1 /*
2 * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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23 * questions.
24 */
25 package java.util.stream;
26
27 import java.util.Spliterator;
28 import java.util.function.IntFunction;
29
30 /**
31 * Helper class for executing
32 * <a href="package-summary.html#StreamPipelines">stream pipelines</a>,
33 * capturing all of the information about a stream pipeline (source, output
34 * shape, stream flags, parallelism, etc) in one place.
35 *
36 * @apiNote
37 * A stream pipeline consists of a source, zero or more intermediate operations,
38 * and a terminal operation. Execution of the stream pipeline begins when the
39 * terminal operation is executed. A {@code PipelineHelper} describes the
40 * portion of a stream pipeline including its source, some or all of its
41 * intermediate operations, and certain information about the terminal (or
42 * stateful) operation which follows the last intermediate operation described
43 * by this {@code PipelineHelper}. The {@code PipelineHelper} is passed to the
44 * {@link TerminalOp#evaluateParallel(PipelineHelper)},
45 * {@link TerminalOp#evaluateSequential(PipelineHelper)}, and
46 * {@link StatefulOp#evaluateParallel(PipelineHelper)}, methods, which can use
47 * the {@code PipelineHelper} to access the source {@code Spliterator} for the
48 * pipeline, information about the pipeline such as input shape, output shape,
49 * stream flags, and size, and use the helper methods such as
50 * {@link #into(Sink, Spliterator)}, {@link #intoWrapped(Sink, Spliterator)},
51 * and {@link #wrapSink(Sink)} to execute pipeline operations.
52 *
53 * @param <P_IN> Type of input elements to the pipeline
54 * @param <P_OUT> Type of output elements from the pipeline
55 * @since 1.8
56 */
57 interface PipelineHelper<P_IN, P_OUT> {
58
59 /**
60 * Gets the {@code StreamShape} describing the input shape of the pipeline
61 * @return The input shape of the pipeline
62 */
63 StreamShape getInputShape();
64
65 /**
66 * Gets the {@code StreamShape} describing the output shape of the pipeline
67 * @return The output shape of the pipeline
68 */
69 StreamShape getOutputShape();
70
71 /**
72 * Gets the combined stream and operation flags for the output of the
73 * pipeline. This will incorporate stream flags from the stream source, all
74 * the intermediate operations and the terminal operation.
75 *
76 * @return the combined stream and operation flags for the output of the
77 * pipeline
78 * @see StreamOpFlag
79 */
80 int getStreamAndOpFlags();
81
82 /**
83 * Gets the operation flags for the terminal operation.
84 *
85 * @return the operation flags for the terminal operation.
86 * @see StreamOpFlag
87 */
88 // @@@ Specifying this concisely is somewhat complicated since since the actual terminal operation flags
89 // are masked by StreamOpFlag.UPSTREAM_TERMINAL_OP_MASK as the flags propagate upstream through parallel
90 // pipeline chunks
91 int getTerminalOpFlags();
92
93 /**
94 * Returns whether this pipeline is parallel or sequential
95 *
96 * @return true if the pipeline is a parallel pipeline, otherwise false
97 */
98 boolean isParallel();
99
100 /**
101 * Gets the {@code Spliterator} for the source of the pipeline. This
102 * {@code Spliterator} reflects only the source elements, not the actions of
103 * any of the intermediate stages.
104 *
105 * @return the source spliterator
106 */
107 Spliterator<P_IN> sourceSpliterator();
108
109 /**
110 * Returns the exact output size of the portion of the output resulting from
111 * applying the pipeline stages described by this {@code PipelineHelper} to
112 * the the portion of the input described by the provided
113 * {@code Spliterator}, if known. If not known or known infinite, will
114 * return {@code -1}.
115 *
116 * @apiNote
117 * The exact output size is known if the {@code Spliterator} has the
118 * {@code SIZED} characteristic, and the operation flags
119 * {@link StreamOpFlag#SIZED} is known on the combined stream and operation
120 * flags.
121 *
122 * @param spliterator the spliterator describing the relevant portion of the
123 * source data
124 * @return the exact size if known, or -1 if infinite or unknown
125 */
126 long exactOutputSizeIfKnown(Spliterator<P_IN> spliterator);
127
128 /**
129 * Applies the pipeline stages described by this {@code PipelineHelper} to
130 * the provided {@code Spliterator} and send the results to the provided
131 * {@code Sink}.
132 *
133 * @implSpec
134 * The implementation behaves as if:
135 * <pre>
136 * intoWrapped(wrapSink(sink), spliterator);
137 * </pre>
138 *
139 * @param sink the {@code Sink} to receive the results
140 * @param spliterator the spliterator describing the portion of the source
141 * input to process
142 */
143 <S extends Sink<P_OUT>> S into(S sink, Spliterator<P_IN> spliterator);
144
145 /**
146 * Pushes elements obtained from the {@code Spliterator} into the provided
147 * {@code Sink}. If the stream pipeline is known to have short-circuiting
148 * stages in it (see {@link StreamOpFlag#SHORT_CIRCUIT}), then the elements
149 * are delivered as per {@link #intoWrappedWithCancel(Sink, Spliterator)}.
150 *
151 * @implSpec
152 * This method conforms to the {@code Sink} protocol of calling
153 * {@code Sink.begin} before pushing elements, via {@code Sink.accept}, and
154 * calling {@code Sink.end} after all elements have been pushed.
155 *
156 * @param wrappedSink the destination {@code Sink}
157 * @param spliterator the source {@code Spliterator}
158 */
159 void intoWrapped(Sink<P_IN> wrappedSink, Spliterator<P_IN> spliterator);
160
161 /**
162 * Pushes elements obtained from the {@code Spliterator} into the provided
163 * {@code Sink}, checking {@link Sink#cancellationRequested()} after each
164 * element, and stopping if cancellation is requested.
165 *
166 * @implSpec
167 * This method conforms to the {@code Sink} protocol of calling
168 * {@code Sink.begin} before pushing elements, via {@code Sink.accept}, and
169 * calling {@code Sink.end} after all elements have been pushed or if
170 * cancellation is requested.
171 *
172 * @param wrappedSink the destination {@code Sink}
173 * @param spliterator the source {@code Spliterator}
174 */
175 void intoWrappedWithCancel(Sink<P_IN> wrappedSink, Spliterator<P_IN> spliterator);
176
177 /**
178 * Takes a {@code Sink} that accepts elements of the output type of the
179 * {@code PipelineHelper}, and wrap it with a {@code Sink} that accepts
180 * elements of the input type and implements all the intermediate operations
181 * described by this {@code PipelineHelper}, delivering the result into the
182 * provided {@code Sink}.
183 *
184 * @param sink the {@code Sink} to receive the results
185 * @return a {@code Sink} that implements the pipeline stages and sends
186 * results to the provided {@code Sink}
187 */
188 Sink<P_IN> wrapSink(Sink<P_OUT> sink);
189
190 /**
191 * Constructs a @{link Node.Builder} compatible with the output shape of
192 * this {@code PipelineHelper}
193 *
194 * @param exactSizeIfKnown if >=0 then a builder will be created that has a
195 * fixed capacity of exactly sizeIfKnown elements; if < 0 then the
196 * builder has variable capacity. A fixed capacity builder will fail
197 * if an element is added and the builder has reached capacity.
198 * @return A {@code Node.Builder} compatible with the output shape of this
199 * {@code PipelineHelper}
200 */
201 Node.Builder<P_OUT> makeNodeBuilder(long exactSizeIfKnown);
202
203 /**
204 * Collects all output elements resulting from applying the pipeline stages
205 * to the source {@code Spliterator} into a {@code Node}.
206 *
207 * @implSpec
208 * If the pipeline has no intermediate operations and the source is backed
209 * by a {@code Node} then that {@code Node} will be returned or flattened
210 * and then returned. This reduces copying for a pipeline consisting of a
211 * stateful operation followed by a terminal operation that returns an
212 * array, such as:
213 * <pre>{@code
214 * stream.sorted().toArray();
215 * }</pre>
216 *
217 * @param flatten if true and the pipeline is a parallel pipeline then the
218 * {@code Node} returned will contain no children, otherwise the
219 * {@code Node} may represent the root in a tree that reflects the
220 * shape of the computation tree.
221 * @return the {@code Node} containing all output elements
222 */
223 Node<P_OUT> collectOutput(boolean flatten);
224
225 /**
226 * Gets an array factory associated with the output type of this pipeline.
227 *
228 * @return a factory for arrays of the output type of this pipeline.
229 */
230 IntFunction<P_OUT[]> arrayGenerator();
231
232 /**
233 * Collects all output elements resulting from the applying the pipeline
234 * stages, plus an additional final stage that is an intermediate operation,
235 * to the source {@code Spliterator} into a {code Node}. The order of
236 * output elements will respect the encounter order of the source stream,
237 * and all computation will happen in the invoking thread.
238 * <p>
239 * Implementations of {@link StatefulOp#evaluateParallel(PipelineHelper)}
240 * can defer to this method if a sequential implementation is acceptable.
241 *
242 * @implSpec
243 * If the intermediate operation injects {@link StreamOpFlag#SHORT_CIRCUIT}
244 * then this implementation must stop collecting output elements when the
245 * sink returned from {@link IntermediateOp#wrapSink(int, Sink)} reports it
246 * is cancelled.
247 * <p>
248 * If the intermediate operation preserves or injects
249 * {@link StreamOpFlag#SIZED} and the output size of the pipeline is known
250 * then this implementation may apply size optimizations since the output
251 * size is known.
252 *
253 * @param op An {@code IntermediateOp} representing the final stage in the
254 * pipeline, typically a {@code StatefulOp}
255 * @return A {@code Node} containing the output of the stream pipeline
256 */
257 Node<P_OUT> evaluateSequential(IntermediateOp<P_OUT, P_OUT> op);
258 }