This commit uses a pthread mutex in shared memory to prevent
almost all cases of multiple processes simultaneously
reading/writing to device sysfs files. The main existing race
condition is when 2 processes are starting at the same time,
setting up their shared memory and mutexes. Since this is meant
to prevent collisions among thread and processes, the small
shared memory segments (big enough for a pthread_mutex) will
persist until reboot.
Chris Freehill
5e24a77193