1GETADDRINFO_A(3)           Linux Programmer's Manual          GETADDRINFO_A(3)
2
3
4

NAME

6       getaddrinfo_a,  gai_suspend,  gai_error, gai_cancel - asynchronous net‐
7       work address and service translation
8

SYNOPSIS

10       #define _GNU_SOURCE         /* See feature_test_macros(7) */
11       #include <netdb.h>
12
13       int getaddrinfo_a(int mode, struct gaicb *list[],
14                       int nitems, struct sigevent *sevp);
15
16       int gai_suspend(const struct gaicb * const list[], int nitems,
17                       const struct timespec *timeout);
18
19       int gai_error(struct gaicb *req);
20
21       int gai_cancel(struct gaicb *req);
22
23       Link with -lanl.
24

DESCRIPTION

26       The getaddrinfo_a() function performs the same task as  getaddrinfo(3),
27       but  allows multiple name look-ups to be performed asynchronously, with
28       optional notification on completion of look-up operations.
29
30       The mode argument has one of the following values:
31
32       GAI_WAIT
33              Perform the look-ups synchronously.  The call blocks  until  the
34              look-ups have completed.
35
36       GAI_NOWAIT
37              Perform  the  look-ups asynchronously.  The call returns immedi‐
38              ately, and the requests are resolved in the background.  See the
39              discussion of the sevp argument below.
40
41       The  array  list specifies the look-up requests to process.  The nitems
42       argument specifies the number of elements in list.  The requested look-
43       up  operations  are  started  in  parallel.   NULL elements in list are
44       ignored.  Each request is described by a gaicb  structure,  defined  as
45       follows:
46
47           struct gaicb {
48               const char            *ar_name;
49               const char            *ar_service;
50               const struct addrinfo *ar_request;
51               struct addrinfo       *ar_result;
52           };
53
54       The  elements  of  this structure correspond to the arguments of getad‐
55       drinfo(3).  Thus, ar_name corresponds to the node argument and  ar_ser‐
56       vice  to  the service argument, identifying an Internet host and a ser‐
57       vice.  The ar_request element corresponds to the hints argument, speci‐
58       fying  the  criteria  for  selecting the returned socket address struc‐
59       tures.  Finally, ar_result corresponds to the res argument; you do  not
60       need  to initialize this element, it will be automatically set when the
61       request is resolved.  The addrinfo structure referenced by the last two
62       elements is described in getaddrinfo(3).
63
64       When  mode  is  specified  as  GAI_NOWAIT, notifications about resolved
65       requests can be obtained by employing the sigevent structure pointed to
66       by  the  sevp argument.  For the definition and general details of this
67       structure, see sigevent(7).  The sevp->sigev_notify field can have  the
68       following values:
69
70       SIGEV_NONE
71              Don't provide any notification.
72
73       SIGEV_SIGNAL
74              When  a  look-up  completes, generate the signal sigev_signo for
75              the process.  See sigevent(7) for general details.  The  si_code
76              field of the siginfo_t structure will be set to SI_ASYNCNL.
77
78       SIGEV_THREAD
79              When  a look-up completes, invoke sigev_notify_function as if it
80              were the start function of a new thread.   See  sigevent(7)  for
81              details.
82
83       For   SIGEV_SIGNAL   and  SIGEV_THREAD,  it  may  be  useful  to  point
84       sevp->sigev_value.sival_ptr to list.
85
86       The gai_suspend() function suspends execution of  the  calling  thread,
87       waiting  for  the completion of one or more requests in the array list.
88       The nitems argument specifies the size of the  array  list.   The  call
89       blocks until one of the following occurs:
90
91       *  One or more of the operations in list completes.
92
93       *  The call is interrupted by a signal that is caught.
94
95       *  The time interval specified in timeout elapses.  This argument spec‐
96          ifies a timeout in seconds plus nanoseconds  (see  nanosleep(2)  for
97          details  of  the  timespec structure).  If timeout is NULL, then the
98          call blocks indefinitely (until one of the events above occurs).
99
100       No explicit indication of which request was  completed  is  given;  you
101       must  determine  which  request(s)  have  completed  by  iterating with
102       gai_error() over the list of requests.
103
104       The gai_error() function returns the status of the request req:  either
105       EAI_INPROGRESS  if  the request was not completed yet, 0 if it was han‐
106       dled successfully, or an  error  code  if  the  request  could  not  be
107       resolved.
108
109       The  gai_cancel() function cancels the request req.  If the request has
110       been canceled successfully, the error status of the request will be set
111       to EAI_CANCELED and normal asynchronous notification will be performed.
112       The request cannot be canceled if it is currently being  processed;  in
113       that case, it will be handled as if gai_cancel() has never been called.
114       If req is NULL, an attempt is made to cancel all  outstanding  requests
115       that the process has made.
116

RETURN VALUE

118       The getaddrinfo_a() function returns 0 if all of the requests have been
119       enqueued successfully, or one of the following nonzero error codes:
120
121       EAI_AGAIN
122              The resources necessary to enqueue the look-up requests were not
123              available.   The  application may check the error status of each
124              request to determine which ones failed.
125
126       EAI_MEMORY
127              Out of memory.
128
129       EAI_SYSTEM
130              mode is invalid.
131
132       The gai_suspend() function returns 0 if at  least  one  of  the  listed
133       requests  has been completed.  Otherwise, it returns one of the follow‐
134       ing nonzero error codes:
135
136       EAI_AGAIN
137              The given timeout expired before any of the  requests  could  be
138              completed.
139
140       EAI_ALLDONE
141              There were no actual requests given to the function.
142
143       EAI_INTR
144              A signal has interrupted the function.  Note that this interrup‐
145              tion might have been caused by signal notification of some  com‐
146              pleted look-up request.
147
148       The  gai_error()  function  can return EAI_INPROGRESS for an unfinished
149       look-up request, 0 for a successfully completed look-up  (as  described
150       above),  one  of  the  error  codes  that  could  be returned by getad‐
151       drinfo(3), or the error code EAI_CANCELED if the request has been  can‐
152       celed explicitly before it could be finished.
153
154       The gai_cancel() function can return one of these values:
155
156       EAI_CANCELED
157              The request has been canceled successfully.
158
159       EAI_NOTCANCELED
160              The request has not been canceled.
161
162       EAI_ALLDONE
163              The request has already completed.
164
165       The  gai_strerror(3)  function  translates these error codes to a human
166       readable string, suitable for error reporting.
167

ATTRIBUTES

169       For  an  explanation  of  the  terms  used   in   this   section,   see
170       attributes(7).
171
172       ┌────────────────────────────────┬───────────────┬─────────┐
173Interface                       Attribute     Value   
174       ├────────────────────────────────┼───────────────┼─────────┤
175getaddrinfo_a(), gai_suspend(), │ Thread safety │ MT-Safe │
176gai_error(), gai_cancel()       │               │         │
177       └────────────────────────────────┴───────────────┴─────────┘
178

CONFORMING TO

180       These functions are GNU extensions; they first  appeared  in  glibc  in
181       version 2.2.3.
182

NOTES

184       The  interface  of  getaddrinfo_a() was modeled after the lio_listio(3)
185       interface.
186

EXAMPLE

188       Two examples are provided:  a  simple  example  that  resolves  several
189       requests  in parallel synchronously, and a complex example showing some
190       of the asynchronous capabilities.
191
192   Synchronous example
193       The program below simply resolves several hostnames in parallel, giving
194       a  speed-up  compared  to  resolving  the  hostnames sequentially using
195       getaddrinfo(3).  The program might be used like this:
196
197           $ ./a.out ftp.us.kernel.org enoent.linuxfoundation.org gnu.cz
198           ftp.us.kernel.org: 128.30.2.36
199           enoent.linuxfoundation.org: Name or service not known
200           gnu.cz: 87.236.197.13
201
202       Here is the program source code
203
204       #define _GNU_SOURCE
205       #include <netdb.h>
206       #include <stdio.h>
207       #include <stdlib.h>
208       #include <string.h>
209
210       int
211       main(int argc, char *argv[])
212       {
213           int i, ret;
214           struct gaicb *reqs[argc - 1];
215           char host[NI_MAXHOST];
216           struct addrinfo *res;
217
218           if (argc < 2) {
219               fprintf(stderr, "Usage: %s HOST...\n", argv[0]);
220               exit(EXIT_FAILURE);
221           }
222
223           for (i = 0; i < argc - 1; i++) {
224               reqs[i] = malloc(sizeof(*reqs[0]));
225               if (reqs[i] == NULL) {
226                   perror("malloc");
227                   exit(EXIT_FAILURE);
228               }
229               memset(reqs[i], 0, sizeof(*reqs[0]));
230               reqs[i]->ar_name = argv[i + 1];
231           }
232
233           ret = getaddrinfo_a(GAI_WAIT, reqs, argc - 1, NULL);
234           if (ret != 0) {
235               fprintf(stderr, "getaddrinfo_a() failed: %s\n",
236                       gai_strerror(ret));
237               exit(EXIT_FAILURE);
238           }
239
240           for (i = 0; i < argc - 1; i++) {
241               printf("%s: ", reqs[i]->ar_name);
242               ret = gai_error(reqs[i]);
243               if (ret == 0) {
244                   res = reqs[i]->ar_result;
245
246                   ret = getnameinfo(res->ai_addr, res->ai_addrlen,
247                           host, sizeof(host),
248                           NULL, 0, NI_NUMERICHOST);
249                   if (ret != 0) {
250                       fprintf(stderr, "getnameinfo() failed: %s\n",
251                               gai_strerror(ret));
252                       exit(EXIT_FAILURE);
253                   }
254                   puts(host);
255
256               } else {
257                   puts(gai_strerror(ret));
258               }
259           }
260           exit(EXIT_SUCCESS);
261       }
262
263   Asynchronous example
264       This example shows a simple interactive getaddrinfo_a() front-end.  The
265       notification facility is not demonstrated.
266
267       An example session might look like this:
268
269           $ ./a.out
270           > a ftp.us.kernel.org enoent.linuxfoundation.org gnu.cz
271           > c 2
272           [2] gnu.cz: Request not canceled
273           > w 0 1
274           [00] ftp.us.kernel.org: Finished
275           > l
276           [00] ftp.us.kernel.org: 216.165.129.139
277           [01] enoent.linuxfoundation.org: Processing request in progress
278           [02] gnu.cz: 87.236.197.13
279           > l
280           [00] ftp.us.kernel.org: 216.165.129.139
281           [01] enoent.linuxfoundation.org: Name or service not known
282           [02] gnu.cz: 87.236.197.13
283
284       The program source is as follows:
285
286       #define _GNU_SOURCE
287       #include <netdb.h>
288       #include <stdio.h>
289       #include <stdlib.h>
290       #include <string.h>
291
292       static struct gaicb **reqs = NULL;
293       static int nreqs = 0;
294
295       static char *
296       getcmd(void)
297       {
298           static char buf[256];
299
300           fputs("> ", stdout); fflush(stdout);
301           if (fgets(buf, sizeof(buf), stdin) == NULL)
302               return NULL;
303
304           if (buf[strlen(buf) - 1] == '\n')
305               buf[strlen(buf) - 1] = 0;
306
307           return buf;
308       }
309
310       /* Add requests for specified hostnames */
311       static void
312       add_requests(void)
313       {
314           int nreqs_base = nreqs;
315           char *host;
316           int ret;
317
318           while ((host = strtok(NULL, " "))) {
319               nreqs++;
320               reqs = realloc(reqs, nreqs * sizeof(reqs[0]));
321
322               reqs[nreqs - 1] = calloc(1, sizeof(*reqs[0]));
323               reqs[nreqs - 1]->ar_name = strdup(host);
324           }
325
326           /* Queue nreqs_base..nreqs requests. */
327
328           ret = getaddrinfo_a(GAI_NOWAIT, &reqs[nreqs_base],
329                               nreqs - nreqs_base, NULL);
330           if (ret) {
331               fprintf(stderr, "getaddrinfo_a() failed: %s\n",
332                       gai_strerror(ret));
333               exit(EXIT_FAILURE);
334           }
335       }
336
337       /* Wait until at least one of specified requests completes */
338       static void
339       wait_requests(void)
340       {
341           char *id;
342           int i, ret, n;
343           struct gaicb const **wait_reqs = calloc(nreqs, sizeof(*wait_reqs));
344                       /* NULL elements are ignored by gai_suspend(). */
345
346           while ((id = strtok(NULL, " ")) != NULL) {
347               n = atoi(id);
348
349               if (n >= nreqs) {
350                   printf("Bad request number: %s\n", id);
351                   return;
352               }
353
354               wait_reqs[n] = reqs[n];
355           }
356
357           ret = gai_suspend(wait_reqs, nreqs, NULL);
358           if (ret) {
359               printf("gai_suspend(): %s\n", gai_strerror(ret));
360               return;
361           }
362
363           for (i = 0; i < nreqs; i++) {
364               if (wait_reqs[i] == NULL)
365                   continue;
366
367               ret = gai_error(reqs[i]);
368               if (ret == EAI_INPROGRESS)
369                   continue;
370
371               printf("[%02d] %s: %s\n", i, reqs[i]->ar_name,
372                      ret == 0 ? "Finished" : gai_strerror(ret));
373           }
374       }
375
376       /* Cancel specified requests */
377       static void
378       cancel_requests(void)
379       {
380           char *id;
381           int ret, n;
382
383           while ((id = strtok(NULL, " ")) != NULL) {
384               n = atoi(id);
385
386               if (n >= nreqs) {
387                   printf("Bad request number: %s\n", id);
388                   return;
389               }
390
391               ret = gai_cancel(reqs[n]);
392               printf("[%s] %s: %s\n", id, reqs[atoi(id)]->ar_name,
393                      gai_strerror(ret));
394           }
395       }
396
397       /* List all requests */
398       static void
399       list_requests(void)
400       {
401           int i, ret;
402           char host[NI_MAXHOST];
403           struct addrinfo *res;
404
405           for (i = 0; i < nreqs; i++) {
406               printf("[%02d] %s: ", i, reqs[i]->ar_name);
407               ret = gai_error(reqs[i]);
408
409               if (!ret) {
410                   res = reqs[i]->ar_result;
411
412                   ret = getnameinfo(res->ai_addr, res->ai_addrlen,
413                                     host, sizeof(host),
414                                     NULL, 0, NI_NUMERICHOST);
415                   if (ret) {
416                       fprintf(stderr, "getnameinfo() failed: %s\n",
417                               gai_strerror(ret));
418                       exit(EXIT_FAILURE);
419                   }
420                   puts(host);
421               } else {
422                   puts(gai_strerror(ret));
423               }
424           }
425       }
426
427       int
428       main(int argc, char *argv[])
429       {
430           char *cmdline;
431           char *cmd;
432
433           while ((cmdline = getcmd()) != NULL) {
434               cmd = strtok(cmdline, " ");
435
436               if (cmd == NULL) {
437                   list_requests();
438               } else {
439                   switch (cmd[0]) {
440                   case 'a':
441                       add_requests();
442                       break;
443                   case 'w':
444                       wait_requests();
445                       break;
446                   case 'c':
447                       cancel_requests();
448                       break;
449                   case 'l':
450                       list_requests();
451                       break;
452                   default:
453                       fprintf(stderr, "Bad command: %c\n", cmd[0]);
454                       break;
455                   }
456               }
457           }
458           exit(EXIT_SUCCESS);
459       }
460

SEE ALSO

462       getaddrinfo(3), inet(3), lio_listio(3), hostname(7), ip(7), sigevent(7)
463

COLOPHON

465       This  page  is  part of release 5.04 of the Linux man-pages project.  A
466       description of the project, information about reporting bugs,  and  the
467       latest     version     of     this    page,    can    be    found    at
468       https://www.kernel.org/doc/man-pages/.
469
470
471
472GNU                               2019-03-06                  GETADDRINFO_A(3)
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