2011-02-12 05:22:29 +00:00
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#ifndef _SEMAPHORE_H
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#define _SEMAPHORE_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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2012-09-08 21:14:52 +00:00
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#include <features.h>
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2012-09-07 02:44:55 +00:00
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2011-03-03 23:32:26 +00:00
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#define __NEED_time_t
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#define __NEED_struct_timespec
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#include <bits/alltypes.h>
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#include <fcntl.h>
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2011-02-12 05:22:29 +00:00
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#define SEM_FAILED ((sem_t *)0)
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typedef struct {
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make all objects used with atomic operations volatile
the memory model we use internally for atomics permits plain loads of
values which may be subject to concurrent modification without
requiring that a special load function be used. since a compiler is
free to make transformations that alter the number of loads or the way
in which loads are performed, the compiler is theoretically free to
break this usage. the most obvious concern is with atomic cas
constructs: something of the form tmp=*p;a_cas(p,tmp,f(tmp)); could be
transformed to a_cas(p,*p,f(*p)); where the latter is intended to show
multiple loads of *p whose resulting values might fail to be equal;
this would break the atomicity of the whole operation. but even more
fundamental breakage is possible.
with the changes being made now, objects that may be modified by
atomics are modeled as volatile, and the atomic operations performed
on them by other threads are modeled as asynchronous stores by
hardware which happens to be acting on the request of another thread.
such modeling of course does not itself address memory synchronization
between cores/cpus, but that aspect was already handled. this all
seems less than ideal, but it's the best we can do without mandating a
C11 compiler and using the C11 model for atomics.
in the case of pthread_once_t, the ABI type of the underlying object
is not volatile-qualified. so we are assuming that accessing the
object through a volatile-qualified lvalue via casts yields volatile
access semantics. the language of the C standard is somewhat unclear
on this matter, but this is an assumption the linux kernel also makes,
and seems to be the correct interpretation of the standard.
2015-03-04 03:50:02 +00:00
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volatile int __val[4*sizeof(long)/sizeof(int)];
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2011-02-12 05:22:29 +00:00
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} sem_t;
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int sem_close(sem_t *);
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int sem_destroy(sem_t *);
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2012-09-07 02:44:55 +00:00
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int sem_getvalue(sem_t *__restrict, int *__restrict);
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2011-02-12 05:22:29 +00:00
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int sem_init(sem_t *, int, unsigned);
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sem_t *sem_open(const char *, int, ...);
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int sem_post(sem_t *);
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2012-09-07 02:44:55 +00:00
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int sem_timedwait(sem_t *__restrict, const struct timespec *__restrict);
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2011-02-12 05:22:29 +00:00
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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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#ifdef __cplusplus
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}
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#endif
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#endif
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