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 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
  76      * halts}.
  77      *
  78      * <p> If this method is invoked after the virtual machine has begun its
  79      * shutdown sequence then if shutdown hooks are being run this method will
  80      * block indefinitely.  If shutdown hooks have already been run and on-exit
  81      * finalization has been enabled then this method halts the virtual machine
  82      * with the given status code if the status is nonzero; otherwise, it
  83      * blocks indefinitely.
  84      *
  85      * <p> The {@link System#exit(int) System.exit} method is the
  86      * conventional and convenient means of invoking this method.
  87      *
  88      * @param  status
  89      *         Termination status.  By convention, a nonzero status code
  90      *         indicates abnormal termination.
  91      *
  92      * @throws SecurityException
  93      *         If a security manager is present and its {@link
  94      *         SecurityManager#checkExit checkExit} method does not permit
  95      *         exiting with the specified status
  96      *
  97      * @see java.lang.SecurityException
  98      * @see java.lang.SecurityManager#checkExit(int)
  99      * @see #addShutdownHook
 100      * @see #removeShutdownHook
 101      * @see #runFinalizersOnExit
 102      * @see #halt(int)
 103      */
 104     public void exit(int status) {
 105         SecurityManager security = System.getSecurityManager();
 106         if (security != null) {
 107             security.checkExit(status);
 108         }
 109         Shutdown.exit(status);
 110     }
 111 
 112     /**
 113      * Registers a new virtual-machine shutdown hook.
 114      *
 115      * <p> The Java virtual machine <i>shuts down</i> in response to two kinds
 116      * of events:
 117      *
 118      *   <ul>
 119      *
 120      *   <li> The program <i>exits</i> normally, when the last non-daemon
 121      *   thread exits or when the {@link #exit exit} (equivalently,
 122      *   {@link System#exit(int) System.exit}) method is invoked, or
 123      *
 124      *   <li> The virtual machine is <i>terminated</i> in response to a
 125      *   user interrupt, such as typing {@literal ^C}, or a system-wide event,
 126      *   such as user logoff or system shutdown.
 127      *
 128      *   </ul>
 129      *
 130      * <p> A <i>shutdown hook</i> is simply an initialized but unstarted
 131      * thread.  When the virtual machine begins its shutdown sequence it will
 132      * start all registered shutdown hooks in some unspecified order and let
 133      * them run concurrently.  When all the hooks have finished it will then
 134      * run all uninvoked finalizers if finalization-on-exit has been enabled.
 135      * Finally, the virtual machine will halt.  Note that daemon threads will
 136      * continue to run during the shutdown sequence, as will non-daemon threads
 137      * if shutdown was initiated by invoking the {@link #exit exit} method.
 138      *
 139      * <p> Once the shutdown sequence has begun it can be stopped only by
 140      * invoking the {@link #halt halt} method, which forcibly
 141      * terminates the virtual machine.
 142      *
 143      * <p> Once the shutdown sequence has begun it is impossible to register a
 144      * new shutdown hook or de-register a previously-registered hook.
 145      * Attempting either of these operations will cause an
 146      * {@link IllegalStateException} to be thrown.
 147      *
 148      * <p> Shutdown hooks run at a delicate time in the life cycle of a virtual
 149      * machine and should therefore be coded defensively.  They should, in
 150      * particular, be written to be thread-safe and to avoid deadlocks insofar
 151      * as possible.  They should also not rely blindly upon services that may
 152      * have registered their own shutdown hooks and therefore may themselves in
 153      * the process of shutting down.  Attempts to use other thread-based
 154      * services such as the AWT event-dispatch thread, for example, may lead to
 155      * deadlocks.
 156      *
 157      * <p> Shutdown hooks should also finish their work quickly.  When a
 158      * program invokes {@link #exit exit} the expectation is
 159      * that the virtual machine will promptly shut down and exit.  When the
 160      * virtual machine is terminated due to user logoff or system shutdown the
 161      * underlying operating system may only allow a fixed amount of time in
 162      * which to shut down and exit.  It is therefore inadvisable to attempt any
 163      * user interaction or to perform a long-running computation in a shutdown
 164      * hook.
 165      *
 166      * <p> Uncaught exceptions are handled in shutdown hooks just as in any
 167      * other thread, by invoking the {@link ThreadGroup#uncaughtException
 168      * uncaughtException} method of the thread's {@link
 169      * ThreadGroup} object.  The default implementation of this method
 170      * prints the exception's stack trace to {@link System#err} and
 171      * terminates the thread; it does not cause the virtual machine to exit or
 172      * halt.
 173      *
 174      * <p> In rare circumstances the virtual machine may <i>abort</i>, that is,
 175      * stop running without shutting down cleanly.  This occurs when the
 176      * virtual machine is terminated externally, for example with the
 177      * {@code SIGKILL} signal on Unix or the {@code TerminateProcess} call on
 178      * Microsoft Windows.  The virtual machine may also abort if a native
 179      * method goes awry by, for example, corrupting internal data structures or
 180      * attempting to access nonexistent memory.  If the virtual machine aborts
 181      * then no guarantee can be made about whether or not any shutdown hooks
 182      * will be run.
 183      *
 184      * @param   hook
 185      *          An initialized but unstarted {@link Thread} object
 186      *
 187      * @throws  IllegalArgumentException
 188      *          If the specified hook has already been registered,
 189      *          or if it can be determined that the hook is already running or
 190      *          has already been run
 191      *
 192      * @throws  IllegalStateException
 193      *          If the virtual machine is already in the process
 194      *          of shutting down
 195      *
 196      * @throws  SecurityException
 197      *          If a security manager is present and it denies
 198      *          {@link RuntimePermission}("shutdownHooks")
 199      *
 200      * @see #removeShutdownHook
 201      * @see #halt(int)
 202      * @see #exit(int)
 203      * @since 1.3
 204      */
 205     public void addShutdownHook(Thread hook) {
 206         SecurityManager sm = System.getSecurityManager();
 207         if (sm != null) {
 208             sm.checkPermission(new RuntimePermission("shutdownHooks"));
 209         }
 210         ApplicationShutdownHooks.add(hook);
 211     }
 212 
 213     /**
 214      * De-registers a previously-registered virtual-machine shutdown hook.
 215      *
 216      * @param hook the hook to remove
 217      * @return {@code true} if the specified hook had previously been
 218      * registered and was successfully de-registered, {@code false}
 219      * otherwise.
 220      *
 221      * @throws  IllegalStateException
 222      *          If the virtual machine is already in the process of shutting
 223      *          down
 224      *
 225      * @throws  SecurityException
 226      *          If a security manager is present and it denies
 227      *          {@link RuntimePermission}("shutdownHooks")
 228      *
 229      * @see #addShutdownHook
 230      * @see #exit(int)
 231      * @since 1.3
 232      */
 233     public boolean removeShutdownHook(Thread hook) {
 234         SecurityManager sm = System.getSecurityManager();
 235         if (sm != null) {
 236             sm.checkPermission(new RuntimePermission("shutdownHooks"));
 237         }
 238         return ApplicationShutdownHooks.remove(hook);
 239     }
 240 
 241     /**
 242      * Forcibly terminates the currently running Java virtual machine.  This
 243      * method never returns normally.
 244      *
 245      * <p> This method should be used with extreme caution.  Unlike the
 246      * {@link #exit exit} method, this method does not cause shutdown
 247      * hooks to be started and does not run uninvoked finalizers if
 248      * finalization-on-exit has been enabled.  If the shutdown sequence has
 249      * already been initiated then this method does not wait for any running
 250      * shutdown hooks or finalizers to finish their work.
 251      *
 252      * @param  status
 253      *         Termination status.  By convention, a nonzero status code
 254      *         indicates abnormal termination.  If the {@link Runtime#exit
 255      *         exit} (equivalently, {@link System#exit(int)
 256      *         System.exit}) method has already been invoked then this
 257      *         status code will override the status code passed to that method.
 258      *
 259      * @throws SecurityException
 260      *         If a security manager is present and its {@link
 261      *         SecurityManager#checkExit checkExit} method does not permit
 262      *         an exit with the specified status
 263      *
 264      * @see #exit
 265      * @see #addShutdownHook
 266      * @see #removeShutdownHook
 267      * @since 1.3
 268      */
 269     public void halt(int status) {
 270         SecurityManager sm = System.getSecurityManager();
 271         if (sm != null) {
 272             sm.checkExit(status);
 273         }
 274         Shutdown.halt(status);
 275     }
 276 
 277     /**
 278      * Enable or disable finalization on exit; doing so specifies that the
 279      * finalizers of all objects that have finalizers that have not yet been
 280      * automatically invoked are to be run before the Java runtime exits.
 281      * By default, finalization on exit is disabled.
 282      *
 283      * <p>If there is a security manager,
 284      * its {@code checkExit} method is first called
 285      * with 0 as its argument to ensure the exit is allowed.
 286      * This could result in a SecurityException.
 287      *
 288      * @param value true to enable finalization on exit, false to disable
 289      * @deprecated  This method is inherently unsafe.  It may result in
 290      *      finalizers being called on live objects while other threads are
 291      *      concurrently manipulating those objects, resulting in erratic
 292      *      behavior or deadlock.
 293      *
 294      * @throws  SecurityException
 295      *        if a security manager exists and its {@code checkExit}
 296      *        method doesn't allow the exit.
 297      *
 298      * @see     java.lang.Runtime#exit(int)
 299      * @see     java.lang.Runtime#gc()
 300      * @see     java.lang.SecurityManager#checkExit(int)
 301      * @since   1.1
 302      */
 303     @Deprecated
 304     public static void runFinalizersOnExit(boolean value) {
 305         SecurityManager security = System.getSecurityManager();
 306         if (security != null) {
 307             try {
 308                 security.checkExit(0);
 309             } catch (SecurityException e) {
 310                 throw new SecurityException("runFinalizersOnExit");
 311             }
 312         }
 313         Shutdown.setRunFinalizersOnExit(value);
 314     }
 315 
 316     /**
 317      * Executes the specified string command in a separate process.
 318      *
 319      * <p>This is a convenience method.  An invocation of the form
 320      * {@code exec(command)}
 321      * behaves in exactly the same way as the invocation
 322      * {@link #exec(String, String[], File) exec}{@code (command, null, null)}.
 323      *
 324      * @param   command   a specified system command.
 325      *
 326      * @return  A new {@link Process} object for managing the subprocess
 327      *
 328      * @throws  SecurityException
 329      *          If a security manager exists and its
 330      *          {@link SecurityManager#checkExec checkExec}
 331      *          method doesn't allow creation of the subprocess
 332      *
 333      * @throws  IOException
 334      *          If an I/O error occurs
 335      *
 336      * @throws  NullPointerException
 337      *          If {@code command} is {@code null}
 338      *
 339      * @throws  IllegalArgumentException
 340      *          If {@code command} is empty
 341      *
 342      * @see     #exec(String[], String[], File)
 343      * @see     ProcessBuilder
 344      */
 345     public Process exec(String command) throws IOException {
 346         return exec(command, null, null);
 347     }
 348 
 349     /**
 350      * Executes the specified string command in a separate process with the
 351      * specified environment.
 352      *
 353      * <p>This is a convenience method.  An invocation of the form
 354      * {@code exec(command, envp)}
 355      * behaves in exactly the same way as the invocation
 356      * {@link #exec(String, String[], File) exec}{@code (command, envp, null)}.
 357      *
 358      * @param   command   a specified system command.
 359      *
 360      * @param   envp      array of strings, each element of which
 361      *                    has environment variable settings in the format
 362      *                    <i>name</i>=<i>value</i>, or
 363      *                    {@code null} if the subprocess should inherit
 364      *                    the environment of the current process.
 365      *
 366      * @return  A new {@link Process} object for managing the subprocess
 367      *
 368      * @throws  SecurityException
 369      *          If a security manager exists and its
 370      *          {@link SecurityManager#checkExec checkExec}
 371      *          method doesn't allow creation of the subprocess
 372      *
 373      * @throws  IOException
 374      *          If an I/O error occurs
 375      *
 376      * @throws  NullPointerException
 377      *          If {@code command} is {@code null},
 378      *          or one of the elements of {@code envp} is {@code null}
 379      *
 380      * @throws  IllegalArgumentException
 381      *          If {@code command} is empty
 382      *
 383      * @see     #exec(String[], String[], File)
 384      * @see     ProcessBuilder
 385      */
 386     public Process exec(String command, String[] envp) throws IOException {
 387         return exec(command, envp, null);
 388     }
 389 
 390     /**
 391      * Executes the specified string command in a separate process with the
 392      * specified environment and working directory.
 393      *
 394      * <p>This is a convenience method.  An invocation of the form
 395      * {@code exec(command, envp, dir)}
 396      * behaves in exactly the same way as the invocation
 397      * {@link #exec(String[], String[], File) exec}{@code (cmdarray, envp, dir)},
 398      * where {@code cmdarray} is an array of all the tokens in
 399      * {@code command}.
 400      *
 401      * <p>More precisely, the {@code command} string is broken
 402      * into tokens using a {@link StringTokenizer} created by the call
 403      * {@code new {@link StringTokenizer}(command)} with no
 404      * further modification of the character categories.  The tokens
 405      * produced by the tokenizer are then placed in the new string
 406      * array {@code cmdarray}, in the same order.
 407      *
 408      * @param   command   a specified system command.
 409      *
 410      * @param   envp      array of strings, each element of which
 411      *                    has environment variable settings in the format
 412      *                    <i>name</i>=<i>value</i>, or
 413      *                    {@code null} if the subprocess should inherit
 414      *                    the environment of the current process.
 415      *
 416      * @param   dir       the working directory of the subprocess, or
 417      *                    {@code null} if the subprocess should inherit
 418      *                    the working directory of the current process.
 419      *
 420      * @return  A new {@link Process} object for managing the subprocess
 421      *
 422      * @throws  SecurityException
 423      *          If a security manager exists and its
 424      *          {@link SecurityManager#checkExec checkExec}
 425      *          method doesn't allow creation of the subprocess
 426      *
 427      * @throws  IOException
 428      *          If an I/O error occurs
 429      *
 430      * @throws  NullPointerException
 431      *          If {@code command} is {@code null},
 432      *          or one of the elements of {@code envp} is {@code null}
 433      *
 434      * @throws  IllegalArgumentException
 435      *          If {@code command} is empty
 436      *
 437      * @see     ProcessBuilder
 438      * @since 1.3
 439      */
 440     public Process exec(String command, String[] envp, File dir)
 441         throws IOException {
 442         if (command.length() == 0)
 443             throw new IllegalArgumentException("Empty command");
 444 
 445         StringTokenizer st = new StringTokenizer(command);
 446         String[] cmdarray = new String[st.countTokens()];
 447         for (int i = 0; st.hasMoreTokens(); i++)
 448             cmdarray[i] = st.nextToken();
 449         return exec(cmdarray, envp, dir);
 450     }
 451 
 452     /**
 453      * Executes the specified command and arguments in a separate process.
 454      *
 455      * <p>This is a convenience method.  An invocation of the form
 456      * {@code exec(cmdarray)}
 457      * behaves in exactly the same way as the invocation
 458      * {@link #exec(String[], String[], File) exec}{@code (cmdarray, null, null)}.
 459      *
 460      * @param   cmdarray  array containing the command to call and
 461      *                    its arguments.
 462      *
 463      * @return  A new {@link Process} object for managing the subprocess
 464      *
 465      * @throws  SecurityException
 466      *          If a security manager exists and its
 467      *          {@link SecurityManager#checkExec checkExec}
 468      *          method doesn't allow creation of the subprocess
 469      *
 470      * @throws  IOException
 471      *          If an I/O error occurs
 472      *
 473      * @throws  NullPointerException
 474      *          If {@code cmdarray} is {@code null},
 475      *          or one of the elements of {@code cmdarray} is {@code null}
 476      *
 477      * @throws  IndexOutOfBoundsException
 478      *          If {@code cmdarray} is an empty array
 479      *          (has length {@code 0})
 480      *
 481      * @see     ProcessBuilder
 482      */
 483     public Process exec(String cmdarray[]) throws IOException {
 484         return exec(cmdarray, null, null);
 485     }
 486 
 487     /**
 488      * Executes the specified command and arguments in a separate process
 489      * with the specified environment.
 490      *
 491      * <p>This is a convenience method.  An invocation of the form
 492      * {@code exec(cmdarray, envp)}
 493      * behaves in exactly the same way as the invocation
 494      * {@link #exec(String[], String[], File) exec}{@code (cmdarray, envp, null)}.
 495      *
 496      * @param   cmdarray  array containing the command to call and
 497      *                    its arguments.
 498      *
 499      * @param   envp      array of strings, each element of which
 500      *                    has environment variable settings in the format
 501      *                    <i>name</i>=<i>value</i>, or
 502      *                    {@code null} if the subprocess should inherit
 503      *                    the environment of the current process.
 504      *
 505      * @return  A new {@link Process} object for managing the subprocess
 506      *
 507      * @throws  SecurityException
 508      *          If a security manager exists and its
 509      *          {@link SecurityManager#checkExec checkExec}
 510      *          method doesn't allow creation of the subprocess
 511      *
 512      * @throws  IOException
 513      *          If an I/O error occurs
 514      *
 515      * @throws  NullPointerException
 516      *          If {@code cmdarray} is {@code null},
 517      *          or one of the elements of {@code cmdarray} is {@code null},
 518      *          or one of the elements of {@code envp} is {@code null}
 519      *
 520      * @throws  IndexOutOfBoundsException
 521      *          If {@code cmdarray} is an empty array
 522      *          (has length {@code 0})
 523      *
 524      * @see     ProcessBuilder
 525      */
 526     public Process exec(String[] cmdarray, String[] envp) throws IOException {
 527         return exec(cmdarray, envp, null);
 528     }
 529 
 530 
 531     /**
 532      * Executes the specified command and arguments in a separate process with
 533      * the specified environment and working directory.
 534      *
 535      * <p>Given an array of strings {@code cmdarray}, representing the
 536      * tokens of a command line, and an array of strings {@code envp},
 537      * representing "environment" variable settings, this method creates
 538      * a new process in which to execute the specified command.
 539      *
 540      * <p>This method checks that {@code cmdarray} is a valid operating
 541      * system command.  Which commands are valid is system-dependent,
 542      * but at the very least the command must be a non-empty list of
 543      * non-null strings.
 544      *
 545      * <p>If {@code envp} is {@code null}, the subprocess inherits the
 546      * environment settings of the current process.
 547      *
 548      * <p>A minimal set of system dependent environment variables may
 549      * be required to start a process on some operating systems.
 550      * As a result, the subprocess may inherit additional environment variable
 551      * settings beyond those in the specified environment.
 552      *
 553      * <p>{@link ProcessBuilder#start()} is now the preferred way to
 554      * start a process with a modified environment.
 555      *
 556      * <p>The working directory of the new subprocess is specified by {@code dir}.
 557      * If {@code dir} is {@code null}, the subprocess inherits the
 558      * current working directory of the current process.
 559      *
 560      * <p>If a security manager exists, its
 561      * {@link SecurityManager#checkExec checkExec}
 562      * method is invoked with the first component of the array
 563      * {@code cmdarray} as its argument. This may result in a
 564      * {@link SecurityException} being thrown.
 565      *
 566      * <p>Starting an operating system process is highly system-dependent.
 567      * Among the many things that can go wrong are:
 568      * <ul>
 569      * <li>The operating system program file was not found.
 570      * <li>Access to the program file was denied.
 571      * <li>The working directory does not exist.
 572      * </ul>
 573      *
 574      * <p>In such cases an exception will be thrown.  The exact nature
 575      * of the exception is system-dependent, but it will always be a
 576      * subclass of {@link IOException}.
 577      *
 578      * <p>If the operating system does not support the creation of
 579      * processes, an {@link UnsupportedOperationException} will be thrown.
 580      *
 581      *
 582      * @param   cmdarray  array containing the command to call and
 583      *                    its arguments.
 584      *
 585      * @param   envp      array of strings, each element of which
 586      *                    has environment variable settings in the format
 587      *                    <i>name</i>=<i>value</i>, or
 588      *                    {@code null} if the subprocess should inherit
 589      *                    the environment of the current process.
 590      *
 591      * @param   dir       the working directory of the subprocess, or
 592      *                    {@code null} if the subprocess should inherit
 593      *                    the working directory of the current process.
 594      *
 595      * @return  A new {@link Process} object for managing the subprocess
 596      *
 597      * @throws  SecurityException
 598      *          If a security manager exists and its
 599      *          {@link SecurityManager#checkExec checkExec}
 600      *          method doesn't allow creation of the subprocess
 601      *
 602      * @throws  UnsupportedOperationException
 603      *          If the operating system does not support the creation of processes.
 604      *
 605      * @throws  IOException
 606      *          If an I/O error occurs
 607      *
 608      * @throws  NullPointerException
 609      *          If {@code cmdarray} is {@code null},
 610      *          or one of the elements of {@code cmdarray} is {@code null},
 611      *          or one of the elements of {@code envp} is {@code null}
 612      *
 613      * @throws  IndexOutOfBoundsException
 614      *          If {@code cmdarray} is an empty array
 615      *          (has length {@code 0})
 616      *
 617      * @see     ProcessBuilder
 618      * @since 1.3
 619      */
 620     public Process exec(String[] cmdarray, String[] envp, File dir)
 621         throws IOException {
 622         return new ProcessBuilder(cmdarray)
 623             .environment(envp)
 624             .directory(dir)
 625             .start();
 626     }
 627 
 628     /**
 629      * Returns the number of processors available to the Java virtual machine.
 630      *
 631      * <p> This value may change during a particular invocation of the virtual
 632      * machine.  Applications that are sensitive to the number of available
 633      * processors should therefore occasionally poll this property and adjust
 634      * their resource usage appropriately. </p>
 635      *
 636      * @return  the maximum number of processors available to the virtual
 637      *          machine; never smaller than one
 638      * @since 1.4
 639      */
 640     public native int availableProcessors();
 641 
 642     /**
 643      * Returns the amount of free memory in the Java Virtual Machine.
 644      * Calling the
 645      * {@code gc} method may result in increasing the value returned
 646      * by {@code freeMemory.}
 647      *
 648      * @return  an approximation to the total amount of memory currently
 649      *          available for future allocated objects, measured in bytes.
 650      */
 651     public native long freeMemory();
 652 
 653     /**
 654      * Returns the total amount of memory in the Java virtual machine.
 655      * The value returned by this method may vary over time, depending on
 656      * the host environment.
 657      * <p>
 658      * Note that the amount of memory required to hold an object of any
 659      * given type may be implementation-dependent.
 660      *
 661      * @return  the total amount of memory currently available for current
 662      *          and future objects, measured in bytes.
 663      */
 664     public native long totalMemory();
 665 
 666     /**
 667      * Returns the maximum amount of memory that the Java virtual machine will
 668      * attempt to use.  If there is no inherent limit then the value {@link
 669      * java.lang.Long#MAX_VALUE} will be returned.
 670      *
 671      * @return  the maximum amount of memory that the virtual machine will
 672      *          attempt to use, measured in bytes
 673      * @since 1.4
 674      */
 675     public native long maxMemory();
 676 
 677     /**
 678      * Runs the garbage collector.
 679      * Calling this method suggests that the Java virtual machine expend
 680      * effort toward recycling unused objects in order to make the memory
 681      * they currently occupy available for quick reuse. When control
 682      * returns from the method call, the virtual machine has made
 683      * its best effort to recycle all discarded objects.
 684      * <p>
 685      * The name {@code gc} stands for "garbage
 686      * collector". The virtual machine performs this recycling
 687      * process automatically as needed, in a separate thread, even if the
 688      * {@code gc} method is not invoked explicitly.
 689      * <p>
 690      * The method {@link System#gc()} is the conventional and convenient
 691      * means of invoking this method.
 692      */
 693     public native void gc();
 694 
 695     /* Wormhole for calling java.lang.ref.Finalizer.runFinalization */
 696     private static native void runFinalization0();
 697 
 698     /**
 699      * Runs the finalization methods of any objects pending finalization.
 700      * Calling this method suggests that the Java virtual machine expend
 701      * effort toward running the {@code finalize} methods of objects
 702      * that have been found to be discarded but whose {@code finalize}
 703      * methods have not yet been run. When control returns from the
 704      * method call, the virtual machine has made a best effort to
 705      * complete all outstanding finalizations.
 706      * <p>
 707      * The virtual machine performs the finalization process
 708      * automatically as needed, in a separate thread, if the
 709      * {@code runFinalization} method is not invoked explicitly.
 710      * <p>
 711      * The method {@link System#runFinalization()} is the conventional
 712      * and convenient means of invoking this method.
 713      *
 714      * @see     java.lang.Object#finalize()
 715      */
 716     public void runFinalization() {
 717         runFinalization0();
 718     }
 719 
 720     /**
 721      * Enables/Disables tracing of instructions.
 722      * If the {@code boolean} argument is {@code true}, this
 723      * method suggests that the Java virtual machine emit debugging
 724      * information for each instruction in the virtual machine as it
 725      * is executed. The format of this information, and the file or other
 726      * output stream to which it is emitted, depends on the host environment.
 727      * The virtual machine may ignore this request if it does not support
 728      * this feature. The destination of the trace output is system
 729      * dependent.
 730      * <p>
 731      * If the {@code boolean} argument is {@code false}, this
 732      * method causes the virtual machine to stop performing the
 733      * detailed instruction trace it is performing.
 734      *
 735      * @param   on   {@code true} to enable instruction tracing;
 736      *               {@code false} to disable this feature.
 737      */
 738     public void traceInstructions(boolean on) { }
 739 
 740     /**
 741      * Enables/Disables tracing of method calls.
 742      * If the {@code boolean} argument is {@code true}, this
 743      * method suggests that the Java virtual machine emit debugging
 744      * information for each method in the virtual machine as it is
 745      * called. The format of this information, and the file or other output
 746      * stream to which it is emitted, depends on the host environment. The
 747      * virtual machine may ignore this request if it does not support
 748      * this feature.
 749      * <p>
 750      * Calling this method with argument false suggests that the
 751      * virtual machine cease emitting per-call debugging information.
 752      *
 753      * @param   on   {@code true} to enable instruction tracing;
 754      *               {@code false} to disable this feature.
 755      */
 756     public void traceMethodCalls(boolean on) { }
 757 
 758     /**
 759      * Loads the native library specified by the filename argument.  The filename
 760      * argument must be an absolute path name.
 761      * (for example
 762      * {@code Runtime.getRuntime().load("/home/avh/lib/libX11.so");}).
 763      *
 764      * If the filename argument, when stripped of any platform-specific library
 765      * prefix, path, and file extension, indicates a library whose name is,
 766      * for example, L, and a native library called L is statically linked
 767      * with the VM, then the JNI_OnLoad_L function exported by the library
 768      * is invoked rather than attempting to load a dynamic library.
 769      * A filename matching the argument does not have to exist in the file
 770      * system. See the JNI Specification for more details.
 771      *
 772      * Otherwise, the filename argument is mapped to a native library image in
 773      * an implementation-dependent manner.
 774      * <p>
 775      * First, if there is a security manager, its {@code checkLink}
 776      * method is called with the {@code filename} as its argument.
 777      * This may result in a security exception.
 778      * <p>
 779      * This is similar to the method {@link #loadLibrary(String)}, but it
 780      * accepts a general file name as an argument rather than just a library
 781      * name, allowing any file of native code to be loaded.
 782      * <p>
 783      * The method {@link System#load(String)} is the conventional and
 784      * convenient means of invoking this method.
 785      *
 786      * @param      filename   the file to load.
 787      * @exception  SecurityException  if a security manager exists and its
 788      *             {@code checkLink} method doesn't allow
 789      *             loading of the specified dynamic library
 790      * @exception  UnsatisfiedLinkError  if either the filename is not an
 791      *             absolute path name, the native library is not statically
 792      *             linked with the VM, or the library cannot be mapped to
 793      *             a native library image by the host system.
 794      * @exception  NullPointerException if {@code filename} is
 795      *             {@code null}
 796      * @see        java.lang.Runtime#getRuntime()
 797      * @see        java.lang.SecurityException
 798      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
 799      */
 800     @CallerSensitive
 801     public void load(String filename) {
 802         load0(Reflection.getCallerClass(), filename);
 803     }
 804 
 805     synchronized void load0(Class<?> fromClass, String filename) {
 806         SecurityManager security = System.getSecurityManager();
 807         if (security != null) {
 808             security.checkLink(filename);
 809         }
 810         if (!(new File(filename).isAbsolute())) {
 811             throw new UnsatisfiedLinkError(
 812                 "Expecting an absolute path of the library: " + filename);
 813         }
 814         ClassLoader.loadLibrary(fromClass, filename, true);
 815     }
 816 
 817     /**
 818      * Loads the native library specified by the {@code libname}
 819      * argument.  The {@code libname} argument must not contain any platform
 820      * specific prefix, file extension or path. If a native library
 821      * called {@code libname} is statically linked with the VM, then the
 822      * JNI_OnLoad_{@code libname} function exported by the library is invoked.
 823      * See the JNI Specification for more details.
 824      *
 825      * Otherwise, the libname argument is loaded from a system library
 826      * location and mapped to a native library image in an implementation-
 827      * dependent manner.
 828      * <p>
 829      * First, if there is a security manager, its {@code checkLink}
 830      * method is called with the {@code libname} as its argument.
 831      * This may result in a security exception.
 832      * <p>
 833      * The method {@link System#loadLibrary(String)} is the conventional
 834      * and convenient means of invoking this method. If native
 835      * methods are to be used in the implementation of a class, a standard
 836      * strategy is to put the native code in a library file (call it
 837      * {@code LibFile}) and then to put a static initializer:
 838      * <blockquote><pre>
 839      * static { System.loadLibrary("LibFile"); }
 840      * </pre></blockquote>
 841      * within the class declaration. When the class is loaded and
 842      * initialized, the necessary native code implementation for the native
 843      * methods will then be loaded as well.
 844      * <p>
 845      * If this method is called more than once with the same library
 846      * name, the second and subsequent calls are ignored.
 847      *
 848      * @param      libname   the name of the library.
 849      * @exception  SecurityException  if a security manager exists and its
 850      *             {@code checkLink} method doesn't allow
 851      *             loading of the specified dynamic library
 852      * @exception  UnsatisfiedLinkError if either the libname argument
 853      *             contains a file path, the native library is not statically
 854      *             linked with the VM,  or the library cannot be mapped to a
 855      *             native library image by the host system.
 856      * @exception  NullPointerException if {@code libname} is
 857      *             {@code null}
 858      * @see        java.lang.SecurityException
 859      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
 860      */
 861     @CallerSensitive
 862     public void loadLibrary(String libname) {
 863         loadLibrary0(Reflection.getCallerClass(), libname);
 864     }
 865 
 866     synchronized void loadLibrary0(Class<?> fromClass, String libname) {
 867         SecurityManager security = System.getSecurityManager();
 868         if (security != null) {
 869             security.checkLink(libname);
 870         }
 871         if (libname.indexOf((int)File.separatorChar) != -1) {
 872             throw new UnsatisfiedLinkError(
 873     "Directory separator should not appear in library name: " + libname);
 874         }
 875         ClassLoader.loadLibrary(fromClass, libname, false);
 876     }
 877 
 878     /**
 879      * Creates a localized version of an input stream. This method takes
 880      * an {@code InputStream} and returns an {@code InputStream}
 881      * equivalent to the argument in all respects except that it is
 882      * localized: as characters in the local character set are read from
 883      * the stream, they are automatically converted from the local
 884      * character set to Unicode.
 885      * <p>
 886      * If the argument is already a localized stream, it may be returned
 887      * as the result.
 888      *
 889      * @param      in InputStream to localize
 890      * @return     a localized input stream
 891      * @see        java.io.InputStream
 892      * @see        java.io.BufferedReader#BufferedReader(java.io.Reader)
 893      * @see        java.io.InputStreamReader#InputStreamReader(java.io.InputStream)
 894      * @deprecated As of JDK&nbsp;1.1, the preferred way to translate a byte
 895      * stream in the local encoding into a character stream in Unicode is via
 896      * the {@code InputStreamReader} and {@code BufferedReader}
 897      * classes.
 898      */
 899     @Deprecated
 900     public InputStream getLocalizedInputStream(InputStream in) {
 901         return in;
 902     }
 903 
 904     /**
 905      * Creates a localized version of an output stream. This method
 906      * takes an {@code OutputStream} and returns an
 907      * {@code OutputStream} equivalent to the argument in all respects
 908      * except that it is localized: as Unicode characters are written to
 909      * the stream, they are automatically converted to the local
 910      * character set.
 911      * <p>
 912      * If the argument is already a localized stream, it may be returned
 913      * as the result.
 914      *
 915      * @deprecated As of JDK&nbsp;1.1, the preferred way to translate a
 916      * Unicode character stream into a byte stream in the local encoding is via
 917      * the {@code OutputStreamWriter}, {@code BufferedWriter}, and
 918      * {@code PrintWriter} classes.
 919      *
 920      * @param      out OutputStream to localize
 921      * @return     a localized output stream
 922      * @see        java.io.OutputStream
 923      * @see        java.io.BufferedWriter#BufferedWriter(java.io.Writer)
 924      * @see        java.io.OutputStreamWriter#OutputStreamWriter(java.io.OutputStream)
 925      * @see        java.io.PrintWriter#PrintWriter(java.io.OutputStream)
 926      */
 927     @Deprecated
 928     public OutputStream getLocalizedOutputStream(OutputStream out) {
 929         return out;
 930     }
 931 
 932 }