/*
 * Copyright (c) 2014, 2017, 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.lang.annotation.Native;
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.ThreadFactory;
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 {
 /**
 * Default size of stack for reaper processes.
 */
 private static long REAPER_DEFAULT_STACKSIZE = 128 * 1024;

 /**
 * Return value from waitForProcessExit0 indicating the process is not a child.
 */
 @Native
 private static final int NOT_A_CHILD = -2;

 /**
 * 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;
 final long stackSize = Boolean.getBoolean("jdk.lang.processReaperUseDefaultStackSize")
 ? 0 : REAPER_DEFAULT_STACKSIZE;

 ThreadFactory threadFactory = grimReaper -> {
 Thread t = new Thread(systemThreadGroup, grimReaper,
 "process reaper", stackSize, false);
 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(new Runnable() {
 // Use inner class to avoid lambda stack overhead
 public void run() {
 int exitValue = waitForProcessExit0(pid, shouldReap);
 if (exitValue == NOT_A_CHILD) {
 // pid not alive or not a child of this process
 // If it is alive wait for it to terminate
 long sleep = 300; // initial milliseconds to sleep
 int incr = 30; // increment to the sleep time

 long startTime = isAlive0(pid);
 long origStart = startTime;
 while (startTime >= 0) {
 try {
 Thread.sleep(Math.min(sleep, 5000L)); // no more than 5 sec
 sleep += incr;
 } catch (InterruptedException ie) {
 // ignore and retry
 }
 startTime = isAlive0(pid); // recheck if it is alive
 if (startTime > 0 && origStart > 0 && startTime != origStart) {
 // start time changed (and is not zero), pid is not the same process
 break;
 }
 }
 exitValue = 0;
 }
 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(pid(), 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 pid() {
 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;
 String commandLine;
 String[] arguments;
 long startTime;
 long totalTime;
 String user;

 Info() {
 command = null;
 commandLine = null;
 arguments = null;
 startTime = -1L;
 totalTime = -1L;
 user = null;
 }

 /**
 * Returns the Info object with the fields from the process.
 * Whatever fields are provided by native are returned.
 * If the startTime of the process does not match the provided
 * startTime then an empty Info is returned.
 *
 * @param pid the native process identifier
 * @param startTime the startTime of the process being queried
 * @return ProcessHandle.Info non-null; individual fields may be null
 * or -1 if not available.
 */
 public static ProcessHandle.Info info(long pid, long startTime) {
 Info info = new Info();
 info.info0(pid);
 if (startTime != info.startTime) {
 info.command = null;
 info.arguments = null;
 info.startTime = -1L;
 info.totalTime = -1L;
 info.user = null;
 }
 return info;
 }

 @Override
 public Optional<String> command() {
 return Optional.ofNullable(command);
 }

 @Override
 public Optional<String> commandLine() {
 if (command != null && arguments != null) {
 return Optional.of(command + " " + String.join(" ", arguments));
 } else {
 return Optional.ofNullable(commandLine);
 }
 }

 @Override
 public Optional<String[]> arguments() {
 return Optional.ofNullable(arguments);
 }

 @Override
 public Optional<Instant> startInstant() {
 return (startTime > 0)
 ? Optional.of(Instant.ofEpochMilli(startTime))
 : Optional.empty();
 }

 @Override
 public Optional<Duration> totalCpuDuration() {
 return (totalTime != -1)
 ? Optional.of(Duration.ofNanos(totalTime))
 : Optional.empty();
 }

 @Override
 public Optional<String> user() {
 return Optional.ofNullable(user);
 }

 @Override
 public String toString() {
 StringBuilder sb = new StringBuilder(60);
 sb.append('[');
 if (user != null) {
 sb.append("user: ");
 sb.append(user());
 }
 if (command != null) {
 if (sb.length() != 0) sb.append(", ");
 sb.append("cmd: ");
 sb.append(command);
 }
 if (arguments != null && arguments.length > 0) {
 if (sb.length() != 0) sb.append(", ");
 sb.append("args: ");
 sb.append(Arrays.toString(arguments));
 }
 if (commandLine != null) {
 if (sb.length() != 0) sb.append(", ");
 sb.append("cmdLine: ");
 sb.append(commandLine);
 }
 if (startTime > 0) {
 if (sb.length() != 0) sb.append(", ");
 sb.append("startTime: ");
 sb.append(startInstant());
 }
 if (totalTime != -1) {
 if (sb.length() != 0) sb.append(", ");
 sb.append("totalTime: ");
 sb.append(totalCpuDuration().toString());
 }
 sb.append(']');
 return sb.toString();
 }
 }
}