PTHREAD_STACK_MIN may not be constant

[jamesjer]

In the upcoming glibc version 2.34, PTHREAD_STACK_MIN will be defined like this if _DYNAMIC_STACK_SIZE_SOURCE is defined (it is enabled by _GNU_SOURCE):

#   define __SC_THREAD_STACK_MIN_VALUE 75
#   define PTHREAD_STACK_MIN __sysconf (__SC_THREAD_STACK_MIN_VALUE)

The glibc maintainers made this change (and a similar change to the definitions of SIGSTKSZ and MINSIGSTKSZ) to deal with CPUs that have varying stack size requirements depending on optional components. This has led to compilation failures for a number of packages, including polyml, due to use of PTHREAD_STACK_MIN in an #if in libpolyml/sighandler.cpp. Are you open to doing a run-time check instead of a compile-time check, something like this?

#ifdef PTHREAD_STACK_MIN
    size_t stacksize = PTHREAD_STACK_MIN; // Only small stack.
    if (stacksize < 4096U) // But not too small; FreeBSD makes it 2k
        stacksize = 4096U;
    pthread_attr_setstacksize(&attrs, stacksize);
#endif

[dcjm]

That seems sensible. Do you want to provide a pull request for this since you may be able to test it? Include a comment to say that PTHREAD_STACK_MIN may be defined as a function call otherwise there's the possibility that it could be changed back at some point.