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

base/android/jni_android.h

 // Copyright (c) 2011 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.
 
 #ifndef BASE_ANDROID_JNI_ANDROID_H_
 #define BASE_ANDROID_JNI_ANDROID_H_
 
 #include <jni.h>
 #include <sys/types.h>
 
@@ skipping 12 matching lines @@
 
 // Initializes the global application context object. The |context| should be
 // the global reference of application context object.  It is not necessarily
 // called after InitVM().
 // TODO: We might combine InitVM() and InitApplicationContext() into one method.
 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.
 jmethodID GetMethodID(JNIEnv* env,
                       jclass clazz,
                       const char* const method,
                       const char* const jni_signature);
 
 // Get the method ID for a class static method. Will clear the pending Java
 // exception and return 0 if the method is not found.
@@ skipping 10 matching lines @@
                     const char* jni_signature);
 
 // Returns true if an exception is pending in the provided JNIEnv*. If an
 // exception is pending, this function prints and then clears it.
 bool CheckException(JNIEnv* env);
 
 }  // namespace android
 }  // namespace base
 
 #endif  // BASE_ANDROID_JNI_ANDROID_H_