CommandBuffer

A command buffer is a sequence of commands prepared by software to be executed by a graphics or compute device, such as a GPU. Commands typically include binding resources, copying or transferring memory, setting pipeline state, issuing draw calls, and dispatching compute workloads. The common workflow is to allocate a command buffer, record a series of commands using an API’s encoders or direct command calls, finalize the recording, and submit the buffer to a device queue for execution. Depending on the API, the same command buffer may be submitted multiple times or reset and re-recorded for reuse.

In modern explicit graphics APIs, command buffers are central to performance and parallelism. Vulkan uses explicit command buffers allocated from a command pool, with primary and secondary levels. Recordings can be reused by multiple submissions, and synchronization is managed with fences, events, and pipeline barriers to control hazards between commands and between queues. Metal exposes MTLCommandBuffer objects created from a command queue; recording is done through render, compute, and blit encoders, and the buffer is committed for GPU execution. Direct3D 12 employs command lists and command allocators, with reusable bundles (pre-recorded command sequences) and synchronization via fences, while emphasizing explicit resource and dependency management.

Advantages of command buffers include reduced CPU-GPU synchronization, improved batching, and the ability to record work on multiple threads before submission, enabling better overlap of computation and rendering. Challenges include managing lifetimes, synchronization, and memory overhead, as well as avoiding serialization bottlenecks. Command buffers are a foundational concept across modern graphics and compute APIs, with each API offering its own terminology and lifecycle details.