Add guard pages to the top of the stack to catch overflow errors.
Moreover, fix a bug where libmthread would keep using a stack that was
just deallocated; a detached thread would deallocate its own stack after
it was finished running).
- Remove sanity checks for initialized mutexes and condition variables. This
significantly boosts performance. The checks can be turned back on by
compiling libmthread with MTHREAD_STRICT. According to POSIX operations on
uninitialized variables are a MAY fail if, therefore allowing this
optimization.
- Test59 has to be accommodated to the lack of sanity checks on uninitialized
variables in the library. It specifically tests for them and will run into
segfaults when the checks are absent in the library.
- Fix a few bugs related to the scheduler
- Do some general code cleanups
Before, the 'main thread' of a process was never taken into account anywhere in
the library, causing mutexes not to work properly (and consequently, neither
did the condition variables). For example, if the 'main thread' (that is, the
thread which is started at the beginning of a process; not a spawned thread by
the library) would lock a mutex, it wasn't actually locked.
