[mojo-edk] Expose portable API for platform handle wrapping

mojo/public/c/system/types.h

Index: mojo/public/c/system/types.h
diff --git a/mojo/public/c/system/types.h b/mojo/public/c/system/types.h
index 6d21b12a172aefc805a98354479dd1fd1ceaef52..76ef5638c4cc168d7367bb0cdfebb58d2ef28c14 100644
--- a/mojo/public/c/system/types.h
+++ b/mojo/public/c/system/types.h
@@ -33,6 +33,21 @@ const MojoHandle MOJO_HANDLE_INVALID = 0;
 #define MOJO_HANDLE_INVALID ((MojoHandle)0)
 #endif
 
+// |MojoPlatformHandle|: A handle to an OS object. On POSIX systems this is
+//     generally a file descriptor. On OS X it might be a Mach port. On Windows,
+//     it's a HANDLE.
+//
+//   |MOJO_PLATFORM_HANDLE_INVALID| - A value that is never treated as a valid
+//       platform handle.
+
+typedef uint64_t MojoPlatformHandle;

[Anand Mistry (off Chromium), 2016/05/20 06:25:40]

I don't like the fact that the meaning here is context specific, and behavior
isn't hidden behind an interface (unlike MojoHandle).

How about a struct instead:
typedef struct _MojoPlatformHandle {
  uint64_t handle;
  uint64_t flags;
} MojoPlatformHandle;

For Mach ports, have a THIS_IS_A_MACH_PORT flag.

See MojoHandleSignalsState for precedence.

[Ken Rockot(use gerrit already), 2016/05/20 22:19:43]

I took it a step further and decided we should have an explicit
MojoPlatformHandleType value to make the handle type explicit. This seems
clearer and more extensible than using flags to modify the treatment of the
handle value.

+
+#ifdef __cplusplus
+const MojoPlatformHandle MOJO_PLATFORM_HANDLE_INVALID = 0xffffffffffffffffULL;

[Anand Mistry (off Chromium), 2016/05/20 06:25:40]

static_cast<>(-1) is the common pattern here.

[Ken Rockot(use gerrit already), 2016/05/20 22:19:43]

WontFix (Obsolete)

With a concept of "handle type", there's no an INVALID handle type, so no need
for special handle values.

+#else
+#define MOJO_PLATFORM_HANDLE_INVALID ((MojoPlatformHandle)0xffffffffffffffffULL)
+#endif
+
 // |MojoResult|: Result codes for Mojo operations. The only success code is zero
 // (|MOJO_RESULT_OK|); all non-zero values should be considered as error/failure
 // codes (even if the value is not recognized).