C Specification

To export a POSIX file descriptor representing the payload of a semaphore, call:

// Provided by VK_KHR_external_semaphore_fd
VkResult vkGetSemaphoreFdKHR(
    VkDevice                                    device,
    const VkSemaphoreGetFdInfoKHR*              pGetFdInfo,
    int*                                        pFd);


  • device is the logical device that created the semaphore being exported.

  • pGetFdInfo is a pointer to a VkSemaphoreGetFdInfoKHR structure containing parameters of the export operation.

  • pFd will return the file descriptor representing the semaphore payload.


Each call to vkGetSemaphoreFdKHR must create a new file descriptor and transfer ownership of it to the application. To avoid leaking resources, the application must release ownership of the file descriptor when it is no longer needed.


Ownership can be released in many ways. For example, the application can call close() on the file descriptor, or transfer ownership back to Vulkan by using the file descriptor to import a semaphore payload.

Where supported by the operating system, the implementation must set the file descriptor to be closed automatically when an execve system call is made.

Exporting a file descriptor from a semaphore may have side effects depending on the transference of the specified handle type, as described in Importing Semaphore State.

Valid Usage (Implicit)
  • VUID-vkGetSemaphoreFdKHR-device-parameter
    device must be a valid VkDevice handle

  • VUID-vkGetSemaphoreFdKHR-pGetFdInfo-parameter
    pGetFdInfo must be a valid pointer to a valid VkSemaphoreGetFdInfoKHR structure

  • VUID-vkGetSemaphoreFdKHR-pFd-parameter
    pFd must be a valid pointer to an int value

Return Codes
On success, this command returns

On failure, this command returns


See Also

Document Notes

For more information, see the Vulkan Specification

This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.

Copyright 2014-2024 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0