/*

 * Copyright (c) 2014, 2015, 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.security.PrivilegedAction;

import java.time.Duration;

import java.time.Instant;

import java.util.Arrays;

import java.util.Optional;

import java.util.concurrent.CompletableFuture;

import java.util.concurrent.ConcurrentHashMap;

import java.util.concurrent.ConcurrentMap;

import java.util.concurrent.Executor;

import java.util.concurrent.Executors;

import java.util.concurrent.ForkJoinPool;

import java.util.concurrent.SynchronousQueue;

import java.util.concurrent.ThreadFactory;

import java.util.concurrent.ThreadPoolExecutor;

import java.util.concurrent.TimeUnit;

import java.util.stream.IntStream;

import java.util.stream.Stream;

import static java.security.AccessController.doPrivileged;

/**

 * ProcessHandleImpl is the implementation of ProcessHandle.

 *

 * @see Process

 * @since 9

 */

final class ProcessHandleImpl implements ProcessHandle {

    /**

     * Cache the ProcessHandle of this process.

     */

    private static final ProcessHandleImpl current;

    /**

     * Map of pids to ExitCompletions.

     */

    private static final ConcurrentMap<Long, ExitCompletion>

            completions = new ConcurrentHashMap<>();

    static {

        initNative();

        long pid = getCurrentPid0();

        current = new ProcessHandleImpl(pid, isAlive0(pid));

    }

    private static native void initNative();

    /**

     * The thread pool of "process reaper" daemon threads.

     */

    private static final Executor processReaperExecutor =

            doPrivileged((PrivilegedAction<Executor>) () -> {

                ThreadGroup tg = Thread.currentThread().getThreadGroup();

                while (tg.getParent() != null) tg = tg.getParent();

                ThreadGroup systemThreadGroup = tg;

                ThreadFactory threadFactory = grimReaper -> {

                    // Our thread stack requirement is quite modest.

                    Thread t = new Thread(systemThreadGroup, grimReaper,

                            "process reaper", 32768);

                    t.setDaemon(true);

                    // A small attempt (probably futile) to avoid priority inversion

                    t.setPriority(Thread.MAX_PRIORITY);

                    return t;

                };

                return Executors.newCachedThreadPool(threadFactory);

            });

    private static class ExitCompletion extends CompletableFuture<Integer> {

        final boolean isReaping;

        ExitCompletion(boolean isReaping) {

            this.isReaping = isReaping;

        }

    }

    /**

     * Returns a CompletableFuture that completes with process exit status when

     * the process completes.

     *

     * @param shouldReap true if the exit value should be reaped

     */

    static CompletableFuture<Integer> completion(long pid, boolean shouldReap) {

        // check canonicalizing cache 1st

        ExitCompletion completion = completions.get(pid);

        // re-try until we get a completion that shouldReap => isReaping

        while (completion == null || (shouldReap && !completion.isReaping)) {

            ExitCompletion newCompletion = new ExitCompletion(shouldReap);

            if (completion == null) {

                completion = completions.putIfAbsent(pid, newCompletion);

            } else {

                completion = completions.replace(pid, completion, newCompletion)

                    ? null : completions.get(pid);

            }

            if (completion == null) {

                // newCompletion has just been installed successfully

                completion = newCompletion;

                // spawn a thread to wait for and deliver the exit value

                processReaperExecutor.execute(() -> {

                    int exitValue = waitForProcessExit0(pid, shouldReap);

                    newCompletion.complete(exitValue);

                    // remove from cache afterwards

                    completions.remove(pid, newCompletion);

                });

            }

        }

        return completion;

    }

    @Override

    public CompletableFuture<ProcessHandle> onExit() {

        if (this.equals(current)) {

            throw new IllegalStateException("onExit for current process not allowed");

        }

        return ProcessHandleImpl.completion(getPid(), false)

                .handleAsync((exitStatus, unusedThrowable) -> this);

    }

    /**

     * Wait for the process to exit, return the value.

     * Conditionally reap the value if requested

     * @param pid the processId

     * @param reapvalue if true, the value is retrieved,

     *                   else return the value and leave the process waitable

     *

     * @return the value or -1 if an error occurs

     */

    private static native int waitForProcessExit0(long pid, boolean reapvalue);

    /**

     * The pid of this ProcessHandle.

     */

    private final long pid;

    /**

     * The start time of this process.

     * If STARTTIME_ANY, the start time of the process is not available from the os.

     * If greater than zero, the start time of the process.

     */

    private final long startTime;

    /* The start time should match any value.

     * Typically, this is because the OS can not supply it.

     * The process is known to exist but not the exact start time.

     */

    private final long STARTTIME_ANY = 0L;

    /* The start time of a Process that does not exist. */

    private final long STARTTIME_PROCESS_UNKNOWN = -1;

    /**

     * Private constructor.  Instances are created by the {@code get(long)} factory.

     * @param pid the pid for this instance

     */

    private ProcessHandleImpl(long pid, long startTime) {

        this.pid = pid;

        this.startTime = startTime;

    }

    /**

     * Returns a ProcessHandle for an existing native process.

     *

     * @param pid the native process identifier

     * @return The ProcessHandle for the pid if the process is alive;

     *      or {@code null} if the process ID does not exist in the native system.

     * @throws SecurityException if RuntimePermission("manageProcess") is not granted

     */

    static Optional<ProcessHandle> get(long pid) {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

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

        }

        long start = isAlive0(pid);

        return (start >= 0)

                ? Optional.of(new ProcessHandleImpl(pid, start))

                : Optional.empty();

    }

    /**

     * Returns a ProcessHandle for an existing native process known to be alive.

     * The startTime of the process is retrieved and stored in the ProcessHandle.

     * It does not perform a security check since it is called from ProcessImpl.

     * @param pid of the known to exist process

     * @return a ProcessHandle corresponding to an existing Process instance

     */

    static ProcessHandleImpl getInternal(long pid) {

        return new ProcessHandleImpl(pid, isAlive0(pid));

    }

    /**

     * Returns the native process ID.

     * A {@code long} is used to be able to fit the system specific binary values

     * for the process.

     *

     * @return the native process ID

     */

    @Override

    public long getPid() {

        return pid;

    }

    /**

     * Returns the ProcessHandle for the current native process.

     *

     * @return The ProcessHandle for the OS process.

     * @throws SecurityException if RuntimePermission("manageProcess") is not granted

     */

    public static ProcessHandleImpl current() {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

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

        }

        return current;

    }

    /**

     * Return the pid of the current process.

     *

     * @return the pid of the  current process

     */

    private static native long getCurrentPid0();

    /**

     * Returns a ProcessHandle for the parent process.

     *

     * @return a ProcessHandle of the parent process; {@code null} is returned

     *         if the child process does not have a parent

     * @throws SecurityException           if permission is not granted by the

     *                                     security policy

     */

    public Optional<ProcessHandle> parent() {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

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

        }

        long ppid = parent0(pid, startTime);

        if (ppid <= 0) {

            return Optional.empty();

        }

        return get(ppid);

    }

    /**

     * Returns the parent of the native pid argument.

     *

     * @param pid the process id

     * @param startTime the startTime of the process

     * @return the parent of the native pid; if any, otherwise -1

     */

    private static native long parent0(long pid, long startTime);

    /**

     * Returns the number of pids filled in to the array.

     * @param pid if {@code pid} equals zero, then all known processes are returned;

     *      otherwise only direct child process pids are returned

     * @param pids an allocated long array to receive the pids

     * @param ppids an allocated long array to receive the parent pids; may be null

     * @param starttimes an allocated long array to receive the child start times; may be null

     * @return if greater than or equals to zero is the number of pids in the array;

     *      if greater than the length of the arrays, the arrays are too small

     */

    private static native int getProcessPids0(long pid, long[] pids,

                                              long[] ppids, long[] starttimes);

    /**

     * Destroy the process for this ProcessHandle.

     * The native code checks the start time before sending the termination request.

     *

     * @param force {@code true} if the process should be terminated forcibly;

     *     else {@code false} for a normal termination

     */

    boolean destroyProcess(boolean force) {

        if (this.equals(current)) {

            throw new IllegalStateException("destroy of current process not allowed");

        }

        return destroy0(pid, startTime, force);

    }

    /**

      * Signal the process to terminate.

      * The process is signaled only if its start time matches the known start time.

      *

      * @param pid  process id to kill

      * @param startTime the start time of the process

      * @param forcibly true to forcibly terminate (SIGKILL vs SIGTERM)

      * @return true if the process was signaled without error; false otherwise

      */

    private static native boolean destroy0(long pid, long startTime, boolean forcibly);

    @Override

    public boolean destroy() {

        return destroyProcess(false);

    }

    @Override

    public boolean destroyForcibly() {

        return destroyProcess(true);

    }

    @Override

    public boolean supportsNormalTermination() {

        return ProcessImpl.SUPPORTS_NORMAL_TERMINATION;

    }

    /**

     * Tests whether the process represented by this {@code ProcessHandle} is alive.

     *

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

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

     * @since 9

     */

    @Override

    public boolean isAlive() {

        long start = isAlive0(pid);

        return (start >= 0 && (start == startTime || start == 0 || startTime == 0));

    }

    /**

     * Returns the process start time depending on whether the pid is alive.

     * This must not reap the exitValue.

     *

     * @param pid the pid to check

     * @return the start time in milliseconds since 1970,

     *         0 if the start time cannot be determined,

     *         -1 if the pid does not exist.

     */

    private static native long isAlive0(long pid);

    @Override

    public Stream<ProcessHandle> children() {

        // The native OS code selects based on matching the requested parent pid.

        // If the original parent exits, the pid may have been re-used for

        // this newer process.

        // Processes started by the original parent (now dead) will all have

        // start times less than the start of this newer parent.

        // Processes started by this newer parent will have start times equal

        // or after this parent.

        return children(pid).filter(ph -> startTime <= ((ProcessHandleImpl)ph).startTime);

    }

    /**

     * Returns a Stream of the children of a process or all processes.

     *

     * @param pid the pid of the process for which to find the children;

     *            0 for all processes

     * @return a stream of ProcessHandles

     */

    static Stream<ProcessHandle> children(long pid) {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

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

        }

        int size = 100;

        long[] childpids = null;

        long[] starttimes = null;

        while (childpids == null || size > childpids.length) {

            childpids = new long[size];

            starttimes = new long[size];

            size = getProcessPids0(pid, childpids, null, starttimes);

        }

        final long[] cpids = childpids;

        final long[] stimes = starttimes;

        return IntStream.range(0, size).mapToObj(i -> new ProcessHandleImpl(cpids[i], stimes[i]));

    }

    @Override

    public Stream<ProcessHandle> descendants() {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

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

        }

        int size = 100;

        long[] pids = null;

        long[] ppids = null;

        long[] starttimes = null;

        while (pids == null || size > pids.length) {

            pids = new long[size];

            ppids = new long[size];

            starttimes = new long[size];

            size = getProcessPids0(0, pids, ppids, starttimes);

        }

        int next = 0;       // index of next process to check

        int count = -1;     // count of subprocesses scanned

        long ppid = pid;    // start looking for this parent

        long ppStart = 0;

        // Find the start time of the parent

        for (int i = 0; i < size; i++) {

            if (pids[i] == ppid) {

                ppStart = starttimes[i];

                break;

            }

        }

        do {

            // Scan from next to size looking for ppid with child start time

            // the same or later than the parent.

            // If found, exchange it with index next

            for (int i = next; i < size; i++) {

                if (ppids[i] == ppid &&

                        ppStart <= starttimes[i]) {

                    swap(pids, i, next);

                    swap(ppids, i, next);

                    swap(starttimes, i, next);

                    next++;

                }

            }

            ppid = pids[++count];   // pick up the next pid to scan for

            ppStart = starttimes[count];    // and its start time

        } while (count < next);

        final long[] cpids = pids;

        final long[] stimes = starttimes;

        return IntStream.range(0, count).mapToObj(i -> new ProcessHandleImpl(cpids[i], stimes[i]));

    }

    // Swap two elements in an array

    private static void swap(long[] array, int x, int y) {

        long v = array[x];

        array[x] = array[y];

        array[y] = v;

    }

    @Override

    public ProcessHandle.Info info() {

        return ProcessHandleImpl.Info.info(pid, startTime);

    }

    @Override

    public int compareTo(ProcessHandle other) {

        return Long.compare(pid, ((ProcessHandleImpl) other).pid);

    }

    @Override

    public String toString() {

        return Long.toString(pid);

    }

    @Override

    public int hashCode() {

        return Long.hashCode(pid);

    }

    @Override

    public boolean equals(Object obj) {

        if (this == obj) {

            return true;

        }

        if (obj instanceof ProcessHandleImpl) {

            ProcessHandleImpl other = (ProcessHandleImpl) obj;

            return (pid == other.pid) &&

                    (startTime == other.startTime

                        || startTime == 0

                        || other.startTime == 0);

        }

        return false;

    }

    /**

     * Implementation of ProcessHandle.Info.

     * Information snapshot about a process.

     * The attributes of a process vary by operating system and are not available

     * in all implementations.  Additionally, information about other processes

     * is limited by the operating system privileges of the process making the request.

     * If a value is not available, either a {@code null} or {@code -1} is stored.

     * The accessor methods return {@code null} if the value is not available.

     */

    static class Info implements ProcessHandle.Info {

        static {

            initIDs();

        }

        /**

         * Initialization of JNI fieldIDs.

         */

        private static native void initIDs();

        /**

         * Fill in this Info instance with information about the native process.

         * If values are not available the native code does not modify the field.

         * @param pid  of the native process

         */

        private native void info0(long pid);

        String command;