Introduce FsEventsDiffAwareness for OS X.

Use FsEvents API (https://developer.apple.com/library/mac/documentation/Darwin/Reference/FSEvents_Ref)
to watch the file system. This change also refactor the LocalDiffAwareness to extract the
WatchService specific part. It now select the FsEventsDiffAwareness on OSX and the
WatchServiceDiffAwareness on Linux.

RELNOTES[NEW]: On OSX, --watchfs now uses FsEvents to be notified of changes from the filesystem
               (previously, this flag had no effect on OS X).

Fixes #1074.

--
Change-Id: I927951468e4543a399e0e0ad0f1dd23d38ce15a0
Reviewed-on: https://bazel-review.googlesource.com/3420
MOS_MIGRATED_REVID=123854017

1 files changed, 108 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/MacOSXFsEventsDiffAwareness.java b/src/main/java/com/google/devtools/build/lib/skyframe/MacOSXFsEventsDiffAwareness.java
new file mode 100644
index 0000000000..cf0fc621b5
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/MacOSXFsEventsDiffAwareness.java
@@ -0,0 +1,108 @@
+// Copyright 2016 The Bazel Authors. All rights reserved.
+//
+// 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.devtools.build.lib.skyframe;
+
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableSet;
+import com.google.devtools.build.lib.UnixJniLoader;
+
+import java.io.File;
+import java.nio.file.Path;
+
+/**
+ * A {@link DiffAwareness} that use fsevents to watch the filesystem to use in lieu of
+ * {@link LocalDiffAwareness}.
+ *
+ * <p>
+ * On OS X, the local diff awareness cannot work because WatchService is dummy and do polling, which
+ * is slow (https://bugs.openjdk.java.net/browse/JDK-7133447).
+ */
+public final class MacOSXFsEventsDiffAwareness extends LocalDiffAwareness {
+
+  private boolean closed;
+
+  // Keep a pointer to a native structure in the JNI code (the FsEvents callback needs that
+  // structure).
+  private long nativePointer;
+
+  /**
+   * Watch changes on the file system under <code>watchRoot</code> with a granularity of
+   * <code>delay</code> seconds.
+   */
+  MacOSXFsEventsDiffAwareness(String watchRoot, double latency) {
+    super(watchRoot);
+    create(new String[] {watchRootPath.toAbsolutePath().toString()}, latency);
+
+    // Start a thread that just contains the OS X run loop.
+    new Thread(
+            new Runnable() {
+              @Override
+              public void run() {
+                MacOSXFsEventsDiffAwareness.this.run();
+              }
+            })
+        .start();
+  }
+
+  /**
+   * Watch changes on the file system under <code>watchRoot</code> with a granularity of 5ms.
+   */
+  MacOSXFsEventsDiffAwareness(String watchRoot) {
+    this(watchRoot, 0.005);
+  }
+
+  /**
+   * Helper function to start the watch of <code>paths</code>, called by the constructor.
+   */
+  private native void create(String[] paths, double latency);
+
+  /**
+   * Run the main loop
+   */
+  private native void run();
+
+  /**
+   * Close this watch service, this service should not be used any longer after closing.
+   */
+  public synchronized void close() {
+    Preconditions.checkState(!closed);
+    closed = true;
+    doClose();
+  }
+
+  /**
+   * JNI code stopping the main loop and shutting down listening to FSEvents.
+   */
+  private synchronized native void doClose();
+
+  /**
+   * JNI code returning the list of absolute path modified since last call.
+   */
+  private native String[] poll();
+
+  static {
+    UnixJniLoader.loadJni();
+  }
+
+  @Override
+  public synchronized View getCurrentView() throws BrokenDiffAwarenessException {
+    Preconditions.checkState(!closed);
+    ImmutableSet.Builder<Path> paths = ImmutableSet.builder();
+    for (String path : poll()) {
+      paths.add(new File(path).toPath());
+    }
+    return newView(paths.build());
+  }
+}