receive.c

来自「这个是学习嵌入式开发的重要例子」· C语言 代码 · 共 157 行

#include <stdio.h>
#include <stdlib.h>
#include <mqueue.h>
#include <string.h>
#include <errno.h>
#include <signal.h>

#define BUFFER_SIZE	1024
#define MQUEUE_NAME	"/mqueue.test.1"

int read_message_queue(void);
void signal_handler(int s);

mqd_t global_mqd;

int main(int argc, char **argv)
{
  if (argc < 2)
  {
    fprintf(stdout, "Usage: %s <name>\n", argv[0]);
    exit(1);
  }

  signal(SIGUSR1, signal_handler);

#if 0
  type = struct mq_attr
  {
    long int mq_flags;
    long int mq_maxmsg;
    long int mq_msgsize;
    long int mq_curmsgs;
    long int __pad[4];
  }
#endif

  struct mq_attr attr;

  memset(&attr, 0, sizeof(attr));

  //attr.mq_flags = 
  attr.mq_maxmsg = 10;
  attr.mq_msgsize = 100;
  //attr.mq_curmsgs = 

  //mqd_t mq_open(const char *name, int oflag, ...);
  //mqd_t mq_open(char *name, int flags, int mode, struct mq_attr *attr);
  if ((global_mqd = mq_open(argv[1], O_RDONLY)) == (mqd_t) - 1)
  {
    fprintf(stderr, "mq_open() failed: %s\n", strerror(errno));
    exit(1);
  }

  fprintf(stdout, "mq_open() successed.\n");

#if 0
  struct sigevent
  {
    sigval_t sigev_value;
    int sigev_signo;
    int sigev_notify;
    union
    {
      int _pad[13];
      __pid_t _tid;
      struct
      {
      ...} _sigev_thread;
    } _sigev_un;
  }
#endif
  struct sigevent e;

  e.sigev_signo = SIGUSR1;
  e.sigev_notify = SIGEV_SIGNAL;

  //int mq_notify(mqd_t mqdes, const struct sigevent *notification);
  mq_notify(global_mqd, &e);

  for (;;)
  {
  }

  mq_close(global_mqd);
  //mq_unlink(MQUEUE_NAME);

  return 0;
}

void signal_handler(int s)
{
  fprintf(stdout, "Catched signal %d\n", s);

  if (s == SIGUSR1)
  {
    struct sigevent e;

    e.sigev_signo = SIGUSR1;
    e.sigev_notify = SIGEV_SIGNAL;

    //int mq_notify(mqd_t mqdes, const struct sigevent *notification);
    mq_notify(global_mqd, &e);
    
    read_message_queue();
  }
}

int read_message_queue(void)
{
  struct mq_attr attr;

  mq_getattr(global_mqd, &attr);

#if 0
  fprintf(stdout, "attr.mq_flags = %ld\n", attr.mq_flags);
  fprintf(stdout, "attr.mq_maxmsg = %ld\n", attr.mq_maxmsg);
  fprintf(stdout, "attr.mq_msgsize = %ld\n", attr.mq_msgsize);
  fprintf(stdout, "attr.mq_curmsgs = %ld\n", attr.mq_curmsgs);
#endif

  //char buf[BUFFER_SIZE];
  char *buf = NULL;
  unsigned int pri;
  ssize_t n;

  if ((buf = (char *) malloc(attr.mq_msgsize)) == NULL)
  {
    fprintf(stderr, "Allocate memory failed: %s\n", strerror(errno));
    // FIXME: try to allocate again.
    exit(1);
  }

  memset(buf, 0, attr.mq_msgsize);
  // Upon successful completion, the mq_receive()    and mq_timedreceive() functions shall return the  length
  // of  the selected message in bytes and the message shall be removed from the queue. Otherwise, no message
  // shall be removed from the queue, the functions shall return a value of -1, and set errno to indicate the
  // error.
  //ssize_t mq_receive(mqd_t mqdes, char *msg_ptr, size_t msg_len, unsigned *msg_prio);
  if ((n = mq_receive(global_mqd, buf, attr.mq_msgsize, &pri)) < 0)
  {
    fprintf(stderr, "mq_receive() failed: %s\n", strerror(errno));
    exit(1);
  }

  //buf[n] = '\0';
  //fprintf(stdout, "Read %d bytes from message queue %s, message: %s, pri: %d\n", n, argv[1], buf, pri);
  fprintf(stdout, "Read %d bytes from message queue, message: %s, pri: %d\n", n, buf, pri);

  if (buf)
  {
    free(buf);
    buf = NULL;
  }

  return n;
}