Add VMDebug.getInstancesOfClasses API.

The API can be used to iterate over instances of a given type on the
heap.

The GetInstancesOfClassesBenchmark run on bullhead shows the run time
of the API grows linearly in the number of classes, C, to get instances
of and the number of total instances, N, allocated on the heap.

C   N=~2^18   N=~2^19
1      13ms      21ms
2      26ms      43ms
4      53ms      87ms

Bug: 69729799
Test: art/test/testrunner/testrunner.py -t 099-vmdebug -b --host

Change-Id: Iebc34e1b079e719a66bb93963c5315a0d24834b1

1 files changed, 67 insertions, 0 deletions

diff --git a/benchmarks/src/benchmarks/GetInstancesOfClassesBenchmark.java b/benchmarks/src/benchmarks/GetInstancesOfClassesBenchmark.java
new file mode 100644
index 0000000000..2e85fae040
--- /dev/null
+++ b/benchmarks/src/benchmarks/GetInstancesOfClassesBenchmark.java
@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2017 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 benchmarks;
+
+import dalvik.system.VMDebug;
+
+public class GetInstancesOfClassesBenchmark {
+    private static class ObjectTree {
+        ObjectTree left;
+        ObjectTree right;
+
+        public ObjectTree(int depth) {
+            if (depth > 1) {
+                left = new ObjectTree(depth - 1);
+                right = new ObjectTree(depth - 1);
+            }
+        }
+    }
+
+    // 2^19 = 524288
+    private static ObjectTree tree = new ObjectTree(19);
+
+    public void timeGetInstancesOf1Class(int reps) {
+        Class[] classes = new Class[]{
+            Integer.class
+        };
+        for (int rep = 0; rep < reps; ++rep) {
+            VMDebug.getInstancesOfClasses(classes, true);
+        }
+    }
+
+    public void timeGetInstancesOf2Classes(int reps) {
+        Class[] classes = new Class[]{
+            Integer.class,
+            Long.class
+        };
+        for (int rep = 0; rep < reps; ++rep) {
+            VMDebug.getInstancesOfClasses(classes, true);
+        }
+    }
+
+    public void timeGetInstancesOf4Classes(int reps) {
+        Class[] classes = new Class[]{
+            Integer.class,
+            Long.class,
+            Float.class,
+            Double.class
+        };
+        for (int rep = 0; rep < reps; ++rep) {
+            VMDebug.getInstancesOfClasses(classes, true);
+        }
+    }
+}