1 /*
2 * Copyright (c) 1995, 2017, 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;
27
28 import java.io.*;
29 import java.lang.ProcessBuilder.Redirect;
30 import java.util.concurrent.CompletableFuture;
31 import java.util.concurrent.ForkJoinPool;
32 import java.util.concurrent.TimeUnit;
33 import java.util.stream.Stream;
34
35 /**
36 * {@code Process} provides control of native processes started by
37 * ProcessBuilder.start and Runtime.exec.
38 * The class provides methods for performing input from the process, performing
39 * output to the process, waiting for the process to complete,
40 * checking the exit status of the process, and destroying (killing)
41 * the process.
42 * The {@link ProcessBuilder#start()} and
43 * {@link Runtime#exec(String[],String[],File) Runtime.exec}
44 * methods create a native process and return an instance of a
45 * subclass of {@code Process} that can be used to control the process
46 * and obtain information about it.
47 *
48 * <p>The methods that create processes may not work well for special
49 * processes on certain native platforms, such as native windowing
50 * processes, daemon processes, Win16/DOS processes on Microsoft
51 * Windows, or shell scripts.
52 *
53 * <p>By default, the created process does not have its own terminal
54 * or console. All its standard I/O (i.e. stdin, stdout, stderr)
55 * operations will be redirected to the parent process, where they can
56 * be accessed via the streams obtained using the methods
57 * {@link #getOutputStream()},
58 * {@link #getInputStream()}, and
59 * {@link #getErrorStream()}.
60 * The parent process uses these streams to feed input to and get output
61 * from the process. Because some native platforms only provide
62 * limited buffer size for standard input and output streams, failure
63 * to promptly write the input stream or read the output stream of
64 * the process may cause the process to block, or even deadlock.
65 *
66 * <p>Where desired, <a href="ProcessBuilder.html#redirect-input">
67 * process I/O can also be redirected</a>
68 * using methods of the {@link ProcessBuilder} class.
69 *
70 * <p>The process is not killed when there are no more references to
71 * the {@code Process} object, but rather the process
72 * continues executing asynchronously.
73 *
74 * <p>There is no requirement that the process represented by a {@code
75 * Process} object execute asynchronously or concurrently with respect
76 * to the Java process that owns the {@code Process} object.
77 *
78 * <p>As of 1.5, {@link ProcessBuilder#start()} is the preferred way
79 * to create a {@code Process}.
80 *
81 * <p>Subclasses of Process should override the {@link #onExit()} and
82 * {@link #toHandle()} methods to provide a fully functional Process including the
83 * {@linkplain #pid() process id},
84 * {@linkplain #info() information about the process},
85 * {@linkplain #children() direct children}, and
86 * {@linkplain #descendants() direct children plus descendants of those children} of the process.
87 * Delegating to the underlying Process or ProcessHandle is typically
88 * easiest and most efficient.
89 *
90 * @since 1.0
91 */
92 public abstract class Process {
93 /**
94 * Default constructor for Process.
95 */
96 public Process() {}
97
98 /**
99 * Returns the output stream connected to the normal input of the
100 * process. Output to the stream is piped into the standard
101 * input of the process represented by this {@code Process} object.
102 *
103 * <p>If the standard input of the process has been redirected using
104 * {@link ProcessBuilder#redirectInput(Redirect)
105 * ProcessBuilder.redirectInput}
106 * then this method will return a
107 * <a href="ProcessBuilder.html#redirect-input">null output stream</a>.
108 *
109 * <p>Implementation note: It is a good idea for the returned
110 * output stream to be buffered.
111 *
112 * @return the output stream connected to the normal input of the
113 * process
114 */
115 public abstract OutputStream getOutputStream();
116
117 /**
118 * Returns the input stream connected to the normal output of the
119 * process. The stream obtains data piped from the standard
120 * output of the process represented by this {@code Process} object.
121 *
122 * <p>If the standard output of the process has been redirected using
123 * {@link ProcessBuilder#redirectOutput(Redirect)
124 * ProcessBuilder.redirectOutput}
125 * then this method will return a
126 * <a href="ProcessBuilder.html#redirect-output">null input stream</a>.
127 *
128 * <p>Otherwise, if the standard error of the process has been
129 * redirected using
130 * {@link ProcessBuilder#redirectErrorStream(boolean)
131 * ProcessBuilder.redirectErrorStream}
132 * then the input stream returned by this method will receive the
133 * merged standard output and the standard error of the process.
134 *
135 * <p>Implementation note: It is a good idea for the returned
136 * input stream to be buffered.
137 *
138 * @return the input stream connected to the normal output of the
139 * process
140 */
141 public abstract InputStream getInputStream();
142
143 /**
144 * Returns the input stream connected to the error output of the
145 * process. The stream obtains data piped from the error output
146 * of the process represented by this {@code Process} object.
147 *
148 * <p>If the standard error of the process has been redirected using
149 * {@link ProcessBuilder#redirectError(Redirect)
150 * ProcessBuilder.redirectError} or
151 * {@link ProcessBuilder#redirectErrorStream(boolean)
152 * ProcessBuilder.redirectErrorStream}
153 * then this method will return a
154 * <a href="ProcessBuilder.html#redirect-output">null input stream</a>.
155 *
156 * <p>Implementation note: It is a good idea for the returned
157 * input stream to be buffered.
158 *
159 * @return the input stream connected to the error output of
160 * the process
161 */
162 public abstract InputStream getErrorStream();
163
164 /**
165 * Causes the current thread to wait, if necessary, until the
166 * process represented by this {@code Process} object has
167 * terminated. This method returns immediately if the process
168 * has already terminated. If the process has not yet
169 * terminated, the calling thread will be blocked until the
170 * process exits.
171 *
172 * @return the exit value of the process represented by this
173 * {@code Process} object. By convention, the value
174 * {@code 0} indicates normal termination.
175 * @throws InterruptedException if the current thread is
176 * {@linkplain Thread#interrupt() interrupted} by another
177 * thread while it is waiting, then the wait is ended and
178 * an {@link InterruptedException} is thrown.
179 */
180 public abstract int waitFor() throws InterruptedException;
181
182 /**
183 * Causes the current thread to wait, if necessary, until the
184 * process represented by this {@code Process} object has
185 * terminated, or the specified waiting time elapses.
186 *
187 * <p>If the process has already terminated then this method returns
188 * immediately with the value {@code true}. If the process has not
189 * terminated and the timeout value is less than, or equal to, zero, then
190 * this method returns immediately with the value {@code false}.
191 *
192 * <p>The default implementation of this methods polls the {@code exitValue}
193 * to check if the process has terminated. Concrete implementations of this
194 * class are strongly encouraged to override this method with a more
195 * efficient implementation.
196 *
197 * @param timeout the maximum time to wait
198 * @param unit the time unit of the {@code timeout} argument
199 * @return {@code true} if the process has exited and {@code false} if
200 * the waiting time elapsed before the process has exited.
201 * @throws InterruptedException if the current thread is interrupted
202 * while waiting.
203 * @throws NullPointerException if unit is null
204 * @since 1.8
205 */
206 public boolean waitFor(long timeout, TimeUnit unit)
207 throws InterruptedException
208 {
209 long startTime = System.nanoTime();
210 long rem = unit.toNanos(timeout);
211
212 do {
213 try {
214 exitValue();
215 return true;
216 } catch(IllegalThreadStateException ex) {
217 if (rem > 0)
218 Thread.sleep(
219 Math.min(TimeUnit.NANOSECONDS.toMillis(rem) + 1, 100));
220 }
221 rem = unit.toNanos(timeout) - (System.nanoTime() - startTime);
222 } while (rem > 0);
223 return false;
224 }
225
226 /**
227 * Returns the exit value for the process.
228 *
229 * @return the exit value of the process represented by this
230 * {@code Process} object. By convention, the value
231 * {@code 0} indicates normal termination.
232 * @throws IllegalThreadStateException if the process represented
233 * by this {@code Process} object has not yet terminated
234 */
235 public abstract int exitValue();
236
237 /**
238 * Kills the process.
239 * Whether the process represented by this {@code Process} object is
240 * {@linkplain #supportsNormalTermination normally terminated} or not is
241 * implementation dependent.
242 * Forcible process destruction is defined as the immediate termination of a
243 * process, whereas normal termination allows the process to shut down cleanly.
244 * If the process is not alive, no action is taken.
245 * <p>
246 * The {@link java.util.concurrent.CompletableFuture} from {@link #onExit} is
247 * {@linkplain java.util.concurrent.CompletableFuture#complete completed}
248 * when the process has terminated.
249 */
250 public abstract void destroy();
251
252 /**
253 * Kills the process forcibly. The process represented by this
254 * {@code Process} object is forcibly terminated.
255 * Forcible process destruction is defined as the immediate termination of a
256 * process, whereas normal termination allows the process to shut down cleanly.
257 * If the process is not alive, no action is taken.
258 * <p>
259 * The {@link java.util.concurrent.CompletableFuture} from {@link #onExit} is
260 * {@linkplain java.util.concurrent.CompletableFuture#complete completed}
261 * when the process has terminated.
262 * <p>
263 * Invoking this method on {@code Process} objects returned by
264 * {@link ProcessBuilder#start} and {@link Runtime#exec} forcibly terminate
265 * the process.
266 *
267 * @implSpec
268 * The default implementation of this method invokes {@link #destroy}
269 * and so may not forcibly terminate the process.
270 * @implNote
271 * Concrete implementations of this class are strongly encouraged to override
272 * this method with a compliant implementation.
273 * @apiNote
274 * The process may not terminate immediately.
275 * i.e. {@code isAlive()} may return true for a brief period
276 * after {@code destroyForcibly()} is called. This method
277 * may be chained to {@code waitFor()} if needed.
278 *
279 * @return the {@code Process} object representing the
280 * process forcibly destroyed
281 * @since 1.8
282 */
283 public Process destroyForcibly() {
284 destroy();
285 return this;
286 }
287
288 /**
289 * Returns {@code true} if the implementation of {@link #destroy} is to
290 * normally terminate the process,
291 * Returns {@code false} if the implementation of {@code destroy}
292 * forcibly and immediately terminates the process.
293 * <p>
294 * Invoking this method on {@code Process} objects returned by
295 * {@link ProcessBuilder#start} and {@link Runtime#exec} return
296 * {@code true} or {@code false} depending on the platform implementation.
297 *
298 * @implSpec
299 * This implementation throws an instance of
300 * {@link java.lang.UnsupportedOperationException} and performs no other action.
301 *
302 * @return {@code true} if the implementation of {@link #destroy} is to
303 * normally terminate the process;
304 * otherwise, {@link #destroy} forcibly terminates the process
305 * @throws UnsupportedOperationException if the Process implementation
306 * does not support this operation
307 * @since 9
308 */
309 public boolean supportsNormalTermination() {
310 throw new UnsupportedOperationException(this.getClass()
311 + ".supportsNormalTermination() not supported" );
312 }
313
314 /**
315 * Tests whether the process represented by this {@code Process} is
316 * alive.
317 *
318 * @return {@code true} if the process represented by this
319 * {@code Process} object has not yet terminated.
320 * @since 1.8
321 */
322 public boolean isAlive() {
323 try {
324 exitValue();
325 return false;
326 } catch(IllegalThreadStateException e) {
327 return true;
328 }
329 }
330
331 /**
332 * Returns the native process ID of the process.
333 * The native process ID is an identification number that the operating
334 * system assigns to the process.
335 *
336 * @implSpec
337 * The implementation of this method returns the process id as:
338 * {@link #toHandle toHandle().pid()}.
339 *
340 * @return the native process id of the process
341 * @throws UnsupportedOperationException if the Process implementation
342 * does not support this operation
343 * @since 9
344 */
345 public long pid() {
346 return toHandle().pid();
347 }
348
349 /**
350 * Returns a {@code CompletableFuture<Process>} for the termination of the Process.
351 * The {@link java.util.concurrent.CompletableFuture} provides the ability
352 * to trigger dependent functions or actions that may be run synchronously
353 * or asynchronously upon process termination.
354 * When the process has terminated the CompletableFuture is
355 * {@link java.util.concurrent.CompletableFuture#complete completed} regardless
356 * of the exit status of the process.
357 * <p>
358 * Calling {@code onExit().get()} waits for the process to terminate and returns
359 * the Process. The future can be used to check if the process is
360 * {@linkplain java.util.concurrent.CompletableFuture#isDone done} or to
361 * {@linkplain java.util.concurrent.CompletableFuture#get() wait} for it to terminate.
362 * {@linkplain java.util.concurrent.CompletableFuture#cancel(boolean) Cancelling}
363 * the CompletableFuture does not affect the Process.
364 * <p>
365 * Processes returned from {@link ProcessBuilder#start} override the
366 * default implementation to provide an efficient mechanism to wait
367 * for process exit.
368 *
369 * @apiNote
370 * Using {@link #onExit() onExit} is an alternative to
371 * {@link #waitFor() waitFor} that enables both additional concurrency
372 * and convenient access to the result of the Process.
373 * Lambda expressions can be used to evaluate the result of the Process
374 * execution.
375 * If there is other processing to be done before the value is used
376 * then {@linkplain #onExit onExit} is a convenient mechanism to
377 * free the current thread and block only if and when the value is needed.
378 * <br>
379 * For example, launching a process to compare two files and get a boolean if they are identical:
380 * <pre> {@code Process p = new ProcessBuilder("cmp", "f1", "f2").start();
381 * Future<Boolean> identical = p.onExit().thenApply(p1 -> p1.exitValue() == 0);
382 * ...
383 * if (identical.get()) { ... }
384 * }</pre>
385 *
386 * @implSpec
387 * This implementation executes {@link #waitFor()} in a separate thread
388 * repeatedly until it returns successfully. If the execution of
389 * {@code waitFor} is interrupted, the thread's interrupt status is preserved.
390 * <p>
391 * When {@link #waitFor()} returns successfully the CompletableFuture is
392 * {@linkplain java.util.concurrent.CompletableFuture#complete completed} regardless
393 * of the exit status of the process.
394 *
395 * This implementation may consume a lot of memory for thread stacks if a
396 * large number of processes are waited for concurrently.
397 * <p>
398 * External implementations should override this method and provide
399 * a more efficient implementation. For example, to delegate to the underlying
400 * process, it can do the following:
401 * <pre>{@code
402 * public CompletableFuture<Process> onExit() {
403 * return delegate.onExit().thenApply(p -> this);
404 * }
405 * }</pre>
406 * @apiNote
407 * The process may be observed to have terminated with {@link #isAlive}
408 * before the ComputableFuture is completed and dependent actions are invoked.
409 *
410 * @return a new {@code CompletableFuture<Process>} for the Process
411 *
412 * @since 9
413 */
414 public CompletableFuture<Process> onExit() {
415 return CompletableFuture.supplyAsync(this::waitForInternal);
416 }
417
418 /**
419 * Wait for the process to exit by calling {@code waitFor}.
420 * If the thread is interrupted, remember the interrupted state to
421 * be restored before returning. Use ForkJoinPool.ManagedBlocker
422 * so that the number of workers in case ForkJoinPool is used is
423 * compensated when the thread blocks in waitFor().
424 *
425 * @return the Process
426 */
427 private Process waitForInternal() {
428 boolean interrupted = false;
429 while (true) {
430 try {
431 ForkJoinPool.managedBlock(new ForkJoinPool.ManagedBlocker() {
432 @Override
433 public boolean block() throws InterruptedException {
434 waitFor();
435 return true;
436 }
437
438 @Override
439 public boolean isReleasable() {
440 return !isAlive();
441 }
442 });
443 break;
444 } catch (InterruptedException x) {
445 interrupted = true;
446 }
447 }
448 if (interrupted) {
449 Thread.currentThread().interrupt();
450 }
451 return this;
452 }
453
454 /**
455 * Returns a ProcessHandle for the Process.
456 *
457 * {@code Process} objects returned by {@link ProcessBuilder#start} and
458 * {@link Runtime#exec} implement {@code toHandle} as the equivalent of
459 * {@link ProcessHandle#of(long) ProcessHandle.of(pid)} including the
460 * check for a SecurityManager and {@code RuntimePermission("manageProcess")}.
461 *
462 * @implSpec
463 * This implementation throws an instance of
464 * {@link java.lang.UnsupportedOperationException} and performs no other action.
465 * Subclasses should override this method to provide a ProcessHandle for the
466 * process. The methods {@link #pid}, {@link #info}, {@link #children},
467 * and {@link #descendants}, unless overridden, operate on the ProcessHandle.
468 *
469 * @return Returns a ProcessHandle for the Process
470 * @throws UnsupportedOperationException if the Process implementation
471 * does not support this operation
472 * @throws SecurityException if a security manager has been installed and
473 * it denies RuntimePermission("manageProcess")
474 * @since 9
475 */
476 public ProcessHandle toHandle() {
477 throw new UnsupportedOperationException(this.getClass()
478 + ".toHandle() not supported");
479 }
480
481 /**
482 * Returns a snapshot of information about the process.
483 *
484 * <p> A {@link ProcessHandle.Info} instance has accessor methods
485 * that return information about the process if it is available.
486 *
487 * @implSpec
488 * This implementation returns information about the process as:
489 * {@link #toHandle toHandle().info()}.
490 *
491 * @return a snapshot of information about the process, always non-null
492 * @throws UnsupportedOperationException if the Process implementation
493 * does not support this operation
494 * @since 9
495 */
496 public ProcessHandle.Info info() {
497 return toHandle().info();
498 }
499
500 /**
501 * Returns a snapshot of the direct children of the process.
502 * The parent of a direct child process is the process.
503 * Typically, a process that is {@linkplain #isAlive not alive} has no children.
504 * <p>
505 * <em>Note that processes are created and terminate asynchronously.
506 * There is no guarantee that a process is {@linkplain #isAlive alive}.
507 * </em>
508 *
509 * @implSpec
510 * This implementation returns the direct children as:
511 * {@link #toHandle toHandle().children()}.
512 *
513 * @return a sequential Stream of ProcessHandles for processes that are
514 * direct children of the process
515 * @throws UnsupportedOperationException if the Process implementation
516 * does not support this operation
517 * @throws SecurityException if a security manager has been installed and
518 * it denies RuntimePermission("manageProcess")
519 * @since 9
520 */
521 public Stream<ProcessHandle> children() {
522 return toHandle().children();
523 }
524
525 /**
526 * Returns a snapshot of the descendants of the process.
527 * The descendants of a process are the children of the process
528 * plus the descendants of those children, recursively.
529 * Typically, a process that is {@linkplain #isAlive not alive} has no children.
530 * <p>
531 * <em>Note that processes are created and terminate asynchronously.
532 * There is no guarantee that a process is {@linkplain #isAlive alive}.
533 * </em>
534 *
535 * @implSpec
536 * This implementation returns all children as:
537 * {@link #toHandle toHandle().descendants()}.
538 *
539 * @return a sequential Stream of ProcessHandles for processes that
540 * are descendants of the process
541 * @throws UnsupportedOperationException if the Process implementation
542 * does not support this operation
543 * @throws SecurityException if a security manager has been installed and
544 * it denies RuntimePermission("manageProcess")
545 * @since 9
546 */
547 public Stream<ProcessHandle> descendants() {
548 return toHandle().descendants();
549 }
550
551 /**
552 * An input stream for a subprocess pipe that skips by reading bytes
553 * instead of seeking, the underlying pipe does not support seek.
554 */
555 static class PipeInputStream extends FileInputStream {
556
557 PipeInputStream(FileDescriptor fd) {
558 super(fd);
559 }
560
561 @Override
562 public long skip(long n) throws IOException {
563 long remaining = n;
564 int nr;
565
566 if (n <= 0) {
567 return 0;
568 }
569
570 int size = (int)Math.min(2048, remaining);
571 byte[] skipBuffer = new byte[size];
572 while (remaining > 0) {
573 nr = read(skipBuffer, 0, (int)Math.min(size, remaining));
574 if (nr < 0) {
575 break;
576 }
577 remaining -= nr;
578 }
579
580 return n - remaining;
581 }
582 }
583 }