Question about rtld-elf. Anyone?.. Anyone?

[Daniel Eischen]

On Mon, 28 Apr 2003, Peter Wemm wrote:

> Daniel Eischen wrote:
> > So I was glancing at rltd-elf, specifically lockdflt.c.  There
> > seems to be an assumption that sigprocmask() can be used to
> > protect a thread from being swapped out.  Am I reading this
> > right?
> 
> I dont think so..   i386/lockdflt.c is just a simple spinlock that happens
> to work with libc_r.
> 
> > There are no such guarantees with libpthread.  A thread
> > will be swapped out whenever its quantum expires, and if
> > you've got higher priority threads, they will always run
> > before those of lower priority -- even if they are spinning.
> 
> If this is happening, it would not suprise me.  lockdflt.c seems more aimed
> at things like the M3 runtime.
> 
> I think the real solution is to provide a way for a thread library to hook
> in its own lock routines that use something that is thread aware.  However,
> this is probably easier said than done.

Well, libc can do it by checking __isthreaded and then using
mutexes.  Libraries such as libgcc can also handle it by making
weak references (not definitions) to pthread_foo and then using
them when they are not null.  I don't know if this works for rtld
though.

> Basically he's describing the exact scenario you're concerned about.  The
> last paragraph suggests a better way.

John, any details about what you were thinking here?

-- 
Dan Eischen