make base::SharedMemoryHandle a class on POSIX.

base/memory/shared_memory_handle.h

Index: base/memory/shared_memory_handle.h
diff --git a/base/memory/shared_memory_handle.h b/base/memory/shared_memory_handle.h
index dc33eeafa11faef22f73be0d44dd30447e43118b..ed8b69bdd5ec05c8808a04cec73d0417f9f75e81 100644
--- a/base/memory/shared_memory_handle.h
+++ b/base/memory/shared_memory_handle.h
@@ -28,7 +28,40 @@ namespace base {
 // SharedMemoryHandle is a platform specific type which represents
 // the underlying OS handle to a shared memory segment.
 #if defined(OS_POSIX) && !(defined(OS_MACOSX) && !defined(OS_IOS))
-typedef FileDescriptor SharedMemoryHandle;
+class BASE_EXPORT SharedMemoryHandle {

[Nico, 2017/04/27 16:24:44]

Since they're now classes everywhere, I think it'd be good to move the #ifs into
the class definition -- some of the class internals are now identical on all
platforms (default ctor, IsValid(), Close() so it'd be nice if those were listed
just once. (Not in this CL.)

[erikchen, 2017/04/27 17:08:10]

Added a TODO.

+ public:
+  // The default constructor returns an invalid SharedMemoryHandle.
+  SharedMemoryHandle();
+
+  // This constructor is deprecated, as it fails to propagate the GUID, which
+  // will be added in the near future.
+  // TODO(rockot): Remove this constructor once Mojo supports GUIDs.
+  // https://crbug.com/713763.
+  explicit SharedMemoryHandle(const base::FileDescriptor& file_descriptor);
+
+  // Creates a SharedMemoryHandle from an |fd| supplied from an external
+  // service.
+  static SharedMemoryHandle ImportHandle(int fd);

[Nico, 2017/04/27 16:24:44]

This type of thing seems to be a ctor instead of a factory function on win and
mac, why the difference?

Also, why even have that, couldn't clients just call the FileDescriptor ctor?

[erikchen, 2017/04/27 17:08:10]

The constructors on Mac/Win will be going away. Once I introduce GUIDs [see the
crbug], all constructors should explicitly specify whether a new GUID needs to
be generated. Importing a handle will require generating a new GUID.
That constructor is deprecated and going away.

+
+  // Returns the underlying OS resource.
+  int GetHandle() const;
+
+  // Whether the underlying OS resource is valid.
+  bool IsValid() const;
+
+  // Closes the underlying OS resource.
+  // The fact that this method needs to be "const" is an artifact of the
+  // original interface for base::SharedMemory::CloseHandle.
+  void Close() const;
+
+  // Invalidates [but doesn't close] the underlying OS resource.

[Nico, 2017/04/27 16:24:44]

Maybe say "leak unless careful" in the comment. Some of our smart pointery
classes call this "Release" and return the internal thing, maybe that'd be good
here?

[erikchen, 2017/04/27 17:08:10]

Done.

+  void Invalidate();
+
+  // Duplicates the underlying OS resource.
+  SharedMemoryHandle Duplicate() const;
+
+  FileDescriptor file_descriptor;

[Nico, 2017/04/27 16:24:44]

make private

[erikchen, 2017/04/27 17:08:10]

Can't do that, Chrome IPC serialization requires that this member be public.
Sorry. :(

[Nico, 2017/04/27 17:38:50]

Add accessors for what's needed by IPC?

[erikchen, 2017/04/27 18:13:42]

Done.

[The Chrome IPC macros don't support non-public members, but we're doing custom
serialization, so everything works.]

+};
 #elif defined(OS_WIN)
 class BASE_EXPORT SharedMemoryHandle {
  public: