1 files changed, 250 insertions, 0 deletions
diff --git a/jimfs/src/main/java/com/google/common/jimfs/PollingWatchService.java b/jimfs/src/main/java/com/google/common/jimfs/PollingWatchService.java
new file mode 100644
index 0000000..d1f5b89
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+++ b/jimfs/src/main/java/com/google/common/jimfs/PollingWatchService.java
@@ -0,0 +1,250 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.common.jimfs;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
+import static java.nio.file.StandardWatchEventKinds.ENTRY_DELETE;
+import static java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.Sets;
+import com.google.common.util.concurrent.ThreadFactoryBuilder;
+import java.io.IOException;
+import java.nio.file.Path;
+import java.nio.file.WatchEvent;
+import java.nio.file.WatchService;
+import java.nio.file.Watchable;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Implementation of {@link WatchService} that polls for changes to directories at registered paths.
+ *
+ * @author Colin Decker
+ */
+final class PollingWatchService extends AbstractWatchService {
+
+  /**
+   * Thread factory for polling threads, which should be daemon threads so as not to keep the VM
+   * running if the user doesn't close the watch service or the file system.
+   */
+  private static final ThreadFactory THREAD_FACTORY =
+      new ThreadFactoryBuilder()
+          .setNameFormat("com.google.common.jimfs.PollingWatchService-thread-%d")
+          .setDaemon(true)
+          .build();
+
+  private final ScheduledExecutorService pollingService =
+      Executors.newSingleThreadScheduledExecutor(THREAD_FACTORY);
+
+  /** Map of keys to the most recent directory snapshot for each key. */
+  private final ConcurrentMap<Key, Snapshot> snapshots = new ConcurrentHashMap<>();
+
+  private final FileSystemView view;
+  private final PathService pathService;
+  private final FileSystemState fileSystemState;
+
+  @VisibleForTesting final long interval;
+  @VisibleForTesting final TimeUnit timeUnit;
+
+  private ScheduledFuture<?> pollingFuture;
+
+  PollingWatchService(
+      FileSystemView view,
+      PathService pathService,
+      FileSystemState fileSystemState,
+      long interval,
+      TimeUnit timeUnit) {
+    this.view = checkNotNull(view);
+    this.pathService = checkNotNull(pathService);
+    this.fileSystemState = checkNotNull(fileSystemState);
+
+    checkArgument(interval >= 0, "interval (%s) may not be negative", interval);
+    this.interval = interval;
+    this.timeUnit = checkNotNull(timeUnit);
+
+    fileSystemState.register(this);
+  }
+
+  @Override
+  public Key register(Watchable watchable, Iterable<? extends WatchEvent.Kind<?>> eventTypes)
+      throws IOException {
+    JimfsPath path = checkWatchable(watchable);
+
+    Key key = super.register(path, eventTypes);
+
+    Snapshot snapshot = takeSnapshot(path);
+
+    synchronized (this) {
+      snapshots.put(key, snapshot);
+      if (pollingFuture == null) {
+        startPolling();
+      }
+    }
+
+    return key;
+  }
+
+  private JimfsPath checkWatchable(Watchable watchable) {
+    if (!(watchable instanceof JimfsPath) || !isSameFileSystem((Path) watchable)) {
+      throw new IllegalArgumentException(
+          "watchable ("
+              + watchable
+              + ") must be a Path "
+              + "associated with the same file system as this watch service");
+    }
+
+    return (JimfsPath) watchable;
+  }
+
+  private boolean isSameFileSystem(Path path) {
+    return ((JimfsFileSystem) path.getFileSystem()).getDefaultView() == view;
+  }
+
+  @VisibleForTesting
+  synchronized boolean isPolling() {
+    return pollingFuture != null;
+  }
+
+  @Override
+  public synchronized void cancelled(Key key) {
+    snapshots.remove(key);
+
+    if (snapshots.isEmpty()) {
+      stopPolling();
+    }
+  }
+
+  @Override
+  public void close() {
+    super.close();
+
+    synchronized (this) {
+      // synchronize to ensure no new
+      for (Key key : snapshots.keySet()) {
+        key.cancel();
+      }
+
+      pollingService.shutdown();
+      fileSystemState.unregister(this);
+    }
+  }
+
+  private void startPolling() {
+    pollingFuture = pollingService.scheduleAtFixedRate(pollingTask, interval, interval, timeUnit);
+  }
+
+  private void stopPolling() {
+    pollingFuture.cancel(false);
+    pollingFuture = null;
+  }
+
+  private final Runnable pollingTask =
+      new Runnable() {
+        @Override
+        public void run() {
+          synchronized (PollingWatchService.this) {
+            for (Map.Entry<Key, Snapshot> entry : snapshots.entrySet()) {
+              Key key = entry.getKey();
+              Snapshot previousSnapshot = entry.getValue();
+
+              JimfsPath path = (JimfsPath) key.watchable();
+              try {
+                Snapshot newSnapshot = takeSnapshot(path);
+                boolean posted = previousSnapshot.postChanges(newSnapshot, key);
+                entry.setValue(newSnapshot);
+                if (posted) {
+                  key.signal();
+                }
+              } catch (IOException e) {
+                // snapshot failed; assume file does not exist or isn't a directory
+                // and cancel the key
+                key.cancel();
+              }
+            }
+          }
+        }
+      };
+
+  private Snapshot takeSnapshot(JimfsPath path) throws IOException {
+    return new Snapshot(view.snapshotModifiedTimes(path));
+  }
+
+  /** Snapshot of the state of a directory at a particular moment. */
+  private final class Snapshot {
+
+    /** Maps directory entry names to last modified times. */
+    private final ImmutableMap<Name, Long> modifiedTimes;
+
+    Snapshot(Map<Name, Long> modifiedTimes) {
+      this.modifiedTimes = ImmutableMap.copyOf(modifiedTimes);
+    }
+
+    /**
+     * Posts events to the given key based on the kinds of events it subscribes to and what events
+     * have occurred between this state and the given new state.
+     */
+    boolean postChanges(Snapshot newState, Key key) {
+      boolean changesPosted = false;
+
+      if (key.subscribesTo(ENTRY_CREATE)) {
+        Set<Name> created =
+            Sets.difference(newState.modifiedTimes.keySet(), modifiedTimes.keySet());
+
+        for (Name name : created) {
+          key.post(new Event<>(ENTRY_CREATE, 1, pathService.createFileName(name)));
+          changesPosted = true;
+        }
+      }
+
+      if (key.subscribesTo(ENTRY_DELETE)) {
+        Set<Name> deleted =
+            Sets.difference(modifiedTimes.keySet(), newState.modifiedTimes.keySet());
+
+        for (Name name : deleted) {
+          key.post(new Event<>(ENTRY_DELETE, 1, pathService.createFileName(name)));
+          changesPosted = true;
+        }
+      }
+
+      if (key.subscribesTo(ENTRY_MODIFY)) {
+        for (Map.Entry<Name, Long> entry : modifiedTimes.entrySet()) {
+          Name name = entry.getKey();
+          Long modifiedTime = entry.getValue();
+
+          Long newModifiedTime = newState.modifiedTimes.get(name);
+          if (newModifiedTime != null && !modifiedTime.equals(newModifiedTime)) {
+            key.post(new Event<>(ENTRY_MODIFY, 1, pathService.createFileName(name)));
+            changesPosted = true;
+          }
+        }
+      }
+
+      return changesPosted;
+    }
+  }
+}