cvs commit: src/lib/libthr/thread Makefile.inc thr_barrier.c thr_cancel.c thr_cond.c thr_create.c thr_detach.c thr_exit.c thr_init.c thr_join.c thr_mutex.c thr_private.h thr_resume_np.c thr_setschedparam.c thr_sig.c thr_syscalls.c

[Mike Makonnen]

mtm         2004/05/20 05:06:17 PDT

  FreeBSD src repository

  Modified files:
    lib/libthr/thread    Makefile.inc thr_barrier.c thr_cancel.c 
                         thr_cond.c thr_create.c thr_detach.c 
                         thr_exit.c thr_init.c thr_join.c 
                         thr_mutex.c thr_private.h thr_resume_np.c 
                         thr_setschedparam.c thr_sig.c 
                         thr_syscalls.c 
  Log:
  Make libthr async-signal-safe without costly signal masking. The guidlines I
  followed are: Only 3 functions (pthread_cancel, pthread_setcancelstate,
  pthread_setcanceltype) are required to be async-signal-safe by POSIX. None of
  the rest of the pthread api is required to be async-signal-safe. This means
  that only the three mentioned functions are safe to use from inside
  signal handlers.
  However, there are certain system/libc calls that are
  cancellation points that a caller may call from within a signal handler,
  and since they are cancellation points calls have to be made into libthr
  to test for cancellation and exit the thread if necessary. So, the
  cancellation test and thread exit code paths must be async-signal-safe
  as well. A summary of the changes follows:
  
  o Almost all of the code paths that masked signals, as well as locking the
    pthread structure now lock only the pthread structure.
  o Signals are masked (and left that way) as soon as a thread enters
    pthread_exit().
  o The active and dead threads locks now explicitly require that signals
    are masked.
  o Access to the isdead field of the pthread structure is protected by both
    the active and dead list locks for writing. Either one is sufficient for
    reading.
  o The thread state and type fields have been combined into one three-state
    switch to make it easier to read without requiring a lock. It doesn't need
    a lock for writing (and therefore for reading either) because only the
    current thread can write to it and it is an integer value.
  o The thread state field of the pthread structure has been eliminated. It
    was an unnecessary field that mostly duplicated the flags field, but
    required additional locking that would make a lot more code paths require
    signal masking. Any truly unique values (such as PS_DEAD) have been
    reborn as separate members of the pthread structure.
  o Since the mutex and condvar pthread functions are not async-signal-safe
    there is no need to muck about with the wait queues when handling
    a signal ...
  o ... which also removes the need for wrapping signal handlers and sigaction(2).
  o The condvar and mutex async-cancellation code had to be revised as a result
    of some of these changes, which resulted in semi-unrelated changes which
    would have been difficult to work on as a separate commit, so they are
    included as well.
  
  The only part of the changes I am worried about is related to locking for
  the pthread joining fields. But, I will take a closer look at them once this
  mega-patch is committed.
  
  Revision  Changes    Path
  1.7       +0 -1      src/lib/libthr/thread/Makefile.inc
  1.2       +10 -10    src/lib/libthr/thread/thr_barrier.c
  1.10      +64 -156   src/lib/libthr/thread/thr_cancel.c
  1.14      +89 -146   src/lib/libthr/thread/thr_cond.c
  1.15      +0 -1      src/lib/libthr/thread/thr_create.c
  1.8       +12 -9     src/lib/libthr/thread/thr_detach.c
  1.13      +12 -29    src/lib/libthr/thread/thr_exit.c
  1.15      +3 -18     src/lib/libthr/thread/thr_init.c
  1.14      +44 -30    src/lib/libthr/thread/thr_join.c
  1.28      +33 -42    src/lib/libthr/thread/thr_mutex.c
  1.36      +41 -37    src/lib/libthr/thread/thr_private.h
  1.7       +7 -6      src/lib/libthr/thread/thr_resume_np.c
  1.7       +4 -4      src/lib/libthr/thread/thr_setschedparam.c
  1.12      +0 -77     src/lib/libthr/thread/thr_sig.c
  1.6       +0 -55     src/lib/libthr/thread/thr_syscalls.c