Browsing Context Embedding

Embedder Element to nsDocShell

In order to render the contents of a BrowsingContext, the embedding element needs to be able to communicate with the nsDocShell which is currently being used to host it’s content. This is done in 3 different ways depending on which combination of processes is in-use.

  • in-process: The nsFrameLoader directly embeds the nsDocShell.

  • remote tab: The parent process is the embedder, and uses a PBrowser, via a BrowserHost. The BrowserChild actor holds the actual nsDocShell alive.

  • remote subframe: A content process is the embedder, and uses a PBrowserBridge, via a BrowserBridgeHost to communicate with the parent process. The parent process then uses a BrowserParent, as in the remote tab case, to communicate with the nsDocShell.

Diagram

digraph embedding { node [shape=rectangle] subgraph cluster_choice { color=transparent; node [shape=none]; "In-Process"; "Remote Tab"; "Remote Subframe"; } "nsFrameLoaderOwner" [label="nsFrameLoaderOwner\ne.g. <iframe>, <xul:browser>, <embed>"] "nsFrameLoaderOwner" -> "nsFrameLoader"; "nsFrameLoader" -> "In-Process" [dir=none]; "nsFrameLoader" -> "Remote Tab" [dir=none]; "nsFrameLoader" -> "Remote Subframe" [dir=none]; "In-Process" -> "nsDocShell"; "Remote Tab" -> "BrowserHost"; "Remote Subframe" -> "BrowserBridgeHost"; "BrowserHost" -> "BrowserParent"; "BrowserParent" -> "BrowserChild" [label="PBrowser" style=dotted]; "BrowserChild" -> "nsDocShell"; "BrowserBridgeHost" -> "BrowserBridgeChild"; "BrowserBridgeChild" -> "BrowserBridgeParent" [label="PBrowserBridge", style=dotted]; "BrowserBridgeParent" -> "BrowserParent"; }

nsDocShell to Document

Embedding an individual document within a nsDocShell is done within the content process, which has that docshell.

Diagram

This diagram shows the objects involved in a content process which is being used to host a given BrowsingContext, along with rough relationships between them. Dotted lines represent a “current” relationship, whereas solid lines are a stronger lifetime relationship.

graph document { node [shape=rectangle] "BrowsingContext" -- "nsDocShell" [style=dotted]; "nsDocShell" -- "nsGlobalWindowOuter"; "nsGlobalWindowOuter" -- "nsGlobalWindowInner" [style=dotted]; "nsGlobalWindowInner" -- "Document" [style=dotted]; "nsDocShell" -- "nsDocumentViewer" [style=dotted]; "nsDocumentViewer" -- "Document"; "nsDocumentViewer" -- "PresShell"; "nsGlobalWindowInner" -- "WindowGlobalChild"; "BrowsingContext" -- "WindowContext" [style=dotted]; "WindowContext" -- "nsGlobalWindowInner"; subgraph cluster_synced { label = "Synced Contexts"; "BrowsingContext" "WindowContext"; } }