Re: PTHREAD_THREADS_MAX missing?

Jakub Jelinek wrote:
>>>>The ltp-20030324 version compile of trace_sched.c fails because
>>>>PTHREAD_THREADS_MAX is not defined. ...
>>
>>... Posix does not require PTHREAD_THREADS_MAX be defined; see
>>http://www.opengroup.org/onlinepubs/007904975/basedefs/pthread.h.html
> 
> 
> Well, better URL would be
> http://www.opengroup.org/onlinepubs/007904975/basedefs/limits.h.html

Ouch.  I stand corrected, thanks.

> "A definition of one of the symbolic names in the following list shall be
> omitted from <limits.h> on specific implementations where the corresponding
> value is equal to or greater than the stated minimum, but is unspecified.
> 
> This indetermination might depend on the amount of available memory space
> on a specific instance of a specific implementation. The actual value
> supported by a specific instance shall be provided by the sysconf()
> function."

That brings up the question: what does sysconf(_SC_THREAD_THREADS_MAX) return in nptl?
Uh-oh, looks like it might be -1; see
http://sources.redhat.com/cgi-bin/cvsweb.cgi/libc/sysdeps/posix/sysconf.c?rev=1.32

     case _SC_THREAD_THREADS_MAX:
#ifdef  PTHREAD_THREADS_MAX
       return PTHREAD_THREADS_MAX;
#else
       return -1;
#endif

Is that compliant?

Maybe sysconf could call a "get max threads" function from the thread addon here.

Is there any sensible expression such a "get max threads" function
could use to compute a reasonable upper bound on the number of threads that's lower
than PID_MAX?  e.g. min(physical memory, PAGE_OFFSET) / (2 * PAGESIZE)?

- Dan

-- 
Dan Kegel
http://www.kegel.com
http://counter.li.org/cgi-bin/runscript/display-person.cgi?user=78045