Function destroy_command_pool 

pub unsafe fn destroy_command_pool(
    device: &Device,
    pool: CommandPool,
    allocator: Option<&AllocationCallbacks>,
) -> Result<(), CallError>

Destroy a command pool and all command buffers allocated from it.

Safety

All command buffers from this pool must have finished execution on the GPU.

Khronos reference: vkDestroyCommandPool