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NAME

       getaddrinfo_a,  gai_suspend,  gai_error,  gai_cancel  -  asynchronous  network address and
       service 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(const struct gaicb * const list[], int nitems,
                       const 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
              completed.

       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,
       identifying an Internet host and a service.  The ar_request  element  corresponds  to  the
       hints  argument,  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 structure 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
       completion 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
       successfully, the error status of the request will  be  set  to  EAI_CANCELED  and  normal
       asynchronous  notification  will  be  performed.   The request cannot be canceled if it is
       currently 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
       successfully, 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
       completed.  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_CANCELED if the request has
       been canceled explicitly before it could be finished.

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

       EAI_CANCELED
              The request has been canceled successfully.

       EAI_NOTCANCELED
              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.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────────────────────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├────────────────────────────────┼───────────────┼─────────┤
       │getaddrinfo_a(), gai_suspend(), │ Thread safety │ MT-Safe │
       │gai_error(), gai_cancel()       │               │         │
       └────────────────────────────────┴───────────────┴─────────┘

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
       compared 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 5.01 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at https://www.kernel.org/doc/man-pages/.