Notes on Firefox's remote texture architecture

remote-texture.org

Remote textures

• Relationships (‘<==>’ means ‘is one-to-one with’)
  • GPU process <==> RemoteTextureMap
  • RemoteTextureOwnerClient <==> WebGPUParent (and thus WebGPUChild)
  • TextureOwner <==> CanvasContext, when configured
• Tracking
  • TextureOwner
    • has various queues of
      • TextureDataHolder, a struct of
        • TextureHost (?)
        • TextureData (?)
        • SharedResourceWrapper, an enum of
          • gl::SharedSurface
          • webgpu::ExternalTexture
  • RemoteTextureMap
    • RemoteTextureMap::Get returns the singleton
    • keys are (pid, owner) pairs:
      • pid is a child process pid
      • owner is an id allocated in that pid
    • values are TextureOwner
  • RemoteTextureOwnerClient tracks groups of TextureOwner objects
    • mostly a front end for RemoteTextureMap that can operate on the group, or individual members
  • WebGPUParent::mRemoteTextureOwner is its RemoteTextureOwnerClient
• Adding TextureOwner objects
  • mozilla::webgpu::CanvasContext::Configure
    • allocates a fresh layers::RemoteTextureOwnerId (saved as mRemoteTextureOwnerId)
    • calls mozilla::webgpu::Device::InitSwapChain passing that owner id
    • calls SendDeviceCreateSwapChain, passing that owner id
    • ***** IPC BOUNDARY *****
    • RecvDeviceCreateSwapChain
      • ensures this WebGPUParent has a RemoteTextureOwnerClient
      • calls RemoteTextureOwnerClient::RegisterTextureOwner for the new owner id
      • calls RemoteTextureMap::RegisterTextureOwner
      • poof, now the CanvasContext has a TextureOwner under its mRemoteTextureOwnerId
• Removing TextureOwner objects
  • CanvasContext::Unconfigure calls SendSwapChainDrop, passing mRemoteTextureOwnerId
  • ***** IPC BOUNDARY *****
  • WebGPUParent::RecvSwapChainDrop
    • calls
      • RemoteTextureOwnerClient::UnregisterTextureOwner
        • calls
          • RemoteTextureMap::UnregisterTextureOwner
            • carefully interacts with compositor, but does eventually remove the entry from RemoteTextureMap::mTextureOwners and destroy it poof
• Adding RemoteTextureOwnerClient objects
  • RecvDeviceCreateSwapChain ensures the WebGPUParent has one, in the process of creating the ~TextureOwner~a
• Removing RemoteTextureOwnerClient objects
  • WebGPUParent::ActorDestroy
    • calls RemoteTextureOwnerClient::UnregisterAllTextureOwners
      • which calls RemoteTextureMap::UnregisterTextureOwners, passing the client’s set of owners
        • which does the same as UnregisterTextureOwner (singular), but only acquires the lock once
    • assigns nullptr to mRemoteTextureOwner to free it
• Initializing the RemoteTextureMap
  • only initialized in the dedicated GPU process or in the main process if the dedicated GPU process is disabled, by calling RemoteTextureMap::Init