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107 lines
3.3 KiB
C
107 lines
3.3 KiB
C
/* sem_wait -- wait on a semaphore. Generic futex-using version.
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Copyright (C) 2003-2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <lowlevellock.h> /* lll_futex* used by the old code. */
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#include "sem_waitcommon.c"
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int
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__new_sem_wait (sem_t *sem)
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{
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/* We need to check whether we need to act upon a cancellation request here
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because POSIX specifies that cancellation points "shall occur" in
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sem_wait and sem_timedwait, which also means that they need to check
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this regardless whether they block or not (unlike "may occur"
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functions). See the POSIX Rationale for this requirement: Section
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"Thread Cancellation Overview" [1] and austin group issue #1076 [2]
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for thoughs on why this may be a suboptimal design.
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[1] http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap02.html
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[2] http://austingroupbugs.net/view.php?id=1076 for thoughts on why this
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*/
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__pthread_testcancel ();
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if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
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return 0;
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else
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return __new_sem_wait_slow((struct new_sem *) sem, NULL);
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}
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versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
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#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
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int
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attribute_compat_text_section
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__old_sem_wait (sem_t *sem)
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{
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int *futex = (int *) sem;
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int err;
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do
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{
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if (atomic_decrement_if_positive (futex) > 0)
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return 0;
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/* Enable asynchronous cancellation. Required by the standard. */
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int oldtype = __pthread_enable_asynccancel ();
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/* Always assume the semaphore is shared. */
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err = lll_futex_wait (futex, 0, LLL_SHARED);
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/* Disable asynchronous cancellation. */
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__pthread_disable_asynccancel (oldtype);
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}
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while (err == 0 || err == -EWOULDBLOCK);
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__set_errno (-err);
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return -1;
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}
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compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
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#endif
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int
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__new_sem_trywait (sem_t *sem)
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{
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/* We must not fail spuriously, so require a definitive result even if this
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may lead to a long execution time. */
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if (__new_sem_wait_fast ((struct new_sem *) sem, 1) == 0)
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return 0;
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__set_errno (EAGAIN);
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return -1;
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}
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versioned_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1);
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#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
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int
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__old_sem_trywait (sem_t *sem)
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{
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int *futex = (int *) sem;
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int val;
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if (*futex > 0)
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{
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val = atomic_decrement_if_positive (futex);
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if (val > 0)
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return 0;
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}
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__set_errno (EAGAIN);
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return -1;
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}
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compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
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#endif
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