasCharacteristics(Spliterator.SUBSIZED)) {
// Because the pipeline is SIZED the slice spliterator
// can be created from the source, this requires matching
// to shape of the source, and is potentially more efficient
// than creating the slice spliterator from the pipeline
// wrapping spliterator
Spliterator<P_IN> s = sliceSpliterator(helper.getSourceShape(), spliterator, skip, limit);
return Nodes.collect(helper, s, true, generator);
} else if (!StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
Spliterator<T> s = unorderedSkipLimitSpliterator(
helper.wrapSpliterator(spliterator),
skip, limit, size);
// Collect using this pipeline, which is empty and therefore
// can be used with the pipeline wrapping spliterator
// Note that we cannot create a slice spliterator from
// the source spliterator if the pipeline is not SIZED
return Nodes.collect(this, s, true, generator);
}
else {
return new SliceTask<>(this, helper, spliterator, generator, skip, limit).
invoke();
}
}
@Override
Sink<T> opWrapSink(int flags, Sink sink) {
return new Sink.ChainedReference<T, T>(sink) {
long n = skip;
long m = limit >= 0 ? limit : Long.MAX_VALUE;
@Override
public void begin(long size) {
downstream.begin(calcSize(size, skip, m));
}
@Override
public void accept(T t) {
if (n == 0) {
if (m > 0) {
m--;
downstream.accept(t);
}
}
else {
n--;
}
}
@Override
public boolean cancellationRequested() {
return m == 0 || downstream.cancellationRequested();
}
};
}
};
}
/**
* Appends a "slice" operation to the provided IntStream. The slice
* operation may be may be skip-only, limit-only, or skip-and-limit.
*
* @param upstream An IntStream
* @param skip The number of elements to skip. Must be >= 0.
* @param limit The maximum size of the resulting stream, or -1 if no limit
* is to be imposed
*/
public static IntStream makeInt(AbstractPipeline<?, Integer, ?> upstream,
long skip, long limit) {
if (skip < 0)
throw new IllegalArgumentException("Skip must be non-negative: " + skip);
return new IntPipeline.StatefulOp<Integer>(upstream, StreamShape.INT_VALUE,
flags(limit)) {
Spliterator.OfInt unorderedSkipLimitSpliterator(
Spliterator.OfInt s, long skip, long limit, long sizeIfKnown) {
if (skip <= sizeIfKnown) {
// Use just the limit if the number of elements
// to skip is <= the known pipeline size
limit = limit >= 0 ? Math.min(limit, sizeIfKnown - skip) : sizeIfKnown - skip;
skip = 0;
}
return new StreamSpliterators.UnorderedSliceSpliterator.OfInt(s, skip, limit);
}
@Override
<P_IN> Spliterator opEvaluateParallelLazy(PipelineHelper helper,
Spliterator<P_IN> spliterator) {
long size = helper.exactOutputSizeIfKnown(spliterator);
if (size > 0 && spliterator.hasCharacteristics(Spliterator.SUBSIZED)) {
return new StreamSpliterators.SliceSpliterator.OfInt(
(Spliterator.OfInt) helper.wrapSpliterator(spliterator),
skip,
calcSliceFence(skip, limit));
} else if (!StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
return unorderedSkipLimitSpliterator(
(Spliterator.OfInt) helper.wrapSpliterator(spliterator),
skip, limit, size);
}
else {
return new SliceTask<>(this, helper, spliterator, Integer[]::new, skip, limit).
invoke().spliterator();
}
}
@Override
<P_IN> Node opEvaluateParallel(PipelineHelper helper,
Spliterator<P_IN> spliterator,
IntFunction<Integer[]> generator) {
long size = helper.exactOutputSizeIfKnown(spliterator);
if (size > 0 && spliterator.hasCharacteristics(Spliterator.SUBSIZED)) {
// Because the pipeline is SIZED the slice spliterator
// can be created from the source, this requires matching
// to shape of the source, and is potentially more efficient
// than creating the slice spliterator from the pipeline
// wrapping spliterator
Spliterator<P_IN> s = sliceSpliterator(helper.getSourceShape(), spliterator, skip, limit);
return Nodes.collectInt(helper, s, true);
} else if (!StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
Spliterator.OfInt s = unorderedSkipLimitSpliterator(
(Spliterator.OfInt) helper.wrapSpliterator(spliterator),
skip, limit, size);
// Collect using this pipeline, which is empty and therefore
// can be used with the pipeline wrapping spliterator
// Note that we cannot create a slice spliterator from
// the source spliterator if the pipeline is not SIZED
return Nodes.collectInt(this, s, true);
}
else {
return new SliceTask<>(this, helper, spliterator, generator, skip, limit).
invoke();
}
}
@Override
Sink<Integer> opWrapSink(int flags, Sink sink) {
return new Sink.ChainedInt<Integer>(sink) {
long n = skip;
long m = limit >= 0 ? limit : Long.MAX_VALUE;
@Override
public void begin(long size) {
downstream.begin(calcSize(size, skip, m));
}
@Override
public void accept(int t) {
if (n == 0) {
if (m > 0) {
m--;
downstream.accept(t);
}
}
else {
n--;
}
}
@Override
public boolean cancellationRequested() {
return m == 0 || downstream.cancellationRequested();
}
};
}
};
}
/**
* Appends a "slice" operation to the provided LongStream. The slice
* operation may be may be skip-only, limit-only, or skip-and-limit.
*
* @param upstream A LongStream
* @param skip The number of elements to skip. Must be >= 0.
* @param limit The maximum size of the resulting stream, or -1 if no limit
* is to be imposed
*/
public static LongStream makeLong(AbstractPipeline<?, Long, ?> upstream,
long skip, long limit) {
if (skip < 0)
throw new IllegalArgumentException("Skip must be non-negative: " + skip);
return new LongPipeline.StatefulOp<Long>(upstream, StreamShape.LONG_VALUE,
flags(limit)) {
Spliterator.OfLong unorderedSkipLimitSpliterator(
Spliterator.OfLong s, long skip, long limit, long sizeIfKnown) {
if (skip <= sizeIfKnown) {
// Use just the limit if the number of elements
// to skip is <= the known pipeline size
limit = limit >= 0 ? Math.min(limit, sizeIfKnown - skip) : sizeIfKnown - skip;
skip = 0;
}
return new StreamSpliterators.UnorderedSliceSpliterator.OfLong(s, skip, limit);
}
@Override
<P_IN> Spliterator opEvaluateParallelLazy(PipelineHelper helper,
Spliterator<P_IN> spliterator) {
long size = helper.exactOutputSizeIfKnown(spliterator);
if (size > 0 && spliterator.hasCharacteristics(Spliterator.SUBSIZED)) {
return new StreamSpliterators.SliceSpliterator.OfLong(
(Spliterator.OfLong) helper.wrapSpliterator(spliterator),
skip,
calcSliceFence(skip, limit));
} else if (!StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
return unorderedSkipLimitSpliterator(
(Spliterator.OfLong) helper.wrapSpliterator(spliterator),
skip, limit, size);
}
else {
return new SliceTask<>(this, helper, spliterator, Long[]::new, skip, limit).
invoke().spliterator();
}
}
@Override
<P_IN> Node opEvaluateParallel(PipelineHelper helper,
Spliterator<P_IN> spliterator,
IntFunction<Long[]> generator) {
long size = helper.exactOutputSizeIfKnown(spliterator);
if (size > 0 && spliterator.hasCharacteristics(Spliterator.SUBSIZED)) {
// Because the pipeline is SIZED the slice spliterator
// can be created from the source, this requires matching
// to shape of the source, and is potentially more efficient
// than creating the slice spliterator from the pipeline
// wrapping spliterator
Spliterator<P_IN> s = sliceSpliterator(helper.getSourceShape(), spliterator, skip, limit);
return Nodes.collectLong(helper, s, true);
} else if (!StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
Spliterator.OfLong s = unorderedSkipLimitSpliterator(
(Spliterator.OfLong) helper.wrapSpliterator(spliterator),
skip, limit, size);
// Collect using this pipeline, which is empty and therefore
// can be used with the pipeline wrapping spliterator
// Note that we cannot create a slice spliterator from
// the source spliterator if the pipeline is not SIZED
return Nodes.collectLong(this, s, true);
}
else {
return new SliceTask<>(this, helper, spliterator, generator, skip, limit).
invoke();
}
}
@Override
Sink<Long> opWrapSink(int flags, Sink sink) {
return new Sink.ChainedLong<Long>(sink) {
long n = skip;
long m = limit >= 0 ? limit : Long.MAX_VALUE;
@Override
public void begin(long size) {
downstream.begin(calcSize(size, skip, m));
}
@Override
public void accept(long t) {
if (n == 0) {
if (m > 0) {
m--;
downstream.accept(t);
}
}
else {
n--;
}
}
@Override
public boolean cancellationRequested() {
return m == 0 || downstream.cancellationRequested();
}
};
}
};
}
/**
* Appends a "slice" operation to the provided DoubleStream. The slice
* operation may be may be skip-only, limit-only, or skip-and-limit.
*
* @param upstream A DoubleStream
* @param skip The number of elements to skip. Must be >= 0.
* @param limit The maximum size of the resulting stream, or -1 if no limit
* is to be imposed
*/
public static DoubleStream makeDouble(AbstractPipeline<?, Double, ?> upstream,
long skip, long limit) {
if (skip < 0)
throw new IllegalArgumentException("Skip must be non-negative: " + skip);
return new DoublePipeline.StatefulOp<Double>(upstream, StreamShape.DOUBLE_VALUE,
flags(limit)) {
Spliterator.OfDouble unorderedSkipLimitSpliterator(
Spliterator.OfDouble s, long skip, long limit, long sizeIfKnown) {
if (skip <= sizeIfKnown) {
// Use just the limit if the number of elements
// to skip is <= the known pipeline size
limit = limit >= 0 ? Math.min(limit, sizeIfKnown - skip) : sizeIfKnown - skip;
skip = 0;
}
return new StreamSpliterators.UnorderedSliceSpliterator.OfDouble(s, skip, limit);
}
@Override
<P_IN> Spliterator opEvaluateParallelLazy(PipelineHelper helper,
Spliterator<P_IN> spliterator) {
long size = helper.exactOutputSizeIfKnown(spliterator);
if (size > 0 && spliterator.hasCharacteristics(Spliterator.SUBSIZED)) {
return new StreamSpliterators.SliceSpliterator.OfDouble(
(Spliterator.OfDouble) helper.wrapSpliterator(spliterator),
skip,
calcSliceFence(skip, limit));
} else if (!StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
return unorderedSkipLimitSpliterator(
(Spliterator.OfDouble) helper.wrapSpliterator(spliterator),
skip, limit, size);
}
else {
return new SliceTask<>(this, helper, spliterator, Double[]::new, skip, limit).
invoke().spliterator();
}
}
@Override
<P_IN> Node opEvaluateParallel(PipelineHelper helper,
Spliterator<P_IN> spliterator,
IntFunction<Double[]> generator) {
long size = helper.exactOutputSizeIfKnown(spliterator);
if (size > 0 && spliterator.hasCharacteristics(Spliterator.SUBSIZED)) {
// Because the pipeline is SIZED the slice spliterator
// can be created from the source, this requires matching
// to shape of the source, and is potentially more efficient
// than creating the slice spliterator from the pipeline
// wrapping spliterator
Spliterator<P_IN> s = sliceSpliterator(helper.getSourceShape(), spliterator, skip, limit);
return Nodes.collectDouble(helper, s, true);
} else if (!StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
Spliterator.OfDouble s = unorderedSkipLimitSpliterator(
(Spliterator.OfDouble) helper.wrapSpliterator(spliterator),
skip, limit, size);
// Collect using this pipeline, which is empty and therefore
// can be used with the pipeline wrapping spliterator
// Note that we cannot create a slice spliterator from
// the source spliterator if the pipeline is not SIZED
return Nodes.collectDouble(this, s, true);
}
else {
return new SliceTask<>(this, helper, spliterator, generator, skip, limit).
invoke();
}
}
@Override
Sink<Double> opWrapSink(int flags, Sink sink) {
return new Sink.ChainedDouble<Double>(sink) {
long n = skip;
long m = limit >= 0 ? limit : Long.MAX_VALUE;
@Override
public void begin(long size) {
downstream.begin(calcSize(size, skip, m));
}
@Override
public void accept(double t) {
if (n == 0) {
if (m > 0) {
m--;
downstream.accept(t);
}
}
else {
n--;
}
}
@Override
public boolean cancellationRequested() {
return m == 0 || downstream.cancellationRequested();
}
};
}
};
}
private static int flags(long limit) {
return StreamOpFlag.NOT_SIZED | ((limit != -1) ? StreamOpFlag.IS_SHORT_CIRCUIT : 0);
}
/**
* {@code ForkJoinTask} implementing slice computation.
*
* @param <P_IN> Input element type to the stream pipeline
* @param <P_OUT> Output element type from the stream pipeline
*/
@SuppressWarnings("serial")
private static final class SliceTask<P_IN, P_OUT>
extends AbstractShortCircuitTask<P_IN, P_OUT, Node> {
private final AbstractPipeline<P_OUT, P_OUT, ?> op;
private final IntFunction<P_OUT[]> generator;
private final long targetOffset, targetSize;
private long thisNodeSize;
private volatile boolean completed;
SliceTask(AbstractPipeline<P_OUT, P_OUT, ?> op,
PipelineHelper<P_OUT> helper,
Spliterator<P_IN> spliterator,
IntFunction<P_OUT[]> generator,
long offset, long size) {
super(helper, spliterator);
this.op = op;
this.generator = generator;
this.targetOffset = offset;
this.targetSize = size;
}
SliceTask(SliceTask<P_IN, P_OUT> parent, Spliterator spliterator) {
super(parent, spliterator);
this.op = parent.op;
this.generator = parent.generator;
this.targetOffset = parent.targetOffset;
this.targetSize = parent.targetSize;
}
@Override
protected SliceTask<P_IN, P_OUT> makeChild(Spliterator spliterator) {
return new SliceTask<>(this, spliterator);
}
@Override
protected final Node<P_OUT> getEmptyResult() {
return Nodes.emptyNode(op.getOutputShape());
}
@Override
protected final Node<P_OUT> doLeaf() {
if (isRoot()) {
long sizeIfKnown = StreamOpFlag.SIZED.isPreserved(op.sourceOrOpFlags)
? op.exactOutputSizeIfKnown(spliterator)
: -1;
final Node.Builder<P_OUT> nb = op.makeNodeBuilder(sizeIfKnown, generator);
Sink<P_OUT> opSink = op.opWrapSink(helper.getStreamAndOpFlags(), nb);
helper.copyIntoWithCancel(helper.wrapSink(opSink), spliterator);
// There is no need to truncate since the op performs the
// skipping and limiting of elements
return nb.build();
}
else {
Node<P_OUT> node = helper.wrapAndCopyInto(helper.makeNodeBuilder(-1, generator),
spliterator).build();
thisNodeSize = node.count();
completed = true;
spliterator = null;
return node;
}
}
@Override
public final void onCompletion(CountedCompleter<?> caller) {
if (!isLeaf()) {
Node<P_OUT> result;
thisNodeSize = leftChild.thisNodeSize + rightChild.thisNodeSize;
if (canceled) {
thisNodeSize = 0;
result = getEmptyResult();
}
else if (thisNodeSize == 0)
result = getEmptyResult();
else if (leftChild.thisNodeSize == 0)
result = rightChild.getLocalResult();
else {
result = Nodes.conc(op.getOutputShape(),
leftChild.getLocalResult(), rightChild.getLocalResult());
}
setLocalResult(isRoot() ? doTruncate(result) : result);
completed = true;
}
if (targetSize >= 0
&& !isRoot()
&& isLeftCompleted(targetOffset + targetSize))
cancelLaterNodes();
super.onCompletion(caller);
}
@Override
protected void cancel() {
super.cancel();
if (completed)
setLocalResult(getEmptyResult());
}
private Node<P_OUT> doTruncate(Node input) {
long to = targetSize >= 0 ? Math.min(input.count(), targetOffset + targetSize) : thisNodeSize;
return input.truncate(targetOffset, to, generator);
}
/**
* Determine if the number of completed elements in this node and nodes
* to the left of this node is greater than or equal to the target size.
*
* @param target the target size
* @return true if the number of elements is greater than or equal to
* the target size, otherwise false.
*/
private boolean isLeftCompleted(long target) {
long size = completed ? thisNodeSize : completedSize(target);
if (size >= target)
return true;
for (SliceTask<P_IN, P_OUT> parent = getParent(), node = this;
parent != null;
node = parent, parent = parent.getParent()) {
if (node == parent.rightChild) {
SliceTask<P_IN, P_OUT> left = parent.leftChild;
if (left != null) {
size += left.completedSize(target);
if (size >= target)
return true;
}
}
}
return size >= target;
}
/**
* Compute the number of completed elements in this node.
* <p>
* Computation terminates if all nodes have been processed or the
* number of completed elements is greater than or equal to the target
* size.
*
* @param target the target size
* @return return the number of completed elements
*/
private long completedSize(long target) {
if (completed)
return thisNodeSize;
else {
SliceTask<P_IN, P_OUT> left = leftChild;
SliceTask<P_IN, P_OUT> right = rightChild;
if (left == null || right == null) {
// must be completed
return thisNodeSize;
}
else {
long leftSize = left.completedSize(target);
return (leftSize >= target) ? leftSize : leftSize + right.completedSize(target);
}
}
}
}
}
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