11.7. Resource Sharing Mode

Buffer and image objects are created with a sharing mode controlling how they can be accessed from queues. The supported sharing modes are:

 

typedef enum VkSharingMode {
    VK_SHARING_MODE_EXCLUSIVE = 0,
    VK_SHARING_MODE_CONCURRENT = 1,
} VkSharingMode;

[Note]Note

VK_SHARING_MODE_CONCURRENT may result in lower performance access to the buffer or image than VK_SHARING_MODE_EXCLUSIVE.

Ranges of buffers and image subresources of image objects created using VK_SHARING_MODE_EXCLUSIVE must only be accessed by queues in the same queue family at any given time. In order for a different queue family to be able to interpret the memory contents of a range or image subresource, the application must transfer exclusive ownership of the range or image subresource between the source and destination queue families with the following sequence of operations:

  1. Release exclusive ownership from the source queue family to the destination queue family.
  2. Use semaphores to ensure proper execution control for the ownership transfer.
  3. Acquire exclusive ownership for the destination queue family from the source queue family.

To release exclusive ownership of a range of a buffer or image subresource of an image object, the application must execute a buffer or image memory barrier, respectively (see VkBufferMemoryBarrier and VkImageMemoryBarrier) on a queue from the source queue family. The srcQueueFamilyIndex parameter of the barrier must be set to the source queue family index, and the dstQueueFamilyIndex parameter to the destination queue family index.

To acquire exclusive ownership, the application must execute the same buffer or image memory barrier on a queue from the destination queue family.

Upon creation, resources using VK_SHARING_MODE_EXCLUSIVE are not owned by any queue family. A buffer or image memory barrier is not required to acquire ownership when no queue family owns the resource - it is implicitly acquired upon first use within a queue. However, images still require a layout transition from VK_IMAGE_LAYOUT_UNDEFINED or VK_IMAGE_LAYOUT_PREINITIALIZED before being used on the first queue. This layout transition can either be accomplished by an image memory barrier or by use in a render pass instance.

Once a queue family has used a range or image subresource of an VK_SHARING_MODE_EXCLUSIVE resource, its contents are undefined to other queue families unless ownership is transferred. The contents may also become undefined for other reasons, e.g. as a result of writes to an image subresource that aliases the same memory. A queue family can take ownership of a range or image subresource without an ownership transfer in the same way as for a resource that was just created, however doing so means any contents written by other queue families or via incompatible aliases are undefined.