VkExternalMemoryAcquireUnmodifiedEXT
An acquire operation may have a performance penalty when acquiring
ownership of a subresource range from one of the special queue families
reserved for external memory ownership transfers described above.
The application can reduce the performance penalty in some cases by adding
a VkExternalMemoryAcquireUnmodifiedEXT structure to the pNext
chain of the acquire operation's memory barrier structure.
The VkExternalMemoryAcquireUnmodifiedEXT structure is defined as:
typedef struct VkExternalMemoryAcquireUnmodifiedEXT {
VkStructureType sType;
const void* pNext;
VkBool32 acquireUnmodifiedMemory;
} VkExternalMemoryAcquireUnmodifiedEXT;
sTypeis a VkStructureType value identifying this structure.pNextisNULLor a pointer to a structure extending this structure.acquireUnmodifiedMemoryspecifies, ifVK_TRUE, that no range of VkDeviceMemory bound to the resource of the memory barrier’s subresource range was modified at any time since the resource’s most recent release of ownership to the queue family specified by the memory barrier’ssrcQueueFamilyIndex. IfVK_FALSE, it specifies nothing.
If the application releases ownership of the subresource range to one of the
special queue families reserved for external memory ownership transfers with
a memory barrier structure, and later re-acquires ownership from the same
queue family with a memory barrier structure, and if no range of
VkDeviceMemory bound to the resource was modified at any time between
the release operation and the acquire operation, then the application
should add a VkExternalMemoryAcquireUnmodifiedEXT structure to the
pNext chain of the acquire operation's memory barrier structure
because this may reduce the performance penalty.
This struct is ignored if acquireUnmodifiedMemory is VK_FALSE.
In particular, VK_FALSE does not specify that memory was modified.
This struct is ignored if the memory barrier’s srcQueueFamilyIndex is
not a special queue family reserved for external memory ownership transfers.
The method by which the application determines whether memory was modified between the release operation and acquire operation is outside the scope of Vulkan.
For any Vulkan operation that accesses a resource, the application must not assume the implementation accesses the resource’s memory as read-only, even for apparently read-only operations such as transfer commands and shader reads.
The validity of
VkExternalMemoryAcquireUnmodifiedEXT::acquireUnmodifiedMemory is
independent of memory ranges outside the ranges of VkDeviceMemory
bound to the resource.
In particular, it is independent of any implementation-private memory
associated with the resource.
Valid Usage
VUID-VkExternalMemoryAcquireUnmodifiedEXT-acquireUnmodifiedMemory-08922
If acquireUnmodifiedMemory is VK_TRUE, and the memory
barrier’s srcQueueFamilyIndex is a special queue family reserved
for external memory ownership transfers (as described in
Queue Family Ownership Transfer), then each range of
VkDeviceMemory bound to the resource must have remained
unmodified during all time since the resource’s most recent release of
ownership to the queue family
Valid Usage (Implicit)
VUID-VkExternalMemoryAcquireUnmodifiedEXT-sType-sType
sType must be VK_STRUCTURE_TYPE_EXTERNAL_MEMORY_ACQUIRE_UNMODIFIED_EXT