Re: hpd command for DisplayValues

[Adam Jocksch <ajocksch@redhat.com>]

Andrew Cagney wrote:
> Adam Jocksch wrote:
>> Hrm, maybe. Although reading in the hpd spec: "By defining 
>> actionpoints, the user may request in advance that target program 
>> execution stop
>
> Nice quote, the display object doesn't fit that model since it is 
> passive - it doesn't directly trigger a stop since it doesn't 
> implement a mechanism for detecting changes in the data (that would be 
> watch).  Instead it detects when the variable has changed after a stop.
>
> For the command line, consider this:
>
>> [] break main
>> [] run ....
>> main hit
>> [] print argc
>> ...
>> [] step
>> [] print argc
>> [] step
>
> vs:
>
>> [] break main
>> [] run ....
>> main hit
>> [] display argc
>> ...
>> [] step
>> ... value of argc changed from 4 to -1
>> [] step
>> [] step
>> Value of argc changed from -1 to 4
>
> For a graphical interface the object facilitates the efficient 
> implementation of a variable display window - it will only trigger a 
> redraw of the display elements of the X display when there's something 
> new to draw.
>
> Andrew
>
>> under certain conditions". Do we want the display to be similar to a 
>> watchpoint, except it applies to an expression rather than a single 
>> variable? Or do we want it to be an expression that is displayed when 
>> the program stops (I remember Andrew saying something about how gdb 
>> does this, and it's bad, so we probably want to avoid that).
>>
>> While what the DisplayValue object is capable is well defined, I 
>> guess I'm not 100% sure of how it will be used.
>
That sounds similar to what I had envisioned.