what do I get for my troubles? libc breaks offcourse!
Reimplement a hack (in libthr) that allows libc to use
rwlocks without initializing them first. The hack was reimplemented
so that only a private libc version of the rwlock locking functions
initializes an uninitialized rwlock. The application version will
correctly fail.
the system call got interrupted and the absolute timeout is
converted to a relative timeout, it may happen that we get a
negative number. In such a case, simply set the timeout to
zero so that if the event that the thread wants to wait for has
happened it can still return successfully, but if it hasn't
happened then the thread doesn't suspend indefinitely. This should
fix certain applications (including mozilla) that seem to hang
indefinitely sometimes.
Noticed and debugged by: Morten Johansen <root@morten-johansen.net>
o Simplify the logic by removing a lot of unnecesary nesting
o Reduce the amount of local variables
o Zero-out the allocated structure and get rid of
all the unnecessary setting to 0 and NULL;
Refactor _pthread_mutex_destroy
o Simplify the logic by removing a lot of unnecesary nesting
o No need to check pointer that the mutex attributes points
to. Checking passed in pointer is enough.
a list in the thread structure to keep track of the locks and
how many times they have been locked. This list is checked
on every lock and unlock. The traversal through the list is
O(n). Most applications don't hold so many locks at once that
this will become a problem. However, if it does become a problem
it might be a good idea to review this once libthr is
off probation and in the optimization cycle.
This fixes:
o deadlock when a thread tries to recursively acquire a
read lock when a writer is waiting on the lock.
o a thread could previously successfully unlock a lock it did not own
o deadlock when a thread tries to acquire a write lock on
a lock it already owns for reading or writing [ this is admittedly
not required by POSIX, but is nice to have ]
code and simply return EINVAL (which is allowed by the standard) in
all those pthread functions that previously initialized it.
o Refactor the pthread_rwlock_[try]rdlock() and pthread_rwlock_[try]wrlock()
functions. They are now completeley condensed into rwlock_rdlock_common()
and rwlock_wrlock_common(), respectively.
o If the application tries to destroy an rwlock that is currently
held by a thread return EBUSY where it previously went ahead and
freed all resources associated with the lock.
o Refactor _pthread_rwlock_init() to make it look (relatively) sane.
o When obtaining a read lock on an rwlock the check for whether it
would exceed the maximum allowed read locks should happen *before*
we obtain the lock.
o The pthread_rwlock_* functions shall *never* return EINTR, so make
sure to requeue/resuspend the thread if it encounters such an error.
o Make a note that pthread_rwlock_unlock() needs to ensure it holds a
lock on an rwlock it tries to unlock. It will be implemented in a
separate commit because it requires some additional rwlock infrastructure.
waiting on a locked mutex. This involves passing a struct timespec
from the pthread mutex locking interfaces all the way down to the
function that suspends the thread until the mutex is released.
The timeout is assumed to be an absolute time (i.e. not relative to
the current time).
Also, in _thread_suspend() make the passed in timespec const.
o Remove some code duplication between _thread_init(), which is run once
to initialize libthr and the intitial thread, and pthread_create(), which
initializes newly created threads, into a new function called from both
places: init_td_common()
o Move initialization of certain parts of libthr into a separate
function. These include:
- Active threads list and it's lock
- Dead threads list and it's lock & condition variable
- Naming and insertion of the initial thread into the
active threads list.
work before anyways, and I didn't want to fix broken code I had no
way of testing. It was necessary however, in order to get rid of GIANT_LOCK.
Pthread priorities will have to wait a little longer to get fixed.
problems: (1) The wrong flag was being checked for in the attribute
(2) The pthread's state was not being set to indicate it was
suspended.
Noticed by: Igor Sysoev <is@rambler-co.ru>
On ia64, where there's no libc_r at all, libkse is now the default
thread library by virtue of these links.
The reasons for this change are:
1. libkse is slated to become the default thread library anyway,
2. active development and maintenance is only present for libkse,
3. GNOME and KDE, both in the process of being supported on ia64,
work better with KSE; even on ia64.
Create a private, single underscore, version of pthread_mutex_unlock for libc.
pthread_mutex_lock already has one. These versions are different from the
ones that applications will link against because they block all signals
from the time a call to lock the mutex is made until it is successfully
unlocked.
a thread receives a spurious wakeup from sigtimedwait(), so make sure
that the call to the queueing code is called only once before entering
the loop (not in the loop). This should fix some fatal errors people
are seeing with messages stating the thread is already on the mutex queue.
These errors may still be triggered from signal handlers; however, since
that part of the code is not locked down yet.
not spinlock_t. Spinlock_t and the associated functions and macros may
require blocking signals in order for async-safe libc functions to behave
appropriately in libthr. This is undesriable for libthr internal locking.
So, this is the first step in completely separating libthr from libc's
locking primitives.
Three new macros should be used for internal libthr locking from now on:
THR_LOCK, THR_TRYLOCK, THR_UNLOCK.
and the disabling of signals. What we are really interested in is
keeping track of recursive disabling of signals. We should not
be recursively acquiring thread locks. Any such situations should
be reorganized to not require a recursive lock.
Separating the two out also allows us to block signals independent of
acquiring thread locks. This will be needed in libthr in the near future when
we put the pieces together to protect libc functions that use pthread mutexes
and low level locks.
implementation and the new improved one. We now precompute the
signal set passed to sigtimedwait, using an inverted set when
necessary for compatibility with older kernels.
exit function has invalidated the need for _spin[un]lock_pthread().
The _spin[un]lock() functions can now dereference curthread without
the danger that the ldtentry containing the pointer to the thread
has been cleared out from under them.
breakages. Note that runtime compatibility is not guaranteed. Future
changes to setjmp/longjmp in libc will break threaded applications
linked against libc_r.so.5 on ia64. We pull our "tier 2" card once
more...
Reviewed by: ru
an application compiled -static with libthr would dump core in
malloc(3) because the stub thread initialization routine in libc would
be used instead of the libthr supplied one.
condition variables. Cosmetic.
Explicitly compare against PTHREAD_MUTEX_INITIALIZER. We shouldn't
encourage calls to the mutex functions with null pointers to mutexes.
Approved by: re/jhb
from multiple threads don't initialze the same condition variable
more than once.
Explicitly compare cond pointers with PTHREAD_COND_INITIALIZER instead
of NULL. Just because it happens to be defined as NULL is no reason
to encourage the idea that people can call those functions with
NULL pointers to a condition variable.
Approved by: re/jhb
The dead list thread is sufficient for synchronization.
Retire the arch_id (ldt array slot) in the gc thread instead of the
doing it in the thread itself.
Approved by: re/jhb
joiner by making sure all locks and unlocks occur in the same order. For
the record the lock order is: DEAD_LIST, THREAD_LIST, exiting thread, joiner
thread.
Approved by: re/rwatson
thread is not dead, the join loop is guaranteed to execute at least
once, so there is no need to pick up the thread list lock after
we return from suspenstion only to release it after the loop.
Approved by: re/blanket libthr
joined and then the joiner thread. There isn't an easy (sane?) way
to make it use the correct order without introducing races involving
the target thread and finding which (active or dead) list it is on. So,
after locking the canceled thread it will try to lock the joined thread
and if it fails release the first lock and try again from the top.
Introduce a new function, _spintrylock, which is simply a wrapper arround
umtx_trylock(), to help accomplish this.
Approved by: re/blanket libthr
Modify the thread creation and thread searching routine
to lock the thread lists with the new locks instead of GIANT_LOCK.
Approved by: re/blanket libthr
list is protected by a spinlock_t, but the dead list uses a pthread_mutex
because it is necessary to synchronize other threads with the garbage
collector thread. Lock/Unlock macros are used so it's easier to make
changes to the locks in the future.
The 'dead thread list' lock is intended to replace the gc mutex.
This doesn't have any practical ramifications. It simply makes it
clearer what the purpose of the lock is. The gc will use this lock,
instead of the gc mutex, to synchronize access to the dead list with
other threads.
Modify _pthread_exit() to use these two new locks instead of GIANT_LOCK,
and also to properly lock and protect thread state changes,
especially with respect to a joining thread.
The gc thread was also re-arranged to be more organized and less nested.
_pthread_join() was also modified to use the thread list locks. However,
locking and unlocking here needs special care because a thread could find
itself in a position where it's joining an exiting thread that is
waiting on the dead list lock, which this thread (joiner) holds. If the
joiner doesn't take care to lock *and* unlock in the same order they
(the joiner and the joinee) could deadlock against each other.
Approved by: re/blanket libthr
pthread_cond_t) internaly in addition to the low-level spinlock_t. The
garbage collector mutex and condition variable are two such examples. This
might lead to critical sections nested within critical sections. Implement
a reference counting mechanism so that signals are masked only on the first
entry and unmasked on the last exit.
I'm not sure I like the idea of nested critical sections, but if
the library is going to use the pthread primitives it might be necessary.
Approved by: re/blanket libthr
Access to the thread's flags and state is protected by
_thread_critical_enter/exit(). When a thread is signaled with a condition
its state must be protected by locking it and disabling
signals before it is taken of the waiters' queue.
Move the implementation of pthread_cond_signal() and pthread_cond_broadcast()
into one function, cond_signal(). Its behaviour is determined by the
last argument, int broadcast. If this is set to 1 it will remove all
waiters, otherwise it will wake up only the first waiter thread.
Remove an extraneous call to pthread_testcancel().
Approved by: re/blanket libthr
that take the address of a struct pthread as their first argument.
_spin[un]lock() just become wrappers arround these two functions.
These new functions are for use in situations where curthread can't be
used. One example is _thread_retire(), where we invalidate the array index
curthread uses to get its pointer..
Approved by: re/blanket libthr
Prevent one thread from messing up another thread's saved signal
mask by saving it in struct pthread instead of leaving it as a
global variable. D'oh!
Approved by: re/blanket libthr
in thr_private.h
o Lock down the ldt_entries array and ldt_free, which points to
the next free slot. As noted in the comments, it's necessary
to special case the initial_thread because %gs is not setup
for it yet. This is ok because that early in the program there
won't be any reentrancy issues anyways.
Approved by: re/blanket libthr
When in either the mutex or cond queue we notice that the thread
is already on one of the queues, don't just simply abort(). Print
out the thread's identifiers and what queue it was on.
Approved by: markm/mentor, re/blanket libthr
is the *only* remaining thread in the application, in which case we
should not core dump, and instead exit gracefully.
Approved by: markm/mentor, re/blanket libthr
of pthread_cond_timedwait() is moved into cond_wait_common().
Pthread_cond_wait() and pthread_cond_timedwait() are now wrappers around
this function. Previously, the former called the latter with the abstime
pointing to 0 time. This violated Posix semantics should an application
have reason to call it with that argument because instead or returning
immediately it would have waited indefinitely for the cv to be signaled.
Approved by: markm/mentor, re/blanket libthr
Reviewed by: jeff
respect to other threads and signal handlers by moving to
the _thread_critical_enter/exit functions.
o Introduce an static function, testcancel(), that is used by
the other functions in this module. This allows it to make
locking assumptions that the top-level functions can't.
o Rework the code flow a bit to reduce indentation levels.
Approved by: markm/mentor, re/blanket libthr
Reviewed by: jeff
Note that the tp register (r13) is reserved as the TLS pointer in
the same way that that gp register (r1) is reserved as the global
pointer. This implementation uses the tp register to point to the
thread structure used by the threads implementation. This is not
in violation with the runtime specification provided the TLS is
a fixed distance from the thread structure. This is only an issue
when code used the __thread keyword to create TLS. This is not
supported at the moment.
libthr. No changes were made to libpthread by request of deischen,
who will soon commit a real implementation for that library.
PR: standards/50848
Submitted by: Sergey A. Osokin <osa@freebsd.org.ru>
MFC after: 1 week
as curthread in the new context, so that it will be set automatically when
the thread is switched to. This fixes a race where we'd run for a little
while with curthread unset in _thread_start.
Reviewed by: jeff
_get_curthread(). This is similar to the kernel's curthread. Doing
this saves stack overhead and is more convenient to the programmer.
- Pass the pointer to the newly created thread to _thread_init().
- Remove _get_curthread_slow().
This was changed because originally we were blocking on the umtx and
allowing the kernel to do the queueing. It was decided that the
lib should queue and start the threads in the order it decides and the
umtx code would just be used like spinlocks.
