iterations

[Martin Hunt]

On Thu, 2005-03-17 at 13:09 -0500, Frank Ch. Eigler wrote:
> > What was the problem [brought up during a call] again?  You wanted
> > to modify the map while iterating through it?
> 
> There are several interesting cases.
> - nested iteration
> - map lookups at multiple indices during iteration
I think these work.

> - map modification during iteration
Is this really necessary?  You can modify the values, but adding or
deleting elements in a map while iterating through it will be dangerous.
Fixing that will reduce efficiency.

> - concurrent reads / writes from different threads
I plan to add a rw spinlock to each map struct and modify the functions
to obtain the proper type of lock.

Iterations are a special problem because it really needs to be locked
between multiple calls.  I had assumed we would modify the calling
sequence, like
        _stp_lock_map (map);
        ... iterate here
        _stp_unlock_map (map);

BTW, I should also mention that I realize that the state data stored in
the map struct must be valid between calls.  That will be changed to be
per-cpu data to eliminate conflicts with multiple CPUs.

So _stp_map_key_xxx() only needs a reader lock as does _stp_map_get_xxx
().  _stp_map_set_xxx() and _stp_map_key_del() need a writer lock.

Martin