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pthread_setcancelstate(3): make it async-signal-safe

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by setting new cancel state and reading old cancel state from the
curthread structure atomic.

Note that this does not play well with async cancellation, since if
cancellation is enabled from a signal handler and cancellation request
is pending, the thread is cancelled immediately, calling user-defined
destructors, which all must be async-signal-safe (but this is a general
requirement for async cancellation anyway).

Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D48200
This commit is contained in:
Konstantin Belousov 2024-12-23 08:42:15 +02:00
parent a944e6d5c0
commit 030f48f78f
2 changed files with 12 additions and 6 deletions
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12
lib/libthr/thread/thr_cancel.c
View file

@ -83,22 +83,22 @@ int
_thr_setcancelstate(int state, int *oldstate)
{
struct pthread *curthread = _get_curthread();
int oldval;
int oldval, val;
oldval = curthread->cancel_enable;
switch (state) {
case PTHREAD_CANCEL_DISABLE:
curthread->cancel_enable = 0;
val = 0;
break;
case PTHREAD_CANCEL_ENABLE:
curthread->cancel_enable = 1;
if (curthread->cancel_async)
testcancel(curthread);
val = 1;
break;
default:
return (EINVAL);
}
oldval = atomic_swap_int(&curthread->cancel_enable, val);
if (state == PTHREAD_CANCEL_ENABLE && curthread->cancel_async)
testcancel(curthread);
if (oldstate != NULL) {
*oldstate = oldval ? PTHREAD_CANCEL_ENABLE :
PTHREAD_CANCEL_DISABLE;

6
share/man/man3/pthread_testcancel.3
View file

@ -34,6 +34,7 @@ are
.Dv PTHREAD_CANCEL_ENABLE
and
.Dv PTHREAD_CANCEL_DISABLE .
The function is async-signal-safe.
.Pp
The
.Fn pthread_setcanceltype
@ -248,6 +249,11 @@ function conforms to
.St -p1003.1-96 .
The standard allows implementations to make many more functions
cancellation points.
.Pp
The
.Fn pthread_setcancelstate
function is async-signal-safe as required by
.St -p1003.1-2024 .
.Sh AUTHORS
This manual page was written by
.An David Leonard Aq Mt d@openbsd.org