/*

 * Copyright (c) 1994, 2019, 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.BufferedInputStream;

import java.io.BufferedOutputStream;

import java.io.Console;

import java.io.FileDescriptor;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.PrintStream;

import java.io.UnsupportedEncodingException;

import java.lang.annotation.Annotation;

import java.lang.module.ModuleDescriptor;

import java.lang.reflect.Constructor;

import java.lang.reflect.Executable;

import java.lang.reflect.Method;

import java.lang.reflect.Modifier;

import java.net.URI;

import java.nio.charset.CharacterCodingException;

import java.security.AccessControlContext;

import java.security.ProtectionDomain;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.nio.channels.Channel;

import java.nio.channels.spi.SelectorProvider;

import java.nio.charset.Charset;

import java.util.Iterator;

import java.util.List;

import java.util.Map;

import java.util.Objects;

import java.util.Properties;

import java.util.PropertyPermission;

import java.util.ResourceBundle;

import java.util.function.Supplier;

import java.util.concurrent.ConcurrentHashMap;

import java.util.stream.Stream;

import jdk.internal.util.StaticProperty;

import jdk.internal.module.ModuleBootstrap;

import jdk.internal.module.ServicesCatalog;

import jdk.internal.reflect.CallerSensitive;

import jdk.internal.reflect.Reflection;

import jdk.internal.HotSpotIntrinsicCandidate;

import jdk.internal.access.JavaLangAccess;

import jdk.internal.access.SharedSecrets;

import jdk.internal.misc.VM;

import jdk.internal.logger.LoggerFinderLoader;

import jdk.internal.logger.LazyLoggers;

import jdk.internal.logger.LocalizedLoggerWrapper;

import jdk.internal.util.SystemProps;

import jdk.internal.vm.annotation.Stable;

import sun.nio.fs.DefaultFileSystemProvider;

import sun.reflect.annotation.AnnotationType;

import sun.nio.ch.Interruptible;

import sun.security.util.SecurityConstants;

/**

 * The {@code System} class contains several useful class fields

 * and methods. It cannot be instantiated.

 *

 * Among the facilities provided by the {@code System} class

 * are standard input, standard output, and error output streams;

 * access to externally defined properties and environment

 * variables; a means of loading files and libraries; and a utility

 * method for quickly copying a portion of an array.

 *

 * @since   1.0

 */

public final class System {

    /* Register the natives via the static initializer.

     *

     * VM will invoke the initializeSystemClass method to complete

     * the initialization for this class separated from clinit.

     * Note that to use properties set by the VM, see the constraints

     * described in the initializeSystemClass method.

     */

    private static native void registerNatives();

    static {

        registerNatives();

    }

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

    private System() {

    }

    /**

     * The "standard" input stream. This stream is already

     * open and ready to supply input data. Typically this stream

     * corresponds to keyboard input or another input source specified by

     * the host environment or user.

     */

    public static final InputStream in = null;

    /**

     * The "standard" output stream. This stream is already

     * open and ready to accept output data. Typically this stream

     * corresponds to display output or another output destination

     * specified by the host environment or user.

     * <p>

     * For simple stand-alone Java applications, a typical way to write

     * a line of output data is:

     * <blockquote><pre>

     *     System.out.println(data)

     * </pre></blockquote>

     * <p>

     * See the {@code println} methods in class {@code PrintStream}.

     *

     * @see     java.io.PrintStream#println()

     * @see     java.io.PrintStream#println(boolean)

     * @see     java.io.PrintStream#println(char)

     * @see     java.io.PrintStream#println(char[])

     * @see     java.io.PrintStream#println(double)

     * @see     java.io.PrintStream#println(float)

     * @see     java.io.PrintStream#println(int)

     * @see     java.io.PrintStream#println(long)

     * @see     java.io.PrintStream#println(java.lang.Object)

     * @see     java.io.PrintStream#println(java.lang.String)

     */

    public static final PrintStream out = null;

    /**

     * The "standard" error output stream. This stream is already

     * open and ready to accept output data.

     * <p>

     * Typically this stream corresponds to display output or another

     * output destination specified by the host environment or user. By

     * convention, this output stream is used to display error messages

     * or other information that should come to the immediate attention

     * of a user even if the principal output stream, the value of the

     * variable {@code out}, has been redirected to a file or other

     * destination that is typically not continuously monitored.

     */

    public static final PrintStream err = null;

    // indicates if a security manager is possible

    private static final int NEVER = 1;

    private static final int MAYBE = 2;

    private static @Stable int allowSecurityManager;

    // current security manager

    private static volatile SecurityManager security;   // read by VM

    // return true if a security manager is allowed

    private static boolean allowSecurityManager() {

        return (allowSecurityManager != NEVER);

    }

    /**

     * Reassigns the "standard" input stream.

     *

     * First, if there is a security manager, its {@code checkPermission}

     * method is called with a {@code RuntimePermission("setIO")} permission

     *  to see if it's ok to reassign the "standard" input stream.

     *

     * @param in the new standard input stream.

     *

     * @throws SecurityException

     *        if a security manager exists and its

     *        {@code checkPermission} method doesn't allow

     *        reassigning of the standard input stream.

     *

     * @see SecurityManager#checkPermission

     * @see java.lang.RuntimePermission

     *

     * @since   1.1

     */

    public static void setIn(InputStream in) {

        checkIO();

        setIn0(in);

    }

    /**

     * Reassigns the "standard" output stream.

     *

     * First, if there is a security manager, its {@code checkPermission}

     * method is called with a {@code RuntimePermission("setIO")} permission

     *  to see if it's ok to reassign the "standard" output stream.

     *

     * @param out the new standard output stream

     *

     * @throws SecurityException

     *        if a security manager exists and its

     *        {@code checkPermission} method doesn't allow

     *        reassigning of the standard output stream.

     *

     * @see SecurityManager#checkPermission

     * @see java.lang.RuntimePermission

     *

     * @since   1.1

     */

    public static void setOut(PrintStream out) {

        checkIO();

        setOut0(out);

    }

    /**

     * Reassigns the "standard" error output stream.

     *

     * First, if there is a security manager, its {@code checkPermission}

     * method is called with a {@code RuntimePermission("setIO")} permission

     *  to see if it's ok to reassign the "standard" error output stream.

     *

     * @param err the new standard error output stream.

     *

     * @throws SecurityException

     *        if a security manager exists and its

     *        {@code checkPermission} method doesn't allow

     *        reassigning of the standard error output stream.

     *

     * @see SecurityManager#checkPermission

     * @see java.lang.RuntimePermission

     *

     * @since   1.1

     */

    public static void setErr(PrintStream err) {

        checkIO();

        setErr0(err);

    }

    private static volatile Console cons;

    /**

     * Returns the unique {@link java.io.Console Console} object associated

     * with the current Java virtual machine, if any.

     *

     * @return  The system console, if any, otherwise {@code null}.

     *

     * @since   1.6

     */

     public static Console console() {

         Console c;

         if ((c = cons) == null) {

             synchronized (System.class) {

                 if ((c = cons) == null) {

                     cons = c = SharedSecrets.getJavaIOAccess().console();

                 }

             }

         }

         return c;

     }

    /**

     * Returns the channel inherited from the entity that created this

     * Java virtual machine.

     *

     * This method returns the channel obtained by invoking the

     * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel

     * inheritedChannel} method of the system-wide default

     * {@link java.nio.channels.spi.SelectorProvider} object.

     *

     * <p> In addition to the network-oriented channels described in

     * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel

     * inheritedChannel}, this method may return other kinds of

     * channels in the future.

     *

     * @return  The inherited channel, if any, otherwise {@code null}.

     *

     * @throws  IOException

     *          If an I/O error occurs

     *

     * @throws  SecurityException

     *          If a security manager is present and it does not

     *          permit access to the channel.

     *

     * @since 1.5

     */

    public static Channel inheritedChannel() throws IOException {

        return SelectorProvider.provider().inheritedChannel();

    }

    private static void checkIO() {

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

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

        }

    }

    private static native void setIn0(InputStream in);

    private static native void setOut0(PrintStream out);

    private static native void setErr0(PrintStream err);

    /**

     * Sets the system-wide security manager.

     *

     * If there is a security manager already installed, this method first

     * calls the security manager's {@code checkPermission} method

     * with a {@code RuntimePermission("setSecurityManager")}

     * permission to ensure it's ok to replace the existing

     * security manager.

     * This may result in throwing a {@code SecurityException}.

     *

     * <p> Otherwise, the argument is established as the current

     * security manager. If the argument is {@code null} and no

     * security manager has been established, then no action is taken and

     * the method simply returns.

     *

     * @implNote In the JDK implementation, if the Java virtual machine is

     * started with the system property {@code java.security.manager} set to

     * the special token "{@code disallow}" then the {@code setSecurityManager}

     * method cannot be used to set a security manager.

     *

     * @param  sm the security manager or {@code null}

     * @throws SecurityException

     *         if the security manager has already been set and its {@code

     *         checkPermission} method doesn't allow it to be replaced

     * @throws UnsupportedOperationException

     *         if {@code sm} is non-null and a security manager is not allowed

     *         to be set dynamically

     * @see #getSecurityManager

     * @see SecurityManager#checkPermission

     * @see java.lang.RuntimePermission

     */

    public static void setSecurityManager(SecurityManager sm) {

        if (allowSecurityManager()) {

            if (security == null) {

                // ensure image reader is initialized

                Object.class.getResource("java/lang/ANY");

                // ensure the default file system is initialized

                DefaultFileSystemProvider.theFileSystem();

            }

            if (sm != null) {

                try {

                    // pre-populates the SecurityManager.packageAccess cache

                    // to avoid recursive permission checking issues with custom

                    // SecurityManager implementations

                    sm.checkPackageAccess("java.lang");

                } catch (Exception e) {

                    // no-op

                }

            }

            setSecurityManager0(sm);

        } else {

            // security manager not allowed

            if (sm != null) {

                throw new UnsupportedOperationException(

                    "Runtime configured to disallow security manager");

            }

        }

    }

    private static synchronized

    void setSecurityManager0(final SecurityManager s) {

        SecurityManager sm = getSecurityManager();

        if (sm != null) {

            // ask the currently installed security manager if we

            // can replace it.

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

        }

        if ((s != null) && (s.getClass().getClassLoader() != null)) {

            // New security manager class is not on bootstrap classpath.

            // Force policy to get initialized before we install the new

            // security manager, in order to prevent infinite loops when

            // trying to initialize the policy (which usually involves

            // accessing some security and/or system properties, which in turn

            // calls the installed security manager's checkPermission method

            // which will loop infinitely if there is a non-system class

            // (in this case: the new security manager class) on the stack).

            AccessController.doPrivileged(new PrivilegedAction<>() {

                public Object run() {

                    s.getClass().getProtectionDomain().implies

                        (SecurityConstants.ALL_PERMISSION);

                    return null;

                }

            });

        }

        security = s;

    }

    /**

     * Gets the system-wide security manager.

     *

     * @return  if a security manager has already been established for the

     *          current application, then that security manager is returned;

     *          otherwise, {@code null} is returned.

     * @see     #setSecurityManager

     */

    public static SecurityManager getSecurityManager() {

        if (allowSecurityManager()) {

            return security;

        } else {

            return null;

        }

    }

    /**

     * Returns the current time in milliseconds.  Note that

     * while the unit of time of the return value is a millisecond,

     * the granularity of the value depends on the underlying

     * operating system and may be larger.  For example, many

     * operating systems measure time in units of tens of

     * milliseconds.

     *

     * <p> See the description of the class {@code Date} for

     * a discussion of slight discrepancies that may arise between

     * "computer time" and coordinated universal time (UTC).

     *

     * @return  the difference, measured in milliseconds, between

     *          the current time and midnight, January 1, 1970 UTC.

     * @see     java.util.Date

     */

    @HotSpotIntrinsicCandidate

    public static native long currentTimeMillis();

    /**

     * Returns the current value of the running Java Virtual Machine's

     * high-resolution time source, in nanoseconds.

     *

     * This method can only be used to measure elapsed time and is

     * not related to any other notion of system or wall-clock time.

     * The value returned represents nanoseconds since some fixed but

     * arbitrary <i>origin</i> time (perhaps in the future, so values

     * may be negative).  The same origin is used by all invocations of

     * this method in an instance of a Java virtual machine; other

     * virtual machine instances are likely to use a different origin.

     *

     * <p>This method provides nanosecond precision, but not necessarily

     * nanosecond resolution (that is, how frequently the value changes)

     * - no guarantees are made except that the resolution is at least as

     * good as that of {@link #currentTimeMillis()}.

     *

     * <p>Differences in successive calls that span greater than

     * approximately 292 years (2<sup>63</sup> nanoseconds) will not

     * correctly compute elapsed time due to numerical overflow.

     *

     * <p>The values returned by this method become meaningful only when

     * the difference between two such values, obtained within the same

     * instance of a Java virtual machine, is computed.

     *

     * <p>For example, to measure how long some code takes to execute:

     * <pre> {@code

     * long startTime = System.nanoTime();

     * // ... the code being measured ...

     * long elapsedNanos = System.nanoTime() - startTime;}</pre>

     *

     * <p>To compare elapsed time against a timeout, use <pre> {@code

     * if (System.nanoTime() - startTime >= timeoutNanos) ...}</pre>

     * instead of <pre> {@code

     * if (System.nanoTime() >= startTime + timeoutNanos) ...}</pre>

     * because of the possibility of numerical overflow.

     *

     * @return the current value of the running Java Virtual Machine's

     *         high-resolution time source, in nanoseconds

     * @since 1.5

     */

    @HotSpotIntrinsicCandidate

    public static native long nanoTime();

    /**

     * Copies an array from the specified source array, beginning at the

     * specified position, to the specified position of the destination array.

     * A subsequence of array components are copied from the source

     * array referenced by {@code src} to the destination array

     * referenced by {@code dest}. The number of components copied is

     * equal to the {@code length} argument. The components at

     * positions {@code srcPos} through

     * {@code srcPos+length-1} in the source array are copied into

     * positions {@code destPos} through

     * {@code destPos+length-1}, respectively, of the destination

     * array.

     * <p>

     * If the {@code src} and {@code dest} arguments refer to the

     * same array object, then the copying is performed as if the

     * components at positions {@code srcPos} through

     * {@code srcPos+length-1} were first copied to a temporary

     * array with {@code length} components and then the contents of

     * the temporary array were copied into positions

     * {@code destPos} through {@code destPos+length-1} of the

     * destination array.

     * <p>

     * If {@code dest} is {@code null}, then a

     * {@code NullPointerException} is thrown.

     * <p>

     * If {@code src} is {@code null}, then a

     * {@code NullPointerException} is thrown and the destination

     * array is not modified.

     * <p>

     * Otherwise, if any of the following is true, an

     * {@code ArrayStoreException} is thrown and the destination is

     * not modified: