1 /* 2 * Copyright (c) 2012, 2015, 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 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 package java.util.stream; 26 27 import java.util.Objects; 28 import java.util.Spliterator; 29 import java.util.function.IntFunction; 30 import java.util.function.Supplier; 31 32 /** 33 * Abstract base class for "pipeline" classes, which are the core 34 * implementations of the Stream interface and its primitive specializations. 35 * Manages construction and evaluation of stream pipelines. 36 * 37 * <p>An {@code AbstractPipeline} represents an initial portion of a stream 38 * pipeline, encapsulating a stream source and zero or more intermediate 39 * operations. The individual {@code AbstractPipeline} objects are often 40 * referred to as <em>stages</em>, where each stage describes either the stream 41 * source or an intermediate operation. 42 * 43 * <p>A concrete intermediate stage is generally built from an 44 * {@code AbstractPipeline}, a shape-specific pipeline class which extends it 45 * (e.g., {@code IntPipeline}) which is also abstract, and an operation-specific 46 * concrete class which extends that. {@code AbstractPipeline} contains most of 47 * the mechanics of evaluating the pipeline, and implements methods that will be 48 * used by the operation; the shape-specific classes add helper methods for 49 * dealing with collection of results into the appropriate shape-specific 50 * containers. 51 * 52 * <p>After chaining a new intermediate operation, or executing a terminal 53 * operation, the stream is considered to be consumed, and no more intermediate 54 * or terminal operations are permitted on this stream instance. 55 * 56 * @implNote 57 * <p>For sequential streams, and parallel streams without 58 * <a href="package-summary.html#StreamOps">stateful intermediate 59 * operations</a>, parallel streams, pipeline evaluation is done in a single 60 * pass that "jams" all the operations together. For parallel streams with 61 * stateful operations, execution is divided into segments, where each 62 * stateful operations marks the end of a segment, and each segment is 63 * evaluated separately and the result used as the input to the next 64 * segment. In all cases, the source data is not consumed until a terminal 65 * operation begins. 66 * 67 * @param <E_IN> type of input elements 68 * @param <E_OUT> type of output elements 69 * @param <S> type of the subclass implementing {@code BaseStream} 70 * @since 1.8 71 */ 72 abstract class AbstractPipeline<E_IN, E_OUT, S extends BaseStream<E_OUT, S>> 73 extends PipelineHelper<E_OUT> implements BaseStream<E_OUT, S> { 74 private static final String MSG_STREAM_LINKED = "stream has already been operated upon or closed"; 75 private static final String MSG_CONSUMED = "source already consumed or closed"; 76 77 /** 78 * Backlink to the head of the pipeline chain (self if this is the source 79 * stage). 80 */ 81 @SuppressWarnings("rawtypes") 82 private final AbstractPipeline sourceStage; 83 84 /** 85 * The "upstream" pipeline, or null if this is the source stage. 86 */ 87 @SuppressWarnings("rawtypes") 88 private final AbstractPipeline previousStage; 89 90 /** 91 * The operation flags for the intermediate operation represented by this 92 * pipeline object. 93 */ 94 protected final int sourceOrOpFlags; 95 96 /** 97 * The next stage in the pipeline, or null if this is the last stage. 98 * Effectively final at the point of linking to the next pipeline. 99 */ 100 @SuppressWarnings("rawtypes") 101 private AbstractPipeline nextStage; 102 103 /** 104 * The number of intermediate operations between this pipeline object 105 * and the stream source if sequential, or the previous stateful if parallel. 106 * Valid at the point of pipeline preparation for evaluation. 107 */ 108 private int depth; 109 110 /** 111 * The combined source and operation flags for the source and all operations 112 * up to and including the operation represented by this pipeline object. 113 * Valid at the point of pipeline preparation for evaluation. 114 */ 115 private int combinedFlags; 116 117 /** 118 * The source spliterator. Only valid for the head pipeline. 119 * Before the pipeline is consumed if non-null then {@code sourceSupplier} 120 * must be null. After the pipeline is consumed if non-null then is set to 121 * null. 122 */ 123 private Spliterator<?> sourceSpliterator; 124 125 /** 126 * The source supplier. Only valid for the head pipeline. Before the 127 * pipeline is consumed if non-null then {@code sourceSpliterator} must be 128 * null. After the pipeline is consumed if non-null then is set to null. 129 */ 130 private Supplier<? extends Spliterator<?>> sourceSupplier; 131 132 /** 133 * True if this pipeline has been linked or consumed 134 */ 135 private boolean linkedOrConsumed; 136 137 /** 138 * True if there are any stateful ops in the pipeline; only valid for the 139 * source stage. 140 */ 141 private boolean sourceAnyStateful; 142 143 private Runnable sourceCloseAction; 144 145 /** 146 * True if pipeline is parallel, otherwise the pipeline is sequential; only 147 * valid for the source stage. 148 */ 149 private boolean parallel; 150 151 /** 152 * Constructor for the head of a stream pipeline. 153 * 154 * @param source {@code Supplier<Spliterator>} describing the stream source 155 * @param sourceFlags The source flags for the stream source, described in 156 * {@link StreamOpFlag} 157 * @param parallel True if the pipeline is parallel 158 */ 159 AbstractPipeline(Supplier<? extends Spliterator<?>> source, 160 int sourceFlags, boolean parallel) { 161 this.previousStage = null; 162 this.sourceSupplier = source; 163 this.sourceStage = this; 164 this.sourceOrOpFlags = sourceFlags & StreamOpFlag.STREAM_MASK; 165 // The following is an optimization of: 166 // StreamOpFlag.combineOpFlags(sourceOrOpFlags, StreamOpFlag.INITIAL_OPS_VALUE); 167 this.combinedFlags = (~(sourceOrOpFlags << 1)) & StreamOpFlag.INITIAL_OPS_VALUE; 168 this.depth = 0; 169 this.parallel = parallel; 170 } 171 172 /** 173 * Constructor for the head of a stream pipeline. 174 * 175 * @param source {@code Spliterator} describing the stream source 176 * @param sourceFlags the source flags for the stream source, described in 177 * {@link StreamOpFlag} 178 * @param parallel {@code true} if the pipeline is parallel 179 */ 180 AbstractPipeline(Spliterator<?> source, 181 int sourceFlags, boolean parallel) { 182 this.previousStage = null; 183 this.sourceSpliterator = source; 184 this.sourceStage = this; 185 this.sourceOrOpFlags = sourceFlags & StreamOpFlag.STREAM_MASK; 186 // The following is an optimization of: 187 // StreamOpFlag.combineOpFlags(sourceOrOpFlags, StreamOpFlag.INITIAL_OPS_VALUE); 188 this.combinedFlags = (~(sourceOrOpFlags << 1)) & StreamOpFlag.INITIAL_OPS_VALUE; 189 this.depth = 0; 190 this.parallel = parallel; 191 } 192 193 /** 194 * Constructor for appending an intermediate operation stage onto an 195 * existing pipeline. 196 * 197 * @param previousStage the upstream pipeline stage 198 * @param opFlags the operation flags for the new stage, described in 199 * {@link StreamOpFlag} 200 */ 201 AbstractPipeline(AbstractPipeline<?, E_IN, ?> previousStage, int opFlags) { 202 if (previousStage.linkedOrConsumed) 203 throw new IllegalStateException(MSG_STREAM_LINKED); 204 previousStage.linkedOrConsumed = true; 205 previousStage.nextStage = this; 206 207 this.previousStage = previousStage; 208 this.sourceOrOpFlags = opFlags & StreamOpFlag.OP_MASK; 209 this.combinedFlags = StreamOpFlag.combineOpFlags(opFlags, previousStage.combinedFlags); 210 this.sourceStage = previousStage.sourceStage; 211 if (opIsStateful()) 212 sourceStage.sourceAnyStateful = true; 213 this.depth = previousStage.depth + 1; 214 } 215 216 217 // Terminal evaluation methods 218 219 /** 220 * Evaluate the pipeline with a terminal operation to produce a result. 221 * 222 * @param <R> the type of result 223 * @param terminalOp the terminal operation to be applied to the pipeline. 224 * @return the result 225 */ 226 final <R> R evaluate(TerminalOp<E_OUT, R> terminalOp) { 227 assert getOutputShape() == terminalOp.inputShape(); 228 if (linkedOrConsumed) 229 throw new IllegalStateException(MSG_STREAM_LINKED); 230 linkedOrConsumed = true; 231 232 return isParallel() 233 ? terminalOp.evaluateParallel(this, sourceSpliterator(terminalOp.getOpFlags())) 234 : terminalOp.evaluateSequential(this, sourceSpliterator(terminalOp.getOpFlags())); 235 } 236 237 /** 238 * Collect the elements output from the pipeline stage. 239 * 240 * @param generator the array generator to be used to create array instances 241 * @return a flat array-backed Node that holds the collected output elements 242 */ 243 @SuppressWarnings("unchecked") 244 final Node<E_OUT> evaluateToArrayNode(IntFunction<E_OUT[]> generator) { 245 if (linkedOrConsumed) 246 throw new IllegalStateException(MSG_STREAM_LINKED); 247 linkedOrConsumed = true; 248 249 // If the last intermediate operation is stateful then 250 // evaluate directly to avoid an extra collection step 251 if (isParallel() && previousStage != null && opIsStateful()) { 252 // Set the depth of this, last, pipeline stage to zero to slice the 253 // pipeline such that this operation will not be included in the 254 // upstream slice and upstream operations will not be included 255 // in this slice 256 depth = 0; 257 return opEvaluateParallel(previousStage, previousStage.sourceSpliterator(0), generator); 258 } 259 else { 260 return evaluate(sourceSpliterator(0), true, generator); 261 } 262 } 263 264 /** 265 * Gets the source stage spliterator if this pipeline stage is the source 266 * stage. The pipeline is consumed after this method is called and 267 * returns successfully. 268 * 269 * @return the source stage spliterator 270 * @throws IllegalStateException if this pipeline stage is not the source 271 * stage. 272 */ 273 @SuppressWarnings("unchecked") 274 final Spliterator<E_OUT> sourceStageSpliterator() { 275 if (this != sourceStage) 276 throw new IllegalStateException(); 277 278 if (linkedOrConsumed) 279 throw new IllegalStateException(MSG_STREAM_LINKED); 280 linkedOrConsumed = true; 281 282 if (sourceStage.sourceSpliterator != null) { 283 @SuppressWarnings("unchecked") 284 Spliterator<E_OUT> s = sourceStage.sourceSpliterator; 285 sourceStage.sourceSpliterator = null; 286 return s; 287 } 288 else if (sourceStage.sourceSupplier != null) { 289 @SuppressWarnings("unchecked") 290 Spliterator<E_OUT> s = (Spliterator<E_OUT>) sourceStage.sourceSupplier.get(); 291 sourceStage.sourceSupplier = null; 292 return s; 293 } 294 else { 295 throw new IllegalStateException(MSG_CONSUMED); 296 } 297 } 298 299 // BaseStream 300 301 @Override 302 @SuppressWarnings("unchecked") 303 public final S sequential() { 304 sourceStage.parallel = false; 305 return (S) this; 306 } 307 308 @Override 309 @SuppressWarnings("unchecked") 310 public final S parallel() { 311 sourceStage.parallel = true; 312 return (S) this; 313 } 314 315 @Override 316 public void close() { 317 linkedOrConsumed = true; 318 sourceSupplier = null; 319 sourceSpliterator = null; 320 if (sourceStage.sourceCloseAction != null) { 321 Runnable closeAction = sourceStage.sourceCloseAction; 322 sourceStage.sourceCloseAction = null; 323 closeAction.run(); 324 } 325 } 326 327 @Override 328 @SuppressWarnings("unchecked") 329 public S onClose(Runnable closeHandler) { 330 if (linkedOrConsumed) 331 throw new IllegalStateException(MSG_STREAM_LINKED); 332 Objects.requireNonNull(closeHandler); 333 Runnable existingHandler = sourceStage.sourceCloseAction; 334 sourceStage.sourceCloseAction = 335 (existingHandler == null) 336 ? closeHandler 337 : Streams.composeWithExceptions(existingHandler, closeHandler); 338 return (S) this; 339 } 340 341 // Primitive specialization use co-variant overrides, hence is not final 342 @Override 343 @SuppressWarnings("unchecked") 344 public Spliterator<E_OUT> spliterator() { 345 if (linkedOrConsumed) 346 throw new IllegalStateException(MSG_STREAM_LINKED); 347 linkedOrConsumed = true; 348 349 if (this == sourceStage) { 350 if (sourceStage.sourceSpliterator != null) { 351 @SuppressWarnings("unchecked") 352 Spliterator<E_OUT> s = (Spliterator<E_OUT>) sourceStage.sourceSpliterator; 353 sourceStage.sourceSpliterator = null; 354 return s; 355 } 356 else if (sourceStage.sourceSupplier != null) { 357 @SuppressWarnings("unchecked") 358 Supplier<Spliterator<E_OUT>> s = (Supplier<Spliterator<E_OUT>>) sourceStage.sourceSupplier; 359 sourceStage.sourceSupplier = null; 360 return lazySpliterator(s); 361 } 362 else { 363 throw new IllegalStateException(MSG_CONSUMED); 364 } 365 } 366 else { 367 return wrap(this, () -> sourceSpliterator(0), isParallel()); 368 } 369 } 370 371 @Override 372 public final boolean isParallel() { 373 return sourceStage.parallel; 374 } 375 376 377 /** 378 * Returns the composition of stream flags of the stream source and all 379 * intermediate operations. 380 * 381 * @return the composition of stream flags of the stream source and all 382 * intermediate operations 383 * @see StreamOpFlag 384 */ 385 final int getStreamFlags() { 386 return StreamOpFlag.toStreamFlags(combinedFlags); 387 } 388 389 /** 390 * Get the source spliterator for this pipeline stage. For a sequential or 391 * stateless parallel pipeline, this is the source spliterator. For a 392 * stateful parallel pipeline, this is a spliterator describing the results 393 * of all computations up to and including the most recent stateful 394 * operation. 395 */ 396 @SuppressWarnings("unchecked") 397 private Spliterator<?> sourceSpliterator(int terminalFlags) { 398 // Get the source spliterator of the pipeline 399 Spliterator<?> spliterator = null; 400 if (sourceStage.sourceSpliterator != null) { 401 spliterator = sourceStage.sourceSpliterator; 402 sourceStage.sourceSpliterator = null; 403 } 404 else if (sourceStage.sourceSupplier != null) { 405 spliterator = (Spliterator<?>) sourceStage.sourceSupplier.get(); 406 sourceStage.sourceSupplier = null; 407 } 408 else { 409 throw new IllegalStateException(MSG_CONSUMED); 410 } 411 412 if (isParallel() && sourceStage.sourceAnyStateful) { 413 // Adapt the source spliterator, evaluating each stateful op 414 // in the pipeline up to and including this pipeline stage. 415 // The depth and flags of each pipeline stage are adjusted accordingly. 416 int depth = 1; 417 for (@SuppressWarnings("rawtypes") AbstractPipeline u = sourceStage, p = sourceStage.nextStage, e = this; 418 u != e; 419 u = p, p = p.nextStage) { 420 421 int thisOpFlags = p.sourceOrOpFlags; 422 if (p.opIsStateful()) { 423 depth = 0; 424 425 if (StreamOpFlag.SHORT_CIRCUIT.isKnown(thisOpFlags)) { 426 // Clear the short circuit flag for next pipeline stage 427 // This stage encapsulates short-circuiting, the next 428 // stage may not have any short-circuit operations, and 429 // if so spliterator.forEachRemaining should be used 430 // for traversal 431 thisOpFlags = thisOpFlags & ~StreamOpFlag.IS_SHORT_CIRCUIT; 432 } 433 434 spliterator = p.opEvaluateParallelLazy(u, spliterator); 435 436 // Inject or clear SIZED on the source pipeline stage 437 // based on the stage's spliterator 438 thisOpFlags = spliterator.hasCharacteristics(Spliterator.SIZED) 439 ? (thisOpFlags & ~StreamOpFlag.NOT_SIZED) | StreamOpFlag.IS_SIZED 440 : (thisOpFlags & ~StreamOpFlag.IS_SIZED) | StreamOpFlag.NOT_SIZED; 441 } 442 p.depth = depth++; 443 p.combinedFlags = StreamOpFlag.combineOpFlags(thisOpFlags, u.combinedFlags); 444 } 445 } 446 447 if (terminalFlags != 0) { 448 // Apply flags from the terminal operation to last pipeline stage 449 combinedFlags = StreamOpFlag.combineOpFlags(terminalFlags, combinedFlags); 450 } 451 452 return spliterator; 453 } 454 455 // PipelineHelper 456 457 @Override 458 final StreamShape getSourceShape() { 459 @SuppressWarnings("rawtypes") 460 AbstractPipeline p = AbstractPipeline.this; 461 while (p.depth > 0) { 462 p = p.previousStage; 463 } 464 return p.getOutputShape(); 465 } 466 467 @Override 468 final <P_IN> long exactOutputSizeIfKnown(Spliterator<P_IN> spliterator) { 469 return StreamOpFlag.SIZED.isKnown(getStreamAndOpFlags()) ? spliterator.getExactSizeIfKnown() : -1; 470 } 471 472 @Override 473 final <P_IN, S extends Sink<E_OUT>> S wrapAndCopyInto(S sink, Spliterator<P_IN> spliterator) { 474 copyInto(wrapSink(Objects.requireNonNull(sink)), spliterator); 475 return sink; 476 } 477 478 @Override 479 final <P_IN> void copyInto(Sink<P_IN> wrappedSink, Spliterator<P_IN> spliterator) { 480 Objects.requireNonNull(wrappedSink); 481 482 if (!StreamOpFlag.SHORT_CIRCUIT.isKnown(getStreamAndOpFlags())) { 483 wrappedSink.begin(spliterator.getExactSizeIfKnown()); 484 spliterator.forEachRemaining(wrappedSink); 485 wrappedSink.end(); 486 } 487 else { 488 copyIntoWithCancel(wrappedSink, spliterator); 489 } 490 } 491 492 @Override 493 @SuppressWarnings("unchecked") 494 final <P_IN> boolean copyIntoWithCancel(Sink<P_IN> wrappedSink, Spliterator<P_IN> spliterator) { 495 @SuppressWarnings({"rawtypes","unchecked"}) 496 AbstractPipeline p = AbstractPipeline.this; 497 while (p.depth > 0) { 498 p = p.previousStage; 499 } 500 501 wrappedSink.begin(spliterator.getExactSizeIfKnown()); 502 boolean cancelled = p.forEachWithCancel(spliterator, wrappedSink); 503 wrappedSink.end(); 504 return cancelled; 505 } 506 507 @Override 508 final int getStreamAndOpFlags() { 509 return combinedFlags; 510 } 511 512 final boolean isOrdered() { 513 return StreamOpFlag.ORDERED.isKnown(combinedFlags); 514 } 515 516 @Override 517 @SuppressWarnings("unchecked") 518 final <P_IN> Sink<P_IN> wrapSink(Sink<E_OUT> sink) { 519 Objects.requireNonNull(sink); 520 521 for ( @SuppressWarnings("rawtypes") AbstractPipeline p=AbstractPipeline.this; p.depth > 0; p=p.previousStage) { 522 sink = p.opWrapSink(p.previousStage.combinedFlags, sink); 523 } 524 return (Sink<P_IN>) sink; 525 } 526 527 @Override 528 @SuppressWarnings("unchecked") 529 final <P_IN> Spliterator<E_OUT> wrapSpliterator(Spliterator<P_IN> sourceSpliterator) { 530 if (depth == 0) { 531 return (Spliterator<E_OUT>) sourceSpliterator; 532 } 533 else { 534 return wrap(this, () -> sourceSpliterator, isParallel()); 535 } 536 } 537 538 @Override 539 @SuppressWarnings("unchecked") 540 final <P_IN> Node<E_OUT> evaluate(Spliterator<P_IN> spliterator, 541 boolean flatten, 542 IntFunction<E_OUT[]> generator) { 543 if (isParallel()) { 544 // @@@ Optimize if op of this pipeline stage is a stateful op 545 return evaluateToNode(this, spliterator, flatten, generator); 546 } 547 else { 548 Node.Builder<E_OUT> nb = makeNodeBuilder( 549 exactOutputSizeIfKnown(spliterator), generator); 550 return wrapAndCopyInto(nb, spliterator).build(); 551 } 552 } 553 554 555 // Shape-specific abstract methods, implemented by XxxPipeline classes 556 557 /** 558 * Get the output shape of the pipeline. If the pipeline is the head, 559 * then it's output shape corresponds to the shape of the source. 560 * Otherwise, it's output shape corresponds to the output shape of the 561 * associated operation. 562 * 563 * @return the output shape 564 */ 565 abstract StreamShape getOutputShape(); 566 567 /** 568 * Collect elements output from a pipeline into a Node that holds elements 569 * of this shape. 570 * 571 * @param helper the pipeline helper describing the pipeline stages 572 * @param spliterator the source spliterator 573 * @param flattenTree true if the returned node should be flattened 574 * @param generator the array generator 575 * @return a Node holding the output of the pipeline 576 */ 577 abstract <P_IN> Node<E_OUT> evaluateToNode(PipelineHelper<E_OUT> helper, 578 Spliterator<P_IN> spliterator, 579 boolean flattenTree, 580 IntFunction<E_OUT[]> generator); 581 582 /** 583 * Create a spliterator that wraps a source spliterator, compatible with 584 * this stream shape, and operations associated with a {@link 585 * PipelineHelper}. 586 * 587 * @param ph the pipeline helper describing the pipeline stages 588 * @param supplier the supplier of a spliterator 589 * @return a wrapping spliterator compatible with this shape 590 */ 591 abstract <P_IN> Spliterator<E_OUT> wrap(PipelineHelper<E_OUT> ph, 592 Supplier<Spliterator<P_IN>> supplier, 593 boolean isParallel); 594 595 /** 596 * Create a lazy spliterator that wraps and obtains the supplied the 597 * spliterator when a method is invoked on the lazy spliterator. 598 * @param supplier the supplier of a spliterator 599 */ 600 abstract Spliterator<E_OUT> lazySpliterator(Supplier<? extends Spliterator<E_OUT>> supplier); 601 602 /** 603 * Traverse the elements of a spliterator compatible with this stream shape, 604 * pushing those elements into a sink. If the sink requests cancellation, 605 * no further elements will be pulled or pushed. 606 * 607 * @param spliterator the spliterator to pull elements from 608 * @param sink the sink to push elements to 609 * @return true if the cancellation was requested 610 */ 611 abstract boolean forEachWithCancel(Spliterator<E_OUT> spliterator, Sink<E_OUT> sink); 612 613 /** 614 * Make a node builder compatible with this stream shape. 615 * 616 * @param exactSizeIfKnown if {@literal >=0}, then a node builder will be 617 * created that has a fixed capacity of at most sizeIfKnown elements. If 618 * {@literal < 0}, then the node builder has an unfixed capacity. A fixed 619 * capacity node builder will throw exceptions if an element is added after 620 * builder has reached capacity, or is built before the builder has reached 621 * capacity. 622 * 623 * @param generator the array generator to be used to create instances of a 624 * T[] array. For implementations supporting primitive nodes, this parameter 625 * may be ignored. 626 * @return a node builder 627 */ 628 @Override 629 abstract Node.Builder<E_OUT> makeNodeBuilder(long exactSizeIfKnown, 630 IntFunction<E_OUT[]> generator); 631 632 633 // Op-specific abstract methods, implemented by the operation class 634 635 /** 636 * Returns whether this operation is stateful or not. If it is stateful, 637 * then the method 638 * {@link #opEvaluateParallel(PipelineHelper, java.util.Spliterator, java.util.function.IntFunction)} 639 * must be overridden. 640 * 641 * @return {@code true} if this operation is stateful 642 */ 643 abstract boolean opIsStateful(); 644 645 /** 646 * Accepts a {@code Sink} which will receive the results of this operation, 647 * and return a {@code Sink} which accepts elements of the input type of 648 * this operation and which performs the operation, passing the results to 649 * the provided {@code Sink}. 650 * 651 * @apiNote 652 * The implementation may use the {@code flags} parameter to optimize the 653 * sink wrapping. For example, if the input is already {@code DISTINCT}, 654 * the implementation for the {@code Stream#distinct()} method could just 655 * return the sink it was passed. 656 * 657 * @param flags The combined stream and operation flags up to, but not 658 * including, this operation 659 * @param sink sink to which elements should be sent after processing 660 * @return a sink which accepts elements, perform the operation upon 661 * each element, and passes the results (if any) to the provided 662 * {@code Sink}. 663 */ 664 abstract Sink<E_IN> opWrapSink(int flags, Sink<E_OUT> sink); 665 666 /** 667 * Performs a parallel evaluation of the operation using the specified 668 * {@code PipelineHelper} which describes the upstream intermediate 669 * operations. Only called on stateful operations. If {@link 670 * #opIsStateful()} returns true then implementations must override the 671 * default implementation. 672 * 673 * @implSpec The default implementation always throw 674 * {@code UnsupportedOperationException}. 675 * 676 * @param helper the pipeline helper describing the pipeline stages 677 * @param spliterator the source {@code Spliterator} 678 * @param generator the array generator 679 * @return a {@code Node} describing the result of the evaluation 680 */ 681 <P_IN> Node<E_OUT> opEvaluateParallel(PipelineHelper<E_OUT> helper, 682 Spliterator<P_IN> spliterator, 683 IntFunction<E_OUT[]> generator) { 684 throw new UnsupportedOperationException("Parallel evaluation is not supported"); 685 } 686 687 /** 688 * Returns a {@code Spliterator} describing a parallel evaluation of the 689 * operation, using the specified {@code PipelineHelper} which describes the 690 * upstream intermediate operations. Only called on stateful operations. 691 * It is not necessary (though acceptable) to do a full computation of the 692 * result here; it is preferable, if possible, to describe the result via a 693 * lazily evaluated spliterator. 694 * 695 * @implSpec The default implementation behaves as if: 696 * <pre>{@code 697 * return evaluateParallel(helper, i -> (E_OUT[]) new 698 * Object[i]).spliterator(); 699 * }</pre> 700 * and is suitable for implementations that cannot do better than a full 701 * synchronous evaluation. 702 * 703 * @param helper the pipeline helper 704 * @param spliterator the source {@code Spliterator} 705 * @return a {@code Spliterator} describing the result of the evaluation 706 */ 707 @SuppressWarnings("unchecked") 708 <P_IN> Spliterator<E_OUT> opEvaluateParallelLazy(PipelineHelper<E_OUT> helper, 709 Spliterator<P_IN> spliterator) { 710 return opEvaluateParallel(helper, spliterator, i -> (E_OUT[]) new Object[i]).spliterator(); 711 } 712 }