1 /*
   2  * Copyright (c) 1995, 2014, 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 import sun.reflect.CallerSensitive;
  31 import sun.reflect.Reflection;
  32 
  33 /**
  34  * Every Java application has a single instance of class
  35  * {@code Runtime} that allows the application to interface with
  36  * the environment in which the application is running. The current
  37  * runtime can be obtained from the {@code getRuntime} method.
  38  * <p>
  39  * An application cannot create its own instance of this class.
  40  *
  41  * @author  unascribed
  42  * @see     java.lang.Runtime#getRuntime()
  43  * @since   1.0
  44  */
  45 
  46 public class Runtime {
  47     private static final Runtime currentRuntime = new Runtime();
  48 
  49     /**
  50      * Returns the runtime object associated with the current Java application.
  51      * Most of the methods of class {@code Runtime} are instance
  52      * methods and must be invoked with respect to the current runtime object.
  53      *
  54      * @return  the {@code Runtime} object associated with the current
  55      *          Java application.
  56      */
  57     public static Runtime getRuntime() {
  58         return currentRuntime;
  59     }
  60 
  61     /** Don't let anyone else instantiate this class */
  62     private Runtime() {}
  63 
  64     /**
  65      * Terminates the currently running Java virtual machine by initiating its
  66      * shutdown sequence.  This method never returns normally.  The argument
  67      * serves as a status code; by convention, a nonzero status code indicates
  68      * abnormal termination.
  69      *
  70      * <p> The virtual machine's shutdown sequence consists of two phases.  In
  71      * the first phase all registered {@link #addShutdownHook shutdown hooks},
  72      * if any, are started in some unspecified order and allowed to run
  73      * concurrently until they finish.  In the second phase all uninvoked
  74      * finalizers are run if {@link #runFinalizersOnExit finalization-on-exit}
  75      * has been enabled.  Once this is done the virtual machine {@link #halt halts}.
  76      *
  77      * <p> If this method is invoked after the virtual machine has begun its
  78      * shutdown sequence then if shutdown hooks are being run this method will
  79      * block indefinitely.  If shutdown hooks have already been run and on-exit
  80      * finalization has been enabled then this method halts the virtual machine
  81      * with the given status code if the status is nonzero; otherwise, it
  82      * blocks indefinitely.
  83      *
  84      * <p> The {@link System#exit(int) System.exit} method is the
  85      * conventional and convenient means of invoking this method.
  86      *
  87      * @param  status
  88      *         Termination status.  By convention, a nonzero status code
  89      *         indicates abnormal termination.
  90      *
  91      * @throws SecurityException
  92      *         If a security manager is present and its
  93      *         {@link SecurityManager#checkExit checkExit} method does not permit
  94      *         exiting with the specified status
  95      *
  96      * @see java.lang.SecurityException
  97      * @see java.lang.SecurityManager#checkExit(int)
  98      * @see #addShutdownHook
  99      * @see #removeShutdownHook
 100      * @see #runFinalizersOnExit
 101      * @see #halt(int)
 102      */
 103     public void exit(int status) {
 104         SecurityManager security = System.getSecurityManager();
 105         if (security != null) {
 106             security.checkExit(status);
 107         }
 108         Shutdown.exit(status);
 109     }
 110 
 111     /**
 112      * Registers a new virtual-machine shutdown hook.
 113      *
 114      * <p> The Java virtual machine <i>shuts down</i> in response to two kinds
 115      * of events:
 116      *
 117      *   <ul>
 118      *
 119      *   <li> The program <i>exits</i> normally, when the last non-daemon
 120      *   thread exits or when the {@link #exit exit} (equivalently,
 121      *   {@link System#exit(int) System.exit}) method is invoked, or
 122      *
 123      *   <li> The virtual machine is <i>terminated</i> in response to a
 124      *   user interrupt, such as typing {@code ^C}, or a system-wide event,
 125      *   such as user logoff or system shutdown.
 126      *
 127      *   </ul>
 128      *
 129      * <p> A <i>shutdown hook</i> is simply an initialized but unstarted
 130      * thread.  When the virtual machine begins its shutdown sequence it will
 131      * start all registered shutdown hooks in some unspecified order and let
 132      * them run concurrently.  When all the hooks have finished it will then
 133      * run all uninvoked finalizers if finalization-on-exit has been enabled.
 134      * Finally, the virtual machine will halt.  Note that daemon threads will
 135      * continue to run during the shutdown sequence, as will non-daemon threads
 136      * if shutdown was initiated by invoking the {@link #exit exit} method.
 137      *
 138      * <p> Once the shutdown sequence has begun it can be stopped only by
 139      * invoking the {@link #halt halt} 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      * {@link IllegalStateException} 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 {@link #exit exit} 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
 167      * {@link ThreadGroup#uncaughtException uncaughtException} method of the
 168      * thread's {@link ThreadGroup} object. The default implementation of this
 169      * method prints the exception's stack trace to {@link System#err} 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      * {@code SIGKILL} signal on Unix or the {@code TerminateProcess} 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.
 182      *
 183      * @param   hook
 184      *          An initialized but unstarted {@link Thread} 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      *          {@link RuntimePermission}("shutdownHooks")
 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.
 214      *
 215      * @param hook the hook to remove
 216      * @return {@code true} if the specified hook had previously been
 217      * registered and was successfully de-registered, {@code false}
 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      *          {@link RuntimePermission}("shutdownHooks")
 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      * {@link #exit exit} 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.
 250      *
 251      * @param  status
 252      *         Termination status. By convention, a nonzero status code
 253      *         indicates abnormal termination. If the {@link Runtime#exit exit}
 254      *         (equivalently, {@link System#exit(int) System.exit}) method
 255      *         has already been invoked then this status code
 256      *         will override the status code passed to that method.
 257      *
 258      * @throws SecurityException
 259      *         If a security manager is present and its
 260      *         {@link SecurityManager#checkExit checkExit} method
 261      *         does not permit 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} 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}
 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   1.1
 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      * {@code exec(command)}
 320      * behaves in exactly the same way as the invocation
 321      * {@link #exec(String, String[], File) exec}{@code (command, null, null)}.
 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} is {@code null}
 337      *
 338      * @throws  IllegalArgumentException
 339      *          If {@code command} 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      * {@code exec(command, envp)}
 354      * behaves in exactly the same way as the invocation
 355      * {@link #exec(String, String[], File) exec}{@code (command, envp, null)}.
 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      *                    {@code null} 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} is {@code null},
 377      *          or one of the elements of {@code envp} is {@code null}
 378      *
 379      * @throws  IllegalArgumentException
 380      *          If {@code command} 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      * {@code exec(command, envp, dir)}
 395      * behaves in exactly the same way as the invocation
 396      * {@link #exec(String[], String[], File) exec}{@code (cmdarray, envp, dir)},
 397      * where {@code cmdarray} is an array of all the tokens in
 398      * {@code command}.
 399      *
 400      * <p>More precisely, the {@code command} string is broken
 401      * into tokens using a {@link StringTokenizer} created by the call
 402      * {@code new {@link StringTokenizer}(command)} 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}, 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      *                    {@code null} if the subprocess should inherit
 413      *                    the environment of the current process.
 414      *
 415      * @param   dir       the working directory of the subprocess, or
 416      *                    {@code null} 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} is {@code null},
 431      *          or one of the elements of {@code envp} is {@code null}
 432      *
 433      * @throws  IllegalArgumentException
 434      *          If {@code command} 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      * {@code exec(cmdarray)}
 456      * behaves in exactly the same way as the invocation
 457      * {@link #exec(String[], String[], File) exec}{@code (cmdarray, null, null)}.
 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} is {@code null},
 474      *          or one of the elements of {@code cmdarray} is {@code null}
 475      *
 476      * @throws  IndexOutOfBoundsException
 477      *          If {@code cmdarray} is an empty array
 478      *          (has length {@code 0})
 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      * {@code exec(cmdarray, envp)}
 492      * behaves in exactly the same way as the invocation
 493      * {@link #exec(String[], String[], File) exec}{@code (cmdarray, envp, null)}.
 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      *                    {@code null} 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} is {@code null},
 516      *          or one of the elements of {@code cmdarray} is {@code null},
 517      *          or one of the elements of {@code envp} is {@code null}
 518      *
 519      * @throws  IndexOutOfBoundsException
 520      *          If {@code cmdarray} is an empty array
 521      *          (has length {@code 0})
 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}, representing the
 535      * tokens of a command line, and an array of strings {@code envp},
 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} 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 {@code envp} is {@code null}, 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 {@code dir}.
 556      * If {@code dir} is {@code null}, 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} 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      * <p>If the operating system does not support the creation of
 578      * processes, an {@link UnsupportedOperationException} will be thrown.
 579      *
 580      *
 581      * @param   cmdarray  array containing the command to call and
 582      *                    its arguments.
 583      *
 584      * @param   envp      array of strings, each element of which
 585      *                    has environment variable settings in the format
 586      *                    <i>name</i>=<i>value</i>, or
 587      *                    {@code null} if the subprocess should inherit
 588      *                    the environment of the current process.
 589      *
 590      * @param   dir       the working directory of the subprocess, or
 591      *                    {@code null} if the subprocess should inherit
 592      *                    the working directory of the current process.
 593      *
 594      * @return  A new {@link Process} object for managing the subprocess
 595      *
 596      * @throws  SecurityException
 597      *          If a security manager exists and its
 598      *          {@link SecurityManager#checkExec checkExec}
 599      *          method doesn't allow creation of the subprocess
 600      *
 601      * @throws  UnsupportedOperationException
 602      *          If the operating system does not support the creation of processes.
 603      *
 604      * @throws  IOException
 605      *          If an I/O error occurs
 606      *
 607      * @throws  NullPointerException
 608      *          If {@code cmdarray} is {@code null},
 609      *          or one of the elements of {@code cmdarray} is {@code null},
 610      *          or one of the elements of {@code envp} is {@code null}
 611      *
 612      * @throws  IndexOutOfBoundsException
 613      *          If {@code cmdarray} is an empty array
 614      *          (has length {@code 0})
 615      *
 616      * @see     ProcessBuilder
 617      * @since 1.3
 618      */
 619     public Process exec(String[] cmdarray, String[] envp, File dir)
 620         throws IOException {
 621         return new ProcessBuilder(cmdarray)
 622             .environment(envp)
 623             .directory(dir)
 624             .start();
 625     }
 626 
 627     /**
 628      * Returns the number of processors available to the Java virtual machine.
 629      *
 630      * <p> This value may change during a particular invocation of the virtual
 631      * machine.  Applications that are sensitive to the number of available
 632      * processors should therefore occasionally poll this property and adjust
 633      * their resource usage appropriately. </p>
 634      *
 635      * @return  the maximum number of processors available to the virtual
 636      *          machine; never smaller than one
 637      * @since 1.4
 638      */
 639     public native int availableProcessors();
 640 
 641     /**
 642      * Returns the amount of free memory in the Java Virtual Machine.
 643      * Calling the
 644      * {@code gc} method may result in increasing the value returned
 645      * by {@code freeMemory.}
 646      *
 647      * @return  an approximation to the total amount of memory currently
 648      *          available for future allocated objects, measured in bytes.
 649      */
 650     public native long freeMemory();
 651 
 652     /**
 653      * Returns the total amount of memory in the Java virtual machine.
 654      * The value returned by this method may vary over time, depending on
 655      * the host environment.
 656      * <p>
 657      * Note that the amount of memory required to hold an object of any
 658      * given type may be implementation-dependent.
 659      *
 660      * @return  the total amount of memory currently available for current
 661      *          and future objects, measured in bytes.
 662      */
 663     public native long totalMemory();
 664 
 665     /**
 666      * Returns the maximum amount of memory that the Java virtual machine
 667      * will attempt to use.  If there is no inherent limit then the value
 668      * {@link java.lang.Long#MAX_VALUE} will be returned.
 669      *
 670      * @return  the maximum amount of memory that the virtual machine will
 671      *          attempt to use, measured in bytes
 672      * @since 1.4
 673      */
 674     public native long maxMemory();
 675 
 676     /**
 677      * Runs the garbage collector.
 678      * Calling this method suggests that the Java virtual machine expend
 679      * effort toward recycling unused objects in order to make the memory
 680      * they currently occupy available for quick reuse. When control
 681      * returns from the method call, the virtual machine has made
 682      * its best effort to recycle all discarded objects.
 683      * <p>
 684      * The name {@code gc} stands for "garbage
 685      * collector". The virtual machine performs this recycling
 686      * process automatically as needed, in a separate thread, even if the
 687      * {@code gc} method is not invoked explicitly.
 688      * <p>
 689      * The method {@link System#gc()} is the conventional and convenient
 690      * means of invoking this method.
 691      */
 692     public native void gc();
 693 
 694     /* Wormhole for calling java.lang.ref.Finalizer.runFinalization */
 695     private static native void runFinalization0();
 696 
 697     /**
 698      * Runs the finalization methods of any objects pending finalization.
 699      * Calling this method suggests that the Java virtual machine expend
 700      * effort toward running the {@code finalize} methods of objects
 701      * that have been found to be discarded but whose {@code finalize}
 702      * methods have not yet been run. When control returns from the
 703      * method call, the virtual machine has made a best effort to
 704      * complete all outstanding finalizations.
 705      * <p>
 706      * The virtual machine performs the finalization process
 707      * automatically as needed, in a separate thread, if the
 708      * {@code runFinalization} method is not invoked explicitly.
 709      * <p>
 710      * The method {@link System#runFinalization()} is the conventional
 711      * and convenient means of invoking this method.
 712      *
 713      * @see     java.lang.Object#finalize()
 714      */
 715     public void runFinalization() {
 716         runFinalization0();
 717     }
 718 
 719     /**
 720      * Enables/Disables tracing of instructions.
 721      * If the {@code boolean} argument is {@code true}, this
 722      * method suggests that the Java virtual machine emit debugging
 723      * information for each instruction in the virtual machine as it
 724      * is executed. The format of this information, and the file or other
 725      * output stream to which it is emitted, depends on the host environment.
 726      * The virtual machine may ignore this request if it does not support
 727      * this feature. The destination of the trace output is system
 728      * dependent.
 729      * <p>
 730      * If the {@code boolean} argument is {@code false}, this
 731      * method causes the virtual machine to stop performing the
 732      * detailed instruction trace it is performing.
 733      *
 734      * @param   on   {@code true} to enable instruction tracing;
 735      *               {@code false} to disable this feature.
 736      */
 737     public void traceInstructions(boolean on) { }
 738 
 739     /**
 740      * Enables/Disables tracing of method calls.
 741      * If the {@code boolean} argument is {@code true}, this
 742      * method suggests that the Java virtual machine emit debugging
 743      * information for each method in the virtual machine as it is
 744      * called. The format of this information, and the file or other output
 745      * stream to which it is emitted, depends on the host environment. The
 746      * virtual machine may ignore this request if it does not support
 747      * this feature.
 748      * <p>
 749      * Calling this method with argument false suggests that the
 750      * virtual machine cease emitting per-call debugging information.
 751      *
 752      * @param   on   {@code true} to enable instruction tracing;
 753      *               {@code false} to disable this feature.
 754      */
 755     public void traceMethodCalls(boolean on) { }
 756 
 757     /**
 758      * Loads the native library specified by the filename argument.  The filename
 759      * argument must be an absolute path name.
 760      * (for example
 761      * {@code Runtime.getRuntime().load("/home/avh/lib/libX11.so");}).
 762      *
 763      * If the filename argument, when stripped of any platform-specific library
 764      * prefix, path, and file extension, indicates a library whose name is,
 765      * for example, L, and a native library called L is statically linked
 766      * with the VM, then the JNI_OnLoad_L function exported by the library
 767      * is invoked rather than attempting to load a dynamic library.
 768      * A filename matching the argument does not have to exist in the file
 769      * system. See the JNI Specification for more details.
 770      *
 771      * Otherwise, the filename argument is mapped to a native library image in
 772      * an implementation-dependent manner.
 773      * <p>
 774      * First, if there is a security manager, its {@code checkLink}
 775      * method is called with the {@code filename} as its argument.
 776      * This may result in a security exception.
 777      * <p>
 778      * This is similar to the method {@link #loadLibrary(String)}, but it
 779      * accepts a general file name as an argument rather than just a library
 780      * name, allowing any file of native code to be loaded.
 781      * <p>
 782      * The method {@link System#load(String)} is the conventional and
 783      * convenient means of invoking this method.
 784      *
 785      * @param      filename   the file to load.
 786      * @exception  SecurityException  if a security manager exists and its
 787      *             {@code checkLink} method doesn't allow
 788      *             loading of the specified dynamic library
 789      * @exception  UnsatisfiedLinkError  if either the filename is not an
 790      *             absolute path name, the native library is not statically
 791      *             linked with the VM, or the library cannot be mapped to
 792      *             a native library image by the host system.
 793      * @exception  NullPointerException if {@code filename} is
 794      *             {@code null}
 795      * @see        java.lang.Runtime#getRuntime()
 796      * @see        java.lang.SecurityException
 797      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
 798      */
 799     @CallerSensitive
 800     public void load(String filename) {
 801         load0(Reflection.getCallerClass(), filename);
 802     }
 803 
 804     synchronized void load0(Class<?> fromClass, String filename) {
 805         SecurityManager security = System.getSecurityManager();
 806         if (security != null) {
 807             security.checkLink(filename);
 808         }
 809         if (!(new File(filename).isAbsolute())) {
 810             throw new UnsatisfiedLinkError(
 811                 "Expecting an absolute path of the library: " + filename);
 812         }
 813         ClassLoader.loadLibrary(fromClass, filename, true);
 814     }
 815 
 816     /**
 817      * Loads the native library specified by the {@code libname}
 818      * argument.  The {@code libname} argument must not contain any platform
 819      * specific prefix, file extension or path. If a native library
 820      * called {@code libname} is statically linked with the VM, then the
 821      * JNI_OnLoad_{@code libname} function exported by the library is invoked.
 822      * See the JNI Specification for more details.
 823      *
 824      * Otherwise, the libname argument is loaded from a system library
 825      * location and mapped to a native library image in an implementation-
 826      * dependent manner.
 827      * <p>
 828      * First, if there is a security manager, its {@code checkLink}
 829      * method is called with the {@code libname} as its argument.
 830      * This may result in a security exception.
 831      * <p>
 832      * The method {@link System#loadLibrary(String)} is the conventional
 833      * and convenient means of invoking this method. If native
 834      * methods are to be used in the implementation of a class, a standard
 835      * strategy is to put the native code in a library file (call it
 836      * {@code LibFile}) and then to put a static initializer:
 837      * <blockquote><pre>
 838      * static { System.loadLibrary("LibFile"); }
 839      * </pre></blockquote>
 840      * within the class declaration. When the class is loaded and
 841      * initialized, the necessary native code implementation for the native
 842      * methods will then be loaded as well.
 843      * <p>
 844      * If this method is called more than once with the same library
 845      * name, the second and subsequent calls are ignored.
 846      *
 847      * @param      libname   the name of the library.
 848      * @exception  SecurityException  if a security manager exists and its
 849      *             {@code checkLink} method doesn't allow
 850      *             loading of the specified dynamic library
 851      * @exception  UnsatisfiedLinkError if either the libname argument
 852      *             contains a file path, the native library is not statically
 853      *             linked with the VM,  or the library cannot be mapped to a
 854      *             native library image by the host system.
 855      * @exception  NullPointerException if {@code libname} is
 856      *             {@code null}
 857      * @see        java.lang.SecurityException
 858      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
 859      */
 860     @CallerSensitive
 861     public void loadLibrary(String libname) {
 862         loadLibrary0(Reflection.getCallerClass(), libname);
 863     }
 864 
 865     synchronized void loadLibrary0(Class<?> fromClass, String libname) {
 866         SecurityManager security = System.getSecurityManager();
 867         if (security != null) {
 868             security.checkLink(libname);
 869         }
 870         if (libname.indexOf((int)File.separatorChar) != -1) {
 871             throw new UnsatisfiedLinkError(
 872     "Directory separator should not appear in library name: " + libname);
 873         }
 874         ClassLoader.loadLibrary(fromClass, libname, false);
 875     }
 876 
 877     /**
 878      * Creates a localized version of an input stream. This method takes
 879      * an {@code InputStream} and returns an {@code InputStream}
 880      * equivalent to the argument in all respects except that it is
 881      * localized: as characters in the local character set are read from
 882      * the stream, they are automatically converted from the local
 883      * character set to Unicode.
 884      * <p>
 885      * If the argument is already a localized stream, it may be returned
 886      * as the result.
 887      *
 888      * @param      in InputStream to localize
 889      * @return     a localized input stream
 890      * @see        java.io.InputStream
 891      * @see        java.io.BufferedReader#BufferedReader(java.io.Reader)
 892      * @see        java.io.InputStreamReader#InputStreamReader(java.io.InputStream)
 893      * @deprecated As of JDK&nbsp;1.1, the preferred way to translate a byte
 894      * stream in the local encoding into a character stream in Unicode is via
 895      * the {@code InputStreamReader} and {@code BufferedReader}
 896      * classes.
 897      */
 898     @Deprecated
 899     public InputStream getLocalizedInputStream(InputStream in) {
 900         return in;
 901     }
 902 
 903     /**
 904      * Creates a localized version of an output stream. This method
 905      * takes an {@code OutputStream} and returns an
 906      * {@code OutputStream} equivalent to the argument in all respects
 907      * except that it is localized: as Unicode characters are written to
 908      * the stream, they are automatically converted to the local
 909      * character set.
 910      * <p>
 911      * If the argument is already a localized stream, it may be returned
 912      * as the result.
 913      *
 914      * @deprecated As of JDK&nbsp;1.1, the preferred way to translate a
 915      * Unicode character stream into a byte stream in the local encoding is via
 916      * the {@code OutputStreamWriter}, {@code BufferedWriter}, and
 917      * {@code PrintWriter} classes.
 918      *
 919      * @param      out OutputStream to localize
 920      * @return     a localized output stream
 921      * @see        java.io.OutputStream
 922      * @see        java.io.BufferedWriter#BufferedWriter(java.io.Writer)
 923      * @see        java.io.OutputStreamWriter#OutputStreamWriter(java.io.OutputStream)
 924      * @see        java.io.PrintWriter#PrintWriter(java.io.OutputStream)
 925      */
 926     @Deprecated
 927     public OutputStream getLocalizedOutputStream(OutputStream out) {
 928         return out;
 929     }
 930 
 931 }