[sync] Componentize sync: Part 6: Add more SYNC_EXPORTs to files in src/sync/

sync/internal_api/public/util/weak_handle.h

 // Copyright 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.
 
 // Weak handles provides a way to refer to weak pointers from another
 // thread.  This is useful because it is not safe to reference a weak
 // pointer from a thread other than the thread on which it was
 // created.
 //
 // Weak handles can be passed across threads, so for example, you can
@@ skipping 40 matching lines @@
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/callback_forward.h"
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
+#include "sync/base/sync_export.h"
 
 namespace base {
 class MessageLoopProxy;
 }  // namespace base
 
 namespace tracked_objects {
 class Location;
 }  // namespace tracked_objects
 
 namespace syncer {
@@ skipping 21 matching lines @@
   typedef const T* ForwardType;
 };
 
 template <typename T>
 struct ParamTraits<T[]> {
   typedef const T* ForwardType;
 };
 
 // Base class for WeakHandleCore<T> to avoid template bloat.  Handles
 // the interaction with the owner thread and its message loop.
-class WeakHandleCoreBase {
+class SYNC_EXPORT WeakHandleCoreBase {
  public:
   // Assumes the current thread is the owner thread.
   WeakHandleCoreBase();
 
   // May be called on any thread.
   bool IsOnOwnerThread() const;
 
  protected:
   // May be destroyed on any thread.
   ~WeakHandleCoreBase();

[rlarocque, 2012/12/22 02:00:49]

Come to think of it, why is this not virtual?

[Raghu Simha, 2012/12/22 02:25:02]

Good catch. Fixed.

[akalin, 2012/12/26 09:39:57]

This non-virtual on purpose.  The inheritance is just to reduce template bloat,
and WeakHandles are never destroyed through a superclass pointer, so there's no
need for virtual destructors.

 
   // May be called on any thread.
   void PostToOwnerThread(const tracked_objects::Location& from_here,
                          const base::Closure& fn) const;
 
  private:
   // May be used on any thread.
   const scoped_refptr<base::MessageLoopProxy> owner_loop_proxy_;
 
   DISALLOW_COPY_AND_ASSIGN(WeakHandleCoreBase);
 };
 
 // WeakHandleCore<T> contains all the logic for WeakHandle<T>.
 template <typename T>
 class WeakHandleCore
-    : public NON_EXPORTED_BASE(WeakHandleCoreBase),

[rlarocque, 2012/12/22 02:00:49]

It seems like this change goes against the original author's intent.  Why won't
this work as written?

[Raghu Simha, 2012/12/22 02:25:02]

I agree. Perhaps the error I saw had to do with the non-virtual destructor. I've
restored this like to what it was.

[akalin, 2012/12/26 09:39:57]

Hmm, I still think this is correct.  Template classes don't need export
declarations since they're templated, but all these inherit from a single
internal class, which shouldn't need to be exported, and NON_EXPORTED_BASE is to
suppress the warning this produces in MSVC.

+    : public WeakHandleCoreBase,
       public base::RefCountedThreadSafe<WeakHandleCore<T> > {
  public:
   // Must be called on |ptr|'s owner thread, which is assumed to be
   // the current thread.
   explicit WeakHandleCore(const base::WeakPtr<T>& ptr) : ptr_(ptr) {}
 
   // Must be called on |ptr_|'s owner thread.
   base::WeakPtr<T> Get() const {
     CHECK(IsOnOwnerThread());
     return ptr_;
@@ skipping 230 matching lines @@
 
 // Makes a WeakHandle from a WeakPtr.
 template <typename T>
 WeakHandle<T> MakeWeakHandle(const base::WeakPtr<T>& ptr) {
   return WeakHandle<T>(ptr);
 }
 
 }  // namespace syncer
 
 #endif  // SYNC_UTIL_WEAK_HANDLE_H_