C Specification

To query the number of additional threads that can usefully be joined to a deferred operation, call:

// Provided by VK_KHR_deferred_host_operations
uint32_t vkGetDeferredOperationMaxConcurrencyKHR(
    VkDevice                                    device,
    VkDeferredOperationKHR                      operation);


  • device is the device which owns operation.

  • operation is the deferred operation to be queried.


The returned value is the maximum number of threads that can usefully execute a deferred operation concurrently, reported for the state of the deferred operation at the point this command is called. This value is intended to be used to better schedule work onto available threads. Applications can join any number of threads to the deferred operation and expect it to eventually complete, though excessive joins may return VK_THREAD_DONE_KHR immediately, performing no useful work.

If operation is complete, vkGetDeferredOperationMaxConcurrencyKHR returns zero.

If operation is currently joined to any threads, the value returned by this command may immediately be out of date.

If operation is pending, implementations must not return zero unless at least one thread is currently executing vkDeferredOperationJoinKHR on operation. If there are such threads, the implementation should return an estimate of the number of additional threads which it could profitably use.

Implementations may return 232-1 to indicate that the maximum concurrency is unknown and cannot be easily derived. Implementations may return values larger than the maximum concurrency available on the host CPU. In these situations, an application should clamp the return value rather than oversubscribing the machine.


The recommended usage pattern for applications is to query this value once, after deferral, and schedule no more than the specified number of threads to join the operation. Each time a joined thread receives VK_THREAD_IDLE_KHR, the application should schedule an additional join at some point in the future, but is not required to do so.

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

  • VUID-vkGetDeferredOperationMaxConcurrencyKHR-operation-parameter
    operation must be a valid VkDeferredOperationKHR handle

  • VUID-vkGetDeferredOperationMaxConcurrencyKHR-operation-parent
    operation must have been created, allocated, or retrieved from device

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 (c) 2014-2020 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0