/* |
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* Copyright (c) 2012, 2021, Oracle and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Oracle designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Oracle in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* questions. |
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*/ |
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package java.util.stream; |
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import java.util.Spliterator; |
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import java.util.function.IntFunction; |
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/** |
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* Helper class for executing <a href="package-summary.html#StreamOps"> |
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* stream pipelines</a>, capturing all of the information about a stream |
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* pipeline (output shape, intermediate operations, stream flags, parallelism, |
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* etc) in one place. |
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* |
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* <p> |
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* A {@code PipelineHelper} describes the initial segment of a stream pipeline, |
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* including its source, intermediate operations, and may additionally |
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* incorporate information about the terminal (or stateful) operation which |
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* follows the last intermediate operation described by this |
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* {@code PipelineHelper}. The {@code PipelineHelper} is passed to the |
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* {@link TerminalOp#evaluateParallel(PipelineHelper, java.util.Spliterator)}, |
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* {@link TerminalOp#evaluateSequential(PipelineHelper, java.util.Spliterator)}, |
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* and {@link AbstractPipeline#opEvaluateParallel(PipelineHelper, java.util.Spliterator, |
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* java.util.function.IntFunction)}, methods, which can use the |
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* {@code PipelineHelper} to access information about the pipeline such as |
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* head shape, stream flags, and size, and use the helper methods |
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* such as {@link #wrapAndCopyInto(Sink, Spliterator)}, |
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* {@link #copyInto(Sink, Spliterator)}, and {@link #wrapSink(Sink)} to execute |
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* pipeline operations. |
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* |
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* @param <P_OUT> type of output elements from the pipeline |
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* @since 1.8 |
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*/ |
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abstract class PipelineHelper<P_OUT> { |
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/** |
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* Gets the stream shape for the source of the pipeline segment. |
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* |
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* @return the stream shape for the source of the pipeline segment. |
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*/ |
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abstract StreamShape getSourceShape(); |
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/** |
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* Gets the combined stream and operation flags for the output of the described |
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* pipeline. This will incorporate stream flags from the stream source, all |
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* the intermediate operations and the terminal operation. |
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* |
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* @return the combined stream and operation flags |
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* @see StreamOpFlag |
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*/ |
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abstract int getStreamAndOpFlags(); |
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/** |
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* Returns the exact output size of the portion of the output resulting from |
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* applying the pipeline stages described by this {@code PipelineHelper} to |
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* the portion of the input described by the provided |
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* {@code Spliterator}, if known. If not known or known infinite, will |
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* return {@code -1}. |
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* |
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* @apiNote |
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* The exact output size is known if the {@code Spliterator} has the |
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* {@code SIZED} characteristic, and the operation flags |
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* {@link StreamOpFlag#SIZED} is known on the combined stream and operation |
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* flags. The exact output size may differ from spliterator size, |
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* if pipeline contains a slice operation. |
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* |
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* @param spliterator the spliterator describing the relevant portion of the |
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* source data |
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* @return the exact size if known, or -1 if infinite or unknown |
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*/ |
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abstract<P_IN> long exactOutputSizeIfKnown(Spliterator<P_IN> spliterator); |
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/** |
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* Applies the pipeline stages described by this {@code PipelineHelper} to |
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* the provided {@code Spliterator} and send the results to the provided |
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* {@code Sink}. |
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* |
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* @implSpec |
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* The implementation behaves as if: |
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* <pre>{@code |
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* copyInto(wrapSink(sink), spliterator); |
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* }</pre> |
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* |
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* @param sink the {@code Sink} to receive the results |
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* @param spliterator the spliterator describing the source input to process |
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*/ |
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abstract<P_IN, S extends Sink<P_OUT>> S wrapAndCopyInto(S sink, Spliterator<P_IN> spliterator); |
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/** |
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* Pushes elements obtained from the {@code Spliterator} into the provided |
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* {@code Sink}. If the stream pipeline is known to have short-circuiting |
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* stages in it (see {@link StreamOpFlag#SHORT_CIRCUIT}), the |
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* {@link Sink#cancellationRequested()} is checked after each |
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* element, stopping if cancellation is requested. |
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* |
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* @implSpec |
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* This method conforms to the {@code Sink} protocol of calling |
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* {@code Sink.begin} before pushing elements, via {@code Sink.accept}, and |
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* calling {@code Sink.end} after all elements have been pushed. |
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* |
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* @param wrappedSink the destination {@code Sink} |
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* @param spliterator the source {@code Spliterator} |
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*/ |
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abstract<P_IN> void copyInto(Sink<P_IN> wrappedSink, Spliterator<P_IN> spliterator); |
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/** |
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* Pushes elements obtained from the {@code Spliterator} into the provided |
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* {@code Sink}, checking {@link Sink#cancellationRequested()} after each |
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* element, and stopping if cancellation is requested. |
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* |
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* @implSpec |
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* This method conforms to the {@code Sink} protocol of calling |
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* {@code Sink.begin} before pushing elements, via {@code Sink.accept}, and |
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* calling {@code Sink.end} after all elements have been pushed or if |
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* cancellation is requested. |
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* |
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* @param wrappedSink the destination {@code Sink} |
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* @param spliterator the source {@code Spliterator} |
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* @return true if the cancellation was requested |
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*/ |
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abstract <P_IN> boolean copyIntoWithCancel(Sink<P_IN> wrappedSink, Spliterator<P_IN> spliterator); |
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/** |
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* Takes a {@code Sink} that accepts elements of the output type of the |
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* {@code PipelineHelper}, and wrap it with a {@code Sink} that accepts |
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* elements of the input type and implements all the intermediate operations |
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* described by this {@code PipelineHelper}, delivering the result into the |
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* provided {@code Sink}. |
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* |
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* @param sink the {@code Sink} to receive the results |
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* @return a {@code Sink} that implements the pipeline stages and sends |
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* results to the provided {@code Sink} |
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*/ |
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abstract<P_IN> Sink<P_IN> wrapSink(Sink<P_OUT> sink); |
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/** |
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* |
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* @param spliterator |
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* @param <P_IN> |
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* @return |
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*/ |
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abstract<P_IN> Spliterator<P_OUT> wrapSpliterator(Spliterator<P_IN> spliterator); |
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/** |
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* Constructs a @{link Node.Builder} compatible with the output shape of |
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* this {@code PipelineHelper}. |
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* |
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* @param exactSizeIfKnown if >=0 then a builder will be created that has a |
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* fixed capacity of exactly sizeIfKnown elements; if < 0 then the |
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* builder has variable capacity. A fixed capacity builder will fail |
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* if an element is added after the builder has reached capacity. |
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* @param generator a factory function for array instances |
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* @return a {@code Node.Builder} compatible with the output shape of this |
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* {@code PipelineHelper} |
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*/ |
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abstract Node.Builder<P_OUT> makeNodeBuilder(long exactSizeIfKnown, |
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IntFunction<P_OUT[]> generator); |
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/** |
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* Collects all output elements resulting from applying the pipeline stages |
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* to the source {@code Spliterator} into a {@code Node}. |
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* |
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* @implNote |
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* If the pipeline has no intermediate operations and the source is backed |
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* by a {@code Node} then that {@code Node} will be returned (or flattened |
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* and then returned). This reduces copying for a pipeline consisting of a |
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* stateful operation followed by a terminal operation that returns an |
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* array, such as: |
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* <pre>{@code |
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* stream.sorted().toArray(); |
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* }</pre> |
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* |
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* @param spliterator the source {@code Spliterator} |
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* @param flatten if true and the pipeline is a parallel pipeline then the |
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* {@code Node} returned will contain no children, otherwise the |
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* {@code Node} may represent the root in a tree that reflects the |
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* shape of the computation tree. |
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* @param generator a factory function for array instances |
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* @return the {@code Node} containing all output elements |
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*/ |
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abstract<P_IN> Node<P_OUT> evaluate(Spliterator<P_IN> spliterator, |
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boolean flatten, |
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IntFunction<P_OUT[]> generator); |
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} |