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Re: [cdt-dev] Freeze invisible GDB variable objects
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On 08/14/2014 12:38 PM, Pascal Rapicault wrote:
On which criteria would the framework emit those commands?
Not quite sure on what your question focuses. But beside the question
how to implement it, in the ideal world, CDT would behave like that (IMHO):
Assume we're in the Expression View, having two root items both of type
class/struct and both contain some members, like this:
======================================= (This is the view top border)
| |_ MyObject | {...} | (assume varobj name="var1")
| |_ m_Member1| value 1 | (assume varobj name="var1.m_Member1")
| |_ m_Member2 | value 2 | ...
| |_ m_Member3 | value 3 |
| |_ m_Member4 | value 4 |
| |_ MyOtherObject | {...} | (assume varobj name="var2")
| |_ m_Array1[20];| {...} | (assume varobj name="var2.m_Array1")
| |_ m_OthrMember2 | value 2 |
| |_ m_OthrMember3 | value 3 |
======================================= (This is the view bottom border)
|_ m_OthrMember5(invisible - therefore don't get value
fromembedded target)
|_ m_OthrMember6(invisible- therefore don't get value from
embedded target)
|_ m_OthrMember7(invisible- therefore don't get value from
embedded target)
...
In that situation, there are more members than can be shown without
scrolling down. Therefore, from "m_OthrMember4" (which is hidden below
the bottom border) and further below, no more members are visible.
Therefore, it is a waste of resources to refresh them, as CDT/GDB is
doing it today. This especially hurts if a struct contains hundreds of
members (e.g. a struct that represents hardware registers with hundreds
or even thousands of members which can easily cumulate to a total size
of 1MByte which happen to be refreshed on every debug event).Btw: this
happens because CDT executes a '-var-update 1 var1' and '-var-update 1
var2' on every debugging event. And because CDT didn't freeze any
members, GDB will just update all members, resulting in reading all the
memory of the struct from the (embedded) target, e.g. 1MByte(!).
If you're question focus on the "how to notice when a member appears or
disappears" from the visible range, e.g. because the user is scrolling
and the like: Well, that's exactly what my initial post tries to find out.
Right now, as I'm writing this, I realize that CDT already does
something like that. E.g. when initially expanding a struct (e.g.
MyOtherObject), then CDT does only execute '-var-evaluate-expression' on
the visible items (m_Array1, OthrMember2and m_OthrMember3in this
example). Then, when I scroll down in the Expression View, so that
m_OthrMember4 appears, CDT executes another "-var-evaluate-expression"
for var2.m_OthrMember4, right when that member starts appearing. I might
study that code to find out more...
Raphael
On 14/08/2014 10:52 AM, Raphael Zulliger wrote:
Hi
To increase debugging performance when having huge data structures in
Variable/Expression View etc., I'd like to make extend CDT with GDB's
"-var-set-frozen" or "-var-set-update-range" features (see
https://sourceware.org/gdb/current/onlinedocs/gdb/GDB_002fMI-Variable-Objects.html).
I'm still quite unfamiliar with the ViewModel concept and how it
finally links to the UI. Therefore, can someone point me towards a
good starting point regarding: How can I know which elements in the
Variable View, Expression View are currently visible? (i.e. if there
are 1000 members in a struct, the view will at most show a few
dozens, depending on the height of the view - all others are
invisible). How could I get notified about changes (e.g. the user
scrolls down the list)?
Any idea/hint would highly be appreciated!
Thanks,
Raphael
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