patch 1/2 debuginfod client

[Frank Ch. Eigler]

Hi -

> > Doing a redundant initialization later is not a problem; there is a
> > counter in there.  The problematic case would be
> > - a multithreaded application
> > - loading debuginfod.so multiply concurrently somehow
> > - and calling the solib ctor concurrently somehow
> > - and all of this concurrently enough to defeat libcurl's init-counter
> > 
> > IMHO, not worth worrying about.  Someday libcurl will do the right
> > thing (tm) and plop this initialization into their solib ctor.
> 
> I do worry about this because any multi-threaded app that uses libdw.so
> might cause trouble because we dlopen libdebuginfod.so lazily and then
> it will call curl_global_init () which explicitly says:
> 
>    This function is not thread safe. You must not call it when any
>    other thread in the program (i.e. a thread sharing the same memory)
>    is running. [...]

That's what the doc says.  What the code does, as far back as the year
2001, is have a static flag/counter in curl_global_init() that
prevents multiple initialization.


> That is why I think doing the dlopen of libdebuginfod.so eagerly from a
> libdw.so constructor function or _init might be necessary to make sure
> no other threads are running yet.

That's not even enough for "sure" - if we're so deep in the
hypotheticals hole, an application could be dlopen()ing libdw.so
itself.

- FChE