returns errno, because errno can be mucked by user's signal handler and
most of pthread api heavily depends on errno to be correct, this change
should improve stability of the thread library.
we set scheduling parameters and cpu binding fully in userland, and
because default scheduling policy is SCHED_RR (time-sharing), we set
default sched_inherit to PTHREAD_SCHED_INHERIT, this saves a system
call.
however if current thread is executing cancellation handler, signal
SIGCANCEL may have already been blocked, this is unexpected, unblock the
signal in new thread if this happens.
MFC after: 1 week
loop count.
2. Add function pthread_mutex_setyieldloops_np to turn a mutex's yield
loop count.
3. Make environment variables PTHREAD_SPINLOOPS and PTHREAD_YIELDLOOPS
to be only used for turnning PTHREAD_MUTEX_ADAPTIVE_NP mutex.
to tune pthread mutex performance:
1. LIBPTHREAD_SPINLOOPS
If a pthread mutex is being locked by another thread, this environment
variable sets total number of spin loops before the current thread
sleeps in kernel, this saves a syscall overhead if the mutex will be
unlocked very soon (well written application code).
2. LIBPTHREAD_YIELDLOOPS
If a pthread mutex is being locked by other threads, this environment
variable sets total number of sched_yield() loops before the currrent
thread sleeps in kernel. if a pthread mutex is locked, the current thread
gives up cpu, but will not sleep in kernel, this means, current thread
does not set contention bit in mutex, but let lock owner to run again
if the owner is on kernel's run queue, and when lock owner unlocks the
mutex, it does not need to enter kernel and do lots of work to resume
mutex waiters, in some cases, this saves lots of syscall overheads for
mutex owner.
In my practice, sometimes LIBPTHREAD_YIELDLOOPS can massively improve performance
than LIBPTHREAD_SPINLOOPS, this depends on application. These two environments
are global to all pthread mutex, there is no interface to set them for each
pthread mutex, the default values are zero, this means spinning is turned off
by default.
into pthread structure to keep track of locked PTHREAD_PRIO_PROTECT mutex,
no real mutex code is changed, the mutex locking and unlocking code should
has same performance as before.
to make it work, turnstile like mechanism to support priority
propagating and other realtime scheduling options in kernel
should be available to userland mutex, for the moment, I just
want to make libthr be simple and efficient thread library.
Discussed with: deischen, julian
operation, the caller is blocked util target threads are really
suspended, also avoid suspending a thread when it is holding a
critical lock.
Fix a bug in _thr_ref_delete which tests a never set flag.
rewritten, now timers created with same sigev_notify_attributes will
run in same thread, this allows user to organize which timers can
run in same thread to save some thread resource.
