1 /*
2 * Copyright (c) 2015, 2016, 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
26 package java.lang.invoke;
27
28 import jdk.internal.org.objectweb.asm.ClassWriter;
29 import jdk.internal.org.objectweb.asm.Label;
30 import jdk.internal.org.objectweb.asm.MethodVisitor;
31 import jdk.internal.org.objectweb.asm.Opcodes;
32 import jdk.internal.vm.annotation.ForceInline;
33 import sun.misc.Unsafe;
34
35 import java.lang.invoke.MethodHandles.Lookup;
36 import java.security.AccessController;
37 import java.security.PrivilegedAction;
38 import java.util.*;
39 import java.util.concurrent.ConcurrentHashMap;
40 import java.util.concurrent.ConcurrentMap;
41 import java.util.function.Function;
42
43 import static jdk.internal.org.objectweb.asm.Opcodes.*;
44
45 /**
46 * <p>Methods to facilitate the creation of String concatenation methods, that
47 * can be used to efficiently concatenate a known number of arguments of known
48 * types, possibly after type adaptation and partial evaluation of arguments.
49 * These methods are typically used as <em>bootstrap methods</em> for {@code
50 * invokedynamic} call sites, to support the <em>string concatenation</em>
51 * feature of the Java Programming Language.
52 *
53 * <p>Indirect access to the behavior specified by the provided {@code
54 * MethodHandle} proceeds in order through two phases:
55 *
56 * <ol>
57 * <li><em>Linkage</em> occurs when the methods in this class are invoked.
58 * They take as arguments a method type describing the concatenated arguments
59 * count and types, and optionally the String <em>recipe</em>, plus the
60 * constants that participate in the String concatenation. The details on
61 * accepted recipe shapes are described further below. Linkage may involve
62 * dynamically loading a new class that implements the expected concatenation
63 * behavior. The {@code CallSite} holds the {@code MethodHandle} pointing to the
64 * exact concatenation method. The concatenation methods may be shared among
65 * different {@code CallSite}s, e.g. if linkage methods produce them as pure
66 * functions.</li>
67 *
68 * <li><em>Invocation</em> occurs when a generated concatenation method is
69 * invoked with the exact dynamic arguments. This may occur many times for a
70 * single concatenation method. The method referenced by the behavior {@code
71 * MethodHandle} is invoked with the static arguments and any additional dynamic
72 * arguments provided on invocation, as if by {@link MethodHandle#invoke(Object...)}.</li>
73 * </ol>
74 *
75 * <p> This class provides two forms of linkage methods: a simple version
76 * ({@link #makeConcat(java.lang.invoke.MethodHandles.Lookup, String,
77 * MethodType)}) using only the dynamic arguments, and an advanced version
78 * ({@link #makeConcatWithConstants(java.lang.invoke.MethodHandles.Lookup,
79 * String, MethodType, String, Object...)} using the advanced forms of capturing
80 * the constant arguments. The advanced strategy can produce marginally better
81 * invocation bytecode, at the expense of exploding the number of shapes of
82 * string concatenation methods present at runtime, because those shapes would
83 * include constant static arguments as well.
84 *
85 * @author Aleksey Shipilev
86 * @author Remi Forax
87 * @author Peter Levart
88 *
89 * @apiNote
90 * <p>There is a JVM limit (classfile structural constraint): no method
91 * can call with more than 255 slots. This limits the number of static and
92 * dynamic arguments one can pass to bootstrap method. Since there are potential
93 * concatenation strategies that use {@code MethodHandle} combinators, we need
94 * to reserve a few empty slots on the parameter lists to to capture the
95 * temporal results. This is why bootstrap methods in this factory do not accept
96 * more than 200 argument slots. Users requiring more than 200 argument slots in
97 * concatenation are expected to split the large concatenation in smaller
98 * expressions.
99 *
100 * @since 9
101 */
102 public final class StringConcatFactory {
103
104 /**
105 * Tag used to demarcate an ordinary argument.
106 */
107 private static final char TAG_ARG = '\u0001';
108
109 /**
110 * Tag used to demarcate a constant.
111 */
112 private static final char TAG_CONST = '\u0002';
113
114 /**
115 * Maximum number of argument slots in String Concat call.
116 *
117 * While the maximum number of argument slots that indy call can handle is 253,
118 * we do not use all those slots, to let the strategies with MethodHandle
119 * combinators to use some arguments.
120 */
121 private static final int MAX_INDY_CONCAT_ARG_SLOTS = 200;
122
123 /**
124 * Concatenation strategy to use. See {@link Strategy} for possible options.
125 * This option is controllable with -Djava.lang.invoke.stringConcat JDK option.
126 */
127 private static final Strategy STRATEGY;
128
129 /**
130 * Default strategy to use for concatenation.
131 */
132 private static final Strategy DEFAULT_STRATEGY = Strategy.BC_SB;
133
134 private enum Strategy {
135 /**
136 * Bytecode generator, calling into {@link java.lang.StringBuilder}.
137 */
138 BC_SB,
139
140 /**
141 * Bytecode generator, calling into {@link java.lang.StringBuilder};
142 * but trying to estimate the required storage.
143 */
144 BC_SB_SIZED,
145
146 /**
147 * Bytecode generator, calling into {@link java.lang.StringBuilder};
148 * but computing the required storage exactly.
149 */
150 BC_SB_SIZED_EXACT,
151
152 /**
153 * MethodHandle-based generator, that in the end calls into {@link java.lang.StringBuilder}.
154 * This strategy also tries to estimate the required storage.
155 */
156 MH_SB_SIZED,
157
158 /**
159 * MethodHandle-based generator, that in the end calls into {@link java.lang.StringBuilder}.
160 * This strategy also estimate the required storage exactly.
161 */
162 MH_SB_SIZED_EXACT,
163
164 /**
165 * MethodHandle-based generator, that constructs its own byte[] array from
166 * the arguments. It computes the required storage exactly.
167 */
168 MH_INLINE_SIZED_EXACT
169 }
170
171 /**
172 * Enables debugging: this may print debugging messages, perform additional (non-neutral for performance)
173 * checks, etc.
174 */
175 private static final boolean DEBUG;
176
177 /**
178 * Enables caching of strategy stubs. This may improve the linkage time by reusing the generated
179 * code, at the expense of contaminating the profiles.
180 */
181 private static final boolean CACHE_ENABLE;
182
183 private static final ConcurrentMap<Key, MethodHandle> CACHE;
184
185 static {
186 // Poke the privileged block once, taking everything we need:
187 final Object[] values = new Object[3];
188 AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
189 values[0] = System.getProperty("java.lang.invoke.stringConcat");
190 values[1] = Boolean.getBoolean("java.lang.invoke.stringConcat.cache");
191 values[2] = Boolean.getBoolean("java.lang.invoke.stringConcat.debug");
192 return null;
193 });
194
195 final String strategy = (String) values[0];
196 CACHE_ENABLE = (Boolean) values[1];
197 DEBUG = (Boolean) values[2];
198
199 STRATEGY = (strategy == null) ? DEFAULT_STRATEGY : Strategy.valueOf(strategy);
200 CACHE = CACHE_ENABLE ? new ConcurrentHashMap<>() : null;
201 }
202
203 private static final class Key {
204 final MethodType mt;
205 final Recipe recipe;
206
207 public Key(MethodType mt, Recipe recipe) {
208 this.mt = mt;
209 this.recipe = recipe;
210 }
211
212 @Override
213 public boolean equals(Object o) {
214 if (this == o) return true;
215 if (o == null || getClass() != o.getClass()) return false;
216
217 Key key = (Key) o;
218
219 if (!mt.equals(key.mt)) return false;
220 if (!recipe.equals(key.recipe)) return false;
221 return true;
222 }
223
224 @Override
225 public int hashCode() {
226 int result = mt.hashCode();
227 result = 31 * result + recipe.hashCode();
228 return result;
229 }
230 }
231
232 /**
233 * Parses the recipe string, and produces the traversable collection of
234 * {@link java.lang.invoke.StringConcatFactory.RecipeElement}-s for generator
235 * strategies. Notably, this class parses out the constants from the recipe
236 * and from other static arguments.
237 */
238 private static final class Recipe {
239 private final List<RecipeElement> elements;
240 private final List<RecipeElement> elementsRev;
241
242 public Recipe(String src, Object[] constants) {
243 List<RecipeElement> el = new ArrayList<>();
244
245 int constC = 0;
246 int argC = 0;
247
248 StringBuilder acc = new StringBuilder();
249
250 for (int i = 0; i < src.length(); i++) {
251 char c = src.charAt(i);
252
253 if (c == TAG_CONST || c == TAG_ARG) {
254 // Detected a special tag, flush all accumulated characters
255 // as a constant first:
256 if (acc.length() > 0) {
257 el.add(new RecipeElement(acc.toString()));
258 acc.setLength(0);
259 }
260 if (c == TAG_CONST) {
261 Object cnst = constants[constC++];
262 el.add(new RecipeElement(cnst));
263 }
264 if (c == TAG_ARG) {
265 el.add(new RecipeElement(argC++));
266 }
267 } else {
268 // Not a special characters, this is a constant embedded into
269 // the recipe itself.
270 acc.append(c);
271 }
272 }
273
274 // Flush the remaining characters as constant:
275 if (acc.length() > 0) {
276 el.add(new RecipeElement(acc.toString()));
277 }
278
279 elements = new ArrayList<>(el);
280 Collections.reverse(el);
281 elementsRev = el;
282 }
283
284 public Collection<RecipeElement> getElements() {
285 return elements;
286 }
287
288 public Collection<RecipeElement> getElementsReversed() {
289 return elementsRev;
290 }
291
292 @Override
293 public boolean equals(Object o) {
294 if (this == o) return true;
295 if (o == null || getClass() != o.getClass()) return false;
296
297 Recipe recipe = (Recipe) o;
298 return elements.equals(recipe.elements);
299 }
300
301 @Override
302 public int hashCode() {
303 return elements.hashCode();
304 }
305 }
306
307 private static final class RecipeElement {
308 private final Object value;
309 private final int argPos;
310 private final Tag tag;
311
312 public RecipeElement(Object cnst) {
313 this.value = Objects.requireNonNull(cnst);
314 this.argPos = -1;
315 this.tag = Tag.CONST;
316 }
317
318 public RecipeElement(int arg) {
319 this.value = null;
320 this.argPos = arg;
321 this.tag = Tag.ARG;
322 }
323
324 public Object getValue() {
325 assert (tag == Tag.CONST);
326 return value;
327 }
328
329 public int getArgPos() {
330 assert (tag == Tag.ARG);
331 return argPos;
332 }
333
334 public Tag getTag() {
335 return tag;
336 }
337
338 @Override
339 public boolean equals(Object o) {
340 if (this == o) return true;
341 if (o == null || getClass() != o.getClass()) return false;
342
343 RecipeElement that = (RecipeElement) o;
344
345 if (tag != that.tag) return false;
346 if (tag == Tag.CONST && (!value.equals(that.value))) return false;
347 if (tag == Tag.ARG && (argPos != that.argPos)) return false;
348 return true;
349 }
350
351 @Override
352 public int hashCode() {
353 return tag.hashCode();
354 }
355 }
356
357 private enum Tag {
358 CONST, ARG
359 }
360
361 /**
362 * Facilitates the creation of optimized String concatenation methods, that
363 * can be used to efficiently concatenate a known number of arguments of
364 * known types, possibly after type adaptation and partial evaluation of
365 * arguments. Typically used as a <em>bootstrap method</em> for {@code
366 * invokedynamic} call sites, to support the <em>string concatenation</em>
367 * feature of the Java Programming Language.
368 *
369 * <p>When the target of the {@code CallSite} returned from this method is
370 * invoked, it returns the result of String concatenation, taking all
371 * function arguments passed to the linkage method as inputs for
372 * concatenation. The target signature is given by {@code concatType}.
373 * The arguments are concatenated as per requirements stated in JLS 15.18.1
374 * "String Concatenation Operator +". Notably, the inputs are converted as
375 * per JLS 5.1.11 "String Conversion", and combined from left to right.
376 *
377 * <p>Assume the linkage arguments are as follows:
378 *
379 * <ul>
380 * <li>{@code concatType}, describing the {@code CallSite} signature</li>
381 * </ul>
382 *
383 * <p>Then the following linkage invariants must hold:
384 *
385 * <ul>
386 * <li>The parameter count in {@code concatType} is less than or equal to 200</li>
387 *
388 * <li>The return type in {@code concatType} is assignable from {@link java.lang.String}</li>
389 * </ul>
390 *
391 * @param lookup Represents a lookup context with the accessibility
392 * privileges of the caller. When used with {@code
393 * invokedynamic}, this is stacked automatically by the VM.
394 * @param name The name of the method to implement. This name is
395 * arbitrary, and has no meaning for this linkage method.
396 * When used with {@code invokedynamic}, this is provided by
397 * the {@code NameAndType} of the {@code InvokeDynamic}
398 * structure and is stacked automatically by the VM.
399 * @param concatType The expected signature of the {@code CallSite}. The
400 * parameter types represent the types of concatenation
401 * arguments; the return type is always assignable from {@link
402 * java.lang.String}. When used with {@code invokedynamic},
403 * this is provided by the {@code NameAndType} of the {@code
404 * InvokeDynamic} structure and is stacked automatically by
405 * the VM.
406 * @return a CallSite whose target can be used to perform String
407 * concatenation, with dynamic concatenation arguments described by the given
408 * {@code concatType}.
409 * @throws StringConcatException If any of the linkage invariants described
410 * here are violated.
411 * @throws NullPointerException If any of the incoming arguments is null.
412 * This will never happen when a bootstrap method
413 * is called with invokedynamic.
414 *
415 * @jls 5.1.11 String Conversion
416 * @jls 15.18.1 String Concatenation Operator +
417 *
418 * @since 9
419 */
420 public static CallSite makeConcat(MethodHandles.Lookup lookup,
421 String name,
422 MethodType concatType) throws StringConcatException {
423 if (DEBUG) {
424 System.out.println("StringConcatFactory " + STRATEGY + " is here for " + concatType);
425 }
426
427 return doStringConcat(lookup, name, concatType, true, null);
428 }
429
430 /**
431 * Facilitates the creation of optimized String concatenation methods, that
432 * can be used to efficiently concatenate a known number of arguments of
433 * known types, possibly after type adaptation and partial evaluation of
434 * arguments. Typically used as a <em>bootstrap method</em> for {@code
435 * invokedynamic} call sites, to support the <em>string concatenation</em>
436 * feature of the Java Programming Language.
437 *
438 * <p>When the target of the {@code CallSite} returned from this method is
439 * invoked, it returns the result of String concatenation, taking all
440 * function arguments and constants passed to the linkage method as inputs for
441 * concatenation. The target signature is given by {@code concatType}, and
442 * does not include constants. The arguments are concatenated as per requirements
443 * stated in JLS 15.18.1 "String Concatenation Operator +". Notably, the inputs
444 * are converted as per JLS 5.1.11 "String Conversion", and combined from left
445 * to right.
446 *
447 * <p>The concatenation <em>recipe</em> is a String description for the way to
448 * construct a concatenated String from the arguments and constants. The
449 * recipe is processed from left to right, and each character represents an
450 * input to concatenation. Recipe characters mean:
451 *
452 * <ul>
453 *
454 * <li><em>\1 (Unicode point 0001)</em>: an ordinary argument. This
455 * input is passed through dynamic argument, and is provided during the
456 * concatenation method invocation. This input can be null.</li>
457 *
458 * <li><em>\2 (Unicode point 0002):</em> a constant. This input passed
459 * through static bootstrap argument. This constant can be any value
460 * representable in constant pool. If necessary, the factory would call
461 * {@code toString} to perform a one-time String conversion.</li>
462 *
463 * <li><em>Any other char value:</em> a single character constant.</li>
464 * </ul>
465 *
466 * <p>Assume the linkage arguments are as follows:
467 *
468 * <ul>
469 * <li>{@code concatType}, describing the {@code CallSite} signature</li>
470 * <li>{@code recipe}, describing the String recipe</li>
471 * <li>{@code constants}, the vararg array of constants</li>
472 * </ul>
473 *
474 * <p>Then the following linkage invariants must hold:
475 *
476 * <ul>
477 * <li>The parameter count in {@code concatType} is less than or equal to
478 * 200</li>
479 *
480 * <li>The parameter count in {@code concatType} equals to number of \1 tags
481 * in {@code recipe}</li>
482 *
483 * <li>The return type in {@code concatType} is assignable
484 * from {@link java.lang.String}, and matches the return type of the
485 * returned {@link MethodHandle}</li>
486 *
487 * <li>The number of elements in {@code constants} equals to number of \2
488 * tags in {@code recipe}</li>
489 * </ul>
490 *
491 * @param lookup Represents a lookup context with the accessibility
492 * privileges of the caller. When used with {@code
493 * invokedynamic}, this is stacked automatically by the
494 * VM.
495 * @param name The name of the method to implement. This name is
496 * arbitrary, and has no meaning for this linkage method.
497 * When used with {@code invokedynamic}, this is provided
498 * by the {@code NameAndType} of the {@code InvokeDynamic}
499 * structure and is stacked automatically by the VM.
500 * @param concatType The expected signature of the {@code CallSite}. The
501 * parameter types represent the types of dynamic concatenation
502 * arguments; the return type is always assignable from {@link
503 * java.lang.String}. When used with {@code
504 * invokedynamic}, this is provided by the {@code
505 * NameAndType} of the {@code InvokeDynamic} structure and
506 * is stacked automatically by the VM.
507 * @param recipe Concatenation recipe, described above.
508 * @param constants A vararg parameter representing the constants passed to
509 * the linkage method.
510 * @return a CallSite whose target can be used to perform String
511 * concatenation, with dynamic concatenation arguments described by the given
512 * {@code concatType}.
513 * @throws StringConcatException If any of the linkage invariants described
514 * here are violated.
515 * @throws NullPointerException If any of the incoming arguments is null, or
516 * any constant in {@code recipe} is null.
517 * This will never happen when a bootstrap method
518 * is called with invokedynamic.
519 * @apiNote Code generators have three distinct ways to process a constant
520 * string operand S in a string concatenation expression. First, S can be
521 * materialized as a reference (using ldc) and passed as an ordinary argument
522 * (recipe '\1'). Or, S can be stored in the constant pool and passed as a
523 * constant (recipe '\2') . Finally, if S contains neither of the recipe
524 * tag characters ('\1', '\2') then S can be interpolated into the recipe
525 * itself, causing its characters to be inserted into the result.
526 *
527 * @jls 5.1.11 String Conversion
528 * @jls 15.18.1 String Concatenation Operator +
529 *
530 * @since 9
531 */
532 public static CallSite makeConcatWithConstants(MethodHandles.Lookup lookup,
533 String name,
534 MethodType concatType,
535 String recipe,
536 Object... constants) throws StringConcatException {
537 if (DEBUG) {
538 System.out.println("StringConcatFactory " + STRATEGY + " is here for " + concatType + ", {" + recipe + "}, " + Arrays.toString(constants));
539 }
540
541 return doStringConcat(lookup, name, concatType, false, recipe, constants);
542 }
543
544 private static CallSite doStringConcat(MethodHandles.Lookup lookup,
545 String name,
546 MethodType concatType,
547 boolean generateRecipe,
548 String recipe,
549 Object... constants) throws StringConcatException {
550 Objects.requireNonNull(lookup, "Lookup is null");
551 Objects.requireNonNull(name, "Name is null");
552 Objects.requireNonNull(concatType, "Concat type is null");
553 Objects.requireNonNull(constants, "Constants are null");
554
555 for (Object o : constants) {
556 Objects.requireNonNull(o, "Cannot accept null constants");
557 }
558
559 int cCount = 0;
560 int oCount = 0;
561 if (generateRecipe) {
562 // Mock the recipe to reuse the concat generator code
563 char[] value = new char[concatType.parameterCount()];
564 Arrays.fill(value, TAG_ARG);
565 recipe = new String(value);
566 oCount = concatType.parameterCount();
567 } else {
568 Objects.requireNonNull(recipe, "Recipe is null");
569
570 for (int i = 0; i < recipe.length(); i++) {
571 char c = recipe.charAt(i);
572 if (c == TAG_CONST) cCount++;
573 if (c == TAG_ARG) oCount++;
574 }
575 }
576
577 if (oCount != concatType.parameterCount()) {
578 throw new StringConcatException(
579 "Mismatched number of concat arguments: recipe wants " +
580 oCount +
581 " arguments, but signature provides " +
582 concatType.parameterCount());
583 }
584
585 if (cCount != constants.length) {
586 throw new StringConcatException(
587 "Mismatched number of concat constants: recipe wants " +
588 cCount +
589 " constants, but only " +
590 constants.length +
591 " are passed");
592 }
593
594 if (!concatType.returnType().isAssignableFrom(String.class)) {
595 throw new StringConcatException(
596 "The return type should be compatible with String, but it is " +
597 concatType.returnType());
598 }
599
600 if (concatType.parameterCount() > MAX_INDY_CONCAT_ARG_SLOTS) {
601 throw new StringConcatException("Too many concat argument slots: " +
602 concatType.parameterCount() +
603 ", can only accept " +
604 MAX_INDY_CONCAT_ARG_SLOTS);
605 }
606
607 MethodType mt = adaptType(concatType);
608
609 Recipe rec = new Recipe(recipe, constants);
610
611 MethodHandle mh;
612 if (CACHE_ENABLE) {
613 Key key = new Key(mt, rec);
614 mh = CACHE.get(key);
615 if (mh == null) {
616 mh = generate(lookup, mt, rec);
617 CACHE.put(key, mh);
618 }
619 } else {
620 mh = generate(lookup, mt, rec);
621 }
622 return new ConstantCallSite(mh.asType(concatType));
623 }
624
625 /**
626 * Adapt method type to an API we are going to use.
627 *
628 * This strips the concrete classes from the signatures, thus preventing
629 * class leakage when we cache the concatenation stubs.
630 *
631 * @param args actual argument types
632 * @return argument types the strategy is going to use
633 */
634 private static MethodType adaptType(MethodType args) {
635 Class<?>[] ptypes = args.parameterArray();
636 boolean changed = false;
637 for (int i = 0; i < ptypes.length; i++) {
638 Class<?> ptype = ptypes[i];
639 if (!ptype.isPrimitive() &&
640 ptype != String.class &&
641 ptype != Object.class) { // truncate to Object
642 ptypes[i] = Object.class;
643 changed = true;
644 }
645 // else other primitives or String or Object (unchanged)
646 }
647 return changed
648 ? MethodType.methodType(args.returnType(), ptypes)
649 : args;
650 }
651
652 private static MethodHandle generate(Lookup lookup, MethodType mt, Recipe recipe) throws StringConcatException {
653 try {
654 switch (STRATEGY) {
655 case BC_SB:
656 return BytecodeStringBuilderStrategy.generate(lookup, mt, recipe, Mode.DEFAULT);
657 case BC_SB_SIZED:
658 return BytecodeStringBuilderStrategy.generate(lookup, mt, recipe, Mode.SIZED);
659 case BC_SB_SIZED_EXACT:
660 return BytecodeStringBuilderStrategy.generate(lookup, mt, recipe, Mode.SIZED_EXACT);
661 case MH_SB_SIZED:
662 return MethodHandleStringBuilderStrategy.generate(mt, recipe, Mode.SIZED);
663 case MH_SB_SIZED_EXACT:
664 return MethodHandleStringBuilderStrategy.generate(mt, recipe, Mode.SIZED_EXACT);
665 case MH_INLINE_SIZED_EXACT:
666 return MethodHandleInlineCopyStrategy.generate(mt, recipe);
667 default:
668 throw new StringConcatException("Concatenation strategy " + STRATEGY + " is not implemented");
669 }
670 } catch (Throwable t) {
671 throw new StringConcatException("Generator failed", t);
672 }
673 }
674
675 private enum Mode {
676 DEFAULT(false, false),
677 SIZED(true, false),
678 SIZED_EXACT(true, true);
679
680 private final boolean sized;
681 private final boolean exact;
682
683 Mode(boolean sized, boolean exact) {
684 this.sized = sized;
685 this.exact = exact;
686 }
687
688 boolean isSized() {
689 return sized;
690 }
691
692 boolean isExact() {
693 return exact;
694 }
695 }
696
697 /**
698 * Bytecode StringBuilder strategy.
699 *
700 * <p>This strategy operates in three modes, gated by {@link Mode}.
701 *
702 * <p><b>{@link Strategy#BC_SB}: "bytecode StringBuilder".</b>
703 *
704 * <p>This strategy spins up the bytecode that has the same StringBuilder
705 * chain javac would otherwise emit. This strategy uses only the public API,
706 * and comes as the baseline for the current JDK behavior. On other words,
707 * this strategy moves the javac generated bytecode to runtime. The
708 * generated bytecode is loaded via Unsafe.defineAnonymousClass, but with
709 * the caller class coming from the BSM -- in other words, the protection
710 * guarantees are inherited from the method where invokedynamic was
711 * originally called. This means, among other things, that the bytecode is
712 * verified for all non-JDK uses.
713 *
714 * <p><b>{@link Strategy#BC_SB_SIZED}: "bytecode StringBuilder, but
715 * sized".</b>
716 *
717 * <p>This strategy acts similarly to {@link Strategy#BC_SB}, but it also
718 * tries to guess the capacity required for StringBuilder to accept all
719 * arguments without resizing. This strategy only makes an educated guess:
720 * it only guesses the space required for known types (e.g. primitives and
721 * Strings), but does not otherwise convert arguments. Therefore, the
722 * capacity estimate may be wrong, and StringBuilder may have to
723 * transparently resize or trim when doing the actual concatenation. While
724 * this does not constitute a correctness issue (in the end, that what BC_SB
725 * has to do anyway), this does pose a potential performance problem.
726 *
727 * <p><b>{@link Strategy#BC_SB_SIZED_EXACT}: "bytecode StringBuilder, but
728 * sized exactly".</b>
729 *
730 * <p>This strategy improves on @link Strategy#BC_SB_SIZED}, by first
731 * converting all arguments to String in order to get the exact capacity
732 * StringBuilder should have. The conversion is done via the public
733 * String.valueOf and/or Object.toString methods, and does not touch any
734 * private String API.
735 */
736 private static final class BytecodeStringBuilderStrategy {
737 static final Unsafe UNSAFE = Unsafe.getUnsafe();
738 static final int CLASSFILE_VERSION = 52;
739 static final String NAME_FACTORY = "concat";
740 static final String CLASS_NAME = "java/lang/String$Concat";
741
742 private BytecodeStringBuilderStrategy() {
743 // no instantiation
744 }
745
746 private static MethodHandle generate(MethodHandles.Lookup lookup, MethodType args, Recipe recipe, Mode mode) throws Exception {
747 ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS + ClassWriter.COMPUTE_FRAMES);
748
749 cw.visit(CLASSFILE_VERSION,
750 ACC_SUPER + ACC_PUBLIC + ACC_FINAL + ACC_SYNTHETIC,
751 CLASS_NAME,
752 null,
753 "java/lang/Object",
754 null
755 );
756
757 MethodVisitor mv = cw.visitMethod(
758 ACC_PUBLIC + ACC_STATIC + ACC_FINAL,
759 NAME_FACTORY,
760 args.toMethodDescriptorString(),
761 null,
762 null);
763
764 mv.visitAnnotation("Ljdk/internal/vm/annotation/ForceInline;", true);
765 mv.visitCode();
766
767 Class<?>[] arr = args.parameterArray();
768 boolean[] guaranteedNonNull = new boolean[arr.length];
769
770 if (mode.isExact()) {
771 /*
772 In exact mode, we need to convert all arguments to their String representations,
773 as this allows to compute their String sizes exactly. We cannot use private
774 methods for primitives in here, therefore we need to convert those as well.
775
776 We also record what arguments are guaranteed to be non-null as the result
777 of the conversion. String.valueOf does the null checks for us. The only
778 corner case to take care of is String.valueOf(Object) returning null itself.
779
780 Also, if any conversion happened, then the slot indices in the incoming
781 arguments are not equal to the final local maps. The only case this may break
782 is when converting 2-slot long/double argument to 1-slot String. Therefore,
783 we get away with tracking modified offset, since no conversion can overwrite
784 the upcoming the argument.
785 */
786
787 int off = 0;
788 int modOff = 0;
789 for (int c = 0; c < arr.length; c++) {
790 Class<?> cl = arr[c];
791 if (cl == String.class) {
792 if (off != modOff) {
793 mv.visitIntInsn(getLoadOpcode(cl), off);
794 mv.visitIntInsn(ASTORE, modOff);
795 }
796 } else {
797 mv.visitIntInsn(getLoadOpcode(cl), off);
798 mv.visitMethodInsn(
799 INVOKESTATIC,
800 "java/lang/String",
801 "valueOf",
802 getStringValueOfDesc(cl),
803 false
804 );
805 mv.visitIntInsn(ASTORE, modOff);
806 arr[c] = String.class;
807 guaranteedNonNull[c] = cl.isPrimitive();
808 }
809 off += getParameterSize(cl);
810 modOff += getParameterSize(String.class);
811 }
812 }
813
814 if (mode.isSized()) {
815 /*
816 When operating in sized mode (this includes exact mode), it makes sense to make
817 StringBuilder append chains look familiar to OptimizeStringConcat. For that, we
818 need to do null-checks early, not make the append chain shape simpler.
819 */
820
821 int off = 0;
822 for (RecipeElement el : recipe.getElements()) {
823 switch (el.getTag()) {
824 case CONST: {
825 // Guaranteed non-null, no null check required.
826 break;
827 }
828 case ARG: {
829 // Null-checks are needed only for String arguments, and when a previous stage
830 // did not do implicit null-checks. If a String is null, we eagerly replace it
831 // with "null" constant. Note, we omit Objects here, because we don't call
832 // .length() on them down below.
833 int ac = el.getArgPos();
834 Class<?> cl = arr[ac];
835 if (cl == String.class && !guaranteedNonNull[ac]) {
836 Label l0 = new Label();
837 mv.visitIntInsn(ALOAD, off);
838 mv.visitJumpInsn(IFNONNULL, l0);
839 mv.visitLdcInsn("null");
840 mv.visitIntInsn(ASTORE, off);
841 mv.visitLabel(l0);
842 }
843 off += getParameterSize(cl);
844 break;
845 }
846 default:
847 throw new StringConcatException("Unhandled tag: " + el.getTag());
848 }
849 }
850 }
851
852 // Prepare StringBuilder instance
853 mv.visitTypeInsn(NEW, "java/lang/StringBuilder");
854 mv.visitInsn(DUP);
855
856 if (mode.isSized()) {
857 /*
858 Sized mode requires us to walk through the arguments, and estimate the final length.
859 In exact mode, this will operate on Strings only. This code would accumulate the
860 final length on stack.
861 */
862 int len = 0;
863 int off = 0;
864
865 mv.visitInsn(ICONST_0);
866
867 for (RecipeElement el : recipe.getElements()) {
868 switch (el.getTag()) {
869 case CONST: {
870 Object cnst = el.getValue();
871 len += cnst.toString().length();
872 break;
873 }
874 case ARG: {
875 /*
876 If an argument is String, then we can call .length() on it. Sized/Exact modes have
877 converted arguments for us. If an argument is primitive, we can provide a guess
878 for its String representation size.
879 */
880 Class<?> cl = arr[el.getArgPos()];
881 if (cl == String.class) {
882 mv.visitIntInsn(ALOAD, off);
883 mv.visitMethodInsn(
884 INVOKEVIRTUAL,
885 "java/lang/String",
886 "length",
887 "()I",
888 false
889 );
890 mv.visitInsn(IADD);
891 } else if (cl.isPrimitive()) {
892 len += estimateSize(cl);
893 }
894 off += getParameterSize(cl);
895 break;
896 }
897 default:
898 throw new StringConcatException("Unhandled tag: " + el.getTag());
899 }
900 }
901
902 // Constants have non-zero length, mix in
903 if (len > 0) {
904 iconst(mv, len);
905 mv.visitInsn(IADD);
906 }
907
908 mv.visitMethodInsn(
909 INVOKESPECIAL,
910 "java/lang/StringBuilder",
911 "<init>",
912 "(I)V",
913 false
914 );
915 } else {
916 mv.visitMethodInsn(
917 INVOKESPECIAL,
918 "java/lang/StringBuilder",
919 "<init>",
920 "()V",
921 false
922 );
923 }
924
925 // At this point, we have a blank StringBuilder on stack, fill it in with .append calls.
926 {
927 int off = 0;
928 for (RecipeElement el : recipe.getElements()) {
929 String desc;
930 switch (el.getTag()) {
931 case CONST: {
932 Object cnst = el.getValue();
933 mv.visitLdcInsn(cnst);
934 desc = getSBAppendDesc(cnst.getClass());
935 break;
936 }
937 case ARG: {
938 Class<?> cl = arr[el.getArgPos()];
939 mv.visitVarInsn(getLoadOpcode(cl), off);
940 off += getParameterSize(cl);
941 desc = getSBAppendDesc(cl);
942 break;
943 }
944 default:
945 throw new StringConcatException("Unhandled tag: " + el.getTag());
946 }
947 mv.visitMethodInsn(
948 INVOKEVIRTUAL,
949 "java/lang/StringBuilder",
950 "append",
951 desc,
952 false
953 );
954 }
955 }
956
957 if (DEBUG && mode.isExact()) {
958 /*
959 Exactness checks compare the final StringBuilder.capacity() with a resulting
960 String.length(). If these values disagree, that means StringBuilder had to perform
961 storage trimming, which defeats the purpose of exact strategies.
962 */
963
964 mv.visitInsn(DUP);
965
966 mv.visitMethodInsn(
967 INVOKEVIRTUAL,
968 "java/lang/StringBuilder",
969 "capacity",
970 "()I",
971 false
972 );
973
974 mv.visitIntInsn(ISTORE, 0);
975
976 mv.visitMethodInsn(
977 INVOKEVIRTUAL,
978 "java/lang/StringBuilder",
979 "toString",
980 "()Ljava/lang/String;",
981 false
982 );
983
984 mv.visitInsn(DUP);
985
986 mv.visitMethodInsn(
987 INVOKEVIRTUAL,
988 "java/lang/String",
989 "length",
990 "()I",
991 false
992 );
993
994 mv.visitIntInsn(ILOAD, 0);
995
996 Label l0 = new Label();
997 mv.visitJumpInsn(IF_ICMPEQ, l0);
998
999 mv.visitTypeInsn(NEW, "java/lang/AssertionError");
1000 mv.visitInsn(DUP);
1001 mv.visitLdcInsn("Failed exactness check");
1002 mv.visitMethodInsn(INVOKESPECIAL,
1003 "java/lang/AssertionError",
1004 "<init>",
1005 "(Ljava/lang/Object;)V",
1006 false);
1007 mv.visitInsn(ATHROW);
1008
1009 mv.visitLabel(l0);
1010 } else {
1011 mv.visitMethodInsn(
1012 INVOKEVIRTUAL,
1013 "java/lang/StringBuilder",
1014 "toString",
1015 "()Ljava/lang/String;",
1016 false
1017 );
1018 }
1019
1020 mv.visitInsn(ARETURN);
1021
1022 mv.visitMaxs(-1, -1);
1023 mv.visitEnd();
1024 cw.visitEnd();
1025
1026 Class<?> targetClass = lookup.lookupClass();
1027 final byte[] classBytes = cw.toByteArray();
1028 final Class<?> innerClass = UNSAFE.defineAnonymousClass(targetClass, classBytes, null);
1029
1030 try {
1031 UNSAFE.ensureClassInitialized(innerClass);
1032 return lookup.findStatic(innerClass, NAME_FACTORY, args);
1033 } catch (ReflectiveOperationException e) {
1034 throw new StringConcatException("Exception finding constructor", e);
1035 }
1036 }
1037
1038 private static String getSBAppendDesc(Class<?> cl) {
1039 if (cl.isPrimitive()) {
1040 if (cl == Integer.TYPE || cl == Byte.TYPE || cl == Short.TYPE) {
1041 return "(I)Ljava/lang/StringBuilder;";
1042 } else if (cl == Boolean.TYPE) {
1043 return "(Z)Ljava/lang/StringBuilder;";
1044 } else if (cl == Character.TYPE) {
1045 return "(C)Ljava/lang/StringBuilder;";
1046 } else if (cl == Double.TYPE) {
1047 return "(D)Ljava/lang/StringBuilder;";
1048 } else if (cl == Float.TYPE) {
1049 return "(F)Ljava/lang/StringBuilder;";
1050 } else if (cl == Long.TYPE) {
1051 return "(J)Ljava/lang/StringBuilder;";
1052 } else {
1053 throw new IllegalStateException("Unhandled primitive StringBuilder.append: " + cl);
1054 }
1055 } else if (cl == String.class) {
1056 return "(Ljava/lang/String;)Ljava/lang/StringBuilder;";
1057 } else {
1058 return "(Ljava/lang/Object;)Ljava/lang/StringBuilder;";
1059 }
1060 }
1061
1062 private static String getStringValueOfDesc(Class<?> cl) {
1063 if (cl.isPrimitive()) {
1064 if (cl == Integer.TYPE || cl == Byte.TYPE || cl == Short.TYPE) {
1065 return "(I)Ljava/lang/String;";
1066 } else if (cl == Boolean.TYPE) {
1067 return "(Z)Ljava/lang/String;";
1068 } else if (cl == Character.TYPE) {
1069 return "(C)Ljava/lang/String;";
1070 } else if (cl == Double.TYPE) {
1071 return "(D)Ljava/lang/String;";
1072 } else if (cl == Float.TYPE) {
1073 return "(F)Ljava/lang/String;";
1074 } else if (cl == Long.TYPE) {
1075 return "(J)Ljava/lang/String;";
1076 } else {
1077 throw new IllegalStateException("Unhandled String.valueOf: " + cl);
1078 }
1079 } else if (cl == String.class) {
1080 return "(Ljava/lang/String;)Ljava/lang/String;";
1081 } else {
1082 return "(Ljava/lang/Object;)Ljava/lang/String;";
1083 }
1084 }
1085
1086 /**
1087 * The following method is copied from
1088 * org.objectweb.asm.commons.InstructionAdapter. Part of ASM: a very small
1089 * and fast Java bytecode manipulation framework.
1090 * Copyright (c) 2000-2005 INRIA, France Telecom All rights reserved.
1091 */
1092 private static void iconst(MethodVisitor mv, final int cst) {
1093 if (cst >= -1 && cst <= 5) {
1094 mv.visitInsn(Opcodes.ICONST_0 + cst);
1095 } else if (cst >= Byte.MIN_VALUE && cst <= Byte.MAX_VALUE) {
1096 mv.visitIntInsn(Opcodes.BIPUSH, cst);
1097 } else if (cst >= Short.MIN_VALUE && cst <= Short.MAX_VALUE) {
1098 mv.visitIntInsn(Opcodes.SIPUSH, cst);
1099 } else {
1100 mv.visitLdcInsn(cst);
1101 }
1102 }
1103
1104 private static int getLoadOpcode(Class<?> c) {
1105 if (c == Void.TYPE) {
1106 throw new InternalError("Unexpected void type of load opcode");
1107 }
1108 return ILOAD + getOpcodeOffset(c);
1109 }
1110
1111 private static int getOpcodeOffset(Class<?> c) {
1112 if (c.isPrimitive()) {
1113 if (c == Long.TYPE) {
1114 return 1;
1115 } else if (c == Float.TYPE) {
1116 return 2;
1117 } else if (c == Double.TYPE) {
1118 return 3;
1119 }
1120 return 0;
1121 } else {
1122 return 4;
1123 }
1124 }
1125
1126 private static int getParameterSize(Class<?> c) {
1127 if (c == Void.TYPE) {
1128 return 0;
1129 } else if (c == Long.TYPE || c == Double.TYPE) {
1130 return 2;
1131 }
1132 return 1;
1133 }
1134 }
1135
1136 /**
1137 * MethodHandle StringBuilder strategy.
1138 *
1139 * <p>This strategy operates in two modes, gated by {@link Mode}.
1140 *
1141 * <p><b>{@link Strategy#MH_SB_SIZED}: "MethodHandles StringBuilder,
1142 * sized".</b>
1143 *
1144 * <p>This strategy avoids spinning up the bytecode by building the
1145 * computation on MethodHandle combinators. The computation is built with
1146 * public MethodHandle APIs, resolved from a public Lookup sequence, and
1147 * ends up calling the public StringBuilder API. Therefore, this strategy
1148 * does not use any private API at all, even the Unsafe.defineAnonymousClass,
1149 * since everything is handled under cover by java.lang.invoke APIs.
1150 *
1151 * <p><b>{@link Strategy#MH_SB_SIZED_EXACT}: "MethodHandles StringBuilder,
1152 * sized exactly".</b>
1153 *
1154 * <p>This strategy improves on @link Strategy#MH_SB_SIZED}, by first
1155 * converting all arguments to String in order to get the exact capacity
1156 * StringBuilder should have. The conversion is done via the public
1157 * String.valueOf and/or Object.toString methods, and does not touch any
1158 * private String API.
1159 */
1160 private static final class MethodHandleStringBuilderStrategy {
1161
1162 private MethodHandleStringBuilderStrategy() {
1163 // no instantiation
1164 }
1165
1166 private static MethodHandle generate(MethodType mt, Recipe recipe, Mode mode) throws Exception {
1167 int pc = mt.parameterCount();
1168
1169 Class<?>[] ptypes = mt.parameterArray();
1170 MethodHandle[] filters = new MethodHandle[ptypes.length];
1171 for (int i = 0; i < ptypes.length; i++) {
1172 MethodHandle filter;
1173 switch (mode) {
1174 case SIZED:
1175 // In sized mode, we convert all references and floats/doubles
1176 // to String: there is no specialization for different
1177 // classes in StringBuilder API, and it will convert to
1178 // String internally anyhow.
1179 filter = Stringifiers.forMost(ptypes[i]);
1180 break;
1181 case SIZED_EXACT:
1182 // In exact mode, we convert everything to String:
1183 // this helps to compute the storage exactly.
1184 filter = Stringifiers.forAny(ptypes[i]);
1185 break;
1186 default:
1187 throw new StringConcatException("Not supported");
1188 }
1189 if (filter != null) {
1190 filters[i] = filter;
1191 ptypes[i] = filter.type().returnType();
1192 }
1193 }
1194
1195 List<Class<?>> ptypesList = Arrays.asList(ptypes);
1196 MethodHandle[] lengthers = new MethodHandle[pc];
1197
1198 // Figure out lengths: constants' lengths can be deduced on the spot.
1199 // All reference arguments were filtered to String in the combinators below, so we can
1200 // call the usual String.length(). Primitive values string sizes can be estimated.
1201 int initial = 0;
1202 for (RecipeElement el : recipe.getElements()) {
1203 switch (el.getTag()) {
1204 case CONST: {
1205 Object cnst = el.getValue();
1206 initial += cnst.toString().length();
1207 break;
1208 }
1209 case ARG: {
1210 final int i = el.getArgPos();
1211 Class<?> type = ptypesList.get(i);
1212 if (type.isPrimitive()) {
1213 MethodHandle est = MethodHandles.constant(int.class, estimateSize(type));
1214 est = MethodHandles.dropArguments(est, 0, type);
1215 lengthers[i] = est;
1216 } else {
1217 lengthers[i] = STRING_LENGTH;
1218 }
1219 break;
1220 }
1221 default:
1222 throw new StringConcatException("Unhandled tag: " + el.getTag());
1223 }
1224 }
1225
1226 // Create (StringBuilder, <args>) shape for appending:
1227 MethodHandle builder = MethodHandles.dropArguments(MethodHandles.identity(StringBuilder.class), 1, ptypesList);
1228
1229 // Compose append calls. This is done in reverse because the application order is
1230 // reverse as well.
1231 for (RecipeElement el : recipe.getElementsReversed()) {
1232 MethodHandle appender;
1233 switch (el.getTag()) {
1234 case CONST: {
1235 Object constant = el.getValue();
1236 MethodHandle mh = appender(adaptToStringBuilder(constant.getClass()));
1237 appender = MethodHandles.insertArguments(mh, 1, constant);
1238 break;
1239 }
1240 case ARG: {
1241 int ac = el.getArgPos();
1242 appender = appender(ptypesList.get(ac));
1243
1244 // Insert dummy arguments to match the prefix in the signature.
1245 // The actual appender argument will be the ac-ith argument.
1246 if (ac != 0) {
1247 appender = MethodHandles.dropArguments(appender, 1, ptypesList.subList(0, ac));
1248 }
1249 break;
1250 }
1251 default:
1252 throw new StringConcatException("Unhandled tag: " + el.getTag());
1253 }
1254 builder = MethodHandles.foldArguments(builder, appender);
1255 }
1256
1257 // Build the sub-tree that adds the sizes and produces a StringBuilder:
1258
1259 // a) Start with the reducer that accepts all arguments, plus one
1260 // slot for the initial value. Inject the initial value right away.
1261 // This produces (<ints>)int shape:
1262 MethodHandle sum = getReducerFor(pc + 1);
1263 MethodHandle adder = MethodHandles.insertArguments(sum, 0, initial);
1264
1265 // b) Apply lengthers to transform arguments to lengths, producing (<args>)int
1266 adder = MethodHandles.filterArguments(adder, 0, lengthers);
1267
1268 // c) Instantiate StringBuilder (<args>)int -> (<args>)StringBuilder
1269 MethodHandle newBuilder = MethodHandles.filterReturnValue(adder, NEW_STRING_BUILDER);
1270
1271 // d) Fold in StringBuilder constructor, this produces (<args>)StringBuilder
1272 MethodHandle mh = MethodHandles.foldArguments(builder, newBuilder);
1273
1274 // Convert non-primitive arguments to Strings
1275 mh = MethodHandles.filterArguments(mh, 0, filters);
1276
1277 // Convert (<args>)StringBuilder to (<args>)String
1278 if (DEBUG && mode.isExact()) {
1279 mh = MethodHandles.filterReturnValue(mh, BUILDER_TO_STRING_CHECKED);
1280 } else {
1281 mh = MethodHandles.filterReturnValue(mh, BUILDER_TO_STRING);
1282 }
1283
1284 return mh;
1285 }
1286
1287 private static MethodHandle getReducerFor(int cnt) {
1288 return SUMMERS.computeIfAbsent(cnt, SUMMER);
1289 }
1290
1291 private static MethodHandle appender(Class<?> appendType) {
1292 MethodHandle appender = lookupVirtual(MethodHandles.publicLookup(), StringBuilder.class, "append",
1293 StringBuilder.class, adaptToStringBuilder(appendType));
1294
1295 // appenders should return void, this would not modify the target signature during folding
1296 MethodType nt = MethodType.methodType(void.class, StringBuilder.class, appendType);
1297 return appender.asType(nt);
1298 }
1299
1300 private static String toStringChecked(StringBuilder sb) {
1301 String s = sb.toString();
1302 if (s.length() != sb.capacity()) {
1303 throw new AssertionError("Exactness check failed: result length = " + s.length() + ", buffer capacity = " + sb.capacity());
1304 }
1305 return s;
1306 }
1307
1308 private static int sum(int v1, int v2) {
1309 return v1 + v2;
1310 }
1311
1312 private static int sum(int v1, int v2, int v3) {
1313 return v1 + v2 + v3;
1314 }
1315
1316 private static int sum(int v1, int v2, int v3, int v4) {
1317 return v1 + v2 + v3 + v4;
1318 }
1319
1320 private static int sum(int v1, int v2, int v3, int v4, int v5) {
1321 return v1 + v2 + v3 + v4 + v5;
1322 }
1323
1324 private static int sum(int v1, int v2, int v3, int v4, int v5, int v6) {
1325 return v1 + v2 + v3 + v4 + v5 + v6;
1326 }
1327
1328 private static int sum(int v1, int v2, int v3, int v4, int v5, int v6, int v7) {
1329 return v1 + v2 + v3 + v4 + v5 + v6 + v7;
1330 }
1331
1332 private static int sum(int v1, int v2, int v3, int v4, int v5, int v6, int v7, int v8) {
1333 return v1 + v2 + v3 + v4 + v5 + v6 + v7 + v8;
1334 }
1335
1336 private static int sum(int initial, int[] vs) {
1337 int sum = initial;
1338 for (int v : vs) {
1339 sum += v;
1340 }
1341 return sum;
1342 }
1343
1344 private static final ConcurrentMap<Integer, MethodHandle> SUMMERS;
1345
1346 // This one is deliberately non-lambdified to optimize startup time:
1347 private static final Function<Integer, MethodHandle> SUMMER = new Function<Integer, MethodHandle>() {
1348 @Override
1349 public MethodHandle apply(Integer cnt) {
1350 if (cnt == 1) {
1351 return MethodHandles.identity(int.class);
1352 } else if (cnt <= 8) {
1353 // Variable-arity collectors are not as efficient as small-count methods,
1354 // unroll some initial sizes.
1355 Class<?>[] cls = new Class<?>[cnt];
1356 Arrays.fill(cls, int.class);
1357 return lookupStatic(Lookup.IMPL_LOOKUP, MethodHandleStringBuilderStrategy.class, "sum", int.class, cls);
1358 } else {
1359 return lookupStatic(Lookup.IMPL_LOOKUP, MethodHandleStringBuilderStrategy.class, "sum", int.class, int.class, int[].class)
1360 .asCollector(int[].class, cnt - 1);
1361 }
1362 }
1363 };
1364
1365 private static final MethodHandle NEW_STRING_BUILDER, STRING_LENGTH, BUILDER_TO_STRING, BUILDER_TO_STRING_CHECKED;
1366
1367 static {
1368 SUMMERS = new ConcurrentHashMap<>();
1369 Lookup publicLookup = MethodHandles.publicLookup();
1370 NEW_STRING_BUILDER = lookupConstructor(publicLookup, StringBuilder.class, int.class);
1371 STRING_LENGTH = lookupVirtual(publicLookup, String.class, "length", int.class);
1372 BUILDER_TO_STRING = lookupVirtual(publicLookup, StringBuilder.class, "toString", String.class);
1373 if (DEBUG) {
1374 BUILDER_TO_STRING_CHECKED = lookupStatic(MethodHandles.Lookup.IMPL_LOOKUP,
1375 MethodHandleStringBuilderStrategy.class, "toStringChecked", String.class, StringBuilder.class);
1376 } else {
1377 BUILDER_TO_STRING_CHECKED = null;
1378 }
1379 }
1380
1381 }
1382
1383
1384 /**
1385 * <p><b>{@link Strategy#MH_INLINE_SIZED_EXACT}: "MethodHandles inline,
1386 * sized exactly".</b>
1387 *
1388 * <p>This strategy replicates what StringBuilders are doing: it builds the
1389 * byte[] array on its own and passes that byte[] array to String
1390 * constructor. This strategy requires access to some private APIs in JDK,
1391 * most notably, the read-only Integer/Long.stringSize methods that measure
1392 * the character length of the integers, and the private String constructor
1393 * that accepts byte[] arrays without copying. While this strategy assumes a
1394 * particular implementation details for String, this opens the door for
1395 * building a very optimal concatenation sequence. This is the only strategy
1396 * that requires porting if there are private JDK changes occur.
1397 */
1398 private static final class MethodHandleInlineCopyStrategy {
1399
1400 private MethodHandleInlineCopyStrategy() {
1401 // no instantiation
1402 }
1403
1404 static MethodHandle generate(MethodType mt, Recipe recipe) throws Throwable {
1405
1406 // Create filters and obtain filtered parameter types. Filters would be used in the beginning
1407 // to convert the incoming arguments into the arguments we can process (e.g. Objects -> Strings).
1408 // The filtered argument type list is used all over in the combinators below.
1409 Class<?>[] ptypes = mt.parameterArray();
1410 MethodHandle[] filters = null;
1411 for (int i = 0; i < ptypes.length; i++) {
1412 MethodHandle filter = Stringifiers.forMost(ptypes[i]);
1413 if (filter != null) {
1414 if (filters == null) {
1415 filters = new MethodHandle[ptypes.length];
1416 }
1417 filters[i] = filter;
1418 ptypes[i] = filter.type().returnType();
1419 }
1420 }
1421 List<Class<?>> ptypesList = Arrays.asList(ptypes);
1422
1423 // Start building the combinator tree. The tree "starts" with (<parameters>)String, and "finishes"
1424 // with the (int, byte[], byte)String in String helper. The combinators are assembled bottom-up,
1425 // which makes the code arguably hard to read.
1426
1427 // Drop all remaining parameter types, leave only helper arguments:
1428 MethodHandle mh;
1429
1430 mh = MethodHandles.dropArguments(NEW_STRING, 2, ptypes);
1431 mh = MethodHandles.dropArguments(mh, 0, int.class);
1432
1433 // In debug mode, check that remaining index is zero.
1434 if (DEBUG) {
1435 mh = MethodHandles.filterArgument(mh, 0, CHECK_INDEX);
1436 }
1437
1438 // Mix in prependers. This happens when (int, byte[], byte) = (index, storage, coder) is already
1439 // known from the combinators below. We are assembling the string backwards, so "index" is the
1440 // *ending* index.
1441 for (RecipeElement el : recipe.getElements()) {
1442 MethodHandle prepender;
1443 switch (el.getTag()) {
1444 case CONST: {
1445 Object cnst = el.getValue();
1446 prepender = MethodHandles.insertArguments(prepender(cnst.getClass()), 3, cnst);
1447 break;
1448 }
1449 case ARG: {
1450 int pos = el.getArgPos();
1451 prepender = selectArgument(prepender(ptypesList.get(pos)), 3, ptypesList, pos);
1452 break;
1453 }
1454 default:
1455 throw new StringConcatException("Unhandled tag: " + el.getTag());
1456 }
1457
1458 // Remove "old" index from arguments
1459 mh = MethodHandles.dropArguments(mh, 1, int.class);
1460
1461 // Do the prepend, and put "new" index at index 0
1462 mh = MethodHandles.foldArguments(mh, prepender);
1463 }
1464
1465 // Prepare the argument list for prepending. The tree below would instantiate
1466 // the storage byte[] into argument 0, so we need to swap "storage" and "index".
1467 // The index at this point equals to "size", and resides at argument 1.
1468 {
1469 MethodType nmt = mh.type()
1470 .changeParameterType(0, byte[].class)
1471 .changeParameterType(1, int.class);
1472 mh = MethodHandles.permuteArguments(mh, nmt, swap10(nmt.parameterCount()));
1473 }
1474
1475 // Fold in byte[] instantiation at argument 0.
1476 MethodHandle combiner = MethodHandles.dropArguments(NEW_ARRAY, 2, ptypesList);
1477 mh = MethodHandles.foldArguments(mh, combiner);
1478
1479 // Start combining length and coder mixers.
1480 //
1481 // Length is easy: constant lengths can be computed on the spot, and all non-constant
1482 // shapes have been either converted to Strings, or explicit methods for getting the
1483 // string length out of primitives are provided.
1484 //
1485 // Coders are more interesting. Only Object, String and char arguments (and constants)
1486 // can have non-Latin1 encoding. It is easier to blindly convert constants to String,
1487 // and deduce the coder from there. Arguments would be either converted to Strings
1488 // during the initial filtering, or handled by primitive specializations in CODER_MIXERS.
1489 //
1490 // The method handle shape after all length and coder mixers is:
1491 // (int, byte, <args>)String = ("index", "coder", <args>)
1492 byte initialCoder = 0; // initial coder
1493 int initialLen = 0; // initial length, in characters
1494 for (RecipeElement el : recipe.getElements()) {
1495 switch (el.getTag()) {
1496 case CONST: {
1497 Object constant = el.getValue();
1498 String s = constant.toString();
1499 initialCoder = (byte) coderMixer(String.class).invoke(initialCoder, s);
1500 initialLen += s.length();
1501 break;
1502 }
1503 case ARG: {
1504 int ac = el.getArgPos();
1505
1506 Class<?> argClass = ptypesList.get(ac);
1507 MethodHandle lm = selectArgument(lengthMixer(argClass), 1, ptypesList, ac);
1508 lm = MethodHandles.dropArguments(lm, 0, byte.class); // (*)
1509 lm = MethodHandles.dropArguments(lm, 2, byte.class);
1510
1511 MethodHandle cm = selectArgument(coderMixer(argClass), 1, ptypesList, ac);
1512 cm = MethodHandles.dropArguments(cm, 0, int.class); // (**)
1513
1514 // Read this bottom up:
1515
1516 // 4. Drop old index and coder, producing ("new-index", "new-coder", <args>)
1517 mh = MethodHandles.dropArguments(mh, 2, int.class, byte.class);
1518
1519 // 3. Compute "new-index", producing ("new-index", "new-coder", "old-index", "old-coder", <args>)
1520 // Length mixer ignores both "new-coder" and "old-coder" due to dropArguments above (*)
1521 mh = MethodHandles.foldArguments(mh, lm);
1522
1523 // 2. Compute "new-coder", producing ("new-coder", "old-index", "old-coder", <args>)
1524 // Coder mixer ignores the "old-index" arg due to dropArguments above (**)
1525 mh = MethodHandles.foldArguments(mh, cm);
1526
1527 // 1. The mh shape here is ("old-index", "old-coder", <args>)
1528 break;
1529 }
1530 default:
1531 throw new StringConcatException("Unhandled tag: " + el.getTag());
1532 }
1533 }
1534
1535 // Insert initial lengths and coders here.
1536 // The method handle shape here is (<args>).
1537 mh = MethodHandles.insertArguments(mh, 0, initialLen, initialCoder);
1538
1539 // Apply filters, converting the arguments:
1540 if (filters != null) {
1541 mh = MethodHandles.filterArguments(mh, 0, filters);
1542 }
1543
1544 return mh;
1545 }
1546
1547 private static int[] swap10(int count) {
1548 int[] perm = new int[count];
1549 perm[0] = 1;
1550 perm[1] = 0;
1551 for (int i = 2; i < count; i++) {
1552 perm[i] = i;
1553 }
1554 return perm;
1555 }
1556
1557 // Adapts: (...prefix..., parameter[pos])R -> (...prefix..., ...parameters...)R
1558 private static MethodHandle selectArgument(MethodHandle mh, int prefix, List<Class<?>> ptypes, int pos) {
1559 if (pos == 0) {
1560 return MethodHandles.dropArguments(mh, prefix + 1, ptypes.subList(1, ptypes.size()));
1561 } else if (pos == ptypes.size() - 1) {
1562 return MethodHandles.dropArguments(mh, prefix, ptypes.subList(0, ptypes.size() - 1));
1563 } else { // 0 < pos < ptypes.size() - 1
1564 MethodHandle t = MethodHandles.dropArguments(mh, prefix, ptypes.subList(0, pos));
1565 return MethodHandles.dropArguments(t, prefix + 1 + pos, ptypes.subList(pos + 1, ptypes.size()));
1566 }
1567 }
1568
1569 @ForceInline
1570 private static byte[] newArray(int length, byte coder) {
1571 return new byte[length << coder];
1572 }
1573
1574 @ForceInline
1575 private static int checkIndex(int index) {
1576 if (index != 0) {
1577 throw new AssertionError("Exactness check failed: " + index + " characters left in the buffer.");
1578 }
1579 return index;
1580 }
1581
1582 private static MethodHandle prepender(Class<?> cl) {
1583 return PREPENDERS.computeIfAbsent(cl, PREPEND);
1584 }
1585
1586 private static MethodHandle coderMixer(Class<?> cl) {
1587 return CODER_MIXERS.computeIfAbsent(cl, CODER_MIX);
1588 }
1589
1590 private static MethodHandle lengthMixer(Class<?> cl) {
1591 return LENGTH_MIXERS.computeIfAbsent(cl, LENGTH_MIX);
1592 }
1593
1594 // This one is deliberately non-lambdified to optimize startup time:
1595 private static final Function<Class<?>, MethodHandle> PREPEND = new Function<Class<?>, MethodHandle>() {
1596 @Override
1597 public MethodHandle apply(Class<?> c) {
1598 return lookupStatic(Lookup.IMPL_LOOKUP, STRING_HELPER, "prepend", int.class, int.class, byte[].class, byte.class, c);
1599 }
1600 };
1601
1602 // This one is deliberately non-lambdified to optimize startup time:
1603 private static final Function<Class<?>, MethodHandle> CODER_MIX = new Function<Class<?>, MethodHandle>() {
1604 @Override
1605 public MethodHandle apply(Class<?> c) {
1606 return lookupStatic(Lookup.IMPL_LOOKUP, STRING_HELPER, "mixCoder", byte.class, byte.class, c);
1607 }
1608 };
1609
1610 // This one is deliberately non-lambdified to optimize startup time:
1611 private static final Function<Class<?>, MethodHandle> LENGTH_MIX = new Function<Class<?>, MethodHandle>() {
1612 @Override
1613 public MethodHandle apply(Class<?> c) {
1614 return lookupStatic(Lookup.IMPL_LOOKUP, STRING_HELPER, "mixLen", int.class, int.class, c);
1615 }
1616 };
1617
1618 private static final MethodHandle NEW_STRING;
1619 private static final MethodHandle CHECK_INDEX;
1620 private static final MethodHandle NEW_ARRAY;
1621 private static final ConcurrentMap<Class<?>, MethodHandle> PREPENDERS;
1622 private static final ConcurrentMap<Class<?>, MethodHandle> LENGTH_MIXERS;
1623 private static final ConcurrentMap<Class<?>, MethodHandle> CODER_MIXERS;
1624 private static final Class<?> STRING_HELPER;
1625
1626 static {
1627 try {
1628 STRING_HELPER = Class.forName("java.lang.StringConcatHelper");
1629 } catch (ClassNotFoundException e) {
1630 throw new AssertionError(e);
1631 }
1632
1633 PREPENDERS = new ConcurrentHashMap<>();
1634 LENGTH_MIXERS = new ConcurrentHashMap<>();
1635 CODER_MIXERS = new ConcurrentHashMap<>();
1636
1637 NEW_STRING = lookupStatic(Lookup.IMPL_LOOKUP, STRING_HELPER, "newString", String.class, byte[].class, byte.class);
1638 NEW_ARRAY = lookupStatic(Lookup.IMPL_LOOKUP, MethodHandleInlineCopyStrategy.class, "newArray", byte[].class, int.class, byte.class);
1639
1640 if (DEBUG) {
1641 CHECK_INDEX = lookupStatic(Lookup.IMPL_LOOKUP, MethodHandleInlineCopyStrategy.class, "checkIndex", int.class, int.class);
1642 } else {
1643 CHECK_INDEX = null;
1644 }
1645 }
1646 }
1647
1648 /**
1649 * Public gateways to public "stringify" methods. These methods have the form String apply(T obj), and normally
1650 * delegate to {@code String.valueOf}, depending on argument's type.
1651 */
1652 private static final class Stringifiers {
1653 private Stringifiers() {
1654 // no instantiation
1655 }
1656
1657 // This one is deliberately non-lambdified to optimize startup time:
1658 private static final Function<Class<?>, MethodHandle> MOST = new Function<Class<?>, MethodHandle>() {
1659 @Override
1660 public MethodHandle apply(Class<?> cl) {
1661 MethodHandle mhObject = lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, Object.class);
1662
1663 // We need the additional conversion here, because String.valueOf(Object) may return null.
1664 // String conversion rules in Java state we need to produce "null" String in this case.
1665 // It can be easily done with applying valueOf the second time.
1666 MethodHandle mhObjectNoNulls = MethodHandles.filterReturnValue(mhObject,
1667 mhObject.asType(MethodType.methodType(String.class, String.class)));
1668
1669 if (cl == String.class) {
1670 return mhObject;
1671 } else if (cl == float.class) {
1672 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, float.class);
1673 } else if (cl == double.class) {
1674 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, double.class);
1675 } else if (!cl.isPrimitive()) {
1676 return mhObjectNoNulls;
1677 }
1678
1679 return null;
1680 }
1681 };
1682
1683 // This one is deliberately non-lambdified to optimize startup time:
1684 private static final Function<Class<?>, MethodHandle> ANY = new Function<Class<?>, MethodHandle>() {
1685 @Override
1686 public MethodHandle apply(Class<?> cl) {
1687 MethodHandle mh = MOST.apply(cl);
1688 if (mh != null) {
1689 return mh;
1690 }
1691
1692 if (cl == byte.class || cl == short.class || cl == int.class) {
1693 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, int.class);
1694 } else if (cl == boolean.class) {
1695 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, boolean.class);
1696 } else if (cl == char.class) {
1697 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, char.class);
1698 } else if (cl == long.class) {
1699 return lookupStatic(Lookup.PUBLIC_LOOKUP, String.class, "valueOf", String.class, long.class);
1700 } else {
1701 throw new IllegalStateException("Unknown class: " + cl);
1702 }
1703 }
1704 };
1705
1706 private static final ConcurrentMap<Class<?>, MethodHandle> STRINGIFIERS_MOST = new ConcurrentHashMap<>();
1707 private static final ConcurrentMap<Class<?>, MethodHandle> STRINGIFIERS_ANY = new ConcurrentHashMap<>();
1708
1709 /**
1710 * Returns a stringifier for references and floats/doubles only.
1711 * Always returns null for other primitives.
1712 *
1713 * @param t class to stringify
1714 * @return stringifier; null, if not available
1715 */
1716 static MethodHandle forMost(Class<?> t) {
1717 return STRINGIFIERS_MOST.computeIfAbsent(t, MOST);
1718 }
1719
1720 /**
1721 * Returns a stringifier for any type. Never returns null.
1722 *
1723 * @param t class to stringify
1724 * @return stringifier
1725 */
1726 static MethodHandle forAny(Class<?> t) {
1727 return STRINGIFIERS_ANY.computeIfAbsent(t, ANY);
1728 }
1729 }
1730
1731 /* ------------------------------- Common utilities ------------------------------------ */
1732
1733 private static MethodHandle lookupStatic(Lookup lookup, Class<?> refc, String name, Class<?> rtype, Class<?>... ptypes) {
1734 try {
1735 return lookup.findStatic(refc, name, MethodType.methodType(rtype, ptypes));
1736 } catch (NoSuchMethodException | IllegalAccessException e) {
1737 throw new AssertionError(e);
1738 }
1739 }
1740
1741 private static MethodHandle lookupVirtual(Lookup lookup, Class<?> refc, String name, Class<?> rtype, Class<?>... ptypes) {
1742 try {
1743 return lookup.findVirtual(refc, name, MethodType.methodType(rtype, ptypes));
1744 } catch (NoSuchMethodException | IllegalAccessException e) {
1745 throw new AssertionError(e);
1746 }
1747 }
1748
1749 private static MethodHandle lookupConstructor(Lookup lookup, Class<?> refc, Class<?> ptypes) {
1750 try {
1751 return lookup.findConstructor(refc, MethodType.methodType(void.class, ptypes));
1752 } catch (NoSuchMethodException | IllegalAccessException e) {
1753 throw new AssertionError(e);
1754 }
1755 }
1756
1757 private static int estimateSize(Class<?> cl) {
1758 if (cl == Integer.TYPE) {
1759 return 11; // "-2147483648"
1760 } else if (cl == Boolean.TYPE) {
1761 return 5; // "false"
1762 } else if (cl == Byte.TYPE) {
1763 return 4; // "-128"
1764 } else if (cl == Character.TYPE) {
1765 return 1; // duh
1766 } else if (cl == Short.TYPE) {
1767 return 6; // "-32768"
1768 } else if (cl == Double.TYPE) {
1769 return 26; // apparently, no larger than this, see FloatingDecimal.BinaryToASCIIBuffer.buffer
1770 } else if (cl == Float.TYPE) {
1771 return 26; // apparently, no larger than this, see FloatingDecimal.BinaryToASCIIBuffer.buffer
1772 } else if (cl == Long.TYPE) {
1773 return 20; // "-9223372036854775808"
1774 } else {
1775 throw new IllegalArgumentException("Cannot estimate the size for " + cl);
1776 }
1777 }
1778
1779 private static Class<?> adaptToStringBuilder(Class<?> c) {
1780 if (c.isPrimitive()) {
1781 if (c == Byte.TYPE || c == Short.TYPE) {
1782 return int.class;
1783 }
1784 } else {
1785 if (c != String.class) {
1786 return Object.class;
1787 }
1788 }
1789 return c;
1790 }
1791
1792 private StringConcatFactory() {
1793 // no instantiation
1794 }
1795
1796 }