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Nested Content Processes: Difference between revisions
Write up how GFX works in nested processes
(Write up how GFX works in nested processes) |
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== Terminology == | == Terminology == | ||
;Chrome Process, Root Process or B2G Process | |||
: The process with highest privilege which can access virtually all resources on the device. Many security and privacy sensitive API could only be performed by the chrome process. Content processes have to delegate the action to the chrome process through IPC. | |||
;Content Process or Child Process | |||
: Processes with lower privilege. Almost all web apps and browser tabs run in this kind of process thus the name content process. | |||
;Grand Child Process | |||
: The content processes whose parents are logically other content processes. In the OS's point of view, every content processes are still siblings. | |||
;IPC Protocol | |||
: The protocol defines IPC messages sent between two threads or two processes. In code, a protocol class is usually named P<something>, see also [[IPC Protocols]]. | |||
;Bridge | |||
: Toplevel protocol usually connects the chrome process with content processes. A bridge protocol connects two content processes. | |||
== Implementation == | == Implementation == | ||
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# Child process A ask chrome process to bridge to grand child process B via PContent::BridgeToChildProcess() | # Child process A ask chrome process to bridge to grand child process B via PContent::BridgeToChildProcess() | ||
# Child process A creates new PBrowser over PContentBridge::PBrowser | # Child process A creates new PBrowser over PContentBridge::PBrowser | ||
=== GFX === | |||
We will talk about how does layer composition work for nested processes. | |||
===== Terms ===== | |||
;RenderFrameParent | |||
: Each TabParent has a RenderFrameParent which maintains the render state of the remote tab. | |||
;nsSubDocumentFrame | |||
: A frame is a layout unit in the frame construction phase. A nsSubDocumentFrame usually corresponding to a <iframe> and alike. | |||
;CompositorChild | |||
: The child counterpart of the PCompositor protocol. Each process could use a CompositorChild to communicate with the compositing process. | |||
;nsDisplayRemote | |||
: A DisplayItem is a command in the DisplayList that describes how to create a layer and draw into it. nsDisplayRemote knows how to build a RefLayer for remote frames. | |||
;RefLayer | |||
: A RefLayer is a anchor point for remote layer trees. It has a unique id for looking up the actual layer tree. | |||
===== Flow ===== | |||
# On Tab creation | |||
## In TabChild::InitRenderingState() it creates the PRenderFrame using SendPRenderFrameConstructor and get a mLayersId back. | |||
##* If the TabParent/RenderFrameParent lives in the b2g process, use CompositorParent::AllocateLayerTreeId() to allocate layerId and register layerId via in process CompositorChild | |||
##* otherwise use ContentChild::GetSingleton()->SendAllocateLayerTreeId(aId) to allocate layerId and register layerId via OOP CompositorChild | |||
## Use the mLayersId to create a shadow layer manager. The shadow layer manager then could used to create layers. | |||
# On composition | |||
## On frame construction we create a nsSubDocumentFrame | |||
## If this nsSubDocumentFrame has a RenderFrameParent, then use it to create a nsDisplayRemote display item | |||
## On layer tree construction, nsDisplayRemote will create a RefLayer and bind the mLayersId of the RenderFrameParent to it. | |||
## When compositing the AsyncCompositionManager will WalkTheTree and resolve RefLayers using the mLayersId | |||
=== Security === | === Security === | ||