/*

 * Copyright (c) 2008, 2011, 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

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 */

package sun.nio.fs;

import java.nio.file.*;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.*;

import java.io.IOException;

import sun.misc.Unsafe;

import static sun.nio.fs.UnixNativeDispatcher.*;

import static sun.nio.fs.UnixConstants.*;

/**

 * Linux implementation of WatchService based on inotify.

 *

 * In summary a background thread polls inotify plus a socket used for the wakeup

 * mechanism. Requests to add or remove a watch, or close the watch service,

 * cause the thread to wakeup and process the request. Events are processed

 * by the thread which causes it to signal/queue the corresponding watch keys.

 */

class LinuxWatchService

    extends AbstractWatchService

{

    private static final Unsafe unsafe = Unsafe.getUnsafe();

    // background thread to read change events

    private final Poller poller;

    LinuxWatchService(UnixFileSystem fs) throws IOException {

        // initialize inotify

        int ifd = - 1;

        try {

            ifd = inotifyInit();

        } catch (UnixException x) {

            throw new IOException(x.errorString());

        }

        // configure inotify to be non-blocking

        // create socketpair used in the close mechanism

        int sp[] = new int[2];

        try {

            configureBlocking(ifd, false);

            socketpair(sp);

            configureBlocking(sp[0], false);

        } catch (UnixException x) {

            UnixNativeDispatcher.close(ifd);

            throw new IOException(x.errorString());

        }

        this.poller = new Poller(fs, this, ifd, sp);

        this.poller.start();

    }

    @Override

    WatchKey register(Path dir,

                      WatchEvent.Kind<?>[] events,

                      WatchEvent.Modifier... modifiers)

         throws IOException

    {

        // delegate to poller

        return poller.register(dir, events, modifiers);

    }

    @Override

    void implClose() throws IOException {

        // delegate to poller

        poller.close();

    }

    /**

     * WatchKey implementation

     */

    private static class LinuxWatchKey extends AbstractWatchKey {

        // inotify descriptor

        private final int ifd;

        // watch descriptor

        private volatile int wd;

        LinuxWatchKey(UnixPath dir, LinuxWatchService watcher, int ifd, int wd) {

            super(dir, watcher);

            this.ifd = ifd;

            this.wd = wd;

        }

        int descriptor() {

            return wd;

        }

        void invalidate(boolean remove) {

            if (remove) {

                try {

                    inotifyRmWatch(ifd, wd);

                } catch (UnixException x) {

                    // ignore

                }

            }

            wd = -1;

        }

        @Override

        public boolean isValid() {

            return (wd != -1);

        }

        @Override

        public void cancel() {

            if (isValid()) {

                // delegate to poller

                ((LinuxWatchService)watcher()).poller.cancel(this);

            }

        }

    }

    /**

     * Background thread to read from inotify

     */

    private static class Poller extends AbstractPoller {

        /**

         * struct inotify_event {

         *     int          wd;

         *     uint32_t     mask;

         *     uint32_t     len;

         *     char name    __flexarr;  // present if len > 0

         * } act_t;

         */

        private static final int SIZEOF_INOTIFY_EVENT  = eventSize();

        private static final int[] offsets             = eventOffsets();

        private static final int OFFSETOF_WD           = offsets[0];

        private static final int OFFSETOF_MASK         = offsets[1];

        private static final int OFFSETOF_LEN          = offsets[3];

        private static final int OFFSETOF_NAME         = offsets[4];

        private static final int IN_MODIFY          = 0x00000002;

        private static final int IN_ATTRIB          = 0x00000004;

        private static final int IN_MOVED_FROM      = 0x00000040;

        private static final int IN_MOVED_TO        = 0x00000080;

        private static final int IN_CREATE          = 0x00000100;

        private static final int IN_DELETE          = 0x00000200;

        private static final int IN_UNMOUNT         = 0x00002000;

        private static final int IN_Q_OVERFLOW      = 0x00004000;

        private static final int IN_IGNORED         = 0x00008000;

        // sizeof buffer for when polling inotify

        private static final int BUFFER_SIZE = 8192;

        private final UnixFileSystem fs;

        private final LinuxWatchService watcher;

        // inotify file descriptor

        private final int ifd;

        // socketpair used to shutdown polling thread

        private final int socketpair[];

        // maps watch descriptor to Key

        private final Map<Integer,LinuxWatchKey> wdToKey;

        // address of read buffer

        private final long address;

        Poller(UnixFileSystem fs, LinuxWatchService watcher, int ifd, int[] sp) {

            this.fs = fs;

            this.watcher = watcher;

            this.ifd = ifd;

            this.socketpair = sp;

            this.wdToKey = new HashMap<Integer,LinuxWatchKey>();

            this.address = unsafe.allocateMemory(BUFFER_SIZE);

        }

        @Override

        void wakeup() throws IOException {

            // write to socketpair to wakeup polling thread

            try {

                write(socketpair[1], address, 1);

            } catch (UnixException x) {

                throw new IOException(x.errorString());

            }

        }

        @Override

        Object implRegister(Path obj,

                            Set<? extends WatchEvent.Kind<?>> events,

                            WatchEvent.Modifier... modifiers)

        {

            UnixPath dir = (UnixPath)obj;

            int mask = 0;

            for (WatchEvent.Kind<?> event: events) {

                if (event == StandardWatchEventKind.ENTRY_CREATE) {

                    mask |= IN_CREATE | IN_MOVED_TO;

                    continue;

                }

                if (event == StandardWatchEventKind.ENTRY_DELETE) {

                    mask |= IN_DELETE | IN_MOVED_FROM;

                    continue;

                }

                if (event == StandardWatchEventKind.ENTRY_MODIFY) {

                    mask |= IN_MODIFY | IN_ATTRIB;

                    continue;

                }

            }

            // no modifiers supported at this time

            if (modifiers.length > 0) {

                for (WatchEvent.Modifier modifier: modifiers) {

                    if (modifier == null)

                        return new NullPointerException();

                    if (modifier instanceof com.sun.nio.file.SensitivityWatchEventModifier)

                        continue; // ignore

                    return new UnsupportedOperationException("Modifier not supported");

                }

            }

            // check file is directory

            UnixFileAttributes attrs = null;

            try {

                attrs = UnixFileAttributes.get(dir, true);

            } catch (UnixException x) {

                return x.asIOException(dir);

            }

            if (!attrs.isDirectory()) {

                return new NotDirectoryException(dir.getPathForExecptionMessage());

            }

            // register with inotify (replaces existing mask if already registered)

            int wd = -1;

            try {

                NativeBuffer buffer =

                    NativeBuffers.asNativeBuffer(dir.getByteArrayForSysCalls());

                try {

                    wd = inotifyAddWatch(ifd, buffer.address(), mask);

                } finally {

                    buffer.release();

                }

            } catch (UnixException x) {

                if (x.errno() == ENOSPC) {

                    return new IOException("User limit of inotify watches reached");

                }

                return x.asIOException(dir);

            }

            // ensure watch descriptor is in map

            LinuxWatchKey key = wdToKey.get(wd);

            if (key == null) {

                key = new LinuxWatchKey(dir, watcher, ifd, wd);

                wdToKey.put(wd, key);

            }

            return key;

        }

        // cancel single key

        @Override

        void implCancelKey(WatchKey obj) {

            LinuxWatchKey key = (LinuxWatchKey)obj;

            if (key.isValid()) {

                wdToKey.remove(key.descriptor());

                key.invalidate(true);

            }

        }

        // close watch service

        @Override

        void implCloseAll() {

            // invalidate all keys

            for (Map.Entry<Integer,LinuxWatchKey> entry: wdToKey.entrySet()) {

                entry.getValue().invalidate(true);

            }

            wdToKey.clear();

            // free resources

            unsafe.freeMemory(address);

            UnixNativeDispatcher.close(socketpair[0]);

            UnixNativeDispatcher.close(socketpair[1]);

            UnixNativeDispatcher.close(ifd);

        }

        /**

         * Poller main loop

         */

        @Override

        public void run() {

            try {

                for (;;) {

                    int nReady, bytesRead;

                    // wait for close or inotify event

                    nReady = poll(ifd, socketpair[0]);

                    // read from inotify

                    try {

                        bytesRead = read(ifd, address, BUFFER_SIZE);

                    } catch (UnixException x) {

                        if (x.errno() != EAGAIN)

                            throw x;

                        bytesRead = 0;

                    }

                    // process any pending requests

                    if ((nReady > 1) || (nReady == 1 && bytesRead == 0)) {

                        try {

                            read(socketpair[0], address, BUFFER_SIZE);

                            boolean shutdown = processRequests();

                            if (shutdown)

                                break;

                        } catch (UnixException x) {

                            if (x.errno() != UnixConstants.EAGAIN)

                                throw x;

                        }

                    }

                    // iterate over buffer to decode events

                    int offset = 0;

                    while (offset < bytesRead) {

                        long event = address + offset;

                        int wd = unsafe.getInt(event + OFFSETOF_WD);

                        int mask = unsafe.getInt(event + OFFSETOF_MASK);

                        int len = unsafe.getInt(event + OFFSETOF_LEN);

                        // file name

                        UnixPath name = null;

                        if (len > 0) {

                            int actual = len;

                            // null-terminated and maybe additional null bytes to

                            // align the next event

                            while (actual > 0) {

                                long last = event + OFFSETOF_NAME + actual - 1;

                                if (unsafe.getByte(last) != 0)

                                    break;

                                actual--;

                            }

                            if (actual > 0) {

                                byte[] buf = new byte[actual];

                                unsafe.copyMemory(null, event + OFFSETOF_NAME,

                                    buf, Unsafe.ARRAY_BYTE_BASE_OFFSET, actual);

                                name = new UnixPath(fs, buf);

                            }

                        }

                        // process event

                        processEvent(wd, mask, name);

                        offset += (SIZEOF_INOTIFY_EVENT + len);

                    }

                }

            } catch (UnixException x) {

                x.printStackTrace();

            }

        }

        /**

         * map inotify event to WatchEvent.Kind

         */

        private WatchEvent.Kind<?> maskToEventKind(int mask) {

            if ((mask & IN_MODIFY) > 0)

                return StandardWatchEventKind.ENTRY_MODIFY;

            if ((mask & IN_ATTRIB) > 0)

                return StandardWatchEventKind.ENTRY_MODIFY;

            if ((mask & IN_CREATE) > 0)

                return StandardWatchEventKind.ENTRY_CREATE;

            if ((mask & IN_MOVED_TO) > 0)

                return StandardWatchEventKind.ENTRY_CREATE;

            if ((mask & IN_DELETE) > 0)

                return StandardWatchEventKind.ENTRY_DELETE;

            if ((mask & IN_MOVED_FROM) > 0)

                return StandardWatchEventKind.ENTRY_DELETE;

            return null;

        }

        /**

         * Process event from inotify

         */

        private void processEvent(int wd, int mask, final UnixPath name) {

            // overflow - signal all keys

            if ((mask & IN_Q_OVERFLOW) > 0) {

                for (Map.Entry<Integer,LinuxWatchKey> entry: wdToKey.entrySet()) {

                    entry.getValue()

                        .signalEvent(StandardWatchEventKind.OVERFLOW, null);

                }

                return;

            }

            // lookup wd to get key

            LinuxWatchKey key = wdToKey.get(wd);

            if (key == null)

                return; // should not happen

            // file deleted

            if ((mask & IN_IGNORED) > 0) {

                wdToKey.remove(wd);

                key.invalidate(false);

                key.signal();

                return;

            }

            // event for directory itself

            if (name == null)

                return;

            // map to event and queue to key

            WatchEvent.Kind<?> kind = maskToEventKind(mask);

            if (kind != null) {

                key.signalEvent(kind, name);

            }

        }

    }

    // -- native methods --

    // sizeof inotify_event

    private static native int eventSize();

    // offsets of inotify_event

    private static native int[] eventOffsets();

    private static native int inotifyInit() throws UnixException;

    private static native int inotifyAddWatch(int fd, long pathAddress, int mask)

        throws UnixException;

    private static native void inotifyRmWatch(int fd, int wd)

        throws UnixException;

    private static native void configureBlocking(int fd, boolean blocking)

        throws UnixException;

    private static native void socketpair(int[] sv) throws UnixException;

    private static native int poll(int fd1, int fd2) throws UnixException;

    static {

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

            public Void run() {

                System.loadLibrary("nio");

                return null;

        }});

    }

}