lib/libasyn/asyn_read.c

   1 /*      asyn_read()                                     Author: Kees J. Bot
   2  *                                                              7 Jul 1997
   3  */
   4 #include "asyn.h"
   5 #include <signal.h>
   6
   7 ssize_t asyn_read(asynchio_t *asyn, int fd, void *buf, size_t len)
   8 /* Asynchronous read().  Try if a read can be done, if not then set a flag
   9  * indicating that select(2) should look out for it.  Returns like a normal
  10  * read or returns -1 with errno set to EAGAIN.
  11  */
  12 {
  13         asynfd_t *afd;
  14
  15         /* Asyn_wait() may block if this counter equals zero indicating that
  16          * all of the asyn_* functions are "in progress".
  17          */
  18         asyn->asyn_more++;
  19
  20         if ((unsigned) fd >= FD_SETSIZE) { errno= EBADF; return -1; }
  21         afd= &asyn->asyn_afd[fd];
  22
  23         /* If this is the first async call on this filedescriptor then
  24          * remember its file flags.
  25          */
  26         if (!afd->afd_seen) {
  27                 if ((afd->afd_flags= fcntl(fd, F_GETFL)) < 0) return -1;
  28                 afd->afd_seen= 1;
  29         }
  30
  31         /* Try to read if I/O is pending. */
  32         if (afd->afd_state[SEL_READ] == PENDING) {
  33                 sigset_t mask;
  34                 ssize_t result;
  35                 int err;
  36
  37                 sigemptyset(&mask);
  38                 if (sigprocmask(SIG_SETMASK, &mask, &mask) < 0) return -1;
  39                 (void) fcntl(fd, F_SETFL, afd->afd_flags | O_NONBLOCK);
  40
  41                 /* Try the actual read. */
  42                 result= read(fd, buf, len);
  43                 err= errno;
  44
  45                 (void) fcntl(fd, F_SETFL, afd->afd_flags);
  46                 (void) sigprocmask(SIG_SETMASK, &mask, nil);
  47
  48                 errno= err;
  49                 if (result != -1 || errno != EAGAIN) {
  50                         afd->afd_state[SEL_READ]= IDLE;
  51                         return result;
  52                 }
  53         }
  54
  55         /* Record this read as "waiting". */
  56         afd->afd_state[SEL_READ]= WAITING;
  57         FD_SET(fd, &asyn->asyn_fdset[SEL_READ]);
  58         errno= EAGAIN;
  59         asyn->asyn_more--;
  60         return -1;
  61 }