1 /*
   2  * Copyright (c) 1995, 2006, 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.util.StringTokenizer;
  30 
  31 /**
  32  * Every Java application has a single instance of class
  33  * <code>Runtime</code> that allows the application to interface with
  34  * the environment in which the application is running. The current
  35  * runtime can be obtained from the <code>getRuntime</code> method.
  36  * <p>
  37  * An application cannot create its own instance of this class.
  38  *
  39  * @author  unascribed
  40  * @see     java.lang.Runtime#getRuntime()
  41  * @since   JDK1.0
  42  */
  43 
  44 public class Runtime {
  45     private static Runtime currentRuntime = new Runtime();
  46 
  47     /**
  48      * Returns the runtime object associated with the current Java application.
  49      * Most of the methods of class <code>Runtime</code> are instance
  50      * methods and must be invoked with respect to the current runtime object.
  51      *
  52      * @return  the <code>Runtime</code> object associated with the current
  53      *          Java application.
  54      */
  55     public static Runtime getRuntime() {
  56         return currentRuntime;
  57     }
  58 
  59     /** Don't let anyone else instantiate this class */
  60     private Runtime() {}
  61 
  62     /**
  63      * Terminates the currently running Java virtual machine by initiating its
  64      * shutdown sequence.  This method never returns normally.  The argument
  65      * serves as a status code; by convention, a nonzero status code indicates
  66      * abnormal termination.
  67      *
  68      * <p> The virtual machine's shutdown sequence consists of two phases.  In
  69      * the first phase all registered {@link #addShutdownHook shutdown hooks},
  70      * if any, are started in some unspecified order and allowed to run
  71      * concurrently until they finish.  In the second phase all uninvoked
  72      * finalizers are run if {@link #runFinalizersOnExit finalization-on-exit}
  73      * has been enabled.  Once this is done the virtual machine {@link #halt
  74      * halts}.
  75      *
  76      * <p> If this method is invoked after the virtual machine has begun its
  77      * shutdown sequence then if shutdown hooks are being run this method will
  78      * block indefinitely.  If shutdown hooks have already been run and on-exit
  79      * finalization has been enabled then this method halts the virtual machine
  80      * with the given status code if the status is nonzero; otherwise, it
  81      * blocks indefinitely.
  82      *
  83      * <p> The <tt>{@link System#exit(int) System.exit}</tt> method is the
  84      * conventional and convenient means of invoking this method. <p>
  85      *
  86      * @param  status
  87      *         Termination status.  By convention, a nonzero status code
  88      *         indicates abnormal termination.
  89      *
  90      * @throws SecurityException
  91      *         If a security manager is present and its <tt>{@link
  92      *         SecurityManager#checkExit checkExit}</tt> method does not permit
  93      *         exiting with the specified status
  94      *
  95      * @see java.lang.SecurityException
  96      * @see java.lang.SecurityManager#checkExit(int)
  97      * @see #addShutdownHook
  98      * @see #removeShutdownHook
  99      * @see #runFinalizersOnExit
 100      * @see #halt(int)
 101      */
 102     public void exit(int status) {
 103         SecurityManager security = System.getSecurityManager();
 104         if (security != null) {
 105             security.checkExit(status);
 106         }
 107         Shutdown.exit(status);
 108     }
 109 
 110     /**
 111      * Registers a new virtual-machine shutdown hook.
 112      *
 113      * <p> The Java virtual machine <i>shuts down</i> in response to two kinds
 114      * of events:
 115      *
 116      *   <ul>
 117      *
 118      *   <p> <li> The program <i>exits</i> normally, when the last non-daemon
 119      *   thread exits or when the <tt>{@link #exit exit}</tt> (equivalently,
 120      *   <tt>{@link System#exit(int) System.exit}</tt>) method is invoked, or
 121      *
 122      *   <p> <li> The virtual machine is <i>terminated</i> in response to a
 123      *   user interrupt, such as typing <tt>^C</tt>, or a system-wide event,
 124      *   such as user logoff or system shutdown.
 125      *
 126      *   </ul>
 127      *
 128      * <p> A <i>shutdown hook</i> is simply an initialized but unstarted
 129      * thread.  When the virtual machine begins its shutdown sequence it will
 130      * start all registered shutdown hooks in some unspecified order and let
 131      * them run concurrently.  When all the hooks have finished it will then
 132      * run all uninvoked finalizers if finalization-on-exit has been enabled.
 133      * Finally, the virtual machine will halt.  Note that daemon threads will
 134      * continue to run during the shutdown sequence, as will non-daemon threads
 135      * if shutdown was initiated by invoking the <tt>{@link #exit exit}</tt>
 136      * method.
 137      *
 138      * <p> Once the shutdown sequence has begun it can be stopped only by
 139      * invoking the <tt>{@link #halt halt}</tt> method, which forcibly
 140      * terminates the virtual machine.
 141      *
 142      * <p> Once the shutdown sequence has begun it is impossible to register a
 143      * new shutdown hook or de-register a previously-registered hook.
 144      * Attempting either of these operations will cause an
 145      * <tt>{@link IllegalStateException}</tt> to be thrown.
 146      *
 147      * <p> Shutdown hooks run at a delicate time in the life cycle of a virtual
 148      * machine and should therefore be coded defensively.  They should, in
 149      * particular, be written to be thread-safe and to avoid deadlocks insofar
 150      * as possible.  They should also not rely blindly upon services that may
 151      * have registered their own shutdown hooks and therefore may themselves in
 152      * the process of shutting down.  Attempts to use other thread-based
 153      * services such as the AWT event-dispatch thread, for example, may lead to
 154      * deadlocks.
 155      *
 156      * <p> Shutdown hooks should also finish their work quickly.  When a
 157      * program invokes <tt>{@link #exit exit}</tt> the expectation is
 158      * that the virtual machine will promptly shut down and exit.  When the
 159      * virtual machine is terminated due to user logoff or system shutdown the
 160      * underlying operating system may only allow a fixed amount of time in
 161      * which to shut down and exit.  It is therefore inadvisable to attempt any
 162      * user interaction or to perform a long-running computation in a shutdown
 163      * hook.
 164      *
 165      * <p> Uncaught exceptions are handled in shutdown hooks just as in any
 166      * other thread, by invoking the <tt>{@link ThreadGroup#uncaughtException
 167      * uncaughtException}</tt> method of the thread's <tt>{@link
 168      * ThreadGroup}</tt> object.  The default implementation of this method
 169      * prints the exception's stack trace to <tt>{@link System#err}</tt> and
 170      * terminates the thread; it does not cause the virtual machine to exit or
 171      * halt.
 172      *
 173      * <p> In rare circumstances the virtual machine may <i>abort</i>, that is,
 174      * stop running without shutting down cleanly.  This occurs when the
 175      * virtual machine is terminated externally, for example with the
 176      * <tt>SIGKILL</tt> signal on Unix or the <tt>TerminateProcess</tt> call on
 177      * Microsoft Windows.  The virtual machine may also abort if a native
 178      * method goes awry by, for example, corrupting internal data structures or
 179      * attempting to access nonexistent memory.  If the virtual machine aborts
 180      * then no guarantee can be made about whether or not any shutdown hooks
 181      * will be run. <p>
 182      *
 183      * @param   hook
 184      *          An initialized but unstarted <tt>{@link Thread}</tt> object
 185      *
 186      * @throws  IllegalArgumentException
 187      *          If the specified hook has already been registered,
 188      *          or if it can be determined that the hook is already running or
 189      *          has already been run
 190      *
 191      * @throws  IllegalStateException
 192      *          If the virtual machine is already in the process
 193      *          of shutting down
 194      *
 195      * @throws  SecurityException
 196      *          If a security manager is present and it denies
 197      *          <tt>{@link RuntimePermission}("shutdownHooks")</tt>
 198      *
 199      * @see #removeShutdownHook
 200      * @see #halt(int)
 201      * @see #exit(int)
 202      * @since 1.3
 203      */
 204     public void addShutdownHook(Thread hook) {
 205         SecurityManager sm = System.getSecurityManager();
 206         if (sm != null) {
 207             sm.checkPermission(new RuntimePermission("shutdownHooks"));
 208         }
 209         ApplicationShutdownHooks.add(hook);
 210     }
 211 
 212     /**
 213      * De-registers a previously-registered virtual-machine shutdown hook. <p>
 214      *
 215      * @param hook the hook to remove
 216      * @return <tt>true</tt> if the specified hook had previously been
 217      * registered and was successfully de-registered, <tt>false</tt>
 218      * otherwise.
 219      *
 220      * @throws  IllegalStateException
 221      *          If the virtual machine is already in the process of shutting
 222      *          down
 223      *
 224      * @throws  SecurityException
 225      *          If a security manager is present and it denies
 226      *          <tt>{@link RuntimePermission}("shutdownHooks")</tt>
 227      *
 228      * @see #addShutdownHook
 229      * @see #exit(int)
 230      * @since 1.3
 231      */
 232     public boolean removeShutdownHook(Thread hook) {
 233         SecurityManager sm = System.getSecurityManager();
 234         if (sm != null) {
 235             sm.checkPermission(new RuntimePermission("shutdownHooks"));
 236         }
 237         return ApplicationShutdownHooks.remove(hook);
 238     }
 239 
 240     /**
 241      * Forcibly terminates the currently running Java virtual machine.  This
 242      * method never returns normally.
 243      *
 244      * <p> This method should be used with extreme caution.  Unlike the
 245      * <tt>{@link #exit exit}</tt> method, this method does not cause shutdown
 246      * hooks to be started and does not run uninvoked finalizers if
 247      * finalization-on-exit has been enabled.  If the shutdown sequence has
 248      * already been initiated then this method does not wait for any running
 249      * shutdown hooks or finalizers to finish their work. <p>
 250      *
 251      * @param  status
 252      *         Termination status.  By convention, a nonzero status code
 253      *         indicates abnormal termination.  If the <tt>{@link Runtime#exit
 254      *         exit}</tt> (equivalently, <tt>{@link System#exit(int)
 255      *         System.exit}</tt>) method has already been invoked then this
 256      *         status code will override the status code passed to that method.
 257      *
 258      * @throws SecurityException
 259      *         If a security manager is present and its <tt>{@link
 260      *         SecurityManager#checkExit checkExit}</tt> method does not permit
 261      *         an exit with the specified status
 262      *
 263      * @see #exit
 264      * @see #addShutdownHook
 265      * @see #removeShutdownHook
 266      * @since 1.3
 267      */
 268     public void halt(int status) {
 269         SecurityManager sm = System.getSecurityManager();
 270         if (sm != null) {
 271             sm.checkExit(status);
 272         }
 273         Shutdown.halt(status);
 274     }
 275 
 276     /**
 277      * Enable or disable finalization on exit; doing so specifies that the
 278      * finalizers of all objects that have finalizers that have not yet been
 279      * automatically invoked are to be run before the Java runtime exits.
 280      * By default, finalization on exit is disabled.
 281      *
 282      * <p>If there is a security manager,
 283      * its <code>checkExit</code> method is first called
 284      * with 0 as its argument to ensure the exit is allowed.
 285      * This could result in a SecurityException.
 286      *
 287      * @param value true to enable finalization on exit, false to disable
 288      * @deprecated  This method is inherently unsafe.  It may result in
 289      *      finalizers being called on live objects while other threads are
 290      *      concurrently manipulating those objects, resulting in erratic
 291      *      behavior or deadlock.
 292      *
 293      * @throws  SecurityException
 294      *        if a security manager exists and its <code>checkExit</code>
 295      *        method doesn't allow the exit.
 296      *
 297      * @see     java.lang.Runtime#exit(int)
 298      * @see     java.lang.Runtime#gc()
 299      * @see     java.lang.SecurityManager#checkExit(int)
 300      * @since   JDK1.1
 301      */
 302     @Deprecated
 303     public static void runFinalizersOnExit(boolean value) {
 304         SecurityManager security = System.getSecurityManager();
 305         if (security != null) {
 306             try {
 307                 security.checkExit(0);
 308             } catch (SecurityException e) {
 309                 throw new SecurityException("runFinalizersOnExit");
 310             }
 311         }
 312         Shutdown.setRunFinalizersOnExit(value);
 313     }
 314 
 315     /**
 316      * Executes the specified string command in a separate process.
 317      *
 318      * <p>This is a convenience method.  An invocation of the form
 319      * <tt>exec(command)</tt>
 320      * behaves in exactly the same way as the invocation
 321      * <tt>{@link #exec(String, String[], File) exec}(command, null, null)</tt>.
 322      *
 323      * @param   command   a specified system command.
 324      *
 325      * @return  A new {@link Process} object for managing the subprocess
 326      *
 327      * @throws  SecurityException
 328      *          If a security manager exists and its
 329      *          {@link SecurityManager#checkExec checkExec}
 330      *          method doesn't allow creation of the subprocess
 331      *
 332      * @throws  IOException
 333      *          If an I/O error occurs
 334      *
 335      * @throws  NullPointerException
 336      *          If <code>command</code> is <code>null</code>
 337      *
 338      * @throws  IllegalArgumentException
 339      *          If <code>command</code> is empty
 340      *
 341      * @see     #exec(String[], String[], File)
 342      * @see     ProcessBuilder
 343      */
 344     public Process exec(String command) throws IOException {
 345         return exec(command, null, null);
 346     }
 347 
 348     /**
 349      * Executes the specified string command in a separate process with the
 350      * specified environment.
 351      *
 352      * <p>This is a convenience method.  An invocation of the form
 353      * <tt>exec(command, envp)</tt>
 354      * behaves in exactly the same way as the invocation
 355      * <tt>{@link #exec(String, String[], File) exec}(command, envp, null)</tt>.
 356      *
 357      * @param   command   a specified system command.
 358      *
 359      * @param   envp      array of strings, each element of which
 360      *                    has environment variable settings in the format
 361      *                    <i>name</i>=<i>value</i>, or
 362      *                    <tt>null</tt> if the subprocess should inherit
 363      *                    the environment of the current process.
 364      *
 365      * @return  A new {@link Process} object for managing the subprocess
 366      *
 367      * @throws  SecurityException
 368      *          If a security manager exists and its
 369      *          {@link SecurityManager#checkExec checkExec}
 370      *          method doesn't allow creation of the subprocess
 371      *
 372      * @throws  IOException
 373      *          If an I/O error occurs
 374      *
 375      * @throws  NullPointerException
 376      *          If <code>command</code> is <code>null</code>,
 377      *          or one of the elements of <code>envp</code> is <code>null</code>
 378      *
 379      * @throws  IllegalArgumentException
 380      *          If <code>command</code> is empty
 381      *
 382      * @see     #exec(String[], String[], File)
 383      * @see     ProcessBuilder
 384      */
 385     public Process exec(String command, String[] envp) throws IOException {
 386         return exec(command, envp, null);
 387     }
 388 
 389     /**
 390      * Executes the specified string command in a separate process with the
 391      * specified environment and working directory.
 392      *
 393      * <p>This is a convenience method.  An invocation of the form
 394      * <tt>exec(command, envp, dir)</tt>
 395      * behaves in exactly the same way as the invocation
 396      * <tt>{@link #exec(String[], String[], File) exec}(cmdarray, envp, dir)</tt>,
 397      * where <code>cmdarray</code> is an array of all the tokens in
 398      * <code>command</code>.
 399      *
 400      * <p>More precisely, the <code>command</code> string is broken
 401      * into tokens using a {@link StringTokenizer} created by the call
 402      * <code>new {@link StringTokenizer}(command)</code> with no
 403      * further modification of the character categories.  The tokens
 404      * produced by the tokenizer are then placed in the new string
 405      * array <code>cmdarray</code>, in the same order.
 406      *
 407      * @param   command   a specified system command.
 408      *
 409      * @param   envp      array of strings, each element of which
 410      *                    has environment variable settings in the format
 411      *                    <i>name</i>=<i>value</i>, or
 412      *                    <tt>null</tt> if the subprocess should inherit
 413      *                    the environment of the current process.
 414      *
 415      * @param   dir       the working directory of the subprocess, or
 416      *                    <tt>null</tt> if the subprocess should inherit
 417      *                    the working directory of the current process.
 418      *
 419      * @return  A new {@link Process} object for managing the subprocess
 420      *
 421      * @throws  SecurityException
 422      *          If a security manager exists and its
 423      *          {@link SecurityManager#checkExec checkExec}
 424      *          method doesn't allow creation of the subprocess
 425      *
 426      * @throws  IOException
 427      *          If an I/O error occurs
 428      *
 429      * @throws  NullPointerException
 430      *          If <code>command</code> is <code>null</code>,
 431      *          or one of the elements of <code>envp</code> is <code>null</code>
 432      *
 433      * @throws  IllegalArgumentException
 434      *          If <code>command</code> is empty
 435      *
 436      * @see     ProcessBuilder
 437      * @since 1.3
 438      */
 439     public Process exec(String command, String[] envp, File dir)
 440         throws IOException {
 441         if (command.length() == 0)
 442             throw new IllegalArgumentException("Empty command");
 443 
 444         StringTokenizer st = new StringTokenizer(command);
 445         String[] cmdarray = new String[st.countTokens()];
 446         for (int i = 0; st.hasMoreTokens(); i++)
 447             cmdarray[i] = st.nextToken();
 448         return exec(cmdarray, envp, dir);
 449     }
 450 
 451     /**
 452      * Executes the specified command and arguments in a separate process.
 453      *
 454      * <p>This is a convenience method.  An invocation of the form
 455      * <tt>exec(cmdarray)</tt>
 456      * behaves in exactly the same way as the invocation
 457      * <tt>{@link #exec(String[], String[], File) exec}(cmdarray, null, null)</tt>.
 458      *
 459      * @param   cmdarray  array containing the command to call and
 460      *                    its arguments.
 461      *
 462      * @return  A new {@link Process} object for managing the subprocess
 463      *
 464      * @throws  SecurityException
 465      *          If a security manager exists and its
 466      *          {@link SecurityManager#checkExec checkExec}
 467      *          method doesn't allow creation of the subprocess
 468      *
 469      * @throws  IOException
 470      *          If an I/O error occurs
 471      *
 472      * @throws  NullPointerException
 473      *          If <code>cmdarray</code> is <code>null</code>,
 474      *          or one of the elements of <code>cmdarray</code> is <code>null</code>
 475      *
 476      * @throws  IndexOutOfBoundsException
 477      *          If <code>cmdarray</code> is an empty array
 478      *          (has length <code>0</code>)
 479      *
 480      * @see     ProcessBuilder
 481      */
 482     public Process exec(String cmdarray[]) throws IOException {
 483         return exec(cmdarray, null, null);
 484     }
 485 
 486     /**
 487      * Executes the specified command and arguments in a separate process
 488      * with the specified environment.
 489      *
 490      * <p>This is a convenience method.  An invocation of the form
 491      * <tt>exec(cmdarray, envp)</tt>
 492      * behaves in exactly the same way as the invocation
 493      * <tt>{@link #exec(String[], String[], File) exec}(cmdarray, envp, null)</tt>.
 494      *
 495      * @param   cmdarray  array containing the command to call and
 496      *                    its arguments.
 497      *
 498      * @param   envp      array of strings, each element of which
 499      *                    has environment variable settings in the format
 500      *                    <i>name</i>=<i>value</i>, or
 501      *                    <tt>null</tt> if the subprocess should inherit
 502      *                    the environment of the current process.
 503      *
 504      * @return  A new {@link Process} object for managing the subprocess
 505      *
 506      * @throws  SecurityException
 507      *          If a security manager exists and its
 508      *          {@link SecurityManager#checkExec checkExec}
 509      *          method doesn't allow creation of the subprocess
 510      *
 511      * @throws  IOException
 512      *          If an I/O error occurs
 513      *
 514      * @throws  NullPointerException
 515      *          If <code>cmdarray</code> is <code>null</code>,
 516      *          or one of the elements of <code>cmdarray</code> is <code>null</code>,
 517      *          or one of the elements of <code>envp</code> is <code>null</code>
 518      *
 519      * @throws  IndexOutOfBoundsException
 520      *          If <code>cmdarray</code> is an empty array
 521      *          (has length <code>0</code>)
 522      *
 523      * @see     ProcessBuilder
 524      */
 525     public Process exec(String[] cmdarray, String[] envp) throws IOException {
 526         return exec(cmdarray, envp, null);
 527     }
 528 
 529 
 530     /**
 531      * Executes the specified command and arguments in a separate process with
 532      * the specified environment and working directory.
 533      *
 534      * <p>Given an array of strings <code>cmdarray</code>, representing the
 535      * tokens of a command line, and an array of strings <code>envp</code>,
 536      * representing "environment" variable settings, this method creates
 537      * a new process in which to execute the specified command.
 538      *
 539      * <p>This method checks that <code>cmdarray</code> is a valid operating
 540      * system command.  Which commands are valid is system-dependent,
 541      * but at the very least the command must be a non-empty list of
 542      * non-null strings.
 543      *
 544      * <p>If <tt>envp</tt> is <tt>null</tt>, the subprocess inherits the
 545      * environment settings of the current process.
 546      *
 547      * <p>A minimal set of system dependent environment variables may
 548      * be required to start a process on some operating systems.
 549      * As a result, the subprocess may inherit additional environment variable
 550      * settings beyond those in the specified environment.
 551      *
 552      * <p>{@link ProcessBuilder#start()} is now the preferred way to
 553      * start a process with a modified environment.
 554      *
 555      * <p>The working directory of the new subprocess is specified by <tt>dir</tt>.
 556      * If <tt>dir</tt> is <tt>null</tt>, the subprocess inherits the
 557      * current working directory of the current process.
 558      *
 559      * <p>If a security manager exists, its
 560      * {@link SecurityManager#checkExec checkExec}
 561      * method is invoked with the first component of the array
 562      * <code>cmdarray</code> as its argument. This may result in a
 563      * {@link SecurityException} being thrown.
 564      *
 565      * <p>Starting an operating system process is highly system-dependent.
 566      * Among the many things that can go wrong are:
 567      * <ul>
 568      * <li>The operating system program file was not found.
 569      * <li>Access to the program file was denied.
 570      * <li>The working directory does not exist.
 571      * </ul>
 572      *
 573      * <p>In such cases an exception will be thrown.  The exact nature
 574      * of the exception is system-dependent, but it will always be a
 575      * subclass of {@link IOException}.
 576      *
 577      *
 578      * @param   cmdarray  array containing the command to call and
 579      *                    its arguments.
 580      *
 581      * @param   envp      array of strings, each element of which
 582      *                    has environment variable settings in the format
 583      *                    <i>name</i>=<i>value</i>, or
 584      *                    <tt>null</tt> if the subprocess should inherit
 585      *                    the environment of the current process.
 586      *
 587      * @param   dir       the working directory of the subprocess, or
 588      *                    <tt>null</tt> if the subprocess should inherit
 589      *                    the working directory of the current process.
 590      *
 591      * @return  A new {@link Process} object for managing the subprocess
 592      *
 593      * @throws  SecurityException
 594      *          If a security manager exists and its
 595      *          {@link SecurityManager#checkExec checkExec}
 596      *          method doesn't allow creation of the subprocess
 597      *
 598      * @throws  IOException
 599      *          If an I/O error occurs
 600      *
 601      * @throws  NullPointerException
 602      *          If <code>cmdarray</code> is <code>null</code>,
 603      *          or one of the elements of <code>cmdarray</code> is <code>null</code>,
 604      *          or one of the elements of <code>envp</code> is <code>null</code>
 605      *
 606      * @throws  IndexOutOfBoundsException
 607      *          If <code>cmdarray</code> is an empty array
 608      *          (has length <code>0</code>)
 609      *
 610      * @see     ProcessBuilder
 611      * @since 1.3
 612      */
 613     public Process exec(String[] cmdarray, String[] envp, File dir)
 614         throws IOException {
 615         return new ProcessBuilder(cmdarray)
 616             .environment(envp)
 617             .directory(dir)
 618             .start();
 619     }
 620 
 621     /**
 622      * Returns the number of processors available to the Java virtual machine.
 623      *
 624      * <p> This value may change during a particular invocation of the virtual
 625      * machine.  Applications that are sensitive to the number of available
 626      * processors should therefore occasionally poll this property and adjust
 627      * their resource usage appropriately. </p>
 628      *
 629      * @return  the maximum number of processors available to the virtual
 630      *          machine; never smaller than one
 631      * @since 1.4
 632      */
 633     public native int availableProcessors();
 634 
 635     /**
 636      * Returns the amount of free memory in the Java Virtual Machine.
 637      * Calling the
 638      * <code>gc</code> method may result in increasing the value returned
 639      * by <code>freeMemory.</code>
 640      *
 641      * @return  an approximation to the total amount of memory currently
 642      *          available for future allocated objects, measured in bytes.
 643      */
 644     public native long freeMemory();
 645 
 646     /**
 647      * Returns the total amount of memory in the Java virtual machine.
 648      * The value returned by this method may vary over time, depending on
 649      * the host environment.
 650      * <p>
 651      * Note that the amount of memory required to hold an object of any
 652      * given type may be implementation-dependent.
 653      *
 654      * @return  the total amount of memory currently available for current
 655      *          and future objects, measured in bytes.
 656      */
 657     public native long totalMemory();
 658 
 659     /**
 660      * Returns the maximum amount of memory that the Java virtual machine will
 661      * attempt to use.  If there is no inherent limit then the value {@link
 662      * java.lang.Long#MAX_VALUE} will be returned. </p>
 663      *
 664      * @return  the maximum amount of memory that the virtual machine will
 665      *          attempt to use, measured in bytes
 666      * @since 1.4
 667      */
 668     public native long maxMemory();
 669 
 670     /**
 671      * Runs the garbage collector.
 672      * Calling this method suggests that the Java virtual machine expend
 673      * effort toward recycling unused objects in order to make the memory
 674      * they currently occupy available for quick reuse. When control
 675      * returns from the method call, the virtual machine has made
 676      * its best effort to recycle all discarded objects.
 677      * <p>
 678      * The name <code>gc</code> stands for "garbage
 679      * collector". The virtual machine performs this recycling
 680      * process automatically as needed, in a separate thread, even if the
 681      * <code>gc</code> method is not invoked explicitly.
 682      * <p>
 683      * The method {@link System#gc()} is the conventional and convenient
 684      * means of invoking this method.
 685      */
 686     public native void gc();
 687 
 688     /* Wormhole for calling java.lang.ref.Finalizer.runFinalization */
 689     private static native void runFinalization0();
 690 
 691     /**
 692      * Runs the finalization methods of any objects pending finalization.
 693      * Calling this method suggests that the Java virtual machine expend
 694      * effort toward running the <code>finalize</code> methods of objects
 695      * that have been found to be discarded but whose <code>finalize</code>
 696      * methods have not yet been run. When control returns from the
 697      * method call, the virtual machine has made a best effort to
 698      * complete all outstanding finalizations.
 699      * <p>
 700      * The virtual machine performs the finalization process
 701      * automatically as needed, in a separate thread, if the
 702      * <code>runFinalization</code> method is not invoked explicitly.
 703      * <p>
 704      * The method {@link System#runFinalization()} is the conventional
 705      * and convenient means of invoking this method.
 706      *
 707      * @see     java.lang.Object#finalize()
 708      */
 709     public void runFinalization() {
 710         runFinalization0();
 711     }
 712 
 713     /**
 714      * Enables/Disables tracing of instructions.
 715      * If the <code>boolean</code> argument is <code>true</code>, this
 716      * method suggests that the Java virtual machine emit debugging
 717      * information for each instruction in the virtual machine as it
 718      * is executed. The format of this information, and the file or other
 719      * output stream to which it is emitted, depends on the host environment.
 720      * The virtual machine may ignore this request if it does not support
 721      * this feature. The destination of the trace output is system
 722      * dependent.
 723      * <p>
 724      * If the <code>boolean</code> argument is <code>false</code>, this
 725      * method causes the virtual machine to stop performing the
 726      * detailed instruction trace it is performing.
 727      *
 728      * @param   on   <code>true</code> to enable instruction tracing;
 729      *               <code>false</code> to disable this feature.
 730      */
 731     public native void traceInstructions(boolean on);
 732 
 733     /**
 734      * Enables/Disables tracing of method calls.
 735      * If the <code>boolean</code> argument is <code>true</code>, this
 736      * method suggests that the Java virtual machine emit debugging
 737      * information for each method in the virtual machine as it is
 738      * called. The format of this information, and the file or other output
 739      * stream to which it is emitted, depends on the host environment. The
 740      * virtual machine may ignore this request if it does not support
 741      * this feature.
 742      * <p>
 743      * Calling this method with argument false suggests that the
 744      * virtual machine cease emitting per-call debugging information.
 745      *
 746      * @param   on   <code>true</code> to enable instruction tracing;
 747      *               <code>false</code> to disable this feature.
 748      */
 749     public native void traceMethodCalls(boolean on);
 750 
 751     /**
 752      * Loads the specified filename as a dynamic library. The filename
 753      * argument must be a complete path name,
 754      * (for example
 755      * <code>Runtime.getRuntime().load("/home/avh/lib/libX11.so");</code>).
 756      * <p>
 757      * First, if there is a security manager, its <code>checkLink</code>
 758      * method is called with the <code>filename</code> as its argument.
 759      * This may result in a security exception.
 760      * <p>
 761      * This is similar to the method {@link #loadLibrary(String)}, but it
 762      * accepts a general file name as an argument rather than just a library
 763      * name, allowing any file of native code to be loaded.
 764      * <p>
 765      * The method {@link System#load(String)} is the conventional and
 766      * convenient means of invoking this method.
 767      *
 768      * @param      filename   the file to load.
 769      * @exception  SecurityException  if a security manager exists and its
 770      *             <code>checkLink</code> method doesn't allow
 771      *             loading of the specified dynamic library
 772      * @exception  UnsatisfiedLinkError  if the file does not exist.
 773      * @exception  NullPointerException if <code>filename</code> is
 774      *             <code>null</code>
 775      * @see        java.lang.Runtime#getRuntime()
 776      * @see        java.lang.SecurityException
 777      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
 778      */
 779     public void load(String filename) {
 780         load0(System.getCallerClass(), filename);
 781     }
 782 
 783     synchronized void load0(Class<?> fromClass, String filename) {
 784         SecurityManager security = System.getSecurityManager();
 785         if (security != null) {
 786             security.checkLink(filename);
 787         }
 788         if (!(new File(filename).isAbsolute())) {
 789             throw new UnsatisfiedLinkError(
 790                 "Expecting an absolute path of the library: " + filename);
 791         }
 792         ClassLoader.loadLibrary(fromClass, filename, true);
 793     }
 794 
 795     /**
 796      * Loads the dynamic library with the specified library name.
 797      * A file containing native code is loaded from the local file system
 798      * from a place where library files are conventionally obtained. The
 799      * details of this process are implementation-dependent. The
 800      * mapping from a library name to a specific filename is done in a
 801      * system-specific manner.
 802      * <p>
 803      * First, if there is a security manager, its <code>checkLink</code>
 804      * method is called with the <code>libname</code> as its argument.
 805      * This may result in a security exception.
 806      * <p>
 807      * The method {@link System#loadLibrary(String)} is the conventional
 808      * and convenient means of invoking this method. If native
 809      * methods are to be used in the implementation of a class, a standard
 810      * strategy is to put the native code in a library file (call it
 811      * <code>LibFile</code>) and then to put a static initializer:
 812      * <blockquote><pre>
 813      * static { System.loadLibrary("LibFile"); }
 814      * </pre></blockquote>
 815      * within the class declaration. When the class is loaded and
 816      * initialized, the necessary native code implementation for the native
 817      * methods will then be loaded as well.
 818      * <p>
 819      * If this method is called more than once with the same library
 820      * name, the second and subsequent calls are ignored.
 821      *
 822      * @param      libname   the name of the library.
 823      * @exception  SecurityException  if a security manager exists and its
 824      *             <code>checkLink</code> method doesn't allow
 825      *             loading of the specified dynamic library
 826      * @exception  UnsatisfiedLinkError  if the library does not exist.
 827      * @exception  NullPointerException if <code>libname</code> is
 828      *             <code>null</code>
 829      * @see        java.lang.SecurityException
 830      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
 831      */
 832     public void loadLibrary(String libname) {
 833         loadLibrary0(System.getCallerClass(), libname);
 834     }
 835 
 836     synchronized void loadLibrary0(Class<?> fromClass, String libname) {
 837         SecurityManager security = System.getSecurityManager();
 838         if (security != null) {
 839             security.checkLink(libname);
 840         }
 841         if (libname.indexOf((int)File.separatorChar) != -1) {
 842             throw new UnsatisfiedLinkError(
 843     "Directory separator should not appear in library name: " + libname);
 844         }
 845         ClassLoader.loadLibrary(fromClass, libname, false);
 846     }
 847 
 848     /**
 849      * Creates a localized version of an input stream. This method takes
 850      * an <code>InputStream</code> and returns an <code>InputStream</code>
 851      * equivalent to the argument in all respects except that it is
 852      * localized: as characters in the local character set are read from
 853      * the stream, they are automatically converted from the local
 854      * character set to Unicode.
 855      * <p>
 856      * If the argument is already a localized stream, it may be returned
 857      * as the result.
 858      *
 859      * @param      in InputStream to localize
 860      * @return     a localized input stream
 861      * @see        java.io.InputStream
 862      * @see        java.io.BufferedReader#BufferedReader(java.io.Reader)
 863      * @see        java.io.InputStreamReader#InputStreamReader(java.io.InputStream)
 864      * @deprecated As of JDK&nbsp;1.1, the preferred way to translate a byte
 865      * stream in the local encoding into a character stream in Unicode is via
 866      * the <code>InputStreamReader</code> and <code>BufferedReader</code>
 867      * classes.
 868      */
 869     @Deprecated
 870     public InputStream getLocalizedInputStream(InputStream in) {
 871         return in;
 872     }
 873 
 874     /**
 875      * Creates a localized version of an output stream. This method
 876      * takes an <code>OutputStream</code> and returns an
 877      * <code>OutputStream</code> equivalent to the argument in all respects
 878      * except that it is localized: as Unicode characters are written to
 879      * the stream, they are automatically converted to the local
 880      * character set.
 881      * <p>
 882      * If the argument is already a localized stream, it may be returned
 883      * as the result.
 884      *
 885      * @deprecated As of JDK&nbsp;1.1, the preferred way to translate a
 886      * Unicode character stream into a byte stream in the local encoding is via
 887      * the <code>OutputStreamWriter</code>, <code>BufferedWriter</code>, and
 888      * <code>PrintWriter</code> classes.
 889      *
 890      * @param      out OutputStream to localize
 891      * @return     a localized output stream
 892      * @see        java.io.OutputStream
 893      * @see        java.io.BufferedWriter#BufferedWriter(java.io.Writer)
 894      * @see        java.io.OutputStreamWriter#OutputStreamWriter(java.io.OutputStream)
 895      * @see        java.io.PrintWriter#PrintWriter(java.io.OutputStream)
 896      */
 897     @Deprecated
 898     public OutputStream getLocalizedOutputStream(OutputStream out) {
 899         return out;
 900     }
 901 
 902 }