Don't use Singleton to cache JNI method IDs in Java Bridge

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 462173f85d38cf48b62e466ebeb97e1b0a6ea006..8c805a6cff7b9b70bb4b0a90aec5749edc75ca42 100644
--- a/base/android/jni_android.h
+++ b/base/android/jni_android.h
@@ -30,19 +30,16 @@ void InitApplicationContext(jobject context);
 // Returns the application context assigned by InitApplicationContext().
 jobject GetApplicationContext();
 
-// Wraps a method ID.
-class MethodID {
- public:
-  jmethodID id() { return id_; }
- protected:
-  // Gets the method ID from the class name. Clears the pending Java exception
-  // and returns NULL if the method is not found. Note that GetMethodID() below
-  // avoids a class lookup, so should be used in preference when possible.
-  MethodID(JNIEnv* env, const char* class_name, const char* method,
-           const char* jni_signature);
- private:
-  jmethodID 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.
+// Note that strings passed to this function must remain unaltered for the
+// entire duration for which this function is in use. In practice, this means

[joth, 2011/12/02 17:35:36]

nit: "entire duration for which this function is in use" is a bit ambiguous.
How about "The strings passed to this function are held in the cache and MUST
remain valid after the function returns, and beyond the duration of all futures
calls to this function, across all threads. In practice..."

+// that the function should only be used with string constants.
+jmethodID GetMethodIDFromClassName(JNIEnv* env,
+                                   const char* class_name,
+                                   const char* method,
+                                   const char* jni_signature);
 
 // Get the method ID for a method. Will clear the pending Java
 // exception and return 0 if the method is not found.