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90 lines
2.5 KiB
C
90 lines
2.5 KiB
C
/* Copyright (C) 2002 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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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, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA. */
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#include <atomic.h>
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/* Implement generic mutex. Basic futex syscall support is required:
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lll_futex_wait(futex, value) - call sys_futex with FUTEX_WAIT
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and third parameter VALUE
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lll_futex_wake(futex, value) - call sys_futex with FUTEX_WAKE
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and third parameter VALUE
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*/
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/* Mutex lock counter:
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bit 31 clear means unlocked;
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bit 31 set means locked.
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All code that looks at bit 31 first increases the 'number of
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interested threads' usage counter, which is in bits 0-30.
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All negative mutex values indicate that the mutex is still locked. */
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static inline void
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__generic_mutex_lock (int *mutex)
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{
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unsigned int v;
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/* Bit 31 was clear, we got the mutex. (this is the fastpath). */
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if (atomic_bit_test_set (mutex, 31) == 0)
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return;
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atomic_increment (mutex);
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while (1)
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{
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if (atomic_bit_test_set (mutex, 31) == 0)
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{
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atomic_decrement (mutex);
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return;
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}
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/* We have to wait now. First make sure the futex value we are
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monitoring is truly negative (i.e. locked). */
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v = *mutex;
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if (v >= 0)
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continue;
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lll_futex_wait (mutex, v);
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}
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}
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static inline void
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__generic_mutex_unlock (int *mutex)
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{
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/* Adding 0x80000000 to the counter results in 0 if and only if
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there are not other interested threads - we can return (this is
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the fastpath). */
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if (atomic_add_zero (mutex, 0x80000000))
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return;
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/* There are other threads waiting for this mutex, wake one of them
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up. */
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lll_futex_wake (mutex, 1);
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}
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#define lll_mutex_lock(futex) __generic_mutex_lock (&(futex))
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#define lll_mutex_unlock(futex) __generic_mutex_unlock (&(futex))
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