// Copyright (c) 2016-2017 Khronos Group. This work is licensed under a
// Creative Commons Attribution 4.0 International License; see
// http://creativecommons.org/licenses/by/4.0/

include::meta/VK_KHR_external_semaphore.txt[]

*Last Modified Date*::
    2016-10-21
*IP Status*::
    No known IP claims.
*Contributors*::
  - Jason Ekstrand, Intel
  - Jesse Hall, Google
  - Tobias Hector, Imagination Technologies
  - James Jones, NVIDIA
  - Jeff Juliano, NVIDIA
  - Matthew Netsch, Qualcomm Technologies, Inc.
  - Ray Smith, ARM
  - Chad Versace, Google

An application using external memory may wish to synchronize access to that
memory using semaphores.
This extension enables an application to create semaphores from which
non-Vulkan handles that reference the underlying synchronization primitive
can be exported.

=== New Object Types

None.

=== New Enum Constants

  * ename:VK_STRUCTURE_TYPE_EXPORT_SEMAPHORE_CREATE_INFO_KHR
  * ename:VK_ERROR_INVALID_EXTERNAL_HANDLE_KHR

=== New Enums

  * elink:VkSemaphoreImportFlagBitsKHR

=== New Structs

  * slink:VkExportSemaphoreCreateInfoKHR

=== New Functions

None.

=== Issues

1) Should there be restrictions on what side effects can occur when waiting
on imported semaphores that are in an invalid state?

*RESOLVED*: Yes.
Normally, validating such state would be the responsibility of the
application, and the implementation would be free to enter an undefined
state if valid usage rules were violated.
However, this could cause security concerns when using imported semaphores,
as it would require the importing application to trust the exporting
application to ensure the state is valid.
Requiring this level of trust is undesireable for many potential use cases.

2) Must implementations validate external handles the application provides
as input to semaphore state import operations?

*RESOLVED*: Implementations must return an error to the application if the
provided semaphore state handle can not be used to complete the requested
import operation.
However, implementations need not validate handles are of the exact type
specified by the application.