NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

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

NAME         top

       getaddrinfo_a, gai_suspend, gai_error, gai_cancel - asynchronous net‐
       work address and service translation

SYNOPSIS         top

       #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         top

       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         top

       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         top

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

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

CONFORMING TO         top

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

NOTES         top

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

EXAMPLE         top

       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         top

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

COLOPHON         top

       This page is part of release 4.07 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/.

GNU                              2015-07-23                 GETADDRINFO_A(3)