Android: lazy initialization for method id.

base/android/jni_android_unittest.cc

Index: base/android/jni_android_unittest.cc
diff --git a/base/android/jni_android_unittest.cc b/base/android/jni_android_unittest.cc
index abecad778b47c72830d1e0a3345f6cf7c1d05140..920b395659025c4784a774439237fb645bcb4831 100644
--- a/base/android/jni_android_unittest.cc
+++ b/base/android/jni_android_unittest.cc
@@ -5,6 +5,7 @@
 #include "base/android/jni_android.h"
 
 #include "base/at_exit.h"
+#include "base/logging.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
@@ -90,5 +91,51 @@ TEST_F(JNIAndroidTest, GetMethodIDFromClassNameCaching) {
   EXPECT_EQ(g_last_method_id, id3);
 }
 
+namespace {
+
+base::subtle::AtomicWord g_atomic_id = 0;
+int LazyMethodIDCall(JNIEnv* env, jclass clazz, int p) {
+  jmethodID id = base::android::MethodID::LazyGet<
+      base::android::MethodID::TYPE_STATIC>(
+      env, clazz,
+      "abs",
+      "(I)I",
+      &g_atomic_id);
+
+  return env->CallStaticIntMethod(clazz, id, p);
+}
+
+int MethodIDCall(JNIEnv* env, jclass clazz, jmethodID id, int p) {
+  return env->CallStaticIntMethod(clazz, id, p);
+}
+
+}  // namespace
+
+TEST(JNIAndroidMicrobenchmark, MethodId) {
+  JNIEnv* env = AttachCurrentThread();
+  ScopedJavaLocalRef<jclass> clazz(GetClass(env, "java/lang/Math"));
+  base::Time start_lazy = base::Time::Now();
+  int o = 0;
+  for (int i = 0; i < 1024; ++i)
+    o += LazyMethodIDCall(env, clazz.obj(), i);
+  base::Time end_lazy = base::Time::Now();
+
+  jmethodID id = reinterpret_cast<jmethodID>(g_atomic_id);
+  base::Time start = base::Time::Now();
+  for (int i = 0; i < 1024; ++i)
+    o += MethodIDCall(env, clazz.obj(), id, i);
+  base::Time end = base::Time::Now();
+
+  // On a Galaxy Nexus, results were in the range of:
+  // JNI LazyMethodIDCall (us) 1984
+  // JNI MethodIDCall (us) 1861
+  LOG(ERROR) << "JNI LazyMethodIDCall (us) " <<
+      base::TimeDelta(end_lazy - start_lazy).InMicroseconds();
+  LOG(ERROR) << "JNI MethodIDCall (us) " <<
+      base::TimeDelta(end - start).InMicroseconds();
+  LOG(ERROR) << "JNI " << o;
+}
+
+
 }  // namespace android
 }  // namespace base