# vkGetDeferredOperationMaxConcurrencyKHR(3) Manual Page

## Name

vkGetDeferredOperationMaxConcurrencyKHR - Query the maximum concurrency on a deferred operation

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## 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);

## Parameters

- `device` is the device which owns `operation`.

- `operation` is the deferred operation to be queried.

## Description

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If `operation` is currently joined to any threads, the value returned by this command may immediately be out of date.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

Note | 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

VK_KHR_deferred_host_operations, VkDeferredOperationKHR, VkDevice

## 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

Copyright 2014-2025 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0