[PATCH] gold: Avoid sharing Plugin_list::iterator

[H.J. Lu]

On Thu, Nov 5, 2020 at 4:42 PM Alan Modra <amodra@gmail.com> wrote:
>
> On Thu, Nov 05, 2020 at 03:49:55PM -0800, H.J. Lu wrote:
> > On Thu, Nov 5, 2020 at 3:04 PM Alan Modra <amodra@gmail.com> wrote:
> > >
> > > On Thu, Nov 05, 2020 at 06:07:55AM -0800, H.J. Lu via Binutils wrote:
> > > > class Plugin_manager has
> > > >
> > > >   // A pointer to the current plugin.  Used while loading plugins.
> > > >   Plugin_list::iterator current_;
> > > >
> > > > The same iterator is shared by all threads. It is OK to use it to load
> > > > plugins since only one thread loads plugins.  Avoid sharing Plugin_list
> > > > iterator in all other cases.
> > >
> > > What two pieces of code are simultaneously changing
> > > Plugin_manager::current_?  I'm concerned that the underlying thread
> >
> > Not about changing.  It is about sharing Plugin_list::iterator.  The current
> > gold uses one global iterator for all threads, similar to
>
> HJ, I don't need to be told why sharing variables among threads can go
> wrong.  I understand that quite well.  I was asking for the specifics
> of what was going wrong.  Now if you haven't analysed the problem to
> that level, that's fine, just say so.

I didn't know what went wrong.

> You do realise that if two threads are simultaneously running
> Plugin_manager::all_symbols_read then your patch hasn't stopped the
> underlying lto all_symbols_read from being called twice?
>

I don't recall this was the issue when I studied it a few months ago.

-- 
H.J.