Re: (known?) Issue with bitmap iterators

[Alexander Monakov <amonakov@ispras.ru>]

On Fri, 26 Jun 2009, Joe Buck wrote:

> On Fri, Jun 26, 2009 at 03:38:31AM -0700, Alexander Monakov wrote:
>> 1. Add bool field `modified_p' in bitmap structure.
>> 2. Make iterator setup functions (e.g. bmp_iter_set_init) reset it to
>> false.
>> 3. Make functions that modify the bitmap set it to true.
>> 4. Make iterator increment function (e.g. bmp_iter_next) assert
>> !modified_p.
>
> Sorry, it doesn't work.  Function foo has a loop that iterates
> over a bitmap.  During the iteration, it calls a function bar.  bar
> modifies the bitmap, then iterates over the bitmap.  It then returns
> to foo, which is in the middle of an iteration, which it continues.
> The bitmap has been modified (by bar), but modified_p was reset to
> false by the iteration that happened at the end of bar.

Good catch, thanks!  Let me patch that up a bit:

1. Add int field `generation' in bitmap structure, initialized arbitrarily 
at bitmap creation time.
2. Make iterator setup functions save initial generation count in the 
iterator (or generation counts for two bitmaps, if needed).
3. Modify generation count when bitmap is modified (e.g. increment it).
4. Verify that saved and current generations match when incrementing the 
iterator.