atomically:
1) Search _thread_list for the thread to join.
2) Search _dead_list for the thread to join.
3) Set the running thread as the joiner.
While we're at it, fix a race in the case where multiple threads try to
join on the same thread. POSIX says that the behavior of multiple joiners
is undefined, but the fix is cheap as a result of the other fix.
keep track of a joiner. POSIX only supports a single joiner, so this
simplification is acceptable.
At the same time, make sure to mark a joined thread as detached so that
its resources can be freed.
Reviewed by: deischen
PR: 24345
_foo - wrapped system call
foo - weak definition to _foo
and for cancellation points:
_foo - wrapped system call
__foo - enter cancellation point, call _foo(), leave
cancellation point
foo - weak definition to __foo
Change use of global _thread_run to call a function to get the
currently running thread.
Make all pthread_foo functions weak definitions to _pthread_foo,
where _pthread_foo is the implementation. This allows an application
to provide its own pthread functions.
Provide slightly different versions of pthread_mutex_lock and
pthread_mutex_init so that we can tell the difference between
a libc mutex and an application mutex. Threads holding mutexes
internal to libc should never be allowed to exit, call signal
handlers, or cancel.
Approved by: -arch
file descriptors needing to be polled (Doh!). Reported
by Dan Nelson <dnelson@emsphone.com>.
Don't install and start the scheduling timer until the
first thread is created. This prevents the overhead of
having a periodic scheduling signal in a single threaded
program. Reported by Dan Nelson <dnelson@emsphone.com>.
Allow builtin longjmps out of application installed
signal handlers without the need perform any post-handler
cleanup:
o Change signal handling to save the threads interrupted
context on the stack. The threads current context is
now always stored in the same place (in the pthread).
If and when a signal handler returns, the interrupted
context is copied back to the storage area in the pthread.
o Before calling invoking a signal handler for a thread,
back the thread out of any internal waiting queues
(mutex, CV, join, etc) to which it belongs.
Rework uthread_info.c a bit to make it easier to change
the format of a thread dump.
Use an alternal signal stack for the thread library's
signal handler. This allows us to fiddle with the main
threads stack without fear of it being in use.
Reviewed by: jasone
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
signal handler. Explicitly check for jumps to anywhere other than the
current stack, since such jumps are undefined according to POSIX.
While we're at it, convert thread cancellation to use continuations, since
it's cleaner than the original cancellation code.
Avoid delivering a signal to a thread twice. This was a pre-existing bug,
but was likely unexposed until these other changes were made.
Defer signals generated by pthread_kill() so that they can be delivered on
the appropriate stack. deischen claims that this is unnecessary, which is
likely true, but without this change, pthread_kill() can cause undefined
priority queue states and/or PANICs in [sig|_]longjmp(), so I'm leaving
this in for now. To compile this code out and exercise the bug, define
the _NO_UNDISPATCH cpp macro. Defining _PTHREADS_INVARIANTS as well will
cause earlier crashes.
PR: kern/14685
Collaboration with: deischen
o Cancellation flags were not getting properly set/cleared.
o Loops waiting for internal locks were not being exited
correctly by a cancelled thread.
o Minor spelling (cancelation -> cancellation) and formatting
corrections (missing tab).
Found by: tg
Reviewed by: 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
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>
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!
threads from invalid ones. The pthread structure is opaque to the user
so this change does not cause any incompatibilities.
Hopefully this change will help code that was written for draft 4
fail gracefully if the programmer ignores the compiler warning about
the change in the level of indirection for the argument passed to
pthread_detach(). I got burnt, so I fixed then (expletive deleted)
thing.
These functions comply with the revised standard. That should shut
Terry up!
functions would return -1 and set errno to indicate the specific error.
POSIX requires that the functions return the error code as the return
value of the function instead.
