1 /*
2 * Copyright (c) 2020, 2023, 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 jdk.internal.vm;
26
27 import java.io.BufferedOutputStream;
28 import java.io.ByteArrayOutputStream;
29 import java.io.IOException;
30 import java.io.OutputStream;
31 import java.io.PrintStream;
32 import java.nio.charset.StandardCharsets;
33 import java.nio.file.FileAlreadyExistsException;
34 import java.nio.file.Files;
35 import java.nio.file.OpenOption;
36 import java.nio.file.Path;
37 import java.nio.file.StandardOpenOption;
38 import java.time.Instant;
39 import java.util.ArrayList;
40 import java.util.Iterator;
41 import java.util.List;
42
43 /**
44 * Thread dump support.
45 *
46 * This class defines methods to dump threads to an output stream or file in plain
47 * text or JSON format.
48 */
49 public class ThreadDumper {
50 private ThreadDumper() { }
51
52 // the maximum byte array to return when generating the thread dump to a byte array
53 private static final int MAX_BYTE_ARRAY_SIZE = 16_000;
54
55 /**
56 * Generate a thread dump in plain text format to a byte array or file, UTF-8 encoded.
57 *
58 * This method is invoked by the VM for the Thread.dump_to_file diagnostic command.
59 *
60 * @param file the file path to the file, null or "-" to return a byte array
61 * @param okayToOverwrite true to overwrite an existing file
62 * @return the UTF-8 encoded thread dump or message to return to the user
63 */
64 public static byte[] dumpThreads(String file, boolean okayToOverwrite) {
65 if (file == null || file.equals("-")) {
66 return dumpThreadsToByteArray(false, MAX_BYTE_ARRAY_SIZE);
67 } else {
68 return dumpThreadsToFile(file, okayToOverwrite, false);
69 }
70 }
71
72 /**
73 * Generate a thread dump in JSON format to a byte array or file, UTF-8 encoded.
74 *
75 * This method is invoked by the VM for the Thread.dump_to_file diagnostic command.
76 *
77 * @param file the file path to the file, null or "-" to return a byte array
78 * @param okayToOverwrite true to overwrite an existing file
79 * @return the UTF-8 encoded thread dump or message to return to the user
80 */
81 public static byte[] dumpThreadsToJson(String file, boolean okayToOverwrite) {
82 if (file == null || file.equals("-")) {
83 return dumpThreadsToByteArray(true, MAX_BYTE_ARRAY_SIZE);
84 } else {
85 return dumpThreadsToFile(file, okayToOverwrite, true);
86 }
87 }
88
89 /**
90 * Generate a thread dump in plain text or JSON format to a byte array, UTF-8 encoded.
91 */
92 private static byte[] dumpThreadsToByteArray(boolean json, int maxSize) {
93 try (var out = new BoundedByteArrayOutputStream(maxSize);
94 PrintStream ps = new PrintStream(out, true, StandardCharsets.UTF_8)) {
95 if (json) {
96 dumpThreadsToJson(ps);
97 } else {
98 dumpThreads(ps);
99 }
100 return out.toByteArray();
101 }
102 }
103
104 /**
105 * Generate a thread dump in plain text or JSON format to the given file, UTF-8 encoded.
106 */
107 private static byte[] dumpThreadsToFile(String file, boolean okayToOverwrite, boolean json) {
108 Path path = Path.of(file).toAbsolutePath();
109 OpenOption[] options = (okayToOverwrite)
110 ? new OpenOption[0]
111 : new OpenOption[] { StandardOpenOption.CREATE_NEW };
112 String reply;
113 try (OutputStream out = Files.newOutputStream(path, options);
114 BufferedOutputStream bos = new BufferedOutputStream(out);
115 PrintStream ps = new PrintStream(bos, false, StandardCharsets.UTF_8)) {
116 if (json) {
117 dumpThreadsToJson(ps);
118 } else {
119 dumpThreads(ps);
120 }
121 reply = String.format("Created %s%n", path);
122 } catch (FileAlreadyExistsException e) {
123 reply = String.format("%s exists, use -overwrite to overwrite%n", path);
124 } catch (IOException ioe) {
125 reply = String.format("Failed: %s%n", ioe);
126 }
127 return reply.getBytes(StandardCharsets.UTF_8);
128 }
129
130 /**
131 * Generate a thread dump in plain text format to the given output stream,
132 * UTF-8 encoded.
133 *
134 * This method is invoked by HotSpotDiagnosticMXBean.dumpThreads.
135 */
136 public static void dumpThreads(OutputStream out) {
137 BufferedOutputStream bos = new BufferedOutputStream(out);
138 PrintStream ps = new PrintStream(bos, false, StandardCharsets.UTF_8);
139 try {
140 dumpThreads(ps);
141 } finally {
142 ps.flush(); // flushes underlying stream
143 }
144 }
145
146 /**
147 * Generate a thread dump in plain text format to the given print stream.
148 */
149 private static void dumpThreads(PrintStream ps) {
150 ps.println(processId());
151 ps.println(Instant.now());
152 ps.println(Runtime.version());
153 ps.println();
154 dumpThreads(ThreadContainers.root(), ps);
155 }
156
157 private static void dumpThreads(ThreadContainer container, PrintStream ps) {
158 container.threads().forEach(t -> dumpThread(t, ps));
159 container.children().forEach(c -> dumpThreads(c, ps));
160 }
161
162 private static void dumpThread(Thread thread, PrintStream ps) {
163 String suffix = thread.isVirtual() ? " virtual" : "";
164 ps.println("#" + thread.threadId() + " \"" + thread.getName() + "\"" + suffix);
165 for (StackTraceElement ste : thread.getStackTrace()) {
166 ps.print(" ");
167 ps.println(ste);
168 }
169 ps.println();
170 }
171
172 /**
173 * Generate a thread dump in JSON format to the given output stream, UTF-8 encoded.
174 *
175 * This method is invoked by HotSpotDiagnosticMXBean.dumpThreads.
176 */
177 public static void dumpThreadsToJson(OutputStream out) {
178 BufferedOutputStream bos = new BufferedOutputStream(out);
179 PrintStream ps = new PrintStream(bos, false, StandardCharsets.UTF_8);
180 try {
181 dumpThreadsToJson(ps);
182 } finally {
183 ps.flush(); // flushes underlying stream
184 }
185 }
186
187 /**
188 * Generate a thread dump to the given print stream in JSON format.
189 */
190 private static void dumpThreadsToJson(PrintStream out) {
191 out.println("{");
192 out.println(" \"threadDump\": {");
193
194 String now = Instant.now().toString();
195 String runtimeVersion = Runtime.version().toString();
196 out.format(" \"processId\": \"%d\",%n", processId());
197 out.format(" \"time\": \"%s\",%n", escape(now));
198 out.format(" \"runtimeVersion\": \"%s\",%n", escape(runtimeVersion));
199
200 out.println(" \"threadContainers\": [");
201 List<ThreadContainer> containers = allContainers();
202 Iterator<ThreadContainer> iterator = containers.iterator();
203 while (iterator.hasNext()) {
204 ThreadContainer container = iterator.next();
205 boolean more = iterator.hasNext();
206 dumpThreadsToJson(container, out, more);
207 }
208 out.println(" ]"); // end of threadContainers
209
210 out.println(" }"); // end threadDump
211 out.println("}"); // end object
212 }
213
214 /**
215 * Dump the given thread container to the print stream in JSON format.
216 */
217 private static void dumpThreadsToJson(ThreadContainer container,
218 PrintStream out,
219 boolean more) {
220 out.println(" {");
221 out.format(" \"container\": \"%s\",%n", escape(container.toString()));
222
223 ThreadContainer parent = container.parent();
224 if (parent == null) {
225 out.format(" \"parent\": null,%n");
226 } else {
227 out.format(" \"parent\": \"%s\",%n", escape(parent.toString()));
228 }
229
230 Thread owner = container.owner();
231 if (owner == null) {
232 out.format(" \"owner\": null,%n");
233 } else {
234 out.format(" \"owner\": \"%d\",%n", owner.threadId());
235 }
236
237 long threadCount = 0;
238 out.println(" \"threads\": [");
239 Iterator<Thread> threads = container.threads().iterator();
240 while (threads.hasNext()) {
241 Thread thread = threads.next();
242 dumpThreadToJson(thread, out, threads.hasNext());
243 threadCount++;
244 }
245 out.println(" ],"); // end of threads
246
247 // thread count
248 if (!ThreadContainers.trackAllThreads()) {
249 threadCount = Long.max(threadCount, container.threadCount());
250 }
251 out.format(" \"threadCount\": \"%d\"%n", threadCount);
252
253 if (more) {
254 out.println(" },");
255 } else {
256 out.println(" }"); // last container, no trailing comma
257 }
258 }
259
260 /**
261 * Dump the given thread and its stack trace to the print stream in JSON format.
262 */
263 private static void dumpThreadToJson(Thread thread, PrintStream out, boolean more) {
264 out.println(" {");
265 out.println(" \"tid\": \"" + thread.threadId() + "\",");
266 out.println(" \"name\": \"" + escape(thread.getName()) + "\",");
267 out.println(" \"stack\": [");
268
269 int i = 0;
270 StackTraceElement[] stackTrace = thread.getStackTrace();
271 while (i < stackTrace.length) {
272 out.print(" \"");
273 out.print(escape(stackTrace[i].toString()));
274 out.print("\"");
275 i++;
276 if (i < stackTrace.length) {
277 out.println(",");
278 } else {
279 out.println(); // last element, no trailing comma
280 }
281 }
282 out.println(" ]");
283 if (more) {
284 out.println(" },");
285 } else {
286 out.println(" }"); // last thread, no trailing comma
287 }
288 }
289
290 /**
291 * Returns a list of all thread containers that are "reachable" from
292 * the root container.
293 */
294 private static List<ThreadContainer> allContainers() {
295 List<ThreadContainer> containers = new ArrayList<>();
296 collect(ThreadContainers.root(), containers);
297 return containers;
298 }
299
300 private static void collect(ThreadContainer container, List<ThreadContainer> containers) {
301 containers.add(container);
302 container.children().forEach(c -> collect(c, containers));
303 }
304
305 /**
306 * Escape any characters that need to be escape in the JSON output.
307 */
308 private static String escape(String value) {
309 StringBuilder sb = new StringBuilder();
310 for (int i = 0; i < value.length(); i++) {
311 char c = value.charAt(i);
312 switch (c) {
313 case '"' -> sb.append("\\\"");
314 case '\\' -> sb.append("\\\\");
315 case '/' -> sb.append("\\/");
316 case '\b' -> sb.append("\\b");
317 case '\f' -> sb.append("\\f");
318 case '\n' -> sb.append("\\n");
319 case '\r' -> sb.append("\\r");
320 case '\t' -> sb.append("\\t");
321 default -> {
322 if (c <= 0x1f) {
323 sb.append(String.format("\\u%04x", c));
324 } else {
325 sb.append(c);
326 }
327 }
328 }
329 }
330 return sb.toString();
331 }
332
333 /**
334 * A ByteArrayOutputStream of bounded size. Once the maximum number of bytes is
335 * written the subsequent bytes are discarded.
336 */
337 private static class BoundedByteArrayOutputStream extends ByteArrayOutputStream {
338 final int max;
339 BoundedByteArrayOutputStream(int max) {
340 this.max = max;
341 }
342 @Override
343 public void write(int b) {
344 if (max < count) {
345 super.write(b);
346 }
347 }
348 @Override
349 public void write(byte[] b, int off, int len) {
350 int remaining = max - count;
351 if (remaining > 0) {
352 super.write(b, off, Integer.min(len, remaining));
353 }
354 }
355 @Override
356 public void close() {
357 }
358 }
359
360 /**
361 * Returns the process ID or -1 if not supported.
362 */
363 private static long processId() {
364 try {
365 return ProcessHandle.current().pid();
366 } catch (UnsupportedOperationException e) {
367 return -1L;
368 }
369 }
370 }