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Message-ID: <20151012023020.GM8645@brightrain.aerifal.cx> Date: Sun, 11 Oct 2015 22:30:20 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: [PATCH v2 2/2] pthread: implement try/timed join variants On Sun, Oct 04, 2015 at 02:55:30PM -0500, Bobby Bingham wrote: > --- > include/pthread.h | 2 ++ > src/thread/pthread_join.c | 29 ++++++++++++++++++++++------- > 2 files changed, 24 insertions(+), 7 deletions(-) > > diff --git a/include/pthread.h b/include/pthread.h > index af70b73..3d2e0c4 100644 > --- a/include/pthread.h > +++ b/include/pthread.h > @@ -214,6 +214,8 @@ struct cpu_set_t; > int pthread_getaffinity_np(pthread_t, size_t, struct cpu_set_t *); > int pthread_setaffinity_np(pthread_t, size_t, const struct cpu_set_t *); > int pthread_getattr_np(pthread_t, pthread_attr_t *); > +int pthread_tryjoin_np(pthread_t, void **); > +int pthread_timedjoin_np(pthread_t, void **, const struct timespec *); > #endif > > #ifdef __cplusplus > diff --git a/src/thread/pthread_join.c b/src/thread/pthread_join.c > index 694d377..b041ff8 100644 > --- a/src/thread/pthread_join.c > +++ b/src/thread/pthread_join.c > @@ -5,18 +5,33 @@ int __munmap(void *, size_t); > void __pthread_testcancel(void); > int __pthread_setcancelstate(int, int *); > > -int __pthread_join(pthread_t t, void **res) > +int __pthread_tryjoin_np(pthread_t t, void **res) > { > - int tmp, cs; > - __pthread_testcancel(); > - __pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs); > - if (cs == PTHREAD_CANCEL_ENABLE) __pthread_setcancelstate(cs, 0); > - while ((tmp = t->tid)) __timedwait_cp(&t->tid, tmp, 0, 0, 0); > - __pthread_setcancelstate(cs, 0); > + if (t->tid) return EBUSY; > a_barrier(); > if (res) *res = t->result; > if (t->map_base) __munmap(t->map_base, t->map_size); > return 0; > } This can spuriously fail when lack of memory synchronization causes the caller not to see that the target thread has exited. However this condition does not seem observable; calling pthread_tryjoin_np from multiple threads where the calls could race is certainly UB, and otherwise there should be no way to distinguish between the state of just-before-exiting and already-exited. So I _think_ this is okay. > +int __pthread_timedjoin_np(pthread_t t, void **res, const struct timespec *at) > +{ > + int tmp, cs, r = 0; > + __pthread_testcancel(); > + __pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs); > + if (cs == PTHREAD_CANCEL_ENABLE) __pthread_setcancelstate(cs, 0); > + while ((tmp = t->tid) && r != ETIMEDOUT && r != EINVAL) > + r = __timedwait_cp(&t->tid, tmp, CLOCK_REALTIME, at, 0); > + __pthread_setcancelstate(cs, 0); > + if (r == ETIMEDOUT || r == EINVAL) return r; > + return __pthread_tryjoin_np(t, res); > +} > + > +int __pthread_join(pthread_t t, void **res) > +{ > + return __pthread_timedjoin_np(t, res, 0); > +} > + > +weak_alias(__pthread_tryjoin_np, pthread_tryjoin_np); > +weak_alias(__pthread_timedjoin_np, pthread_timedjoin_np); > weak_alias(__pthread_join, pthread_join); This all looks okay to me. I'll probably commit the patch as-is, as long as nobody thinks the reasoning on the tryjoin issue above is wrong. Rich
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