PipelineHelper.java revision d0a2645e29a9b84d7e5ec822eb9904e93bd6c013
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25package java.util.stream;
26
27import java.util.Spliterator;
28import java.util.function.IntFunction;
29
30/**
31 * Helper class for executing <a href="package-summary.html#StreamOps">
32 * stream pipelines</a>, capturing all of the information about a stream
33 * pipeline (output shape, intermediate operations, stream flags, parallelism,
34 * etc) in one place.
35 *
36 * <p>
37 * A {@code PipelineHelper} describes the initial segment of a stream pipeline,
38 * including its source, intermediate operations, and may additionally
39 * incorporate information about the terminal (or stateful) operation which
40 * follows the last intermediate operation described by this
41 * {@code PipelineHelper}. The {@code PipelineHelper} is passed to the
42 * {@link TerminalOp#evaluateParallel(PipelineHelper, java.util.Spliterator)},
43 * {@link TerminalOp#evaluateSequential(PipelineHelper, java.util.Spliterator)},
44 * and {@link AbstractPipeline#opEvaluateParallel(PipelineHelper, java.util.Spliterator,
45 * java.util.function.IntFunction)}, methods, which can use the
46 * {@code PipelineHelper} to access information about the pipeline such as
47 * head shape, stream flags, and size, and use the helper methods
48 * such as {@link #wrapAndCopyInto(Sink, Spliterator)},
49 * {@link #copyInto(Sink, Spliterator)}, and {@link #wrapSink(Sink)} to execute
50 * pipeline operations.
51 *
52 * @param  type of output elements from the pipeline
53 * @since 1.8
54 */
55abstract class PipelineHelper<P_OUT> {
56
57    /**
58     * Gets the stream shape for the source of the pipeline segment.
59     *
60     * @return the stream shape for the source of the pipeline segment.
61     */
62    abstract StreamShape getSourceShape();
63
64    /**
65     * Gets the combined stream and operation flags for the output of the described
66     * pipeline.  This will incorporate stream flags from the stream source, all
67     * the intermediate operations and the terminal operation.
68     *
69     * @return the combined stream and operation flags
70     * @see StreamOpFlag
71     */
72    abstract int getStreamAndOpFlags();
73
74    /**
75     * Returns the exact output size of the portion of the output resulting from
76     * applying the pipeline stages described by this {@code PipelineHelper} to
77     * the the portion of the input described by the provided
78     * {@code Spliterator}, if known.  If not known or known infinite, will
79     * return {@code -1}.
80     *
81     * @apiNote
82     * The exact output size is known if the {@code Spliterator} has the
83     * {@code SIZED} characteristic, and the operation flags
84     * {@link StreamOpFlag#SIZED} is known on the combined stream and operation
85     * flags.
86     *
87     * @param spliterator the spliterator describing the relevant portion of the
88     *        source data
89     * @return the exact size if known, or -1 if infinite or unknown
90     */
91    abstract<P_IN> long exactOutputSizeIfKnown(Spliterator<P_IN> spliterator);
92
93    /**
94     * Applies the pipeline stages described by this {@code PipelineHelper} to
95     * the provided {@code Spliterator} and send the results to the provided
96     * {@code Sink}.
97     *
98     * @implSpec
99     * The implementation behaves as if:
100     * <pre>{@code
101     *     intoWrapped(wrapSink(sink), spliterator);
102     * }</pre>
103     *
104     * @param sink the {@code Sink} to receive the results
105     * @param spliterator the spliterator describing the source input to process
106     */
107    abstract<P_IN, S extends Sink<P_OUT>> S wrapAndCopyInto(S sink, Spliterator<P_IN> spliterator);
108
109    /**
110     * Pushes elements obtained from the {@code Spliterator} into the provided
111     * {@code Sink}.  If the stream pipeline is known to have short-circuiting
112     * stages in it (see {@link StreamOpFlag#SHORT_CIRCUIT}), the
113     * {@link Sink#cancellationRequested()} is checked after each
114     * element, stopping if cancellation is requested.
115     *
116     * @implSpec
117     * This method conforms to the {@code Sink} protocol of calling
118     * {@code Sink.begin} before pushing elements, via {@code Sink.accept}, and
119     * calling {@code Sink.end} after all elements have been pushed.
120     *
121     * @param wrappedSink the destination {@code Sink}
122     * @param spliterator the source {@code Spliterator}
123     */
124    abstract<P_IN> void copyInto(Sink<P_IN> wrappedSink, Spliterator<P_IN> spliterator);
125
126    /**
127     * Pushes elements obtained from the {@code Spliterator} into the provided
128     * {@code Sink}, checking {@link Sink#cancellationRequested()} after each
129     * element, and stopping if cancellation is requested.
130     *
131     * @implSpec
132     * This method conforms to the {@code Sink} protocol of calling
133     * {@code Sink.begin} before pushing elements, via {@code Sink.accept}, and
134     * calling {@code Sink.end} after all elements have been pushed or if
135     * cancellation is requested.
136     *
137     * @param wrappedSink the destination {@code Sink}
138     * @param spliterator the source {@code Spliterator}
139     */
140    abstract <P_IN> void copyIntoWithCancel(Sink<P_IN> wrappedSink, Spliterator<P_IN> spliterator);
141
142    /**
143     * Takes a {@code Sink} that accepts elements of the output type of the
144     * {@code PipelineHelper}, and wrap it with a {@code Sink} that accepts
145     * elements of the input type and implements all the intermediate operations
146     * described by this {@code PipelineHelper}, delivering the result into the
147     * provided {@code Sink}.
148     *
149     * @param sink the {@code Sink} to receive the results
150     * @return a {@code Sink} that implements the pipeline stages and sends
151     *         results to the provided {@code Sink}
152     */
153    abstract<P_IN> Sink<P_IN> wrapSink(Sink<P_OUT> sink);
154
155    /**
156     *
157     * @param spliterator
158     * @param 
159     * @return
160     */
161    abstract<P_IN> Spliterator<P_OUT> wrapSpliterator(Spliterator<P_IN> spliterator);
162
163    /**
164     * Constructs a @{link Node.Builder} compatible with the output shape of
165     * this {@code PipelineHelper}.
166     *
167     * @param exactSizeIfKnown if >=0 then a builder will be created that has a
168     *        fixed capacity of exactly sizeIfKnown elements; if < 0 then the
169     *        builder has variable capacity.  A fixed capacity builder will fail
170     *        if an element is added after the builder has reached capacity.
171     * @param generator a factory function for array instances
172     * @return a {@code Node.Builder} compatible with the output shape of this
173     *         {@code PipelineHelper}
174     */
175    abstract Node.Builder<P_OUT> makeNodeBuilder(long exactSizeIfKnown,
176                                                 IntFunction<P_OUT[]> generator);
177
178    /**
179     * Collects all output elements resulting from applying the pipeline stages
180     * to the source {@code Spliterator} into a {@code Node}.
181     *
182     * @implNote
183     * If the pipeline has no intermediate operations and the source is backed
184     * by a {@code Node} then that {@code Node} will be returned (or flattened
185     * and then returned). This reduces copying for a pipeline consisting of a
186     * stateful operation followed by a terminal operation that returns an
187     * array, such as:
188     * <pre>{@code
189     *     stream.sorted().toArray();
190     * }</pre>
191     *
192     * @param spliterator the source {@code Spliterator}
193     * @param flatten if true and the pipeline is a parallel pipeline then the
194     *        {@code Node} returned will contain no children, otherwise the
195     *        {@code Node} may represent the root in a tree that reflects the
196     *        shape of the computation tree.
197     * @param generator a factory function for array instances
198     * @return the {@code Node} containing all output elements
199     */
200    abstract<P_IN> Node<P_OUT> evaluate(Spliterator<P_IN> spliterator,
201                                        boolean flatten,
202                                        IntFunction<P_OUT[]> generator);
203}
204