/*

 * Copyright (c) 1995, 2012, 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.concurrent.TimeUnit;

/**

 * The {@link ProcessBuilder#start()} and

 * {@link Runtime#exec(String[],String[],File) Runtime.exec}

 * methods create a native process and return an instance of a

 * subclass of {@code Process} that can be used to control the process

 * and obtain information about it.  The class {@code Process}

 * provides methods for performing input from the process, performing

 * output to the process, waiting for the process to complete,

 * checking the exit status of the process, and destroying (killing)

 * the process.

 *

 * <p>The methods that create processes may not work well for special

 * processes on certain native platforms, such as native windowing

 * processes, daemon processes, Win16/DOS processes on Microsoft

 * Windows, or shell scripts.

 *

 * <p>By default, the created subprocess does not have its own terminal

 * or console.  All its standard I/O (i.e. stdin, stdout, stderr)

 * operations will be redirected to the parent process, where they can

 * be accessed via the streams obtained using the methods

 * {@link #getOutputStream()},

 * {@link #getInputStream()}, and

 * {@link #getErrorStream()}.

 * The parent process uses these streams to feed input to and get output

 * from the subprocess.  Because some native platforms only provide

 * limited buffer size for standard input and output streams, failure

 * to promptly write the input stream or read the output stream of

 * the subprocess may cause the subprocess to block, or even deadlock.

 *

 * <p>Where desired, <a href="ProcessBuilder.html#redirect-input">

 * subprocess I/O can also be redirected</a>

 * using methods of the {@link ProcessBuilder} class.

 *

 * <p>The subprocess is not killed when there are no more references to

 * the {@code Process} object, but rather the subprocess

 * continues executing asynchronously.

 *

 * <p>There is no requirement that a process represented by a {@code

 * Process} object execute asynchronously or concurrently with respect

 * to the Java process that owns the {@code Process} object.

 *

 * <p>As of 1.5, {@link ProcessBuilder#start()} is the preferred way

 * to create a {@code Process}.

 *

 * @since   JDK1.0

 */

public abstract class Process {

    /**

     * Returns the output stream connected to the normal input of the

     * subprocess.  Output to the stream is piped into the standard

     * input of the process represented by this {@code Process} object.

     *

     * <p>If the standard input of the subprocess has been redirected using

     * {@link ProcessBuilder#redirectInput(Redirect)

     * ProcessBuilder.redirectInput}

     * then this method will return a

     * <a href="ProcessBuilder.html#redirect-input">null output stream</a>.

     *

     * <p>Implementation note: It is a good idea for the returned

     * output stream to be buffered.

     *

     * @return the output stream connected to the normal input of the

     *         subprocess

     */

    public abstract OutputStream getOutputStream();

    /**

     * Returns the input stream connected to the normal output of the

     * subprocess.  The stream obtains data piped from the standard

     * output of the process represented by this {@code Process} object.

     *

     * <p>If the standard output of the subprocess has been redirected using

     * {@link ProcessBuilder#redirectOutput(Redirect)

     * ProcessBuilder.redirectOutput}

     * then this method will return a

     * <a href="ProcessBuilder.html#redirect-output">null input stream</a>.

     *

     * <p>Otherwise, if the standard error of the subprocess has been

     * redirected using

     * {@link ProcessBuilder#redirectErrorStream(boolean)

     * ProcessBuilder.redirectErrorStream}

     * then the input stream returned by this method will receive the

     * merged standard output and the standard error of the subprocess.

     *

     * <p>Implementation note: It is a good idea for the returned

     * input stream to be buffered.

     *

     * @return the input stream connected to the normal output of the

     *         subprocess

     */

    public abstract InputStream getInputStream();

    /**

     * Returns the input stream connected to the error output of the

     * subprocess.  The stream obtains data piped from the error output

     * of the process represented by this {@code Process} object.

     *

     * <p>If the standard error of the subprocess has been redirected using

     * {@link ProcessBuilder#redirectError(Redirect)

     * ProcessBuilder.redirectError} or

     * {@link ProcessBuilder#redirectErrorStream(boolean)

     * ProcessBuilder.redirectErrorStream}

     * then this method will return a

     * <a href="ProcessBuilder.html#redirect-output">null input stream</a>.

     *

     * <p>Implementation note: It is a good idea for the returned

     * input stream to be buffered.

     *

     * @return the input stream connected to the error output of

     *         the subprocess

     */

    public abstract InputStream getErrorStream();

    /**

     * Causes the current thread to wait, if necessary, until the

     * process represented by this {@code Process} object has

     * terminated.  This method returns immediately if the subprocess

     * has already terminated.  If the subprocess has not yet

     * terminated, the calling thread will be blocked until the

     * subprocess exits.

     *

     * @return the exit value of the subprocess represented by this

     *         {@code Process} object.  By convention, the value

     *         {@code 0} indicates normal termination.

     * @throws InterruptedException if the current thread is

     *         {@linkplain Thread#interrupt() interrupted} by another

     *         thread while it is waiting, then the wait is ended and

     *         an {@link InterruptedException} is thrown.

     */

    public abstract int waitFor() throws InterruptedException;

    /**

     * Causes the current thread to wait, if necessary, until the

     * subprocess represented by this {@code Process} object has

     * terminated, or the specified waiting time elapses.

     *

     * <p>If the subprocess has already terminated then this method returns

     * immediately with the value {@code true}.  If the process has not

     * terminated and the timeout value is less than, or equal to, zero, then

     * this method returns immediately with the value {@code false}.

     *

     * <p>The default implementation of this methods polls the {@code exitValue}

     * to check if the process has terminated. Concrete implementations of this

     * class are strongly encouraged to override this method with a more

     * efficient implementation.

     *

     * @param timeout the maximum time to wait

     * @param unit the time unit of the {@code timeout} argument

     * @return {@code true} if the subprocess has exited and {@code false} if

     *         the waiting time elapsed before the subprocess has exited.

     * @throws InterruptedException if the current thread is interrupted

     *         while waiting.

     * @throws NullPointerException if unit is null

     * @since 1.8

     */

    public boolean waitFor(long timeout, TimeUnit unit)

        throws InterruptedException

    {

        long startTime = System.nanoTime();

        long rem = unit.toNanos(timeout);

        do {

            try {

                exitValue();

                return true;

            } catch(IllegalThreadStateException ex) {

                if (rem > 0)

                    Thread.sleep(

                        Math.min(TimeUnit.NANOSECONDS.toMillis(rem) + 1, 100));

            }

            rem = unit.toNanos(timeout) - (System.nanoTime() - startTime);

        } while (rem > 0);

        return false;

    }

    /**

     * Returns the exit value for the subprocess.

     *

     * @return the exit value of the subprocess represented by this

     *         {@code Process} object.  By convention, the value

     *         {@code 0} indicates normal termination.

     * @throws IllegalThreadStateException if the subprocess represented

     *         by this {@code Process} object has not yet terminated

     */

    public abstract int exitValue();

    /**

     * Kills the subprocess. Whether the subprocess represented by this

     * {@code Process} object is forcibly terminated or not is

     * implementation dependent.

     */

    public abstract void destroy();

    /**

     * Kills the subprocess. The subprocess represented by this

     * {@code Process} object is forcibly terminated.

     *

     * <p>The default implementation of this method invokes {@link #destroy}

     * and so may not forcibly terminate the process. Concrete implementations

     * of this class are strongly encouraged to override this method with a

     * compliant implementation.  Invoking this method on {@code Process}

     * objects returned by {@link ProcessBuilder#start} and

     * {@link Runtime#exec} will forcibly terminate the process.

     *

     * <p>Note: The subprocess may not terminate immediately.

     * i.e. {@code isAlive()} may return true for a brief period

     * after {@code destroyForcibly()} is called. This method

     * may be chained to {@code waitFor()} if needed.

     *

     * @return the {@code Process} object representing the

     *         subprocess to be forcibly destroyed.

     * @since 1.8

     */

    public Process destroyForcibly() {

        destroy();

        return this;

    }

    /**

     * Tests whether the subprocess represented by this {@code Process} is

     * alive.

     *

     * @return {@code true} if the subprocess represented by this

     *         {@code Process} object has not yet terminated.

     * @since 1.8

     */

    public boolean isAlive() {

        try {

            exitValue();

            return false;

        } catch(IllegalThreadStateException e) {

            return true;

        }

    }

}