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

mojo/public/c/system/types.h

 // Copyright 2014 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.
 
 // This file contains types and constants/macros common to different Mojo system
 // APIs.
 //
 // Note: This header should be compilable as C.
 
 #ifndef MOJO_PUBLIC_C_SYSTEM_TYPES_H_
@@ skipping 15 matching lines @@
 //   |MOJO_HANDLE_INVALID| - A value that is never a valid handle.
 
 typedef uint32_t MojoHandle;
 
 #ifdef __cplusplus
 const MojoHandle MOJO_HANDLE_INVALID = 0;
 #else
 #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).
 //   |MOJO_RESULT_OK| - Not an error; returned on success.
 //   |MOJO_RESULT_CANCELLED| - Operation was cancelled, typically by the caller.
 //   |MOJO_RESULT_UNKNOWN| - Unknown error (e.g., if not enough information is
 //       available for a more specific error).
 //   |MOJO_RESULT_INVALID_ARGUMENT| - Caller specified an invalid argument. This
 //       differs from |MOJO_RESULT_FAILED_PRECONDITION| in that the former
 //       indicates arguments that are invalid regardless of the state of the
@@ skipping 150 matching lines @@
 const MojoWatchNotificationFlags MOJO_WATCH_NOTIFICATION_FLAG_NONE = 0;
 const MojoWatchNotificationFlags MOJO_WATCH_NOTIFICATION_FLAG_FROM_SYSTEM =
     1 << 0;
 #else
 #define MOJO_WATCH_NOTIFICATION_FLAG_NONE ((MojoWatchNotificationFlags)0)
 #define MOJO_WATCH_NOTIFICATION_FLAG_FROM_SYSTEM \
     ((MojoWatchNotificationFlags)1 << 0);
 #endif
 
 #endif  // MOJO_PUBLIC_C_SYSTEM_TYPES_H_