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..65b5265ed66bed668559a34ecfc490852981bf0f 100644
--- a/base/android/jni_android_unittest.cc
+++ b/base/android/jni_android_unittest.cc
@@ -33,6 +33,24 @@ jmethodID GetMethodIDWrapper(JNIEnv* env, jclass clazz, const char* method,
   return g_last_method_id;
 }
 
+

[joth, 2012/10/02 17:47:43]

\n nit

[bulach, 2012/10/03 13:09:00]

Done.

+static jmethodID g_method_id = 0;

[joth, 2012/10/02 17:47:43]

this should be declared as an AtomicWord

nit: static not needed in anon namespace

[bulach, 2012/10/03 13:09:00]

Done.

+int LazyMethodIDCall(JNIEnv* env, jclass clazz, int p) {
+  base::android::LazyMethodID::Get<
+      base::android::LazyMethodID::METHODTYPE_STATIC,
+      base::android::LazyMethodID::EXCEPTIONCHECK_NO>(
+      env, clazz,
+      "abs",
+      "(I)I",
+      &g_method_id);

[joth, 2012/10/02 17:47:43]

are you specifically using a global method id rather than just declare it in the
test on stack and pass through as a param?

[bulach, 2012/10/03 13:09:00]

yes. I'm trying to reproduce as much as possible the same code path that the
(new) generated JNI code would call versus the old one.

+
+  return env->CallStaticIntMethod(clazz, g_method_id, p);
+}
+
+int MethodIDCall(JNIEnv* env, jclass clazz, int p) {
+  return env->CallStaticIntMethod(clazz, g_method_id, p);
+}

[joth, 2012/10/02 17:47:43]

AIUI it's preferred to put single-use anon methods like these down immediately
before the test that uses them. (fine for a file to have multiple anon namespace
blocks)

[bulach, 2012/10/03 13:09:00]

moved to its own file..

+
 }  // namespace
 
 class JNIAndroidTest : public testing::Test {
@@ -90,5 +108,26 @@ TEST_F(JNIAndroidTest, GetMethodIDFromClassNameCaching) {
   EXPECT_EQ(g_last_method_id, id3);
 }
 
+TEST(JNIAndroidMicrobenchmark, MethodId) {

[joth, 2012/10/02 17:47:43]

in net/ they put micro benchmarks into a different test target (and don't run
every day). I think these are fast enough running to not be an issue in here
though? I'm pretty sure base has some already but I can't find now...

[bulach, 2012/10/03 13:09:00]

yeah, the extra target doesn't seem to be worth the hassle..

+  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();
+
+  base::Time start = base::Time::Now();
+  for (int i = 0; i < 1024; ++i)
+    o += MethodIDCall(env, clazz.obj(), i);
+  base::Time end = base::Time::Now();
+
+  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;

[joth, 2012/10/02 17:47:43]

can you include in comment here as to typical results (and what machine you ran
it on)

[bulach, 2012/10/03 13:09:00]

good point! done

+}
+
 }  // namespace android
 }  // namespace base