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man:gai_suspend

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

NAME

     getaddrinfo_a,  gai_suspend,  gai_error, gai_cancel - asynchronous net-
     work 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 immedi-
            ately, 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 getad-
     drinfo(3).  Thus, ar_name corresponds to the node argument and  ar_ser-
     vice  to  the service argument, identifying an Internet host and a ser-
     vice.  The ar_request element corresponds to the hints argument, speci-
     fying  the  criteria  for  selecting the returned socket address struc-
     tures.  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 spec-

ifies 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 han-
     dled 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 follow-
     ing 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 interrup-
            tion might have been caused by signal notification of some  com-
            pleted 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 getad-
     drinfo(3), or the error code EAI_CANCELED if the request has been  can-
     celed 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).
     allbox;  lbw31  lb  lb  l  l  l.   Interface Attribute Value  T{ getad-
     drinfo_a(),  gai_suspend(),   gai_error(),   gai_cancel()   T}   Thread
     safety  MT-Safe

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.ker-
         nel.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 4.16 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 2017-09-15 GETADDRINFO_A(3)

/data/webs/external/dokuwiki/data/pages/man/gai_suspend.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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