rev 54134 : [mq]: 8220684-Process-waitFor-long-TimeUnit-can-return-false-for-a-process-that-exited-within-the-timeout

   1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
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  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).
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  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 }
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