* [PATCH] thread: do not attempt to join detached threads in pthread_join()
@ 2017-08-01 22:46 William Pitcock
2017-08-01 22:56 ` Rich Felker
0 siblings, 1 reply; 3+ messages in thread
From: William Pitcock @ 2017-08-01 22:46 UTC (permalink / raw)
To: musl; +Cc: William Pitcock
A thread which is detached releases it's resources and TCB upon thread termination.
Therefore a thread which is detached is not joinable as any underlying futex will not
be incremented, resulting in a deadlock. Accordingly, we return EINVAL instead of
attempting to wait on a detached thread.
Other pthread implementations such as glibc NPTL and FreeBSD also reject attempts
to join detached threads with EINVAL.
---
src/thread/pthread_join.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/src/thread/pthread_join.c b/src/thread/pthread_join.c
index 52111489..7c4bde23 100644
--- a/src/thread/pthread_join.c
+++ b/src/thread/pthread_join.c
@@ -11,6 +11,7 @@ int __pthread_timedjoin_np(pthread_t t, void **res, const struct timespec *at)
__pthread_testcancel();
__pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
if (cs == PTHREAD_CANCEL_ENABLE) __pthread_setcancelstate(cs, 0);
+ if (t->detached) r = EINVAL;
while ((tmp = t->tid) && r != ETIMEDOUT && r != EINVAL)
r = __timedwait_cp(&t->tid, tmp, CLOCK_REALTIME, at, 0);
__pthread_setcancelstate(cs, 0);
--
2.13.3
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] thread: do not attempt to join detached threads in pthread_join()
2017-08-01 22:46 [PATCH] thread: do not attempt to join detached threads in pthread_join() William Pitcock
@ 2017-08-01 22:56 ` Rich Felker
0 siblings, 0 replies; 3+ messages in thread
From: Rich Felker @ 2017-08-01 22:56 UTC (permalink / raw)
To: musl
On Tue, Aug 01, 2017 at 10:46:13PM +0000, William Pitcock wrote:
> A thread which is detached releases it's resources and TCB upon thread termination.
> Therefore a thread which is detached is not joinable as any underlying futex will not
> be incremented, resulting in a deadlock. Accordingly, we return EINVAL instead of
> attempting to wait on a detached thread.
>
> Other pthread implementations such as glibc NPTL and FreeBSD also reject attempts
> to join detached threads with EINVAL.
Since the behavior is undefined and *can't be defined* in the general
case (where the detached thread may already have exited and its id may
even have been reused for a new thread), if any change is to be made,
the function should be made to crash in this case. Returning EINVAL
hides the (serious) programming error.
Rich
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH] thread: do not attempt to join detached threads in pthread_join()
@ 2017-08-01 23:12 William Pitcock
0 siblings, 0 replies; 3+ messages in thread
From: William Pitcock @ 2017-08-01 23:12 UTC (permalink / raw)
To: musl; +Cc: William Pitcock
A thread which is detached releases it's resources and TCB upon thread termination.
Therefore a thread which is detached is not joinable as any underlying futex will not
be incremented, resulting in a deadlock. Accordingly, POSIX defines calling
pthread_join() on a detached thread as undefined behaviour.
We attempt, where possible, to detect attempts to join detached threads and crash
instead, to bring the undefined behaviour to the programmer's attention.
---
src/thread/pthread_join.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/src/thread/pthread_join.c b/src/thread/pthread_join.c
index 52111489..b7175c09 100644
--- a/src/thread/pthread_join.c
+++ b/src/thread/pthread_join.c
@@ -11,6 +11,7 @@ int __pthread_timedjoin_np(pthread_t t, void **res, const struct timespec *at)
__pthread_testcancel();
__pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
if (cs == PTHREAD_CANCEL_ENABLE) __pthread_setcancelstate(cs, 0);
+ if (t->detached) a_crash();
while ((tmp = t->tid) && r != ETIMEDOUT && r != EINVAL)
r = __timedwait_cp(&t->tid, tmp, CLOCK_REALTIME, at, 0);
__pthread_setcancelstate(cs, 0);
--
2.13.3
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2017-08-01 23:12 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2017-08-01 22:46 [PATCH] thread: do not attempt to join detached threads in pthread_join() William Pitcock
2017-08-01 22:56 ` Rich Felker
2017-08-01 23:12 William Pitcock
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