1565704 - [jsdbg2] Debugger API Handler base class makes memory tracking difficult

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P2)

Description

[Jim Blandy :jimb]

The design of the js::Handler abstract base class, used for Debugger API handlers at the C++ level, makes it difficult to properly support the new js::gc::MemoryUse-based allocation tracking.

For example, DebuggerFrame::setOnStepHandler reports when a DebuggerFrame takes ownership of a handler, but that method is not in a position to know whether the handler is owned exclusively by that DebuggerFrame or shared as the handler for many events. (We don't have any shared handlers at the moment, but as we extend the C++-level API to support other uses of the debugger, we expect them to exist.)

Comment 1

[Jim Blandy :jimb]

Attachment: Bug 1565704: Clarify ownership reporting in Debugger's js::Handler base class. r?jonco

Extend js::Handler, the base class for Debugger API handler functions, with a
hold method, to act as a pair with the drop method. Clarify comments
explaining how they're to be used, with a more explicit explanation of how
reference-counted handlers could be implemented.

Following the new rules:

• Change ScriptedOnStepHandler and ScriptedOnPopHandler to report the
  handler's ownership.

• Change DebuggerFrame::setOnStepHandler and DebuggerFrame::setOnPopHandler
  to let the handler deal with that.

Change the owner argument type from DebuggerFrame to the looser JSObject;
the Handler base class isn't specific to stack frames at all, but is meant to
eventually be used for onNewScript and onEnterFrame as well.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/fe8cfb80b5b8
Clarify ownership reporting in Debugger's js::Handler base class. r=jonco

Comment 3

[Oana Pop-Rus]

https://hg.mozilla.org/mozilla-central/rev/fe8cfb80b5b8