Android: lazy initialization for method id.

base/android/jni_android_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/android/jni_android.h"
 
 #include "base/at_exit.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
@@ skipping 15 matching lines @@
 
 jmethodID GetMethodIDWrapper(JNIEnv* env, jclass clazz, const char* method,
                              const char* jni_signature) {
   g_last_method = method;
   g_last_jni_signature = jni_signature;
   g_last_method_id = g_previous_functions->GetMethodID(env, clazz, method,
                                                        jni_signature);
   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 {
  protected:
   virtual void SetUp() {
     JNIEnv* env = AttachCurrentThread();
     g_previous_functions = env->functions;
     hooked_functions = *g_previous_functions;
     env->functions = &hooked_functions;
     hooked_functions.GetMethodID = &GetMethodIDWrapper;
@@ skipping 37 matching lines @@
   EXPECT_EQ(id1, id2);
 
   Reset();
   jmethodID id3 = GetMethodIDFromClassName(env, kJavaLangObject, kToString,
                                            kReturningJavaLangString);
   EXPECT_STREQ(kToString, g_last_method);
   EXPECT_STREQ(kReturningJavaLangString, g_last_jni_signature);
   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