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56fbaa3bbe
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.
70 lines
1.4 KiB
C
70 lines
1.4 KiB
C
#ifndef _AIO_H
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#define _AIO_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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#include <features.h>
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#include <signal.h>
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#include <time.h>
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#define __NEED_ssize_t
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#define __NEED_off_t
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#include <bits/alltypes.h>
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struct aiocb {
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int aio_fildes, aio_lio_opcode, aio_reqprio;
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volatile void *aio_buf;
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size_t aio_nbytes;
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struct sigevent aio_sigevent;
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void *__td;
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int __lock[2];
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volatile int __err;
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ssize_t __ret;
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off_t aio_offset;
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void *__next, *__prev;
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char __dummy4[32-2*sizeof(void *)];
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};
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#define AIO_CANCELED 0
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#define AIO_NOTCANCELED 1
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#define AIO_ALLDONE 2
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#define LIO_READ 0
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#define LIO_WRITE 1
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#define LIO_NOP 2
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#define LIO_WAIT 0
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#define LIO_NOWAIT 1
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int aio_read(struct aiocb *);
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int aio_write(struct aiocb *);
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int aio_error(const struct aiocb *);
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ssize_t aio_return(struct aiocb *);
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int aio_cancel(int, struct aiocb *);
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int aio_suspend(const struct aiocb *const [], int, const struct timespec *);
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int aio_fsync(int, struct aiocb *);
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int lio_listio(int, struct aiocb *__restrict const *__restrict, int, struct sigevent *__restrict);
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#if defined(_LARGEFILE64_SOURCE) || defined(_GNU_SOURCE)
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#define aiocb64 aiocb
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#define aio_read64 aio_read
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#define aio_write64 aio_write
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#define aio_error64 aio_error
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#define aio_return64 aio_return
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#define aio_cancel64 aio_cancel
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#define aio_suspend64 aio_suspend
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#define aio_fsync64 aio_fsync
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#define lio_listio64 lio_listio
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#define off64_t off_t
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#endif
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#ifdef __cplusplus
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}
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#endif
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#endif
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