xref: /src/lib/libpthread/TODO

Bugs to fix:

- pthread_cond_timedwait() doesn't work if SA's aren't running yet,
  because the alarm system isn't up and running. It would be weird to
  use them that way, but it's perfectly legal.
- There is a race between pthread_cancel() and
  pthread_cond_broadcast() or pthread_exit() about removing an item
  from the sleep queue. The locking protocols there need a little
  adjustment.
- pthread_sig.c: sigaction() currently hard-codes __sigtramp_sigcontext_1:
  this is incorrect.  Instead of calling __sigaction_sigtramp() directly,
  libc should export a __libc_sigaction14() which sigaction() can call.
  Also, pthread_sig.c should probably be built with __LIBC12_SOURCE__ so
  that the signal version of sigaction(), et al can be explicit.
- pthread_sig.c: pthread__signal_tramp() is broken.  It gets a ucontext,
  but then hands off an empty (garbage from stack!) sigcontext to the
  handler.  The ucontext MUST be converted to a sigcontext, the handler
  called, and then the sigcontext converted back to ucontext, before the
  ucontext is used to perform the sigreturn-analogue.  This is necessary
  for e.g. C++/Java exceptions and some garbage-collectors.
- pthread_sig.c: pthread__signal_tramp() should be changed so that it is
  easy to add support for SA_SIGINFO later.  (Mostly a function signature
  issue.)
- Consider moving pthread__signal_tramp() to its own file, and building
  it with -fasync-unwind-tables, so that DWARF2 EH unwinding works through
  it.  (This is required for e.g. GCC's libjava.)
- locks: Add support for RAS on uniprocessors.
- pthread_lock.c: pthread_spin_lock() should use a loop around
  __cpu_simple_lock_try() so that it is easy to add support for RAS.


Interfaces/features to implement:
- pthread_kill()
- pthread_atfork()
- pthread_rwlock... These are currently stubbed to MUTEX in libc!!
- priority scheduling
- libc integration: 
   - foo_r interfaces
- system integration
   - some macros and prototypes belong in headers other than pthread.h


Features that need more/better regression tests:
 - pthread_cond_broadcast()
 - pthread_once()
 - pthread_get/setspecific()
 - signals


Things that need fixing:
- Recycle dead threads for new threads.

Ideas to play with:
- Explore the trapcontext vs. usercontext distinction in ucontext_t.
- Get rid of thread structures when too many accumulate (is this
  actually a good idea?)
- Adaptive spin/sleep locks for mutexes.
- Supporting different mutex types would be nice (normal, debugging,
  recursive, etc).
- Currently, each thread uses two real pages of memory: one at the top
  of the stack for actual stack data, and one at the bottom for the
  pthread_st. If we can get suitable space above the initial stack for
  main(), we can cut this to one page per thread. Perhaps crt0 should
  do something different (give us more space) if libpthread is linked
  in?
- Figure out whether/how to expose the inline version of
  pthread_self().