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in a separate word from the _count. This does not permit both items to be updated atomically in a portable manner. As a result, sem_post() must always perform a system call to safely clear _has_waiters. This change removes the _has_waiters field and instead uses the high bit of _count as the _has_waiters flag. A new umtx object type (_usem2) and two new umtx operations are added (SEM_WAIT2 and SEM_WAKE2) to implement these semantics. The older operations are still supported under the COMPAT_FREEBSD9/10 options. The POSIX semaphore API in libc has been updated to use the new implementation. Note that the new implementation is not compatible with the previous implementation. However, this only affects static binaries (which cannot be helped by symbol versioning). Binaries using a dynamic libc will continue to work fine. SEM_MAGIC has been bumped so that mismatched binaries will error rather than corrupting a shared semaphore. In addition, a padding field has been added to sem_t so that it remains the same size. Differential Revision: https://reviews.freebsd.org/D961 Reported by: adrian Reviewed by: kib, jilles (earlier version) Sponsored by: Norse
66 lines
2.1 KiB
C
66 lines
2.1 KiB
C
/*
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* Copyright (c) 2010 David Xu <davidxu@freebsd.org>
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*
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice unmodified, this list of conditions, and the following
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* disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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/* semaphore.h: POSIX 1003.1b semaphores */
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#ifndef _SEMAPHORE_H_
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#define _SEMAPHORE_H_
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#include <sys/cdefs.h>
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#include <sys/_types.h>
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#include <sys/_umtx.h>
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struct _sem {
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__uint32_t _magic;
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struct _usem2 _kern;
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__uint32_t _padding; /* Preserve structure size */
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};
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typedef struct _sem sem_t;
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#define SEM_FAILED ((sem_t *)0)
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#define SEM_VALUE_MAX __INT_MAX
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struct timespec;
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__BEGIN_DECLS
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int sem_close(sem_t *);
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int sem_destroy(sem_t *);
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int sem_getvalue(sem_t * __restrict, int * __restrict);
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int sem_init(sem_t *, int, unsigned int);
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sem_t *sem_open(const char *, int, ...);
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int sem_post(sem_t *);
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int sem_timedwait(sem_t * __restrict, const struct timespec * __restrict);
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int sem_trywait(sem_t *);
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int sem_unlink(const char *);
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int sem_wait(sem_t *);
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__END_DECLS
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#endif /* !_SEMAPHORE_H_ */
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