[lldb-dev] lldb.frame.EvaluateExpression slows down when called a lot

[Greg Clayton]

Since you are dealing with a global, you are not tied to a stack frame, so you should be able to cache this value and re-use it:



    if not self.ruby_current_vm:
	self.ruby_current_vm = lldb.value(lldb.target.FindFirstGlobalVariable('ruby_current_vm'))

Then you should be able to use this over and over without re-fetching it. And you should be really fast. Each time you fetch a variable from SBTarget::FindFirstGlobalVariable(), it re-wraps the variable in a new VariableObjectSP which has its own cluster manager. Why? Because you might do something like:

f = lldb.value(lldb.target.FindFirstGlobalVariable('g_ptr'))

f = f.a.b.c.d

Now we need a reference to the ValueObjectSP for "g_ptr" (the underlying variable that roots the entire expression) to stay alive as long as anyone has a reference to anything that is a child of "g_ptr". Here "f" now reference "g_ptr->a.b.c.d", so any value in this chain is correctly reference counted using a ClusterMananger that keeps all of them alive as long as someone has a reference to any of them.

So if you reuse your "self.ruby_current_vm", you should only have a single ClusterManager and they should stay shared as long as you use them. Currently you are re-creating the root with each call and then referencing a bunch of children which adds new shared references to each cluster manager.

Let me know how reusing the one instance goes.

Greg


On Apr 17, 2014, at 5:22 PM, Scott Knight <knightsc at gmail.com> wrote:

> I attached the instruments trace here in case it might be helpful. Seems like a lot of time is spent in the ClusterManager. It seems like thats called from all the ValueObject. I do realize that I'm getting values over and over again in a loop, but it seems to just take longer each time through the loop. I also attached the python script I'm using in the zip file as well.
> 
> -Scott
> 
> 
> On Thu, Apr 17, 2014 at 7:56 PM, Greg Clayton <gclayton at apple.com> wrote:
> No idea. If you are running this on MacOSX, I would run a time profile in instruments on it and see what is going on.
> 
> On Apr 17, 2014, at 4:32 PM, Scott Knight <knightsc at gmail.com> wrote:
> 
> > Any of idea why making that call over and over again would seem to slow down over time?
> >
> > -Scott
> >
> > On Apr 17, 2014 7:29 PM, "Greg Clayton" <gclayton at apple.com> wrote:
> > Yep, it is the python keyword... You currently need to use your workaround:
> >
> > rvalue.__getattr__("as")
> >
> > Glad we found it and that there is nothing wrong with the API (we are finding children of anonymous unions, phew!).
> >
> > Greg
> >
> > On Apr 17, 2014, at 3:46 PM, Scott Knight <knightsc at gmail.com> wrote:
> >
> > > typedef struct RVALUE {
> > >     union {
> > >       struct {
> > >           VALUE flags;                /* always 0 for freed obj */
> > >           struct RVALUE *next;
> > >       } free;
> > >       struct RBasic  basic;
> > >       struct RObject object;
> > >       struct RClass  klass;
> > >       struct RFloat  flonum;
> > >       struct RString string;
> > >       struct RArray  array;
> > >       struct RRegexp regexp;
> > >       struct RHash   hash;
> > >       struct RData   data;
> > >       struct RTypedData   typeddata;
> > >       struct RStruct rstruct;
> > >       struct RBignum bignum;
> > >       struct RFile   file;
> > >       struct RNode   node;
> > >       struct RMatch  match;
> > >       struct RRational rational;
> > >       struct RComplex complex;
> > >       struct {
> > >           struct RBasic basic;
> > >           VALUE v1;
> > >           VALUE v2;
> > >           VALUE v3;
> > >       } values;
> > >     } as;
> > > #if GC_DEBUG
> > >     const char *file;
> > >     VALUE line;
> > > #endif
> > > } RVALUE;
> > >
> >
> 
> 
> <lldb-cpu-time.zip>