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linux下异步IO的简单例子

作者:  时间: 2010-11-29
首先,贴一下异步IO中用的的一些结构体,因为平常很少用,整理起来方便查看。

aio.h中的struct aiocb

struct aiocb
{
  int aio_fildes;        /* File desriptor. */
  int aio_lio_opcode;        /* Operation to be performed. */
  int aio_reqprio;        /* Request priority offset. */
  volatile void *aio_buf;    /* Location of buffer. */
  size_t aio_nbytes;        /* Length of transfer. */
  struct sigevent aio_sigevent;    /* Signal number and value. */

  /* Internal members. */
  struct aiocb *__next_prio;
  int __abs_prio;
  int __policy;
  int __error_code;
  __ssize_t __return_value;
};


siginfo.h中的struct sigevent和union sigval

typedef struct sigevent
  {
    sigval_t sigev_value;
    int sigev_signo;
    int sigev_notify;

    union
      {
    int _pad[__SIGEV_PAD_SIZE];

    /* When SIGEV_SIGNAL and SIGEV_THREAD_ID set, LWP ID of the
     thread to receive the signal. */

    __pid_t _tid;

    struct
     {
     void (*_function) (sigval_t);    /* Function to start. */
     void *_attribute;            /* Really pthread_attr_t. */
     } _sigev_thread;
      } _sigev_un;
  } sigevent_t;

/* POSIX names to access some of the members. */
# define sigev_notify_function _sigev_un._sigev_thread._function
# define sigev_notify_attributes _sigev_un._sigev_thread._attribute


typedef union sigval
  {
    int sival_int;
    void *sival_ptr;
  } sigval_t;


例子1:

#include <aio.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <signal.h>

void async_read(int s, siginfo_t * info, void * context)
{
    struct aiocb *ptr =
        (struct aiocb *)info->si_value.sival_ptr;
    printf("read=%s", (char *)ptr->aio_buf);    
}

int main(void)
{
    struct aiocb cb;
    char sbuf[100];
    int ret;
    struct sigaction act;
    sigemptyset(&act.sa_mask);
    act.sa_flags = SA_RESTART | SA_SIGINFO;
    act.sa_sigaction = async_read;

    sigaction(SIGUSR1, &act, NULL);

    bzero(&cb, sizeof(cb));

    cb.aio_fildes = 0;
    cb.aio_buf = sbuf;
    cb.aio_nbytes = 100;
    cb.aio_offset = 0;

    cb.aio_sigevent.sigev_value.sival_ptr = &cb;
    cb.aio_sigevent.sigev_notify = SIGEV_SIGNAL;
    cb.aio_sigevent.sigev_signo = SIGUSR1;
    ret = aio_read(&cb);
    if (ret == -1) {
        perror("aio_read");
        exit(1);
    }
    int i = 0;
    while (1) {
        printf("%d\n",i++);
        sleep(3);
    }

    return 0;
}

运行结果:
注意:要加相应的库,-lrt

 $ ./gcc -o test aio_signal.c -lrt 

$ ./test
0
1
h2
ell3
o
read=hello
4
^C


例子2:

#include <aio.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>

void async_read(sigval_t val)
{
    struct aiocb *ptr =
        (struct aiocb *)val.sival_ptr;
    printf("read=%s", (char *)ptr->aio_buf);    
}

int main(void)
{
    struct aiocb cb;
    char sbuf[100];
    int ret;

    bzero(&cb, sizeof(cb));

    cb.aio_fildes = 0;
    cb.aio_buf = sbuf;
    cb.aio_nbytes = 100;
    cb.aio_offset = 0;

    cb.aio_sigevent.sigev_value.sival_ptr = &cb;
    cb.aio_sigevent.sigev_notify = SIGEV_THREAD;
    cb.aio_sigevent.sigev_notify_function =
        async_read;
    cb.aio_sigevent.sigev_notify_attributes = NULL;    

    ret = aio_read(&cb);
    if (ret == -1) {
        perror("aio_read");
        exit(1);
    }
    
    int i = 0;
    while (1) {
        printf("%d\n",i++);
        sleep(1);
    }

    return 0;
}

运行结果同上。