1 files changed, 59 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeIncrementalBuildMonitor.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeIncrementalBuildMonitor.java
new file mode 100644
index 0000000000..c0fea268f3
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeIncrementalBuildMonitor.java
@@ -0,0 +1,59 @@
+// Copyright 2014 Google Inc. 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.eventbus.EventBus;
+import com.google.devtools.build.lib.actions.ChangedFilesMessage;
+import com.google.devtools.build.lib.concurrent.ThreadSafety;
+import com.google.devtools.build.lib.vfs.PathFragment;
+import com.google.devtools.build.lib.vfs.RootedPath;
+import com.google.devtools.build.skyframe.SkyKey;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * A package-private class intended to track a small number of modified files during the build. This
+ * class should stop recording changed files if there are too many of them, instead of holding onto
+ * a large collection of files.
+ */
+@ThreadSafety.ThreadCompatible
+class SkyframeIncrementalBuildMonitor {
+  private Set<PathFragment> files = new HashSet<>();
+  private static final int MAX_FILES = 100;
+
+  public void accrue(Iterable<SkyKey> invalidatedValues) {
+    for (SkyKey skyKey : invalidatedValues) {
+      if (skyKey.functionName() == SkyFunctions.FILE_STATE) {
+        RootedPath file = (RootedPath) skyKey.argument();
+        maybeAddFile(file.getRelativePath());
+      }
+    }
+  }
+
+  private void maybeAddFile(PathFragment path) {
+    if (files != null) {
+      files.add(path);
+      if (files.size() >= MAX_FILES) {
+        files = null;
+      }
+    }
+  }
+
+  public void alertListeners(EventBus eventBus) {
+    if (files != null) {
+      eventBus.post(new ChangedFilesMessage(files));
+    }
+  }
+}