/*

 * Copyright (c) 1995, 2014, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.lang;

import java.io.*;

import java.util.StringTokenizer;

/**

 * Every Java application has a single instance of class

 * {@code Runtime} that allows the application to interface with

 * the environment in which the application is running. The current

 * runtime can be obtained from the {@code getRuntime} method.

 * <p>

 * An application cannot create its own instance of this class.

 *

 * @author  unascribed

 * @see     java.lang.Runtime#getRuntime()

 * @since   1.0

 */

public class Runtime {

    private static final Runtime currentRuntime = new Runtime();

    /**

     * Returns the runtime object associated with the current Java application.

     * Most of the methods of class {@code Runtime} are instance

     * methods and must be invoked with respect to the current runtime object.

     *

     * @return  the {@code Runtime} object associated with the current

     *          Java application.

     */

    public static Runtime getRuntime() {

        return currentRuntime;

    }

    /** Don't let anyone else instantiate this class */

    private Runtime() {}

    /**

     * Terminates the currently running Java virtual machine by initiating its

     * shutdown sequence.  This method never returns normally.  The argument

     * serves as a status code; by convention, a nonzero status code indicates

     * abnormal termination.

     *

     * <p> The virtual machine's shutdown sequence consists of two phases.  In

     * the first phase all registered {@link #addShutdownHook shutdown hooks},

     * if any, are started in some unspecified order and allowed to run

     * concurrently until they finish.  In the second phase all uninvoked

     * finalizers are run if {@link #runFinalizersOnExit finalization-on-exit}

     * has been enabled.  Once this is done the virtual machine {@link #halt halts}.

     *

     * <p> If this method is invoked after the virtual machine has begun its

     * shutdown sequence then if shutdown hooks are being run this method will

     * block indefinitely.  If shutdown hooks have already been run and on-exit

     * finalization has been enabled then this method halts the virtual machine

     * with the given status code if the status is nonzero; otherwise, it

     * blocks indefinitely.

     *

     * <p> The {@link System#exit(int) System.exit} method is the

     * conventional and convenient means of invoking this method.

     *

     * @param  status

     *         Termination status.  By convention, a nonzero status code

     *         indicates abnormal termination.

     *

     * @throws SecurityException

     *         If a security manager is present and its

     *         {@link SecurityManager#checkExit checkExit} method does not permit

     *         exiting with the specified status

     *

     * @see java.lang.SecurityException

     * @see java.lang.SecurityManager#checkExit(int)

     * @see #addShutdownHook

     * @see #removeShutdownHook

     * @see #runFinalizersOnExit

     * @see #halt(int)

     */

    public void exit(int status) {

        SecurityManager security = System.getSecurityManager();

        if (security != null) {

            security.checkExit(status);

        }

        Shutdown.exit(status);

    }

    /**

     * Registers a new virtual-machine shutdown hook.

     *

     * <p> The Java virtual machine <i>shuts down</i> in response to two kinds

     * of events:

     *

     *   <ul>

     *

     *   <li> The program <i>exits</i> normally, when the last non-daemon

     *   thread exits or when the {@link #exit exit} (equivalently,

     *   {@link System#exit(int) System.exit}) method is invoked, or

     *

     *   <li> The virtual machine is <i>terminated</i> in response to a

     *   user interrupt, such as typing {@code ^C}, or a system-wide event,

     *   such as user logoff or system shutdown.

     *

     *   </ul>

     *

     * <p> A <i>shutdown hook</i> is simply an initialized but unstarted

     * thread.  When the virtual machine begins its shutdown sequence it will

     * start all registered shutdown hooks in some unspecified order and let

     * them run concurrently.  When all the hooks have finished it will then

     * run all uninvoked finalizers if finalization-on-exit has been enabled.

     * Finally, the virtual machine will halt.  Note that daemon threads will

     * continue to run during the shutdown sequence, as will non-daemon threads

     * if shutdown was initiated by invoking the {@link #exit exit} method.

     *

     * <p> Once the shutdown sequence has begun it can be stopped only by

     * invoking the {@link #halt halt} method, which forcibly

     * terminates the virtual machine.

     *

     * <p> Once the shutdown sequence has begun it is impossible to register a

     * new shutdown hook or de-register a previously-registered hook.

     * Attempting either of these operations will cause an

     * {@link IllegalStateException} to be thrown.

     *

     * <p> Shutdown hooks run at a delicate time in the life cycle of a virtual

     * machine and should therefore be coded defensively.  They should, in

     * particular, be written to be thread-safe and to avoid deadlocks insofar

     * as possible.  They should also not rely blindly upon services that may

     * have registered their own shutdown hooks and therefore may themselves in

     * the process of shutting down.  Attempts to use other thread-based

     * services such as the AWT event-dispatch thread, for example, may lead to

     * deadlocks.

     *

     * <p> Shutdown hooks should also finish their work quickly.  When a

     * program invokes {@link #exit exit} the expectation is

     * that the virtual machine will promptly shut down and exit.  When the

     * virtual machine is terminated due to user logoff or system shutdown the

     * underlying operating system may only allow a fixed amount of time in

     * which to shut down and exit.  It is therefore inadvisable to attempt any

     * user interaction or to perform a long-running computation in a shutdown

     * hook.

     *

     * <p> Uncaught exceptions are handled in shutdown hooks just as in any

     * other thread, by invoking the

     * {@link ThreadGroup#uncaughtException uncaughtException} method of the

     * thread's {@link ThreadGroup} object. The default implementation of this

     * method prints the exception's stack trace to {@link System#err} and

     * terminates the thread; it does not cause the virtual machine to exit or

     * halt.

     *

     * <p> In rare circumstances the virtual machine may <i>abort</i>, that is,

     * stop running without shutting down cleanly.  This occurs when the

     * virtual machine is terminated externally, for example with the

     * {@code SIGKILL} signal on Unix or the {@code TerminateProcess} call on

     * Microsoft Windows.  The virtual machine may also abort if a native

     * method goes awry by, for example, corrupting internal data structures or

     * attempting to access nonexistent memory.  If the virtual machine aborts

     * then no guarantee can be made about whether or not any shutdown hooks

     * will be run.

     *

     * @param   hook

     *          An initialized but unstarted {@link Thread} object

     *

     * @throws  IllegalArgumentException

     *          If the specified hook has already been registered,

     *          or if it can be determined that the hook is already running or

     *          has already been run

     *

     * @throws  IllegalStateException

     *          If the virtual machine is already in the process

     *          of shutting down

     *

     * @throws  SecurityException

     *          If a security manager is present and it denies

     *          {@link RuntimePermission}("shutdownHooks")

     *

     * @see #removeShutdownHook

     * @see #halt(int)

     * @see #exit(int)

     * @since 1.3

     */

    public void addShutdownHook(Thread hook) {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new RuntimePermission("shutdownHooks"));

        }

        ApplicationShutdownHooks.add(hook);

    }

    /**

     * De-registers a previously-registered virtual-machine shutdown hook.

     *

     * @param hook the hook to remove

     * @return {@code true} if the specified hook had previously been

     * registered and was successfully de-registered, {@code false}

     * otherwise.

     *

     * @throws  IllegalStateException

     *          If the virtual machine is already in the process of shutting

     *          down

     *

     * @throws  SecurityException

     *          If a security manager is present and it denies

     *          {@link RuntimePermission}("shutdownHooks")

     *

     * @see #addShutdownHook

     * @see #exit(int)

     * @since 1.3

     */

    public boolean removeShutdownHook(Thread hook) {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new RuntimePermission("shutdownHooks"));

        }

        return ApplicationShutdownHooks.remove(hook);

    }

    /**

     * Forcibly terminates the currently running Java virtual machine.  This

     * method never returns normally.

     *

     * <p> This method should be used with extreme caution.  Unlike the

     * {@link #exit exit} method, this method does not cause shutdown

     * hooks to be started and does not run uninvoked finalizers if

     * finalization-on-exit has been enabled.  If the shutdown sequence has

     * already been initiated then this method does not wait for any running

     * shutdown hooks or finalizers to finish their work.

     *

     * @param  status

     *         Termination status. By convention, a nonzero status code

     *         indicates abnormal termination. If the {@link Runtime#exit exit}

     *         (equivalently, {@link System#exit(int) System.exit}) method

     *         has already been invoked then this status code

     *         will override the status code passed to that method.

     *

     * @throws SecurityException

     *         If a security manager is present and its

     *         {@link SecurityManager#checkExit checkExit} method

     *         does not permit an exit with the specified status

     *

     * @see #exit

     * @see #addShutdownHook

     * @see #removeShutdownHook

     * @since 1.3

     */

    public void halt(int status) {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkExit(status);

        }

        Shutdown.halt(status);

    }

    /**

     * Enable or disable finalization on exit; doing so specifies that the

     * finalizers of all objects that have finalizers that have not yet been

     * automatically invoked are to be run before the Java runtime exits.

     * By default, finalization on exit is disabled.

     *

     * <p>If there is a security manager,

     * its {@code checkExit} method is first called

     * with 0 as its argument to ensure the exit is allowed.

     * This could result in a SecurityException.

     *

     * @param value true to enable finalization on exit, false to disable

     * @deprecated  This method is inherently unsafe.  It may result in

     *      finalizers being called on live objects while other threads are

     *      concurrently manipulating those objects, resulting in erratic

     *      behavior or deadlock.

     *

     * @throws  SecurityException

     *        if a security manager exists and its {@code checkExit}

     *        method doesn't allow the exit.

     *

     * @see     java.lang.Runtime#exit(int)

     * @see     java.lang.Runtime#gc()

     * @see     java.lang.SecurityManager#checkExit(int)

     * @since   1.1

     */

    @Deprecated

    public static void runFinalizersOnExit(boolean value) {

        SecurityManager security = System.getSecurityManager();

        if (security != null) {

            try {

                security.checkExit(0);

            } catch (SecurityException e) {

                throw new SecurityException("runFinalizersOnExit");

            }

        }

        Shutdown.setRunFinalizersOnExit(value);

    }

    /**

     * Executes the specified string command in a separate process.

     *

     * <p>This is a convenience method.  An invocation of the form

     * {@code exec(command)}

     * behaves in exactly the same way as the invocation

     * {@link #exec(String, String[], File) exec}{@code (command, null, null)}.

     *

     * @param   command   a specified system command.

     *

     * @return  A new {@link Process} object for managing the subprocess

     *

     * @throws  SecurityException

     *          If a security manager exists and its

     *          {@link SecurityManager#checkExec checkExec}

     *          method doesn't allow creation of the subprocess

     *

     * @throws  IOException

     *          If an I/O error occurs

     *

     * @throws  NullPointerException

     *          If {@code command} is {@code null}

     *

     * @throws  IllegalArgumentException

     *          If {@code command} is empty

     *

     * @see     #exec(String[], String[], File)

     * @see     ProcessBuilder

     */

    public Process exec(String command) throws IOException {

        return exec(command, null, null);

    }

    /**

     * Executes the specified string command in a separate process with the

     * specified environment.

     *

     * <p>This is a convenience method.  An invocation of the form

     * {@code exec(command, envp)}

     * behaves in exactly the same way as the invocation

     * {@link #exec(String, String[], File) exec}{@code (command, envp, null)}.

     *

     * @param   command   a specified system command.

     *

     * @param   envp      array of strings, each element of which

     *                    has environment variable settings in the format

     *                    <i>name</i>=<i>value</i>, or

     *                    {@code null} if the subprocess should inherit

     *                    the environment of the current process.

     *

     * @return  A new {@link Process} object for managing the subprocess

     *

     * @throws  SecurityException

     *          If a security manager exists and its

     *          {@link SecurityManager#checkExec checkExec}

     *          method doesn't allow creation of the subprocess

     *

     * @throws  IOException

     *          If an I/O error occurs

     *

     * @throws  NullPointerException

     *          If {@code command} is {@code null},

     *          or one of the elements of {@code envp} is {@code null}

     *

     * @throws  IllegalArgumentException

     *          If {@code command} is empty

     *

     * @see     #exec(String[], String[], File)

     * @see     ProcessBuilder

     */

    public Process exec(String command, String[] envp) throws IOException {

        return exec(command, envp, null);

    }

    /**

     * Executes the specified string command in a separate process with the

     * specified environment and working directory.

     *

     * <p>This is a convenience method.  An invocation of the form

     * {@code exec(command, envp, dir)}

     * behaves in exactly the same way as the invocation

     * {@link #exec(String[], String[], File) exec}{@code (cmdarray, envp, dir)},

     * where {@code cmdarray} is an array of all the tokens in

     * {@code command}.

     *

     * <p>More precisely, the {@code command} string is broken

     * into tokens using a {@link StringTokenizer} created by the call

     * {@code new {@link StringTokenizer}(command)} with no

     * further modification of the character categories.  The tokens

     * produced by the tokenizer are then placed in the new string

     * array {@code cmdarray}, in the same order.

     *

     * @param   command   a specified system command.

     *

     * @param   envp      array of strings, each element of which

     *                    has environment variable settings in the format

     *                    <i>name</i>=<i>value</i>, or

     *                    {@code null} if the subprocess should inherit

     *                    the environment of the current process.

     *

     * @param   dir       the working directory of the subprocess, or

     *                    {@code null} if the subprocess should inherit

     *                    the working directory of the current process.

     *

     * @return  A new {@link Process} object for managing the subprocess

     *

     * @throws  SecurityException

     *          If a security manager exists and its

     *          {@link SecurityManager#checkExec checkExec}

     *          method doesn't allow creation of the subprocess

     *

     * @throws  IOException

     *          If an I/O error occurs

     *

     * @throws  NullPointerException

     *          If {@code command} is {@code null},

     *          or one of the elements of {@code envp} is {@code null}

     *

     * @throws  IllegalArgumentException

     *          If {@code command} is empty

     *

     * @see     ProcessBuilder

     * @since 1.3

     */

    public Process exec(String command, String[] envp, File dir)

        throws IOException {

        if (command.length() == 0)

            throw new IllegalArgumentException("Empty command");

        StringTokenizer st = new StringTokenizer(command);

        String[] cmdarray = new String[st.countTokens()];

        for (int i = 0; st.hasMoreTokens(); i++)

            cmdarray[i] = st.nextToken();

        return exec(cmdarray, envp, dir);

    }

    /**

     * Executes the specified command and arguments in a separate process.

     *

     * <p>This is a convenience method.  An invocation of the form

     * {@code exec(cmdarray)}

     * behaves in exactly the same way as the invocation

     * {@link #exec(String[], String[], File) exec}{@code (cmdarray, null, null)}.

     *

     * @param   cmdarray  array containing the command to call and

     *                    its arguments.

     *

     * @return  A new {@link Process} object for managing the subprocess

     *

     * @throws  SecurityException

     *          If a security manager exists and its

     *          {@link SecurityManager#checkExec checkExec}

     *          method doesn't allow creation of the subprocess

     *

     * @throws  IOException

     *          If an I/O error occurs

     *

     * @throws  NullPointerException

     *          If {@code cmdarray} is {@code null},

     *          or one of the elements of {@code cmdarray} is {@code null}

     *

     * @throws  IndexOutOfBoundsException

     *          If {@code cmdarray} is an empty array

     *          (has length {@code 0})

     *

     * @see     ProcessBuilder

     */

    public Process exec(String cmdarray[]) throws IOException {

        return exec(cmdarray, null, null);

    }

    /**

     * Executes the specified command and arguments in a separate process

     * with the specified environment.

     *

     * <p>This is a convenience method.  An invocation of the form

     * {@code exec(cmdarray, envp)}

     * behaves in exactly the same way as the invocation

     * {@link #exec(String[], String[], File) exec}{@code (cmdarray, envp, null)}.

     *

     * @param   cmdarray  array containing the command to call and

     *                    its arguments.

     *

     * @param   envp      array of strings, each element of which

     *                    has environment variable settings in the format

     *                    <i>name</i>=<i>value</i>, or

     *                    {@code null} if the subprocess should inherit

     *                    the environment of the current process.

     *

     * @return  A new {@link Process} object for managing the subprocess

     *

     * @throws  SecurityException

     *          If a security manager exists and its

     *          {@link SecurityManager#checkExec checkExec}

     *          method doesn't allow creation of the subprocess

     *

     * @throws  IOException

     *          If an I/O error occurs

     *

     * @throws  NullPointerException