1 /*
2 * Copyright (c) 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.lang;
26
27 import sun.reflect.CallerSensitive;
28
29 import java.util.*;
30 import java.util.function.Consumer;
31 import java.util.function.Function;
32 import java.util.stream.Stream;
33
34 /**
35 * A stack walker.
36 *
37 * <p> The {@link StackWalker#walk walk} method opens a sequential stream
38 * of {@link StackFrame StackFrame}s for the current thread and then applies
39 * the given function to walk the {@code StackFrame} stream.
40 * The stream reports stack frame elements in order, from the top most frame
41 * that represents the execution point at which the stack was generated to
42 * the bottom most frame.
43 * The {@code StackFrame} stream is closed when the {@code walk} method returns.
44 * If an attempt is made to reuse the closed stream,
45 * {@code IllegalStateException} will be thrown.
46 *
47 * <p> The {@linkplain Option <em>stack walking options</em>} of a
48 * {@code StackWalker} determines the information of
49 * {@link StackFrame StackFrame} objects to be returned.
50 * By default, stack frames of the reflection API and implementation
51 * classes are {@linkplain Option#SHOW_HIDDEN_FRAMES hidden}
52 * and {@code StackFrame}s have the class name and method name
53 * available but not the {@link StackFrame#getDeclaringClass() Class reference}.
54 *
55 * <p> {@code StackWalker} is thread-safe. Multiple threads can share
56 * a single {@code StackWalker} object to traverse its own stack.
57 * A permission check is performed when a {@code StackWalker} is created,
58 * according to the options it requests.
59 * No further permission check is done at stack walking time.
60 *
61 * @apiNote
62 * Examples
63 *
64 * <p>1. To find the first caller filtering a known list of implementation class:
65 * <pre>{@code
66 * StackWalker walker = StackWalker.getInstance(Option.RETAIN_CLASS_REFERENCE);
67 * Optional<Class<?>> callerClass = walker.walk(s ->
68 * s.map(StackFrame::getDeclaringClass)
69 * .filter(interestingClasses::contains)
70 * .findFirst());
71 * }</pre>
72 *
73 * <p>2. To snapshot the top 10 stack frames of the current thread,
74 * <pre>{@code
75 * List<StackFrame> stack = StackWalker.getInstance().walk(s ->
76 * s.limit(10).collect(Collectors.toList()));
77 * }</pre>
78 *
79 * Unless otherwise noted, passing a {@code null} argument to a
80 * constructor or method in this {@code StackWalker} class
81 * will cause a {@link NullPointerException NullPointerException}
82 * to be thrown.
83 *
84 * @since 9
85 */
86 public final class StackWalker {
87 /**
88 * A {@code StackFrame} object represents a method invocation returned by
89 * {@link StackWalker}.
90 *
91 * <p> The {@link #getDeclaringClass()} method may be unsupported as determined
92 * by the {@linkplain Option stack walking options} of a {@linkplain
93 * StackWalker stack walker}.
94 *
95 * @since 9
96 * @jvms 2.6
97 */
98 public static interface StackFrame {
99 /**
100 * Gets the <a href="ClassLoader.html#name">binary name</a>
101 * of the declaring class of the method represented by this stack frame.
102 *
103 * @return the binary name of the declaring class of the method
104 * represented by this stack frame
105 *
106 * @jls 13.1 The Form of a Binary
107 */
108 public String getClassName();
109
110 /**
111 * Gets the name of the method represented by this stack frame.
112 * @return the name of the method represented by this stack frame
113 */
114 public String getMethodName();
115
116 /**
117 * Gets the declaring {@code Class} for the method represented by
118 * this stack frame.
119 *
120 * @return the declaring {@code Class} of the method represented by
121 * this stack frame
122 *
123 * @throws UnsupportedOperationException if this {@code StackWalker}
124 * is not configured with {@link Option#RETAIN_CLASS_REFERENCE
125 * Option.RETAIN_CLASS_REFERENCE}.
126 */
127 public Class<?> getDeclaringClass();
128
129 /**
130 * Returns {@code true} if the method containing the execution point
131 * represented by this stack frame is a native method.
132 *
133 * @return {@code true} if the method containing the execution point
134 * represented by this stack frame is a native method.
135 */
136 public boolean isNativeMethod();
137
138 /**
139 * Gets a {@code StackTraceElement} for this stack frame.
140 *
141 * @return {@code StackTraceElement} for this stack frame.
142 */
143 public StackTraceElement toStackTraceElement();
144 }
145
146 /**
147 * Stack walker option to configure the {@linkplain StackFrame stack frame}
148 * information obtained by a {@code StackWalker}.
149 *
150 * @since 9
151 */
152 public enum Option {
153 /**
154 * Retains {@code Class} object in {@code StackFrame}s
155 * walked by this {@code StackWalker}.
156 *
157 * <p> A {@code StackWalker} configured with this option will support
158 * {@link StackWalker#getCallerClass()} and
159 * {@link StackFrame#getDeclaringClass() StackFrame.getDeclaringClass()}.
160 */
161 RETAIN_CLASS_REFERENCE,
162 /**
163 * Shows all reflection frames.
164 *
165 * <p>By default, reflection frames are hidden. This includes the
166 * {@link java.lang.reflect.Method#invoke} method
167 * and the reflection implementation classes. A {@code StackWalker} with
168 * this {@code SHOW_REFLECT_FRAMES} option will show all reflection frames.
169 * The {@link #SHOW_HIDDEN_FRAMES} option can also be used to show all
170 * reflection frames and it will also show other hidden frames that
171 * are implementation-specific.
172 */
173 SHOW_REFLECT_FRAMES,
174 /**
175 * Shows all hidden frames.
176 *
177 * <p>A Java Virtual Machine implementation may hide implementation
178 * specific frames in addition to {@linkplain #SHOW_REFLECT_FRAMES
179 * reflection frames}. A {@code StackWalker} with this {@code SHOW_HIDDEN_FRAMES}
180 * option will show all hidden frames (including reflection frames).
181 */
182 SHOW_HIDDEN_FRAMES;
183 }
184
185 enum ExtendedOption {
186 /**
187 * Obtain monitors, locals and operands.
188 */
189 LOCALS_AND_OPERANDS
190 };
191
192 static final EnumSet<Option> DEFAULT_EMPTY_OPTION = EnumSet.noneOf(Option.class);
193
194 private final static StackWalker DEFAULT_WALKER =
195 new StackWalker(DEFAULT_EMPTY_OPTION);
196
197 private final Set<Option> options;
198 private final ExtendedOption extendedOption;
199 private final int estimateDepth;
200
201 /**
202 * Returns a {@code StackWalker} instance.
203 *
204 * <p> This {@code StackWalker} is configured to skip all
205 * {@linkplain Option#SHOW_HIDDEN_FRAMES hidden frames} and
206 * no {@linkplain Option#RETAIN_CLASS_REFERENCE class reference} is retained.
207 *
208 * @return a {@code StackWalker} configured to skip all
209 * {@linkplain Option#SHOW_HIDDEN_FRAMES hidden frames} and
210 * no {@linkplain Option#RETAIN_CLASS_REFERENCE class reference} is retained.
211 *
212 */
213 public static StackWalker getInstance() {
214 // no permission check needed
215 return DEFAULT_WALKER;
216 }
217
218 /**
219 * Returns a {@code StackWalker} instance with the given option specifying
220 * the stack frame information it can access.
221 *
222 * <p>
223 * If a security manager is present and the given {@code option} is
224 * {@link Option#RETAIN_CLASS_REFERENCE Option.RETAIN_CLASS_REFERENCE},
225 * it calls its {@link SecurityManager#checkPermission checkPermission}
226 * method for {@code StackFramePermission("retainClassReference")}.
227 *
228 * @param option {@link Option stack walking option}
229 *
230 * @return a {@code StackWalker} configured with the given option
231 *
232 * @throws SecurityException if a security manager exists and its
233 * {@code checkPermission} method denies access.
234 */
235 public static StackWalker getInstance(Option option) {
236 return getInstance(EnumSet.of(Objects.requireNonNull(option)));
237 }
238
239 /**
240 * Returns a {@code StackWalker} instance with the given {@code options} specifying
241 * the stack frame information it can access. If the given {@code options}
242 * is empty, this {@code StackWalker} is configured to skip all
243 * {@linkplain Option#SHOW_HIDDEN_FRAMES hidden frames} and no
244 * {@linkplain Option#RETAIN_CLASS_REFERENCE class reference} is retained.
245 *
246 * <p>
247 * If a security manager is present and the given {@code options} contains
248 * {@link Option#RETAIN_CLASS_REFERENCE Option.RETAIN_CLASS_REFERENCE},
249 * it calls its {@link SecurityManager#checkPermission checkPermission}
250 * method for {@code StackFramePermission("retainClassReference")}.
251 *
252 * @param options {@link Option stack walking option}
253 *
254 * @return a {@code StackWalker} configured with the given options
255 *
256 * @throws SecurityException if a security manager exists and its
257 * {@code checkPermission} method denies access.
258 */
259 public static StackWalker getInstance(Set<Option> options) {
260 if (options.isEmpty()) {
261 return DEFAULT_WALKER;
262 }
263
264 checkPermission(options);
265 return new StackWalker(toEnumSet(options));
266 }
267
268 /**
269 * Returns a {@code StackWalker} instance with the given {@code options} specifying
270 * the stack frame information it can access. If the given {@code options}
271 * is empty, this {@code StackWalker} is configured to skip all
272 * {@linkplain Option#SHOW_HIDDEN_FRAMES hidden frames} and no
273 * {@linkplain Option#RETAIN_CLASS_REFERENCE class reference} is retained.
274 *
275 * <p>
276 * If a security manager is present and the given {@code options} contains
277 * {@link Option#RETAIN_CLASS_REFERENCE Option.RETAIN_CLASS_REFERENCE},
278 * it calls its {@link SecurityManager#checkPermission checkPermission}
279 * method for {@code StackFramePermission("retainClassReference")}.
280 *
281 * <p>
282 * The {@code estimateDepth} specifies the estimate number of stack frames
283 * this {@code StackWalker} will traverse that the {@code StackWalker} could
284 * use as a hint for the buffer size.
285 *
286 * @param options {@link Option stack walking options}
287 * @param estimateDepth Estimate number of stack frames to be traversed.
288 *
289 * @return a {@code StackWalker} configured with the given options
290 *
291 * @throws IllegalArgumentException if {@code estimateDepth <= 0}
292 * @throws SecurityException if a security manager exists and its
293 * {@code checkPermission} method denies access.
294 */
295 public static StackWalker getInstance(Set<Option> options, int estimateDepth) {
296 if (estimateDepth <= 0) {
297 throw new IllegalArgumentException("estimateDepth must be > 0");
298 }
299 checkPermission(options);
300 return new StackWalker(toEnumSet(options), estimateDepth);
301 }
302
303 // ----- private constructors ------
304 private StackWalker(EnumSet<Option> options) {
305 this(options, 0, null);
306 }
307 private StackWalker(EnumSet<Option> options, int estimateDepth) {
308 this(options, estimateDepth, null);
309 }
310 private StackWalker(EnumSet<Option> options, int estimateDepth, ExtendedOption extendedOption) {
311 this.options = options;
312 this.estimateDepth = estimateDepth;
313 this.extendedOption = extendedOption;
314 }
315
316 private static void checkPermission(Set<Option> options) {
317 Objects.requireNonNull(options);
318 SecurityManager sm = System.getSecurityManager();
319 if (sm != null) {
320 if (options.contains(Option.RETAIN_CLASS_REFERENCE)) {
321 sm.checkPermission(new StackFramePermission("retainClassReference"));
322 }
323 }
324 }
325
326 /*
327 * Returns a defensive copy
328 */
329 private static EnumSet<Option> toEnumSet(Set<Option> options) {
330 Objects.requireNonNull(options);
331 if (options.isEmpty()) {
332 return DEFAULT_EMPTY_OPTION;
333 } else {
334 return EnumSet.copyOf(options);
335 }
336 }
337
338 /**
339 * Applies the given function to the stream of {@code StackFrame}s
340 * for the current thread, traversing from the top frame of the stack,
341 * which is the method calling this {@code walk} method.
342 *
343 * <p>The {@code StackFrame} stream will be closed when
344 * this method returns. When a closed {@code Stream<StackFrame>} object
345 * is reused, {@code IllegalStateException} will be thrown.
346 *
347 * @apiNote
348 * For example, to find the first 10 calling frames, first skipping those frames
349 * whose declaring class is in package {@code com.foo}:
350 * <blockquote>
351 * <pre>{@code
352 * List<StackFrame> frames = StackWalker.getInstance().walk(s ->
353 * s.dropWhile(f -> f.getClassName().startsWith("com.foo."))
354 * .limit(10)
355 * .collect(Collectors.toList()));
356 * }</pre></blockquote>
357 *
358 * <p>This method takes a {@code Function} accepting a {@code Stream<StackFrame>},
359 * rather than returning a {@code Stream<StackFrame>} and allowing the
360 * caller to directly manipulate the stream. The Java virtual machine is
361 * free to reorganize a thread's control stack, for example, via
362 * deoptimization. By taking a {@code Function} parameter, this method
363 * allows access to stack frames through a stable view of a thread's control
364 * stack.
365 *
366 * <p>Parallel execution is effectively disabled and stream pipeline
367 * execution will only occur on the current thread.
368 *
369 * @implNote The implementation stabilizes the stack by anchoring a frame
370 * specific to the stack walking and ensures that the stack walking is
371 * performed above the anchored frame. When the stream object is closed or
372 * being reused, {@code IllegalStateException} will be thrown.
373 *
374 * @param function a function that takes a stream of
375 * {@linkplain StackFrame stack frames} and returns a result.
376 * @param <T> The type of the result of applying the function to the
377 * stream of {@linkplain StackFrame stack frame}.
378 *
379 * @return the result of applying the function to the stream of
380 * {@linkplain StackFrame stack frame}.
381 */
382 @CallerSensitive
383 public <T> T walk(Function<? super Stream<StackFrame>, ? extends T> function) {
384 // Returning a Stream<StackFrame> would be unsafe, as the stream could
385 // be used to access the stack frames in an uncontrolled manner. For
386 // example, a caller might pass a Spliterator of stack frames after one
387 // or more frames had been traversed. There is no robust way to detect
388 // whether the execution point when
389 // Spliterator.tryAdvance(java.util.function.Consumer<? super T>) is
390 // invoked is the exact same execution point where the stack frame
391 // traversal is expected to resume.
392
393 Objects.requireNonNull(function);
394 return StackStreamFactory.makeStackTraverser(this, function)
395 .walk();
396 }
397
398 /**
399 * Performs the given action on each element of {@code StackFrame} stream
400 * of the current thread, traversing from the top frame of the stack,
401 * which is the method calling this {@code forEach} method.
402 *
403 * <p> This method is equivalent to calling
404 * <blockquote>
405 * {@code walk(s -> { s.forEach(action); return null; });}
406 * </blockquote>
407 *
408 * @param action an action to be performed on each {@code StackFrame}
409 * of the stack of the current thread
410 */
411 @CallerSensitive
412 public void forEach(Consumer<? super StackFrame> action) {
413 Objects.requireNonNull(action);
414 StackStreamFactory.makeStackTraverser(this, s -> {
415 s.forEach(action);
416 return null;
417 }).walk();
418 }
419
420 /**
421 * Gets the {@code Class} object of the caller invoking the method
422 * that calls this {@code getCallerClass} method.
423 *
424 * <p> Reflection frames, {@link java.lang.invoke.MethodHandle} and
425 * hidden frames are filtered regardless of the
426 * {@link Option#SHOW_REFLECT_FRAMES SHOW_REFLECT_FRAMES}
427 * and {@link Option#SHOW_HIDDEN_FRAMES SHOW_HIDDEN_FRAMES} options
428 * this {@code StackWalker} has been configured.
429 *
430 * <p> This method throws {@code UnsupportedOperationException}
431 * if this {@code StackWalker} is not configured with
432 * {@link Option#RETAIN_CLASS_REFERENCE RETAIN_CLASS_REFERENCE} option,
433 * This method should be called when a caller frame is present. If
434 * it is called from the last frame on the stack;
435 * {@code IllegalStateException} will be thrown.
436 *
437 * @apiNote
438 * For example, {@code Util::getResourceBundle} loads a resource bundle
439 * on behalf of the caller. It calls this {@code getCallerClass} method
440 * to find the method calling {@code Util::getResourceBundle} and use the caller's
441 * class loader to load the resource bundle. The caller class in this example
442 * is the {@code MyTool} class.
443 *
444 * <pre>{@code
445 * class Util {
446 * private final StackWalker walker = StackWalker.getInstance(Option.RETAIN_CLASS_REFERENCE);
447 * public ResourceBundle getResourceBundle(String bundleName) {
448 * Class<?> caller = walker.getCallerClass();
449 * return ResourceBundle.getBundle(bundleName, Locale.getDefault(), caller.getClassLoader());
450 * }
451 * }
452 *
453 * class MyTool {
454 * private final Util util = new Util();
455 * private void init() {
456 * ResourceBundle rb = util.getResourceBundle("mybundle");
457 * }
458 * }
459 * }</pre>
460 *
461 * An equivalent way to find the caller class using the
462 * {@link StackWalker#walk walk} method is as follows
463 * (filtering the reflection frames, {@code MethodHandle} and hidden frames
464 * not shown below):
465 * <pre>{@code
466 * Optional<Class<?>> caller = walker.walk(s ->
467 * s.map(StackFrame::getDeclaringClass)
468 * .skip(2)
469 * .findFirst());
470 * }</pre>
471 *
472 * When the {@code getCallerClass} method is called from a method that
473 * is the last frame on the stack,
474 * for example, {@code static public void main} method launched by the
475 * {@code java} launcher or a method invoked from a JNI attached thread.
476 * {@code IllegalStateException} is thrown.
477 *
478 * @return {@code Class} object of the caller's caller invoking this method.
479 *
480 * @throws UnsupportedOperationException if this {@code StackWalker}
481 * is not configured with {@link Option#RETAIN_CLASS_REFERENCE
482 * Option.RETAIN_CLASS_REFERENCE}.
483 * @throws IllegalStateException if there is no caller frame, i.e.
484 * when this {@code getCallerClass} method is called from a method
485 * which is the last frame on the stack.
486 */
487 @CallerSensitive
488 public Class<?> getCallerClass() {
489 if (!options.contains(Option.RETAIN_CLASS_REFERENCE)) {
490 throw new UnsupportedOperationException("This stack walker " +
491 "does not have RETAIN_CLASS_REFERENCE access");
492 }
493
494 return StackStreamFactory.makeCallerFinder(this).findCaller();
495 }
496
497 // ---- package access ----
498 static StackWalker newInstanceNoCheck(EnumSet<Option> options) {
499 return new StackWalker(options, 0, null);
500 }
501
502 static StackWalker newInstance(Set<Option> options, ExtendedOption extendedOption) {
503 checkPermission(options);
504 return new StackWalker(toEnumSet(options), 0, extendedOption);
505 }
506
507 int estimateDepth() {
508 return estimateDepth;
509 }
510
511 boolean hasOption(Option option) {
512 return options.contains(option);
513 }
514
515 boolean hasLocalsOperandsOption() {
516 return extendedOption == ExtendedOption.LOCALS_AND_OPERANDS;
517 }
518
519 void ensureAccessEnabled(Option access) {
520 if (!hasOption(access)) {
521 throw new UnsupportedOperationException("No access to " + access +
522 ": " + options.toString());
523 }
524 }
525 }