Synchronization

Synchronization is one of the most powerful but also most complex parts of using Vulkan. The application developer is now responsible for managing synchronization using the various link:https://docs.vulkan.org/spec/latest/chapters/synchronization.html#synchronization-pipeline-barriersVulkan synchronization primitives]. Improper use of synchronization can lead to hard-to-find bugs as well as poor performance in cases where the the GPU is unnecessarily idle.

There are a set of examples and a Understanding Vulkan Synchronization blog provided by Khronos on how to use some of the synchronization primitives. There are also presentations from Tobias Hector from past Vulkan talks: part 1 slides (video) and part 2 slides (video).

The following is an overview diagram of the difference between VkEvent, VkFence, and VkSemaphore

synchronization_overview.png

Validation

The Khronos Validation Layer has implemented some validation for synchronization. It can easily be enabled by the Vulkan Configurator included with the Vulkan SDK. A detailed whitepaper discussing the synchronization validation has been written as well and released as a Khronos Blog.

Pipeline Barriers

Pipeline Barriers give control over which pipeline stages need to wait on previous pipeline stages when a command buffer is executed.

synchronization_pipeline_barrieres.png

While Pipeline Barriers might be hard to understand at first, there are many great Khronos talks and other resources that go more in depth on the topic.

VK_KHR_synchronization2

The VK_KHR_synchronization2 extension overhauls the original core synchronization APIs to reduce complexity for application developers, as well as adding a few additional features not present in the original APIs.

Read the VK_KHR_synchronization2 chapter for more info about the difference in the synchronization APIs and how to port over to using the new extension