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/* sem_wait -- wait on a semaphore. Generic futex-using version.
Copyright (C) 2003-2020 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <lowlevellock.h> /* lll_futex* used by the old code. */
#include "sem_waitcommon.c"
int
__new_sem_wait (sem_t *sem)
{
/* We need to check whether we need to act upon a cancellation request here
because POSIX specifies that cancellation points "shall occur" in
sem_wait and sem_timedwait, which also means that they need to check
this regardless whether they block or not (unlike "may occur"
functions). See the POSIX Rationale for this requirement: Section
"Thread Cancellation Overview" [1] and austin group issue #1076 [2]
for thoughs on why this may be a suboptimal design.
[1] http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap02.html
[2] http://austingroupbugs.net/view.php?id=1076 for thoughts on why this
*/
__pthread_testcancel ();
if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
return 0;
else
return __new_sem_wait_slow ((struct new_sem *) sem,
CLOCK_REALTIME, NULL);
}
versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
int
attribute_compat_text_section
__old_sem_wait (sem_t *sem)
{
int *futex = (int *) sem;
int err;
do
{
if (atomic_decrement_if_positive (futex) > 0)
return 0;
/* Always assume the semaphore is shared. */
err = lll_futex_wait_cancel (futex, 0, LLL_SHARED);
}
while (err == 0 || err == -EWOULDBLOCK);
__set_errno (-err);
return -1;
}
compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
#endif
int
__new_sem_trywait (sem_t *sem)
{
/* We must not fail spuriously, so require a definitive result even if this
may lead to a long execution time. */
if (__new_sem_wait_fast ((struct new_sem *) sem, 1) == 0)
return 0;
__set_errno (EAGAIN);
return -1;
}
versioned_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1);
#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
int
__old_sem_trywait (sem_t *sem)
{
int *futex = (int *) sem;
int val;
if (*futex > 0)
{
val = atomic_decrement_if_positive (futex);
if (val > 0)
return 0;
}
__set_errno (EAGAIN);
return -1;
}
compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
#endif
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