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Tracing Wrappers from V8 to Blink

hlopko@, hpayer@, eisinger@, haraken@, ulan@, mlippautz@

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Story of two Garbage Collectors

Blink

V8

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V8 Handles

Handles keep V8 objects alive

(V8 object will be collected only after the handle is reset)

Blink

V8

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Blink Wrappers

Wrappers keep Blink objects alive

(Blink object will be collected only after the wrapper is collected by V8)

Blink

V8

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Some wrappers like to keep friends alive - Object grouping to the rescue!

For V8 gc, we iterate all handles and ask them which group they want to be in

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Rules are defined by SetWrapperReferenceFrom, SetWrapperReferenceTo, Custom=VisitDOMWrapper

Blink

V8

Confidential + Proprietary

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With great power comes great complexity

Unfortunate arrangement of wrappers and handles lead to a memory leak

Blink

V8

Confidential + Proprietary

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Tracing Wrappers begins

Blink

V8

Confidential + Proprietary

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V8 marks all reachable objects

Blink

V8

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V8 asks Blink to trace wrappers from the found ones

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Blink

V8

Confidential + Proprietary

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V8 asks Blink to trace wrappers from the found ones

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Blink

V8

Confidential + Proprietary

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V8 asks Blink to trace wrappers from the found ones

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Blink

V8

Confidential + Proprietary

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V8 asks Blink to trace wrappers from the found ones

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Blink

V8

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Blink reports new wrappers to V8

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Blink

V8

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V8 continues marking from wrappers

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Blink

V8

Confidential + Proprietary

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V8 continues marking from wrappers

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Blink

V8

Confidential + Proprietary

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V8 continues marking from wrappers

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Blink

V8

Confidential + Proprietary

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V8 continues marking from wrappers

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Blink

V8

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… until the fixed point is reached

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Blink

V8

Confidential + Proprietary

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And the garbage is collected

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Blink

V8

Confidential + Proprietary

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TraceWrappers API

DEFINE_TRACE_WRAPPERS(Node)

{

visitor->traceWrappers(m_parent);

visitor->traceWrappers(m_previous);

visitor->traceWrappers(m_next);

}

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Next step

Make wrapper tracing incremental to reduce latency

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