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New pthread_barrier algorithm to fulfill barrier destruction requirements.

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The previous barrier implementation did not fulfill the POSIX requirements
for when a barrier can be destroyed.  Specifically, it was possible that
threads that haven't noticed yet that their round is complete still access
the barrier's memory, and that those accesses can happen after the barrier
has been legally destroyed.
The new algorithm does not have this issue, and it avoids using a lock
internally.
This commit is contained in:
Torvald Riegel
2015-06-24 14:37:32 +02:00
parent a3e5b4feeb
commit b02840bacd
18 changed files with 417 additions and 762 deletions
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23
nptl/pthread_barrier_init.c
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@ -18,7 +18,7 @@
#include <errno.h>
#include "pthreadP.h"
#include <lowlevellock.h>
#include <futex-internal.h>
#include <kernel-features.h>
@ -34,8 +34,10 @@ __pthread_barrier_init (pthread_barrier_t *barrier,
{
struct pthread_barrier *ibarrier;
/* XXX EINVAL is not specified by POSIX as a possible error code. */
if (__glibc_unlikely (count == 0))
/* XXX EINVAL is not specified by POSIX as a possible error code for COUNT
being too large. See pthread_barrier_wait for the reason for the
comparison with BARRIER_IN_THRESHOLD. */
if (__glibc_unlikely (count == 0 || count >= BARRIER_IN_THRESHOLD))
return EINVAL;
const struct pthread_barrierattr *iattr
@ -46,15 +48,12 @@ __pthread_barrier_init (pthread_barrier_t *barrier,
ibarrier = (struct pthread_barrier *) barrier;
/* Initialize the individual fields. */
ibarrier->lock = LLL_LOCK_INITIALIZER;
ibarrier->left = count;
ibarrier->init_count = count;
ibarrier->curr_event = 0;
/* XXX Don't use FUTEX_SHARED or FUTEX_PRIVATE as long as there are still
assembly implementations that expect the value determined below. */
ibarrier->private = (iattr->pshared != PTHREAD_PROCESS_PRIVATE
? 0 : FUTEX_PRIVATE_FLAG);
ibarrier->in = 0;
ibarrier->out = 0;
ibarrier->count = count;
ibarrier->current_round = 0;
ibarrier->shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
? FUTEX_PRIVATE : FUTEX_SHARED);
return 0;
}