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 * Copyright (c) 2016, 2018, 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

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package jdk.jfr.internal;

import java.security.AccessControlContext;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.ArrayList;

import java.util.Collection;

import java.util.List;

import java.util.Objects;

import java.util.concurrent.CopyOnWriteArrayList;

import java.util.function.Predicate;

public final class RequestEngine {

    private final static JVM jvm = JVM.getJVM();

    final static class RequestHook {

        private final Runnable hook;

        private final PlatformEventType type;

        private final AccessControlContext accessControllerContext;

        private long delta;

        // Java events

        private RequestHook(AccessControlContext acc, PlatformEventType eventType, Runnable hook) {

            this.hook = hook;

            this.type = eventType;

            this.accessControllerContext = acc;

        }

        // native events

        RequestHook(PlatformEventType eventType) {

            this(null, eventType, null);

        }

        private void execute() {

            try {

                if (accessControllerContext == null) { // native

                    jvm.emitEvent(type.getId(), JVM.counterTime(), 0);

                    Logger.log(LogTag.JFR_SYSTEM_EVENT, LogLevel.DEBUG, ()-> "Executed periodic hook for " + type.getLogName());

                } else {

                    executeSecure();

                }

            } catch (Throwable e) {

                // Prevent malicious user to propagate exception callback in the wrong context

                Logger.log(LogTag.JFR_SYSTEM_EVENT, LogLevel.WARN, "Exception occured during execution of period hook for " + type.getLogName());

            }

        }

        private void executeSecure() {

            AccessController.doPrivileged(new PrivilegedAction<Void>() {

                @Override

                public Void run() {

                    try {

                        hook.run();

                        Logger.log(LogTag.JFR_EVENT, LogLevel.DEBUG, ()-> "Executed periodic hook for " + type.getLogName());

                    } catch (Throwable t) {

                        // Prevent malicious user to propagate exception callback in the wrong context

                        Logger.log(LogTag.JFR_EVENT, LogLevel.WARN, "Exception occured during execution of period hook for " + type.getLogName());

                    }

                    return null;

                }

            }, accessControllerContext);

        }

    }

    private final static List<RequestHook> entries = new CopyOnWriteArrayList<>();

    private static long lastTimeMillis;

    // Insertion takes O(2*n), could be O(1) with HashMap, but

    // thinking is that CopyOnWriteArrayList is faster

    // to iterate over, which will happen more over time.

    public static void addHook(AccessControlContext acc, PlatformEventType type, Runnable hook) {

        Objects.requireNonNull(acc);

        RequestHook he = new RequestHook(acc, type, hook);

        for (RequestHook e : entries) {

            if (e.hook == hook) {

                throw new IllegalArgumentException("Hook has already been added");

            }

        }

        he.type.setEventHook(true);

        entries.add(he);

        logHook("Added", type);

    }

    private static void logHook(String action, PlatformEventType type) {

        if (type.isJDK() || type.isJVM()) {

            Logger.log(LogTag.JFR_SYSTEM_EVENT, LogLevel.INFO, action + " periodic hook for " + type.getLogName());

        } else {

            Logger.log(LogTag.JFR_EVENT, LogLevel.INFO, action + " periodic hook for " + type.getLogName());

        }

    }

    // Takes O(2*n), see addHook.

    public static boolean removeHook(Runnable hook) {

        for (RequestHook rh : entries) {

            if (rh.hook == hook) {

                entries.remove(rh);

                rh.type.setEventHook(false);

                logHook("Removed", rh.type);

                return true;

            }

        }

        return false;

    }

    // Only to be used for JVM events. No access control contest

    // or check if hook already exists

    static void addHooks(List<RequestHook> newEntries) {

        List<RequestHook> addEntries = new ArrayList<>();

        for (RequestHook rh : newEntries) {

            rh.type.setEventHook(true);

            addEntries.add(rh);

            logHook("Added", rh.type);

        }

        entries.addAll(newEntries);

    }

    static void doChunkEnd() {

        doChunk(x -> x.isEndChunk());

    }

    static void doChunkBegin() {

        doChunk(x -> x.isBeginChunk());

    }

    private static void doChunk(Predicate<PlatformEventType> predicate) {

        for (RequestHook requestHook : entries) {

            PlatformEventType s = requestHook.type;

            if (s.isEnabled() && predicate.test(s)) {

                requestHook.execute();

            }

        }

    }

    static long doPeriodic() {

        return run_requests(entries);

    }

    // code copied from native impl.

    private static long run_requests(Collection<RequestHook> entries) {

        long last = lastTimeMillis;

        // Bug 9000556 - current time millis has rather lame resolution

        // The use of os::elapsed_counter() is deliberate here, we don't

        // want it exchanged for os::ft_elapsed_counter().

        // Keeping direct call os::elapsed_counter() here for reliable

        // real time values in order to decide when registered requestable

        // events are due.

        long now = System.currentTimeMillis();

        long min = 0;

        long delta = 0;

        if (last == 0) {

            last = now;

        }

        // time from then to now

        delta = now - last;

        if (delta < 0) {

            // to handle time adjustments

            // for example Daylight Savings

            lastTimeMillis = now;

            return 0;

        }

        for (RequestHook he : entries) {

            long left = 0;

            PlatformEventType es = he.type;

            // Not enabled, skip.

            if (!es.isEnabled() || es.isEveryChunk()) {

                continue;

            }

            long r_period = es.getPeriod();

            long r_delta = he.delta;

            // add time elapsed.

            r_delta += delta;

            // above threshold?

            if (r_delta >= r_period) {

                // Bug 9000556 - don't try to compensate

                // for wait > period

                r_delta = 0;

                he.execute();

                ;

            }

            // calculate time left

            left = (r_period - r_delta);

            /**

             * nothing outside checks that a period is >= 0, so left can end up

             * negative here. ex. (r_period =(-1)) - (r_delta = 0) if it is,

             * handle it.

             */

            if (left < 0) {

                left = 0;

            }

            // assign delta back

            he.delta = r_delta;

            if (min == 0 || left < min) {

                min = left;

            }

        }

        lastTimeMillis = now;

        return min;

    }

}