Cache AndroidBlockGuardPolicy to avoid allocation.

Every incoming Binder call ends up triggering a BlockGuardPolicy
update, which would thrash between new AndroidBlockGuardPolicy
instances and BlockGuard.LAX_POLICY, causing GC churn.

This change avoids the extra allocations by recycling a single
AndroidBlockGuardPolicy in a ThreadLocal.  Worst-case thrashing case
is now 10% faster; from 7.46us to 6.65us.

Bug: 9424568
Change-Id: I9c3b1c097a2aecc9b1f109a824cf3ea319fb3393

1 files changed, 34 insertions, 0 deletions

diff --git a/core/tests/benchmarks/src/android/os/StrictModeBenchmark.java b/core/tests/benchmarks/src/android/os/StrictModeBenchmark.java
new file mode 100644
index 0000000..41af3820
--- /dev/null
+++ b/core/tests/benchmarks/src/android/os/StrictModeBenchmark.java
@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * 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 android.os;
+
+import android.os.StrictMode.ThreadPolicy;
+
+import com.google.caliper.SimpleBenchmark;
+
+public class StrictModeBenchmark extends SimpleBenchmark {
+
+    private ThreadPolicy mOff = new ThreadPolicy.Builder().build();
+    private ThreadPolicy mOn = new ThreadPolicy.Builder().detectAll().build();
+
+    public void timeToggleThreadPolicy(int reps) {
+        for (int i = 0; i < reps; i++) {
+            StrictMode.setThreadPolicy(mOn);
+            StrictMode.setThreadPolicy(mOff);
+        }
+    }
+}