[RFA] deleting breakpoints inside of 'commands' [Repost]

[Andrew Cagney]

> 
> I have the same concerns.
> We haven't heard from Don yet.  Maybe he has some compromise solution.
> 
> Anyway, I find the copy solution a hack.
> 
> One way to fix this is to have the chain of commands as an object with
> use count.  It is only freed when the count is down to zero again.
> 
> When you associate it with a breakpoint it goes up to 1.  When you
> get it to execute it goes up to 2.
> 
> When a breakpoint is deleted, it deallocates it.  If the count goes 
> to zero memory is freed.  But if the script is being executed (and
> is deleting self) the count will go to 1 and nothing else happens
> until the script finishes executing and the chain is freed (then
> the count goes to zero and memory is deallocated).

Rememeber, the patch doesn't have to be perfect, just acceptable.  In 
this case, the change eliminates a stray pointer problem (which would 
likely still occure with reference counters) and hence makes gdb far 
more robust - I put robustness and maintainability at a much higher 
priority level then performance.
When someone manages to demonstrate that the copy is a significant 
overhead (using ``set maint profile on/off'' [:-)]) then I think we 
should refine the code to do what you propose (or gasp add a garbage 
collector :-/).  However, Don, if you're upto the task.

Andrew