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GETADDRINFO_A(3)		    Linux Programmer's Manual			 GETADDRINFO_A(3)

NAME
       getaddrinfo_a,  gai_suspend, gai_error, gai_cancel - asynchronous network address and ser-
       vice translation

SYNOPSIS
       #define _GNU_SOURCE	   /* See feature_test_macros(7) */
       #include <netdb.h>

       int getaddrinfo_a(int mode, struct gaicb *list[],
		       int nitems, struct sigevent *sevp);

       int gai_suspend(struct gaicb *list[], int nitems,
		       struct timespec *timeout);

       int gai_error(struct gaicb *req);

       int gai_cancel(struct gaicb *req);

       Link with -lanl.

DESCRIPTION
       The getaddrinfo_a() function performs the same task as getaddrinfo(3), but allows multiple
       name  look-ups to be performed asynchronously, with optional notification on completion of
       look-up operations.

       The mode argument has one of the following values:

       GAI_WAIT
	      Perform the look-ups synchronously.  The call blocks until the look-ups  have  com-
	      pleted.

       GAI_NOWAIT
	      Perform  the  look-ups  asynchronously.	The  call  returns  immediately,  and the
	      requests are resolved in the background.	See the discussion of the  sevp  argument
	      below.

       The  array  list specifies the look-up requests to process.  The nitems argument specifies
       the number of elements in list.	The requested look-up operations are started in parallel.
       NULL  elements  in  list  are  ignored.	 Each  request is described by a gaicb structure,
       defined as follows:

	   struct gaicb {
	       const char	     *ar_name;
	       const char	     *ar_service;
	       const struct addrinfo *ar_request;
	       struct addrinfo	     *ar_result;
	   };

       The elements of this structure correspond  to  the  arguments  of  getaddrinfo(3).   Thus,
       ar_name corresponds to the node argument and ar_service to the service argument, identify-
       ing an Internet host and a service.  The ar_request element corresponds to the hints argu-
       ment,  specifying  the  criteria  for  selecting  the  returned socket address structures.
       Finally, ar_result corresponds to the res argument; you do not  need  to  initialize  this
       element,  it  will be automatically set when the request is resolved.  The addrinfo struc-
       ture referenced by the last two elements is described in getaddrinfo(3).

       When mode is specified  as  GAI_NOWAIT,	notifications  about  resolved	requests  can  be
       obtained  by  employing	the  sigevent structure pointed to by the sevp argument.  For the
       definition and general details of this structure, see sigevent(7).  The sevp->sigev_notify
       field can have the following values:

       SIGEV_NONE
	      Don't provide any notification.

       SIGEV_SIGNAL
	      When  a  look-up	completes,  generate the signal sigev_signo for the process.  See
	      sigevent(7) for general details.	The si_code field of the siginfo_t structure will
	      be set to SI_ASYNCNL.

       SIGEV_THREAD
	      When  a  look-up	completes,  invoke  sigev_notify_function as if it were the start
	      function of a new thread.  See sigevent(7) for details.

       For SIGEV_SIGNAL and SIGEV_THREAD, it may be useful to  point  sevp->sigev_value.sival_ptr
       to list.

       The  gai_suspend() function suspends execution of the calling thread, waiting for the com-
       pletion of one or more requests in the array list.  The nitems argument specifies the size
       of the array list.  The call blocks until one of the following occurs:

       *  One or more of the operations in list completes.

       *  The call is interrupted by a signal that is caught.

       *  The  time  interval specified in timeout elapses.  This argument specifies a timeout in
	  seconds plus nanoseconds (see nanosleep(2) for details of the timespec structure).   If
	  timeout  is  NULL,  then  the  call  blocks indefinitely (until one of the events above
	  occurs).

       No explicit indication of which request was completed is given; you must  determine  which
       request(s) have completed by iterating with gai_error() over the list of requests.

       The  gai_error()  function returns the status of the request req: either EAI_INPROGRESS if
       the request was not completed yet, 0 if it was handled successfully, or an error  code  if
       the request could not be resolved.

       The  gai_cancel() function cancels the request req.  If the request has been canceled suc-
       cessfully, the error status of the request will be set to EAI_CANCELLED and  normal  asyn-
       chronous  notification  will  be  performed.  The request cannot be canceled if it is cur-
       rently being processed; in that case, it will be handled as if gai_cancel() has never been
       called.	 If  req  is NULL, an attempt is made to cancel all outstanding requests that the
       process has made.

RETURN VALUE
       The getaddrinfo_a() function returns 0 if all of the requests have been enqueued  success-
       fully, or one of the following nonzero error codes:

       EAI_AGAIN
	      The  resources  necessary  to enqueue the look-up requests were not available.  The
	      application may check the error status of each  request  to  determine  which  ones
	      failed.

       EAI_MEMORY
	      Out of memory.

       EAI_SYSTEM
	      mode is invalid.

       The  gai_suspend() function returns 0 if at least one of the listed requests has been com-
       pleted.	Otherwise, it returns one of the following nonzero error codes:

       EAI_AGAIN
	      The given timeout expired before any of the requests could be completed.

       EAI_ALLDONE
	      There were no actual requests given to the function.

       EAI_INTR
	      A signal has interrupted the function.  Note that this interruption might have been
	      caused by signal notification of some completed look-up request.

       The  gai_error()  function  can return EAI_INPROGRESS for an unfinished look-up request, 0
       for a successfully completed look-up (as described above), one of  the  error  codes  that
       could  be  returned  by getaddrinfo(3), or the error code EAI_CANCELLED if the request has
       been canceled explicitly before it could be finished.

       The gai_cancel() function can return one of these values:

       EAI_CANCELLED
	      The request has been canceled successfully.

       EAI_NOTCANCELLED
	      The request has not been canceled.

       EAI_ALLDONE
	      The request has already completed.

       The gai_strerror(3) function translates these error codes  to  a  human	readable  string,
       suitable for error reporting.

CONFORMING TO
       These functions are GNU extensions; they first appeared in glibc in version 2.2.3.

NOTES
       The interface of getaddrinfo_a() was modeled after the lio_listio(3) interface.

EXAMPLE
       Two  examples  are  provided:  a simple example that resolves several requests in parallel
       synchronously, and a complex example showing some of the asynchronous capabilities.

   Synchronous example
       The program below simply resolves several hostnames in parallel, giving	a  speed-up  com-
       pared  to resolving the hostnames sequentially using getaddrinfo(3).  The program might be
       used like this:

	   $ ./a.out ftp.us.kernel.org enoent.linuxfoundation.org gnu.cz
	   ftp.us.kernel.org: 128.30.2.36
	   enoent.linuxfoundation.org: Name or service not known
	   gnu.cz: 87.236.197.13

       Here is the program source code

       #define _GNU_SOURCE
       #include <netdb.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>

       int
       main(int argc, char *argv[])
       {
	   int i, ret;
	   struct gaicb *reqs[argc - 1];
	   char host[NI_MAXHOST];
	   struct addrinfo *res;

	   if (argc < 2) {
	       fprintf(stderr, "Usage: %s HOST...\n", argv[0]);
	       exit(EXIT_FAILURE);
	   }

	   for (i = 0; i < argc - 1; i++) {
	       reqs[i] = malloc(sizeof(*reqs[0]));
	       if (reqs[i] == NULL) {
		   perror("malloc");
		   exit(EXIT_FAILURE);
	       }
	       memset(reqs[i], 0, sizeof(*reqs[0]));
	       reqs[i]->ar_name = argv[i + 1];
	   }

	   ret = getaddrinfo_a(GAI_WAIT, reqs, argc - 1, NULL);
	   if (ret != 0) {
	       fprintf(stderr, "getaddrinfo_a() failed: %s\n",
		       gai_strerror(ret));
	       exit(EXIT_FAILURE);
	   }

	   for (i = 0; i < argc - 1; i++) {
	       printf("%s: ", reqs[i]->ar_name);
	       ret = gai_error(reqs[i]);
	       if (ret == 0) {
		   res = reqs[i]->ar_result;

		   ret = getnameinfo(res->ai_addr, res->ai_addrlen,
			   host, sizeof(host),
			   NULL, 0, NI_NUMERICHOST);
		   if (ret != 0) {
		       fprintf(stderr, "getnameinfo() failed: %s\n",
			       gai_strerror(ret));
		       exit(EXIT_FAILURE);
		   }
		   puts(host);

	       } else {
		   puts(gai_strerror(ret));
	       }
	   }
	   exit(EXIT_SUCCESS);
       }

   Asynchronous example
       This example shows a  simple  interactive  getaddrinfo_a()  front-end.	The  notification
       facility is not demonstrated.

       An example session might look like this:

	   $ ./a.out
	   > a ftp.us.kernel.org enoent.linuxfoundation.org gnu.cz
	   > c 2
	   [2] gnu.cz: Request not canceled
	   > w 0 1
	   [00] ftp.us.kernel.org: Finished
	   > l
	   [00] ftp.us.kernel.org: 216.165.129.139
	   [01] enoent.linuxfoundation.org: Processing request in progress
	   [02] gnu.cz: 87.236.197.13
	   > l
	   [00] ftp.us.kernel.org: 216.165.129.139
	   [01] enoent.linuxfoundation.org: Name or service not known
	   [02] gnu.cz: 87.236.197.13

       The program source is as follows:

       #define _GNU_SOURCE
       #include <netdb.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>

       static struct gaicb **reqs = NULL;
       static int nreqs = 0;

       static char *
       getcmd(void)
       {
	   static char buf[256];

	   fputs("> ", stdout); fflush(stdout);
	   if (fgets(buf, sizeof(buf), stdin) == NULL)
	       return NULL;

	   if (buf[strlen(buf) - 1] == '\n')
	       buf[strlen(buf) - 1] = 0;

	   return buf;
       }

       /* Add requests for specified hostnames */
       static void
       add_requests(void)
       {
	   int nreqs_base = nreqs;
	   char *host;
	   int ret;

	   while ((host = strtok(NULL, " "))) {
	       nreqs++;
	       reqs = realloc(reqs, nreqs * sizeof(reqs[0]));

	       reqs[nreqs - 1] = calloc(1, sizeof(*reqs[0]));
	       reqs[nreqs - 1]->ar_name = strdup(host);
	   }

	   /* Queue nreqs_base..nreqs requests. */

	   ret = getaddrinfo_a(GAI_NOWAIT, &reqs[nreqs_base],
			       nreqs - nreqs_base, NULL);
	   if (ret) {
	       fprintf(stderr, "getaddrinfo_a() failed: %s\n",
		       gai_strerror(ret));
	       exit(EXIT_FAILURE);
	   }
       }

       /* Wait until at least one of specified requests completes */
       static void
       wait_requests(void)
       {
	   char *id;
	   int i, ret, n;
	   struct gaicb const **wait_reqs = calloc(nreqs, sizeof(*wait_reqs));
		       /* NULL elements are ignored by gai_suspend(). */

	   while ((id = strtok(NULL, " ")) != NULL) {
	       n = atoi(id);

	       if (n >= nreqs) {
		   printf("Bad request number: %s\n", id);
		   return;
	       }

	       wait_reqs[n] = reqs[n];
	   }

	   ret = gai_suspend(wait_reqs, nreqs, NULL);
	   if (ret) {
	       printf("gai_suspend(): %s\n", gai_strerror(ret));
	       return;
	   }

	   for (i = 0; i < nreqs; i++) {
	       if (wait_reqs[i] == NULL)
		   continue;

	       ret = gai_error(reqs[i]);
	       if (ret == EAI_INPROGRESS)
		   continue;

	       printf("[%02d] %s: %s\n", i, reqs[i]->ar_name,
		      ret == 0 ? "Finished" : gai_strerror(ret));
	   }
       }

       /* Cancel specified requests */
       static void
       cancel_requests(void)
       {
	   char *id;
	   int ret, n;

	   while ((id = strtok(NULL, " ")) != NULL) {
	       n = atoi(id);

	       if (n >= nreqs) {
		   printf("Bad request number: %s\n", id);
		   return;
	       }

	       ret = gai_cancel(reqs[n]);
	       printf("[%s] %s: %s\n", id, reqs[atoi(id)]->ar_name,
		      gai_strerror(ret));
	   }
       }

       /* List all requests */
       static void
       list_requests(void)
       {
	   int i, ret;
	   char host[NI_MAXHOST];
	   struct addrinfo *res;

	   for (i = 0; i < nreqs; i++) {
	       printf("[%02d] %s: ", i, reqs[i]->ar_name);
	       ret = gai_error(reqs[i]);

	       if (!ret) {
		   res = reqs[i]->ar_result;

		   ret = getnameinfo(res->ai_addr, res->ai_addrlen,
				     host, sizeof(host),
				     NULL, 0, NI_NUMERICHOST);
		   if (ret) {
		       fprintf(stderr, "getnameinfo() failed: %s\n",
			       gai_strerror(ret));
		       exit(EXIT_FAILURE);
		   }
		   puts(host);
	       } else {
		   puts(gai_strerror(ret));
	       }
	   }
       }

       int
       main(int argc, char *argv[])
       {
	   char *cmdline;
	   char *cmd;

	   while ((cmdline = getcmd()) != NULL) {
	       cmd = strtok(cmdline, " ");

	       if (cmd == NULL) {
		   list_requests();
	       } else {
		   switch (cmd[0]) {
		   case 'a':
		       add_requests();
		       break;
		   case 'w':
		       wait_requests();
		       break;
		   case 'c':
		       cancel_requests();
		       break;
		   case 'l':
		       list_requests();
		       break;
		   default:
		       fprintf(stderr, "Bad command: %c\n", cmd[0]);
		       break;
		   }
	       }
	   }
	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       getaddrinfo(3), inet(3), lio_listio(3), hostname(7), ip(7), sigevent(7)

COLOPHON
       This  page  is  part of release 3.53 of the Linux man-pages project.  A description of the
       project,    and	  information	 about	  reporting    bugs,	can    be    found     at
       http://www.kernel.org/doc/man-pages/.

GNU					    2010-09-27				 GETADDRINFO_A(3)
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