thread switches should be on par with that under scheduler
activations.
o Timing is achieved through the use of a fixed interval
timer (ITIMER_PROF) to count scheduling ticks instead
of retrieving the time-of-day upon every thread switch
and calculating elapsed real time.
o Polling for I/O readiness is performed once for each
scheduling tick instead of every thread switch.
o The non-signal saving/restoring versions of setjmp/longjmp
are used to save and restore thread contexts. This may
allow the removal of _THREAD_SAFE macros from setjmp()
and longjmp() - needs more investigation.
Change signal handling so that signals are handled in the
context of the thread that is receiving the signal. When
signals are dispatched to a thread, a special signal handling
frame is created on top of the target threads stack. The
frame contains the threads saved state information and a new
context in which the thread can run. The applications signal
handler is invoked through a wrapper routine that knows how
to restore the threads saved state and unwind to previous
frames.
Fix interruption of threads due to signals. Some states
were being improperly interrupted while other states were
not being interrupted. This should fix several PRs.
Signal handlers, which are invoked as a result of a process
signal (not by pthread_kill()), are now called with the
code (or siginfo_t if SA_SIGINFO was set in sa_flags) and
sigcontext_t as received from the process signal handler.
Modify the search for a thread to which a signal is delivered.
The search algorithm is now:
o First thread found in sigwait() with signal in wait mask.
o First thread found sigsuspend()'d on the signal.
o Current thread if signal is unmasked.
o First thread found with signal unmasked.
Collapse machine dependent support into macros defined in
pthread_private.h. These should probably eventually be moved
into separate MD files.
Change the range of settable priorities to be compliant with
POSIX (0-31). The threads library uses higher priorities
internally for real-time threads (not yet implemented) and
threads executing signal handlers. Real-time threads and
threads running signal handlers add 64 and 32, respectively,
to a threads base priority.
Some other small changes and cleanups.
PR: 17757 18559 21943
Reviewed by: jasone
not have a user-supplied signal handler, when a signal is delivered, one
thread will receive the signal, and then the code reverts to having no
signal handler for the signal. This can leave the other sigwait()ing
threads stranded permanently if the signal is later ignored, or can result
in process termination when the process should have delivered the signal to
one of the threads in sigwait().
To fix this problem, maintain a count of sigwait()ers for each signal that
has no default signal handler. Use the count to correctly install/uninstall
dummy signal handlers.
Reviewed by: deischen
just use _foo() <-- foo(). In the case of a libpthread that doesn't do
call conversion (such as linuxthreads and our upcoming libpthread), this
is adequate. In the case of libc_r, we still need three names, which are
now _thread_sys_foo() <-- _foo() <-- foo().
Convert all internal libc usage of: aio_suspend(), close(), fsync(), msync(),
nanosleep(), open(), fcntl(), read(), and write() to _foo() instead of foo().
Remove all internal libc usage of: creat(), pause(), sleep(), system(),
tcdrain(), wait(), and waitpid().
Make thread cancellation fully POSIX-compliant.
Suggested by: deischen
Before this change, a signal was delivered to each thread that
didn't have the signal masked. Signals also improperly woke up
threads waiting on I/O. With this change, signals are now
handled in the following way:
o If a thread is waiting in a sigwait for the signal,
then the thread is woken up.
o If no threads are sigwait'ing on the signal and a
thread is in a sigsuspend waiting for the signal,
then the thread is woken up.
o In the case that no threads are waiting or suspended
on the signal, then the signal is delivered to the
first thread we find that has the signal unmasked.
o If no threads are waiting or suspended on the signal,
and no threads have the signal unmasked, then the signal
is added to the process wide pending signal set. The
signal will be delivered to the first thread that unmasks
the signal.
If there is an installed signal handler, it is only invoked
if the chosen thread was not in a sigwait.
In the case that multiple threads are waiting or suspended
on a signal, or multiple threads have the signal unmasked,
we wake up/deliver the signal to the first thread we find.
The above rules still apply.
Reported by: Scott Hess <scott@avantgo.com>
Reviewed by: jb, jasone
eischen (Daniel Eischen) added wrappers to protect against cancled
threads orphaning internal resources.
the cancelability code is still a bit fuzzy but works for test
programs of my own, OpenBSD's and some examples from ORA's books.
add readdir_r to both libc and libc_r
add some 'const' attributes to function parameters
Reviewed by: eischen, jasone
-----------------------------
Most of the userland changes are in libc. For both the alpha
and the i386 setjmp has been changed to accomodate for the
new sigset_t. Internally, libc is mostly rewritten to use the
new syscalls. The exception is in compat-43/sigcompat.c
The POSIX thread library has also been rewritten to use the
new sigset_t. Except, that it currently only handles NSIG
signals instead of the maximum _SIG_MAXSIG. This should not
be a problem because current applications don't use any
signals higher than NSIG.
There are version bumps for the following libraries:
libdialog
libreadline
libc
libc_r
libedit
libftpio
libss
These libraries either a) have one of the modified structures
visible in the interface, or b) use sigset_t internally and
may cause breakage if new binaries are used against libraries
that don't have the sigset_t change. This not an immediate
issue, but will be as soon as applications start using the
new range to its fullest.
NOTE: libncurses already had an version bump and has not been
given one now.
NOTE: doscmd is a real casualty and has been disconnected for
the moment. Reconnection will eventually happen after
doscmd has been fixed. I'm aware that being the last one
to touch it, I'm automaticly promoted to being maintainer.
According to good taste this means that I will receive a
badge which either will be glued or mechanically stapled,
drilled or otherwise violently forced onto me :-)
NOTE: pcvt/vttest cannot be compiled with -traditional. The
change cause sys/types to be included along the way which
contains the const and volatile modifiers. I don't consider
this a solution, but more a workaround.
o The polling mechanism for I/O readiness was changed from
select() to poll(). In additon, a wrapped version of poll()
is now provided.
o The wrapped select routine now converts each fd_set to a
poll array so that the thread scheduler doesn't have to
perform a bitwise search for selected fds each time file
descriptors are polled for I/O readiness.
o The thread scheduler was modified to use a new queue (_workq)
for threads that need work. Threads waiting for I/O readiness
and spinblocks are added to the work queue in addition to the
waiting queue. This reduces the time spent forming/searching
the array of file descriptors being polled.
o The waiting queue (_waitingq) is now maintained in order of
thread wakeup time. This allows the thread scheduler to
find the nearest wakeup time by looking at the first thread
in the queue instead of searching the entire queue.
o Removed file descriptor locking for select/poll routines. An
application should not rely on the threads library for providing
this locking; if necessary, the application should use mutexes
to protect selecting/polling of file descriptors.
o Retrieve and use the kernel clock rate/resolution at startup
instead of hardcoding the clock resolution to 10 msec (tested
with kernel running at 1000 HZ).
o All queues have been changed to use queue.h macros. These
include the queues of all threads, dead threads, and threads
waiting for file descriptor locks.
o Added reinitialization of the GC mutex and condition variable
after a fork. Also prevented reallocation of the ready queue
after a fork.
o Prevented the wrapped close routine from closing the thread
kernel pipes.
o Initialized file descriptor table for stdio entries at thread
init.
o Provided additional flags to indicate to what queues threads
belong.
o Moved TAILQ initialization for statically allocated mutex and
condition variables to after the spinlock.
o Added dispatching of signals to pthread_kill. Removing the
dispatching of signals from thread activation broke sigsuspend
when pthread_kill was used to send a signal to a thread.
o Temporarily set the state of a thread to PS_SUSPENDED when it
is first created and placed in the list of threads so that it
will not be accidentally scheduled before becoming a member
of one of the scheduling queues.
o Change the signal handler to queue signals to the thread kernel
pipe if the scheduling queues are protected. When scheduling
queues are unprotected, signals are then dequeued and handled.
o Ensured that all installed signal handlers block the scheduling
signal and that the scheduling signal handler blocks all
other signals. This ensures that the signal handler is only
interruptible for and by non-scheduling signals. An atomic
lock is used to decide which instance of the signal handler
will handle pending signals.
o Removed _lock_thread_list and _unlock_thread_list as they are
no longer used to protect the thread list.
o Added missing RCS IDs to modified files.
o Added checks for appropriate queue membership and activity when
adding, removing, and searching the scheduling queues. These
checks add very little overhead and are enabled when compiled
with _PTHREADS_INVARIANTS defined. Suggested and implemented
by Tor Egge with some modification by me.
o Close a race condition in uthread_close. (Tor Egge)
o Protect the scheduling queues while modifying them in
pthread_cond_signal and _thread_fd_unlock. (Tor Egge)
o Ensure that when a thread gets a mutex, the mutex is on that
threads list of owned mutexes. (Tor Egge)
o Set the kernel-in-scheduler flag in _thread_kern_sched_state
and _thread_kern_sched_state_unlock to prevent a scheduling
signal from calling the scheduler again. (Tor Egge)
o Don't use TAILQ_FOREACH macro while searching the waiting
queue for threads in a sigwait state, because a change of
state destroys the TAILQ link. It is actually safe to do
so, though, because once a sigwaiting thread is found, the
loop ends and the function returns. (Tor Egge)
o When dispatching signals to threads, make the thread inherit
the signal deferral flag of the currently running thread.
(Tor Egge)
Submitted by: Daniel Eischen <eischen@vigrid.com> and
Tor Egge <Tor.Egge@fast.no>
o Runnable threads are now maintained in priority queues. The
implementation requires two things:
1.) The priority queues must be protected during insertion
and removal of threads. Since the kernel scheduler
must modify the priority queues, a spinlock for
protection cannot be used. The functions
_thread_kern_sched_defer() and _thread_kern_sched_undefer()
were added to {un}defer kernel scheduler activation.
2.) A thread (active) priority change can be performed only
when the thread is removed from the priority queue. The
implementation uses a threads active priority when
inserting it into the queue.
A by-product is that thread switches are much faster. A
separate queue is used for waiting and/or blocked threads,
and it is searched at most 2 times in the kernel scheduler
when there are active threads. It should be possible to
reduce this to once by combining polling of threads waiting
on I/O with the loop that looks for timed out threads and
the minimum timeout value.
o Functions to defer kernel scheduler activation were added. These
are _thread_kern_sched_defer() and _thread_kern_sched_undefer()
and may be called recursively. These routines do not block the
scheduling signal, but latch its occurrence. The signal handler
will not call the kernel scheduler when the running thread has
deferred scheduling, but it will be called when running thread
undefers scheduling.
o Added support for _POSIX_THREAD_PRIORITY_SCHEDULING. All the
POSIX routines required by this should now be implemented.
One note, SCHED_OTHER, SCHED_FIFO, and SCHED_RR are required
to be defined by including pthread.h. These defines are currently
in sched.h. I modified pthread.h to include sched.h but don't
know if this is the proper thing to do.
o Added support for priority protection and inheritence mutexes.
This allows definition of _POSIX_THREAD_PRIO_PROTECT and
_POSIX_THREAD_PRIO_INHERIT.
o Added additional error checks required by POSIX for mutexes and
condition variables.
o Provided a wrapper for sigpending which is marked as a hidden
syscall.
o Added a non-portable function as a debugging aid to allow an
application to monitor thread context switches. An application
can install a routine that gets called everytime a thread
(explicitly created by the application) gets context switched.
The routine gets passed the pthread IDs of the threads that are
being switched in and out.
Submitted by: Dan Eischen <eischen@vigrid.com>
Changes by me:
o Added a PS_SPINBLOCK state to deal with the priority inversion
problem most often (I think) seen by threads calling malloc/free/realloc.
o Dispatch signals to the running thread directly rather than at a
context switch to avoid the situation where the switch never occurs.
for the process, not a separate set for each thread). By default, the
process now only has signal handlers installed for SIGVTALRM, SIGINFO
and SIGCHLD. The thread kernel signal handler is installed for other
signals on demand. This means that SIG_IGN and SIG_DFL processing is now
left to the kernel, not the thread kernel.
Change the signal dispatch to no longer use a signal thread, and
call the signal handler using the stack of the thread that has the
signal pending.
Change the atomic lock method to use test-and-set asm code with
a yield if blocked. This introduces separate locks for each type
of object instead of blocking signals to prevent a context
switch. It was this blocking of signals that caused the performance
degradation the people have noted.
This is a *big* change!
