arc: Use GET_INTERFACE_FOR_METHOD macro

components/arc/instance_holder.h

 // Copyright 2015 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 COMPONENTS_ARC_INSTANCE_HOLDER_H_
 #define COMPONENTS_ARC_INSTANCE_HOLDER_H_
 
 #include <string>
+#include <type_traits>
 #include <utility>
 
 #include "base/bind.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
 #include "base/threading/thread_checker.h"
 
+// A convenience macro to call arc::InstanceHolder<T>::GetInstanceForVersion().
+// In order to avoid exposing method names from within the Mojo bindings, we
+// will rely on stringification and the fact that the method min versions have a
+// consistent naming scheme.
+#define GET_INSTANCE_FOR_METHOD(holder, method_name)            \

[Yusuke Sato, 2017/01/04 19:59:12]

nit: I'm a bit concerned about defining a macro without a prefix (e.g. component
name) in a header file. What about adding 'ARC' to the name? Maybe
ARC_GET_INSTANCE_FOR_METHOD or GET_ARC_INSTANCE_FOR_METHOD. WDYT?

[Luis Héctor Chávez, 2017/01/04 20:38:56]

sgtm, used the former.

+  (holder)->GetInstanceForVersion(                              \
+      std::remove_pointer<decltype(                             \
+          holder)>::type::Instance::k##method_name##MinVersion, \
+      #method_name)
+
 namespace arc {
 
 // Holds a Mojo instance+version pair. This also allows for listening for state
 // changes for the particular instance. T should be a Mojo interface type
 // (arc::mojom::XxxInstance).
 template <typename T>
 class InstanceHolder {
  public:
   // Notifies about connection events for individual instances.
   class Observer {
    public:
     // Called once the instance is ready.
     virtual void OnInstanceReady() {}
 
     // Called when the connection to the instance is closed.
     virtual void OnInstanceClosed() {}
 
    protected:
     virtual ~Observer() = default;
   };
 
+  using Instance = T;
+
   InstanceHolder() = default;
 
   // Returns true if the Mojo interface is ready at least for its version 0
   // interface. Use an Observer if you want to be notified when this is ready.
   // This can only be called on the thread that this class was created on.
   bool has_instance() const { return instance_; }
 
   // Gets the Mojo interface that's intended to call for
   // |method_name_for_logging|, but only if its reported version is at least
   // |min_version|. Returns nullptr if the instance is either not ready or does
   // not have the requested version, and logs appropriately.
-  // TODO(lhchavez): Improve the API. (crbug.com/649782)
-  T* GetInstanceForMethod(const std::string& method_name_for_logging,
-                          uint32_t min_version) {
+  // This function should not be called directly. Instead, use the
+  // GET_INSTANCE_FOR_METHOD() macro.
+  T* GetInstanceForVersion(uint32_t min_version,
+                           const char method_name_for_logging[]) {
     if (!instance_) {
       VLOG(1) << "Instance for " << T::Name_ << "::" << method_name_for_logging
               << " not available.";
       return nullptr;
     }
     if (version_ < min_version) {
       LOG(ERROR) << "Instance for " << T::Name_
                  << "::" << method_name_for_logging
                  << " version mismatch. Expected " << min_version << " got "
                  << version_;
       return nullptr;
     }
     return instance_;
   }
 
-  // Same as the above, but for the version zero.
-  T* GetInstanceForMethod(const std::string& method_name_for_logging) {
-    return GetInstanceForMethod(method_name_for_logging, 0u);
-  }
-
   // Adds or removes observers. This can only be called on the thread that this
   // class was created on. RemoveObserver does nothing if |observer| is not in
   // the list.
   void AddObserver(Observer* observer) {
     DCHECK(thread_checker_.CalledOnValidThread());
     observer_list_.AddObserver(observer);
 
     if (instance_)
       observer->OnInstanceReady();
   }
@@ skipping 34 matching lines @@
 
   base::ThreadChecker thread_checker_;
   base::ObserverList<Observer> observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(InstanceHolder<T>);
 };
 
 }  // namespace arc
 
 #endif  // COMPONENTS_ARC_INSTANCE_HOLDER_H_