Introducing gpu::CommandBufferId as a distinct, IdType<...>-based type.

ipc/ipc_message_utils.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 IPC_IPC_MESSAGE_UTILS_H_
 #define IPC_IPC_MESSAGE_UTILS_H_
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
 #include <map>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/containers/small_map.h"
 #include "base/containers/stack_container.h"
 #include "base/files/file.h"
 #include "base/format_macros.h"
+#include "base/id_type.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/scoped_vector.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/tuple.h"
 #include "build/build_config.h"
 #include "ipc/brokerable_attachment.h"
 #include "ipc/ipc_message_start.h"
 #include "ipc/ipc_param_traits.h"
@@ skipping 937 matching lines @@
     return true;
   }
   static void Log(const param_type& p, std::string* l) {
     if (p)
       LogParam(*p, l);
     else
       l->append("NULL");
   }
 };
 
+template <typename TypeMarker, typename WrappedType, WrappedType kInvalidValue>
+struct ParamTraits<base::IdType<TypeMarker, WrappedType, kInvalidValue>> {
+  typedef base::IdType<TypeMarker, WrappedType, kInvalidValue> param_type;
+  typedef ParamTraits<WrappedType> base_param_traits;
+  static void Write(base::Pickle* m, const param_type& p) {
+    base_param_traits::Write(m, p.GetUnsafeValue());
+  }
+  static bool Read(const base::Pickle* m,
+                   base::PickleIterator* iter,
+                   param_type* r) {
+    WrappedType value;
+    if (!base_param_traits::Read(m, iter, &value))
+      return false;
+    *r = param_type::FromUnsafeValue(value);
+    return true;
+  }
+  static void Log(const param_type& p, std::string* l) {
+    base_param_traits::Log(p.GetUnsafeValue(), l);
+  }
+};

[Nico, 2016/02/09 20:04:29]

This isn't more type-safe than just sending the inner int type, right? Why is it
necessary to send IdTypes over ipc?

[Łukasz Anforowicz, 2016/02/09 23:06:32]

It *is* more type-safe to use gpu::CommandBufferId instead of a raw integer in a
definition of an IPC message (i.e. PpapiHostMsg_PPBGraphics3D_Create in
crrev.com/1548443002/patch/40001/50064).  This means that the constructor of the
message is type-safe (i.e. won't accept a random integer) as are the handlers of
the message (i.e. PPB_Graphics3D_Proxy::OnMsgCreate in
crrev.com/1548443002/patch/40001/50065).  In other words - having IPC support
avoids unnecessary GetUnsafeValue / FromUnsafeValue calls.

+
 // IPC types ParamTraits -------------------------------------------------------
 
 // A ChannelHandle is basically a platform-inspecific wrapper around the
 // fact that IPC endpoints are handled specially on POSIX.  See above comments
 // on FileDescriptor for more background.
 template<>
 struct IPC_EXPORT ParamTraits<IPC::ChannelHandle> {
   typedef ChannelHandle param_type;
   static void Write(base::Pickle* m, const param_type& p);
   static bool Read(const base::Pickle* m,
@@ skipping 188 matching lines @@
   template <typename... Ts>
   static void WriteReplyParams(Message* reply, Ts... args) {
     ReplyParam p(args...);
     WriteParam(reply, p);
   }
 };
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_MESSAGE_UTILS_H_