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From: Kaz Kylheku <kaz@kylheku.com>
Newsgroups: comp.os.linux.development.apps
Subject: Re: object file memory
Date: Mon, 6 Feb 2012 23:07:27 +0000 (UTC)
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On 2012-02-06, Bill M <wpmccormick@just_about_everywhere.com> wrote:
> I have an object file foo.o that I want to link to an executable. The 
> main executable creates a number of child threads that use code and 
> variables from foo.o.

Do you have the source code for foo.o that you can tweak and recompile?

> I've included a very simplistic representation at 
> the end. My question is, how can each child thread (worker) get it's own 
> private copy of global variables foo_char and foo_int? Or does that just 
> happen auto-magically?

Why would that happen automagically? It's completely the wrong thing which
would break most programs.

> ** foo.c **
> char foo_char;
> int foo_int;

These are static variables, which are understood to be single-instance,
and any correct program relies on them being that way.  Automagically making
these thread-local would be broken behavior.

GCC has extensions for declaring statics thread local. Check the GCC
documentation for the setion on "Thread-Local Storage", but the gist of it is:

  __thread char foo_char;

There is also an explicit POSIX API for managing thread-specific values
accessed by keys: pthread_key_create, pthread_setspecific, etc.