Field G. Van Zee 9bb23e6c2a Added support for systemless build (no pthreads). ...

Details:
- Added a configure option, --[enable|disable]-system, which determines
  whether the modest operating system dependencies in BLIS are included.
  The most notable example of this on Linux and BSD/OSX is the use of
  POSIX threads to ensure thread safety for when application-level
  threads call BLIS. When --disable-system is given, the bli_pthreads
  implementation is dummied out entirely, allowing the calling code
  within BLIS to remain unchanged. Why would anyone want to build BLIS
  like this? The motivating example was submitted via #454 in which a
  user wanted to build BLIS for a simulator such as gem5 where thread
  safety may not be a concern (and where the operating system is largely
  absent anyway). Thanks to Stepan Nassyr for suggesting this feature.
- Another, more minor side effect of the --disable-system option is that
  the implementation of bli_clock() unconditionally returns 0.0 instead
  of the time elapsed since some fixed point in the past. The reasoning
  for this is that if the operating system is truly minimal, the system
  function call upon which bli_clock() would normally be implemented
  (e.g. clock_gettime()) may not be available.
- Refactored preprocess-guarded code in bli_pthread.c and bli_pthread.h
  to remove redundancies.
- Removed old comments and commented #include of "bli_pthread_wrap.h"
  from bli_system.h.
- Documented bli_clock() and bli_clock_min_diff() in BLISObjectAPI.md
  and BLISTypedAPI.md, with a note that both are non-functional when
  BLIS is configured with --disable-system.

2020-11-16 15:55:45 -06:00

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