Android: lazy initialization for method id.

base/android/jni_android.h

Index: base/android/jni_android.h
diff --git a/base/android/jni_android.h b/base/android/jni_android.h
index 40e235943c64b88e04a1bd16166f107c81c574cf..6b831a74f795ce63d1936e4c2f660ac029af60a4 100644
--- a/base/android/jni_android.h
+++ b/base/android/jni_android.h
@@ -9,6 +9,7 @@
 #include <sys/types.h>
 
 #include "base/android/scoped_java_ref.h"
+#include "base/atomicops.h"
 #include "base/compiler_specific.h"
 
 namespace base {
@@ -57,56 +58,44 @@ jclass GetUnscopedClass(JNIEnv* env, const char* class_name) WARN_UNUSED_RESULT;
 // Returns true iff the class |class_name| could be found.
 bool HasClass(JNIEnv* env, const char* class_name);
 
-// Returns the method ID for the method with the specified name and signature.
-// This method triggers a fatal assertion if the method could not be found.
-// Use HasMethod if you need to check whether a method exists.
-jmethodID GetMethodID(JNIEnv* env,
-                      const JavaRef<jclass>& clazz,
-                      const char* method_name,
-                      const char* jni_signature);
-
-// Similar to GetMethodID, but takes a raw jclass.
-jmethodID GetMethodID(JNIEnv* env,
-                      jclass clazz,
-                      const char* method_name,
-                      const char* jni_signature);
-
-// Unlike GetMethodID, returns NULL if the method could not be found.
-jmethodID GetMethodIDOrNull(JNIEnv* env,
-                            jclass clazz,
-                            const char* method_name,
-                            const char* jni_signature);
-
-// Returns the method ID for the static method with the specified name and
-// signature.
-// This method triggers a fatal assertion if the method could not be found.
-// Use HasMethod if you need to check whether a method exists.
-jmethodID GetStaticMethodID(JNIEnv* env,
-                            const JavaRef<jclass>& clazz,
-                            const char* method_name,
-                            const char* jni_signature);
-
-// Similar to the GetStaticMethodID, but takes a raw jclass.
-jmethodID GetStaticMethodID(JNIEnv* env,
-                            jclass clazz,
-                            const char* method_name,
-                            const char* jni_signature);
-
-// Unlike GetStaticMethodID, returns NULL if the method could not be found.
-jmethodID GetStaticMethodIDOrNull(JNIEnv* env,
-                                  jclass clazz,
-                                  const char* method_name,
-                                  const char* jni_signature);
-
-// Returns true iff |clazz| has a method with the specified name and signature.
-bool HasMethod(JNIEnv* env,
-               const JavaRef<jclass>& clazz,
-               const char* method_name,
-               const char* jni_signature);
+// This class is a wrapper for JNIEnv Get(Static)MethodID.
+class MethodID {
+ public:
+  enum MethodType {
+    METHODTYPE_STATIC,
+    METHODTYPE_NORMAL,
+  };
+
+  // Wether or not to CHECK if an exception happens when
+  // trying to obtain a method id.
+  enum ExceptionCheck {
+    EXCEPTIONCHECK_NO,
+    EXCEPTIONCHECK_YES,
+  };
+
+  template<MethodType method_type,
+           ExceptionCheck exception_check>
+  static jmethodID Get(JNIEnv* env,
+                       jclass clazz,
+                       const char* method_name,
+                       const char* jni_signature);
+
+  // The caller is responsible to zero-initialize |atomic_method_id|.
+  // If it's set, it'll return immediately. Otherwise, it'll call into
+  // ::Get() above. If there's a race, it's ok since the values are the same

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

nit: if there's a race... is all implementation detail, moving into the .cc as
not needed on the API. (could just call out here that it's fine to
simultaneously call this on multiple threads referencing the same
|atomic_method_id|

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

Done.

+  // (and the duplicated effort will happen only once).
+  template<MethodType method_type,
+           ExceptionCheck exception_check>
+  static jmethodID LazyGet(JNIEnv* env,
+                           jclass clazz,
+                           const char* method_name,
+                           const char* jni_signature,
+                           base::subtle::AtomicWord* atomic_method_id);
+};
 
 // Gets the method ID from the class name. Clears the pending Java exception
 // and returns NULL if the method is not found. Caches results. Note that
-// GetMethodID() below avoids a class lookup, but does not cache results.
+// MethodID() above avoids a class lookup, but does not cache results.

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

nit: MethodID above is not a function. MethodID::Get()

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

Done.

 // Strings passed to this function are held in the cache and MUST remain valid
 // beyond the duration of all future calls to this function, across all
 // threads. In practice, this means that the function should only be used with