Refactor the way singleton-style resources are exposed via PPB_Instance

ppapi/thunk/enter.h

 // 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.
 
 #ifndef PPAPI_THUNK_ENTER_H_
 #define PPAPI_THUNK_ENTER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 227 matching lines @@
   EnterInstanceNoLock(PP_Instance instance,
                       const PP_CompletionCallback& callback);
   ~EnterInstanceNoLock();
 
   PPB_Instance_API* functions() { return functions_; }
 
  private:
   PPB_Instance_API* functions_;
 };
 
+// EnterInstanceAPI ------------------------------------------------------------
+
+template<typename ApiT, bool lock_on_entry = true>
+class PPAPI_THUNK_EXPORT EnterInstanceAPI
+    : public subtle::EnterBase,
+      public subtle::LockOnEntry<lock_on_entry> {
+ public:
+  EnterInstanceAPI(PP_Instance instance) : EnterBase() {
+    functions_ = NULL;
+    PPB_Instance_API* ppb_instance =
+        PpapiGlobals::Get()->GetInstanceAPI(instance);
+    if (ppb_instance) {
+      Resource* resource =
+          ppb_instance->GetSingletonResource(instance,
+                                             ApiT::kSingletonResourceID);
+      if (resource)
+        functions_ = resource->GetAs<ApiT>();
+    }
+    SetStateForFunctionError(instance, functions_, true);
+  }
+  ~EnterInstanceAPI() {}
+
+  bool succeeded() const { return !!functions_; }
+  bool failed() const { return !functions_; }
+
+  ApiT* functions() { return functions_; }
+
+ private:
+  ApiT* functions_;
+};
+
+template<typename ApiT>
+class PPAPI_THUNK_EXPORT EnterInstanceAPINoLock
+    : public EnterInstanceAPI<ApiT, false> {
+ public:
+  EnterInstanceAPINoLock(PP_Instance instance)
+      : EnterInstanceAPI<ApiT, false>(instance) {
+  }
+};
+
 // EnterResourceCreation -------------------------------------------------------
 
 class PPAPI_THUNK_EXPORT EnterResourceCreation
     : public subtle::EnterBase,
       public subtle::LockOnEntry<true> {
  public:
   EnterResourceCreation(PP_Instance instance);
   ~EnterResourceCreation();
 
   ResourceCreationAPI* functions() { return functions_; }
@@ skipping 12 matching lines @@
   ResourceCreationAPI* functions() { return functions_; }
 
  private:
   ResourceCreationAPI* functions_;
 };
 
 }  // namespace thunk
 }  // namespace ppapi
 
 #endif  // PPAPI_THUNK_ENTER_H_