Android: lazy initialization for method id.

base/android/jni_generator/jni_generator.py

 #!/usr/bin/env python
 # 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.
 
 # TODO (qinmin): Need to refactor this file as base should not know about
 # higher level concepts. Currently this file has knowledge about higher level
 # java classes.
 
 """Extracts native methods from a Java file and generates the JNI bindings.
@@ skipping 583 matching lines @@
 namespace {
 $CLASS_PATH_DEFINITIONS
 }  // namespace
 
 $OPEN_NAMESPACE
 $FORWARD_DECLARATIONS
 
 // Step 2: method stubs.
 $METHOD_STUBS
 
-// Step 3: GetMethodIDs and RegisterNatives.
-static void GetMethodIDsImpl(JNIEnv* env) {
-$GET_METHOD_IDS_IMPL
-}
+// Step 3: RegisterNatives.
 
 static bool RegisterNativesImpl(JNIEnv* env) {
-  GetMethodIDsImpl(env);

[joth, 2012/10/04 17:59:59]

one thing I did remember this morning: currently if there's some build/config
problem we get a crash on startup if any (app custom class) method can't be
found. with this change, we'll only get the crash way down line when method is
called, so will rely on 100% code coverage to find such issues...
would is be worth leaving in a debug-only variant of GetMethodIDs here that
merely DCHECKS(HasMethod(...)) for each of the (non-system) method IDs? i.e.
leave the registrations themselves to use LazyGet, but still have the benefit of
debug startup sanity check on this?

[bulach, 2012/10/04 18:58:17]

I agree in principle, but for app classes, how can there be a mismatch?
 
I mean, unless we have a broken build system :) but other than that, the JNI
should surely match the classes that are in the APK?

 $REGISTER_NATIVES_IMPL
   return true;
 }
 $CLOSE_NAMESPACE
 #endif  // ${HEADER_GUARD}
 """)
     script_components = os.path.abspath(sys.argv[0]).split(os.path.sep)
     base_index = script_components.index('base')
     script_name = os.sep.join(script_components[base_index:])
     values = {
         'SCRIPT_NAME': script_name,
         'FULLY_QUALIFIED_CLASS': self.fully_qualified_class,
         'CLASS_PATH_DEFINITIONS': self.GetClassPathDefinitionsString(),
         'FORWARD_DECLARATIONS': self.GetForwardDeclarationsString(),
         'METHOD_STUBS': self.GetMethodStubsString(),
         'OPEN_NAMESPACE': self.GetOpenNamespaceString(),
-        'GET_METHOD_IDS_IMPL': self.GetMethodIDsImplString(),
         'REGISTER_NATIVES_IMPL': self.GetRegisterNativesImplString(),
         'CLOSE_NAMESPACE': self.GetCloseNamespaceString(),
         'HEADER_GUARD': self.header_guard,
     }
     return WrapOutput(template.substitute(values))
 
   def GetClassPathDefinitionsString(self):
     ret = []
     ret += [self.GetClassPathDefinitions()]
     return '\n'.join(ret)
@@ skipping 15 matching lines @@
     return '\n'.join(ret)
 
   def GetKMethodsString(self, clazz):
     ret = []
     for native in self.natives:
       if (native.java_class_name == clazz or
           (not native.java_class_name and clazz == self.class_name)):
         ret += [self.GetKMethodArrayEntry(native)]
     return '\n'.join(ret)
 
-  def GetMethodIDsImplString(self):
-    ret = []
-    ret += [self.GetFindClasses()]
-    for called_by_native in self.called_by_natives:
-      ret += [self.GetMethodIDImpl(called_by_native)]
-    return '\n'.join(ret)
-
   def GetRegisterNativesImplString(self):
     """Returns the implementation for RegisterNatives."""
     template = Template("""\
   static const JNINativeMethod kMethods${JAVA_CLASS}[] = {
 ${KMETHODS}
   };
   const int kMethods${JAVA_CLASS}Size = arraysize(kMethods${JAVA_CLASS});
 
   if (env->RegisterNatives(g_${JAVA_CLASS}_clazz,
                            kMethods${JAVA_CLASS},
                            kMethods${JAVA_CLASS}Size) < 0) {
     LOG(ERROR) << "RegisterNatives failed in " << __FILE__;
     return false;
   }
 """)
-    ret = []
+    ret = [self.GetFindClasses()]
     all_classes = self.GetUniqueClasses(self.natives)
     all_classes[self.class_name] = self.fully_qualified_class
     for clazz in all_classes:
       kmethods = self.GetKMethodsString(clazz)
       if kmethods:
         values = {'JAVA_CLASS': clazz,
                   'KMETHODS': kmethods}
         ret += [template.substitute(values)]
     if not ret: return ''
     return '\n' + '\n'.join(ret)
@@ skipping 88 matching lines @@
     """Returns a string."""
     function_signature_template = Template("""\
 static ${RETURN_TYPE} Java_${JAVA_CLASS}_${METHOD_ID_VAR_NAME}(\
 JNIEnv* env${FIRST_PARAM_IN_DECLARATION}${PARAMS_IN_DECLARATION})""")
     function_header_template = Template("""\
 ${FUNCTION_SIGNATURE} {""")
     function_header_with_unused_template = Template("""\
 ${FUNCTION_SIGNATURE} __attribute__ ((unused));
 ${FUNCTION_SIGNATURE} {""")
     template = Template("""
-static jmethodID g_${JAVA_CLASS}_${METHOD_ID_VAR_NAME} = 0;
+static base::subtle::AtomicWord g_${JAVA_CLASS}_${METHOD_ID_VAR_NAME} = 0;
 ${FUNCTION_HEADER}
   /* Must call RegisterNativesImpl()  */
   DCHECK(g_${JAVA_CLASS}_clazz);
-  DCHECK(g_${JAVA_CLASS}_${METHOD_ID_VAR_NAME});
+  jmethodID method_id =
+    ${GET_METHOD_ID_IMPL}
   ${RETURN_DECLARATION}
   ${PRE_CALL}env->${ENV_CALL}(${FIRST_PARAM_IN_CALL},
-      g_${JAVA_CLASS}_${METHOD_ID_VAR_NAME}${PARAMS_IN_CALL})${POST_CALL};
+      method_id${PARAMS_IN_CALL})${POST_CALL};
   ${CHECK_EXCEPTION}
   ${RETURN_CLAUSE}
 }""")
     if called_by_native.static or called_by_native.is_constructor:
       first_param_in_declaration = ''
       first_param_in_call = ('g_%s_clazz' %
                              (called_by_native.java_class_name or
                               self.class_name))
     else:
       first_param_in_declaration = ', jobject obj'
@@ skipping 34 matching lines @@
         'FIRST_PARAM_IN_DECLARATION': first_param_in_declaration,
         'PARAMS_IN_DECLARATION': params_in_declaration,
         'STATIC': 'Static' if called_by_native.static else '',
         'PRE_CALL': pre_call,
         'POST_CALL': post_call,
         'ENV_CALL': called_by_native.env_call,
         'FIRST_PARAM_IN_CALL': first_param_in_call,
         'PARAMS_IN_CALL': params_for_call,
         'METHOD_ID_VAR_NAME': called_by_native.method_id_var_name,
         'CHECK_EXCEPTION': check_exception,
+        'GET_METHOD_ID_IMPL': self.GetMethodIDImpl(called_by_native)
     }
     values['FUNCTION_SIGNATURE'] = (
         function_signature_template.substitute(values))
     if called_by_native.system_class:
       values['FUNCTION_HEADER'] = (
           function_header_with_unused_template.substitute(values))
     else:
       values['FUNCTION_HEADER'] = function_header_template.substitute(values)
     return template.substitute(values)
 
@@ skipping 48 matching lines @@
   g_${JAVA_CLASS}_clazz = reinterpret_cast<jclass>(env->NewGlobalRef(
       base::android::GetUnscopedClass(env, k${JAVA_CLASS}ClassPath)));""")
     ret = []
     for clazz in self.GetUniqueClasses(self.called_by_natives):
       values = {'JAVA_CLASS': clazz}
       ret += [template.substitute(values)]
     return '\n'.join(ret)
 
   def GetMethodIDImpl(self, called_by_native):
     """Returns the implementation of GetMethodID."""
-    template = Template("""\
-  g_${JAVA_CLASS}_${METHOD_ID_VAR_NAME} =
-      base::android::Get${STATIC}MethodID${SUFFIX}(
-          env, g_${JAVA_CLASS}_clazz,
-          "${JNI_NAME}",
-          ${JNI_SIGNATURE});
+    template = Template("""
+  base::android::MethodID::LazyGet<
+      base::android::MethodID::METHODTYPE_${STATIC},
+      base::android::MethodID::EXCEPTIONCHECK_${CHECK_EXCEPTION}>(
+      env, g_${JAVA_CLASS}_clazz,
+      "${JNI_NAME}",
+      ${JNI_SIGNATURE},
+      &g_${JAVA_CLASS}_${METHOD_ID_VAR_NAME});
 """)
     jni_name = called_by_native.name
     jni_return_type = called_by_native.return_type
     if called_by_native.is_constructor:
       jni_name = '<init>'
       jni_return_type = 'void'
     values = {
         'JAVA_CLASS': called_by_native.java_class_name or self.class_name,
         'JNI_NAME': jni_name,
         'METHOD_ID_VAR_NAME': called_by_native.method_id_var_name,
-        'STATIC': 'Static' if called_by_native.static else '',
-        'SUFFIX': 'OrNull' if called_by_native.system_class else '',
+        'STATIC': 'STATIC' if called_by_native.static else 'NORMAL',
+        'CHECK_EXCEPTION': 'NO' if called_by_native.system_class else 'YES',
         'JNI_SIGNATURE': JniSignature(called_by_native.params,
                                       jni_return_type,
                                       True)
     }
     return template.substitute(values)
 
 
 def WrapOutput(output):
   ret = []
   for line in output.splitlines():
@@ skipping 92 matching lines @@
     input_file = options.input_file
   output_file = None
   if options.output_dir:
     root_name = os.path.splitext(os.path.basename(input_file))[0]
     output_file = os.path.join(options.output_dir, root_name) + '_jni.h'
   GenerateJNIHeader(input_file, output_file, options.namespace)
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))