[Webkit-unassigned] [Bug 92198] Web Inspector: [JSC] debugging long-running scripts with conditional breakpoints consumes huge amounts of memory

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=92198





--- Comment #9 from Peter Wang <peter.wang at torchmobile.com.cn>  2012-12-14 01:16:49 PST ---
(In reply to comment #8)
> (In reply to comment #7)
> > (In reply to comment #6)
> > > (In reply to comment #2)
> > > > This problem is more obvious in memory-limited environment (e.g. mobile).
> > > > 
> > > > The root reason is that, for failed condition of breakpoint, JSC doesn't run the EventLoop, so in a dense loop of js code, there is no chance to recycle garbage caused by evaluating the breakpoint's condition.
> > > > 
> > > It sounds weird that the issue is specific to breakpoint conditions. How does it work in case of eval producing a lot of garbage in a tight loop in user code?
> > > 
> > Sorry to reply so late, since I spent some time to investigate the related code of JSC. For the code like this:
> > for (var i=0;i<0xfffff;i++) {
> > ...
> > eval("...");
> > ...
> > }
> > The "EvalExecutable" is allocated just once and saved as an argument of current callFrame (Interpreter.cpp:149).
> > 
> > But to evaluate the condition of breakpoint, the DebuggerCallFrame::evaluate is invoked, the "EvalExecutable" is allocated every time. Maybe, because it's difficult to bind the breakpoint-condition's string with a certain callFrame.
> 
> Why JSC cannot run GC automatically during the breakpoint condition evaluation if it needs to free some memory? We need someone who understands JSC garbage collector details to look at this change.

I'm not expert of it. It depends on the strategy of port, usually JSC does GC with a interval-changeable timer. So need to run EventLoop to handle the timer message.
I believe the design of JSC takes repeat "eval()" into account, but the mechanism of debugger works-around it.

Welcome JSC's experts to have a look.

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