freebsd-nq/lib/libthr/thread/thr_cancel.c
Mike Makonnen d39d651258 _pthread_cancel() breaks the normal lock order of first locking the
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
2003-05-25 08:48:11 +00:00

234 lines
5.3 KiB
C

/*
* David Leonard <d@openbsd.org>, 1999. Public domain.
* $FreeBSD$
*/
#include <sys/errno.h>
#include <pthread.h>
#include <stdlib.h>
#include "thr_private.h"
/*
* Static prototypes
*/
static void testcancel(void);
__weak_reference(_pthread_cancel, pthread_cancel);
__weak_reference(_pthread_setcancelstate, pthread_setcancelstate);
__weak_reference(_pthread_setcanceltype, pthread_setcanceltype);
__weak_reference(_pthread_testcancel, pthread_testcancel);
int
_pthread_cancel(pthread_t pthread)
{
int ret;
pthread_t joined;
/*
* When canceling a thread that has joined another thread, this
* routine breaks the normal lock order of locking first the
* joined and then the joiner. Therefore, it is necessary that
* if it can't obtain the second lock, that it release the first
* one and restart from the top.
*/
retry:
if ((ret = _find_thread(pthread)) != 0)
/* The thread is not on the list of active threads */
goto out;
_thread_critical_enter(pthread);
if (pthread->state == PS_DEAD || pthread->state == PS_DEADLOCK
|| (pthread->flags & PTHREAD_EXITING) != 0) {
/*
* The thread is in the process of (or has already) exited
* or is deadlocked.
*/
_thread_critical_exit(pthread);
ret = 0;
goto out;
}
/*
* The thread is on the active thread list and is not in the process
* of exiting.
*/
if (((pthread->cancelflags & PTHREAD_CANCEL_DISABLE) != 0) ||
(((pthread->cancelflags & PTHREAD_CANCEL_ASYNCHRONOUS) == 0) &&
((pthread->cancelflags & PTHREAD_AT_CANCEL_POINT) == 0)))
/* Just mark it for cancellation: */
pthread->cancelflags |= PTHREAD_CANCELLING;
else {
/*
* Check if we need to kick it back into the
* run queue:
*/
switch (pthread->state) {
case PS_RUNNING:
/* No need to resume: */
pthread->cancelflags |= PTHREAD_CANCELLING;
break;
case PS_SLEEP_WAIT:
case PS_WAIT_WAIT:
pthread->cancelflags |= PTHREAD_CANCELLING;
PTHREAD_NEW_STATE(pthread, PS_RUNNING);
break;
case PS_JOIN:
/*
* Disconnect the thread from the joinee:
*/
if ((joined = pthread->join_status.thread) != NULL) {
if (_spintrylock(&joined->lock) == EBUSY) {
_thread_critical_exit(pthread);
goto retry;
}
pthread->join_status.thread->joiner = NULL;
_spinunlock(&joined->lock);
joined = pthread->join_status.thread = NULL;
}
pthread->cancelflags |= PTHREAD_CANCELLING;
PTHREAD_NEW_STATE(pthread, PS_RUNNING);
break;
case PS_MUTEX_WAIT:
case PS_COND_WAIT:
/*
* Threads in these states may be in queues.
* In order to preserve queue integrity, the
* cancelled thread must remove itself from the
* queue. When the thread resumes, it will
* remove itself from the queue and call the
* cancellation routine.
*/
pthread->cancelflags |= PTHREAD_CANCELLING;
PTHREAD_NEW_STATE(pthread, PS_RUNNING);
break;
case PS_DEAD:
case PS_DEADLOCK:
case PS_STATE_MAX:
/* Ignore - only here to silence -Wall: */
break;
}
}
/* Unprotect the scheduling queues: */
_thread_critical_exit(pthread);
ret = 0;
out:
return (ret);
}
int
_pthread_setcancelstate(int state, int *oldstate)
{
int ostate, ret;
ret = 0;
_thread_critical_enter(curthread);
ostate = curthread->cancelflags & PTHREAD_CANCEL_DISABLE;
switch (state) {
case PTHREAD_CANCEL_ENABLE:
if (oldstate != NULL)
*oldstate = ostate;
curthread->cancelflags &= ~PTHREAD_CANCEL_DISABLE;
if ((curthread->cancelflags & PTHREAD_CANCEL_ASYNCHRONOUS) == 0)
break;
testcancel();
break;
case PTHREAD_CANCEL_DISABLE:
if (oldstate != NULL)
*oldstate = ostate;
curthread->cancelflags |= PTHREAD_CANCEL_DISABLE;
break;
default:
ret = EINVAL;
}
_thread_critical_exit(curthread);
return (ret);
}
int
_pthread_setcanceltype(int type, int *oldtype)
{
int otype;
_thread_critical_enter(curthread);
otype = curthread->cancelflags & PTHREAD_CANCEL_ASYNCHRONOUS;
switch (type) {
case PTHREAD_CANCEL_ASYNCHRONOUS:
if (oldtype != NULL)
*oldtype = otype;
curthread->cancelflags |= PTHREAD_CANCEL_ASYNCHRONOUS;
testcancel();
break;
case PTHREAD_CANCEL_DEFERRED:
if (oldtype != NULL)
*oldtype = otype;
curthread->cancelflags &= ~PTHREAD_CANCEL_ASYNCHRONOUS;
break;
default:
return (EINVAL);
}
_thread_critical_exit(curthread);
return (0);
}
void
_pthread_testcancel(void)
{
_thread_critical_enter(curthread);
testcancel();
_thread_critical_exit(curthread);
}
static void
testcancel()
{
/*
* This pthread should already be locked by the caller.
*/
if (((curthread->cancelflags & PTHREAD_CANCEL_DISABLE) == 0) &&
((curthread->cancelflags & PTHREAD_CANCELLING) != 0) &&
((curthread->flags & PTHREAD_EXITING) == 0)) {
/*
* It is possible for this thread to be swapped out
* while performing cancellation; do not allow it
* to be cancelled again.
*/
curthread->cancelflags &= ~PTHREAD_CANCELLING;
_thread_critical_exit(curthread);
_thread_exit_cleanup();
pthread_exit(PTHREAD_CANCELED);
PANIC("cancel");
}
}
void
_thread_enter_cancellation_point(void)
{
_thread_critical_enter(curthread);
testcancel();
curthread->cancelflags |= PTHREAD_AT_CANCEL_POINT;
_thread_critical_exit(curthread);
}
void
_thread_leave_cancellation_point(void)
{
_thread_critical_enter(curthread);
curthread->cancelflags &= ~PTHREAD_AT_CANCEL_POINT;
testcancel();
_thread_critical_exit(curthread);
}