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package java.lang;

import java.io.*;

import java.lang.ProcessBuilder.Redirect;

import java.util.concurrent.CompletableFuture;

import java.util.concurrent.ForkJoinPool;

import java.util.concurrent.TimeUnit;

import java.util.stream.Stream;

/**

 * {@code Process} provides control of native processes started by

 * ProcessBuilder.start and Runtime.exec.

 * The class 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.

 * 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.

 *

 * <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 process 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 process.  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 process may cause the process to block, or even deadlock.

 *

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

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

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

 *

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

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

 * continues executing asynchronously.

 *

 * <p>There is no requirement that the 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}.

 *

 * <p>Subclasses of Process should override the {@link #onExit()} and

 * {@link #toHandle()} methods to provide a fully functional Process including the

 * Delegating to the underlying Process or ProcessHandle is typically

 * easiest and most efficient.

 *

 * @since   1.0

 */

public abstract class Process {

    /**

     * Default constructor for Process.

     */

    public Process() {}

    /**

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

     * process.  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 process 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

     *         process

     */

    public abstract OutputStream getOutputStream();

    /**

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

     * process.  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 process 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 process 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 process.

     *

     * <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

     *         process

     */

    public abstract InputStream getInputStream();

    /**

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

     * process.  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 process 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 process

     */

    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 process

     * has already terminated.  If the process has not yet

     * terminated, the calling thread will be blocked until the

     * process exits.

     *

     * @return the exit value of the process 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

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

     * terminated, or the specified waiting time elapses.

     *

     * <p>If the process 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 process has exited and {@code false} if

     *         the waiting time elapsed before the process 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 process.

     *

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

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

     *         {@code 0} indicates normal termination.

     * @throws IllegalThreadStateException if the process represented

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

     */

    public abstract int exitValue();

    /**

     * Kills the process.

     * Whether the process represented by this {@code Process} object is

     * implementation dependent.

     * Forcible process destruction is defined as the immediate termination of a

     * process, whereas normal termination allows the process to shut down cleanly.

     * If the process is not alive, no action is taken.

     * <p>

     * The {@link java.util.concurrent.CompletableFuture} from {@link #onExit} is

     * when the process has terminated.

     */

    public abstract void destroy();

    /**

     * Kills the process forcibly. The process represented by this

     * {@code Process} object is forcibly terminated.

     * Forcible process destruction is defined as the immediate termination of a

     * process, whereas normal termination allows the process to shut down cleanly.

     * If the process is not alive, no action is taken.

     * <p>

     * The {@link java.util.concurrent.CompletableFuture} from {@link #onExit} is

     * when the process has terminated.

     * <p>

     * Invoking this method on {@code Process} objects returned by

     * {@link ProcessBuilder#start} and {@link Runtime#exec} forcibly terminate

     * the process.

     *

     * @implSpec

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

     * and so may not forcibly terminate the process.

     * @implNote

     * Concrete implementations of this class are strongly encouraged to override

     * this method with a compliant implementation.

     * @apiNote

     * The process 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

     *         process forcibly destroyed

     * @since 1.8

     */

    public Process destroyForcibly() {

        destroy();

        return this;

    }

    /**

     * Returns {@code true} if the implementation of {@link #destroy} is to

     * normally terminate the process,

     * Returns {@code false} if the implementation of {@code destroy}

     * forcibly and immediately terminates the process.

     * <p>

     * Invoking this method on {@code Process} objects returned by

     * {@link ProcessBuilder#start} and {@link Runtime#exec} return

     * {@code true} or {@code false} depending on the platform implementation.

     *

     * @implSpec

     * This implementation throws an instance of

     * {@link java.lang.UnsupportedOperationException} and performs no other action.

     *

     * @return {@code true} if the implementation of {@link #destroy} is to

     *         normally terminate the process;

     *         otherwise, {@link #destroy} forcibly terminates the process

     * @throws UnsupportedOperationException if the Process implementation

     *         does not support this operation

     * @since 9

     */

    public boolean supportsNormalTermination() {

        throw new UnsupportedOperationException(this.getClass()

                + ".supportsNormalTermination() not supported" );

    }

    /**

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

     * alive.

     *

     * @return {@code true} if the process 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;

        }

    }

    /**

     * Returns the native process ID of the process.

     * The native process ID is an identification number that the operating

     * system assigns to the process.

     *

     * @implSpec

     * The implementation of this method returns the process id as:

     *

     * @return the native process id of the process

     * @throws UnsupportedOperationException if the Process implementation

     *         does not support this operation

     * @since 9

     */

    }

    /**

     * Returns a {@code CompletableFuture<Process>} for the termination of the Process.

     * The {@link java.util.concurrent.CompletableFuture} provides the ability

     * to trigger dependent functions or actions that may be run synchronously

     * or asynchronously upon process termination.

     * When the process has terminated the CompletableFuture is

     * {@link java.util.concurrent.CompletableFuture#complete completed} regardless

     * of the exit status of the process.

     * <p>

     * Calling {@code onExit().get()} waits for the process to terminate and returns

     * the Process. The future can be used to check if the process is

     * the CompletableFuture does not affect the Process.

     * <p>

     * Processes returned from {@link ProcessBuilder#start} override the

     * default implementation to provide an efficient mechanism to wait

     * for process exit.

     *

     * @apiNote

     * Using {@link #onExit() onExit} is an alternative to

     * {@link #waitFor() waitFor} that enables both additional concurrency

     * and convenient access to the result of the Process.

     * Lambda expressions can be used to evaluate the result of the Process

     * execution.

     * If there is other processing to be done before the value is used

     * then {@linkplain #onExit onExit} is a convenient mechanism to

     * free the current thread and block only if and when the value is needed.

     * <br>

     * For example, launching a process to compare two files and get a boolean if they are identical:

     * <pre> {@code   Process p = new ProcessBuilder("cmp", "f1", "f2").start();

     *    Future<Boolean> identical = p.onExit().thenApply(p1 -> p1.exitValue() == 0);

     *    ...

     *    if (identical.get()) { ... }

     * }</pre>

     *

     * @implSpec

     * This implementation executes {@link #waitFor()} in a separate thread

     * repeatedly until it returns successfully. If the execution of

     * {@code waitFor} is interrupted, the thread's interrupt status is preserved.

     * <p>

     * When {@link #waitFor()} returns successfully the CompletableFuture is

     * of the exit status of the process.

     *

     * This implementation may consume a lot of memory for thread stacks if a

     * large number of processes are waited for concurrently.

     * <p>

     * External implementations should override this method and provide

     * a more efficient implementation. For example, to delegate to the underlying

     * process, it can do the following:

     * <pre>{@code

     *    public CompletableFuture<Process> onExit() {

     *       return delegate.onExit().thenApply(p -> this);

     *    }

     * }</pre>

     * @apiNote

     * The process may be observed to have terminated with {@link #isAlive}

     * before the ComputableFuture is completed and dependent actions are invoked.

     *

     * @return a new {@code CompletableFuture<Process>} for the Process

     *

     * @since 9

     */

    public CompletableFuture<Process> onExit() {

        return CompletableFuture.supplyAsync(this::waitForInternal);

    }

    /**

     * Wait for the process to exit by calling {@code waitFor}.

     * If the thread is interrupted, remember the interrupted state to

     * be restored before returning. Use ForkJoinPool.ManagedBlocker

     * so that the number of workers in case ForkJoinPool is used is

     * compensated when the thread blocks in waitFor().

     *

     * @return the Process

     */

    private Process waitForInternal() {

        boolean interrupted = false;

        while (true) {

            try {

                ForkJoinPool.managedBlock(new ForkJoinPool.ManagedBlocker() {

                    @Override

                    public boolean block() throws InterruptedException {

                        waitFor();

                        return true;

                    }

                    @Override

                    public boolean isReleasable() {

                        return !isAlive();

                    }

                });

                break;

            } catch (InterruptedException x) {

                interrupted = true;

            }

        }

        if (interrupted) {

            Thread.currentThread().interrupt();

        }

        return this;

    }

    /**

     * Returns a ProcessHandle for the Process.

     *

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

     * {@link Runtime#exec} implement {@code toHandle} as the equivalent of

     * {@link ProcessHandle#of(long) ProcessHandle.of(pid)} including the

     * check for a SecurityManager and {@code RuntimePermission("manageProcess")}.

     *

     * @implSpec

     * This implementation throws an instance of

     * {@link java.lang.UnsupportedOperationException} and performs no other action.

     * Subclasses should override this method to provide a ProcessHandle for the

     * and {@link #descendants}, unless overridden, operate on the ProcessHandle.

     *

     * @return Returns a ProcessHandle for the Process

     * @throws UnsupportedOperationException if the Process implementation

     *         does not support this operation

     * @throws SecurityException if a security manager has been installed and

     *         it denies RuntimePermission("manageProcess")

     * @since 9

     */

    public ProcessHandle toHandle() {

        throw new UnsupportedOperationException(this.getClass()

                + ".toHandle() not supported");

    }

    /**

     * Returns a snapshot of information about the process.

     *

     * <p> A {@link ProcessHandle.Info} instance has accessor methods

     * that return information about the process if it is available.

     *

     * @implSpec

     * This implementation returns information about the process as:

     * {@link #toHandle toHandle().info()}.

     *

     * @return a snapshot of information about the process, always non-null

     * @throws UnsupportedOperationException if the Process implementation