001// License: GPL. For details, see LICENSE file.
002package org.openstreetmap.josm.io;
003
004import java.io.File;
005import java.io.IOException;
006import java.nio.file.FileSystems;
007import java.nio.file.Files;
008import java.nio.file.Path;
009import java.nio.file.StandardWatchEventKinds;
010import java.nio.file.WatchEvent;
011import java.nio.file.WatchEvent.Kind;
012import java.nio.file.WatchKey;
013import java.nio.file.WatchService;
014import java.util.EnumMap;
015import java.util.HashMap;
016import java.util.Map;
017import java.util.Objects;
018import java.util.function.Consumer;
019
020import org.openstreetmap.josm.data.preferences.sources.SourceEntry;
021import org.openstreetmap.josm.data.preferences.sources.SourceType;
022import org.openstreetmap.josm.tools.CheckParameterUtil;
023import org.openstreetmap.josm.tools.Logging;
024
025/**
026 * Background thread that monitors certain files and perform relevant actions when they change.
027 * @since 7185
028 */
029public class FileWatcher {
030
031    private WatchService watcher;
032    private Thread thread;
033
034    private static final Map<SourceType, Consumer<SourceEntry>> loaderMap = new EnumMap<>(SourceType.class);
035    private final Map<Path, SourceEntry> sourceMap = new HashMap<>();
036
037    /**
038     * Constructs a new {@code FileWatcher}.
039     */
040    public FileWatcher() {
041        try {
042            watcher = FileSystems.getDefault().newWatchService();
043            thread = new Thread((Runnable) this::processEvents, "File Watcher");
044        } catch (IOException e) {
045            Logging.error(e);
046        }
047    }
048
049    /**
050     * Starts the File Watcher thread.
051     */
052    public final void start() {
053        if (thread != null && !thread.isAlive()) {
054            thread.start();
055        }
056    }
057
058    /**
059     * Registers a source for local file changes, allowing dynamic reloading.
060     * @param src The source to watch
061     * @throws IllegalArgumentException if {@code rule} is null or if it does not provide a local file
062     * @throws IllegalStateException if the watcher service failed to start
063     * @throws IOException if an I/O error occurs
064     * @since 12825
065     */
066    public void registerSource(SourceEntry src) throws IOException {
067        CheckParameterUtil.ensureParameterNotNull(src, "src");
068        if (watcher == null) {
069            throw new IllegalStateException("File watcher is not available");
070        }
071        // Get local file, as this method is only called for local style sources
072        File file = new File(src.url);
073        // Get parent directory as WatchService allows only to monitor directories, not single files
074        File dir = file.getParentFile();
075        if (dir == null) {
076            throw new IllegalArgumentException("Resource "+src+" does not have a parent directory");
077        }
078        synchronized (this) {
079            // Register directory. Can be called several times for a same directory without problem
080            // (it returns the same key so it should not send events several times)
081            dir.toPath().register(watcher, StandardWatchEventKinds.ENTRY_MODIFY, StandardWatchEventKinds.ENTRY_CREATE);
082            sourceMap.put(file.toPath(), src);
083        }
084    }
085
086    /**
087     * Registers a source loader, allowing dynamic reloading when an entry changes.
088     * @param type the source type for which the loader operates
089     * @param loader the loader in charge of reloading any source of given type when it changes
090     * @return the previous loader registered for this source type, if any
091     * @since 12825
092     */
093    public static Consumer<SourceEntry> registerLoader(SourceType type, Consumer<SourceEntry> loader) {
094        return loaderMap.put(Objects.requireNonNull(type, "type"), Objects.requireNonNull(loader, "loader"));
095    }
096
097    /**
098     * Process all events for the key queued to the watcher.
099     */
100    private void processEvents() {
101        Logging.debug("File watcher thread started");
102        while (true) {
103
104            // wait for key to be signaled
105            WatchKey key;
106            try {
107                key = watcher.take();
108            } catch (InterruptedException ex) {
109                Thread.currentThread().interrupt();
110                return;
111            }
112
113            for (WatchEvent<?> event: key.pollEvents()) {
114                Kind<?> kind = event.kind();
115
116                if (StandardWatchEventKinds.OVERFLOW.equals(kind)) {
117                    continue;
118                }
119
120                // The filename is the context of the event.
121                @SuppressWarnings("unchecked")
122                WatchEvent<Path> ev = (WatchEvent<Path>) event;
123                Path filename = ev.context();
124                if (filename == null) {
125                    continue;
126                }
127
128                // Only way to get full path (http://stackoverflow.com/a/7802029/2257172)
129                Path fullPath = ((Path) key.watchable()).resolve(filename);
130
131                try {
132                    // Some filesystems fire two events when a file is modified. Skip first event (file is empty)
133                    if (Files.size(fullPath) == 0) {
134                        continue;
135                    }
136                } catch (IOException ex) {
137                    Logging.trace(ex);
138                    continue;
139                }
140
141                synchronized (this) {
142                    SourceEntry source = sourceMap.get(fullPath);
143                    if (source != null) {
144                        Consumer<SourceEntry> loader = loaderMap.get(source.type);
145                        if (loader != null) {
146                            Logging.info("Source "+source.getDisplayString()+" has been modified. Reloading it...");
147                            loader.accept(source);
148                        } else {
149                            Logging.warn("Received {0} event for unregistered source type: {1}", kind.name(), source.type);
150                        }
151                    } else if (Logging.isDebugEnabled()) {
152                        Logging.debug("Received {0} event for unregistered file: {1}", kind.name(), fullPath);
153                    }
154                }
155            }
156
157            // Reset the key -- this step is critical to receive
158            // further watch events. If the key is no longer valid, the directory
159            // is inaccessible so exit the loop.
160            if (!key.reset()) {
161                break;
162            }
163        }
164    }
165}