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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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getaddrinfo_a(3) Library Functions Manual getaddrinfo_a(3)
getaddrinfo_a, gai_suspend, gai_error, gai_cancel - asynchronous
network address and service translation
Asynchronous name lookup library (libanl, -lanl)
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <netdb.h>
int getaddrinfo_a(int mode, struct gaicb *list[restrict],
int nitems, struct sigevent *restrict 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);
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(3type). 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(3type) 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(3type) 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.
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.
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() │ │ │
└─────────────────────────────────────┴───────────────┴─────────┘
GNU.
glibc 2.2.3.
The interface of getaddrinfo_a() was modeled after the
lio_listio(3) interface.
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 mirrors.kernel.org enoent.linuxfoundation.org gnu.org
mirrors.kernel.org: 139.178.88.99
enoent.linuxfoundation.org: Name or service not known
gnu.org: 209.51.188.116
Here is the program source code
#define _GNU_SOURCE
#include <err.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MALLOC(n, type) ((type *) reallocarray(NULL, n, sizeof(type)))
int
main(int argc, char *argv[])
{
int 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 (size_t i = 0; i < argc - 1; i++) {
reqs[i] = MALLOC(1, struct gaicb);
if (reqs[i] == NULL)
err(EXIT_FAILURE, "malloc");
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 (size_t 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 mirrors.kernel.org enoent.linuxfoundation.org gnu.org
> c 2
[2] gnu.org: Request not canceled
> w 0 1
[00] mirrors.kernel.org: Finished
> l
[00] mirrors.kernel.org: 139.178.88.99
[01] enoent.linuxfoundation.org: Processing request in progress
[02] gnu.org: 209.51.188.116
> l
[00] mirrors.kernel.org: 139.178.88.99
[01] enoent.linuxfoundation.org: Name or service not known
[02] gnu.org: 209.51.188.116
The program source is as follows:
#define _GNU_SOURCE
#include <assert.h>
#include <err.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define CALLOC(n, type) ((type *) calloc(n, sizeof(type)))
#define REALLOCF(ptr, n, type) \
({ \
static_assert(__builtin_types_compatible_p(typeof(ptr), type *)); \
\
(type *) reallocarrayf(ptr, n, sizeof(type)); \
})
static struct gaicb **reqs = NULL;
static size_t nreqs = 0;
static inline void *
reallocarrayf(void *p, size_t nmemb, size_t size)
{
void *q;
q = reallocarray(p, nmemb, size);
if (q == NULL && nmemb != 0 && size != 0)
free(p);
return q;
}
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)
{
size_t nreqs_base = nreqs;
char *host;
int ret;
while ((host = strtok(NULL, " "))) {
nreqs++;
reqs = REALLOCF(reqs, nreqs, struct gaicb *);
if (reqs == NULL)
err(EXIT_FAILURE, "reallocf");
reqs[nreqs - 1] = CALLOC(1, struct gaicb);
if (reqs[nreqs - 1] == NULL)
err(EXIT_FAILURE, "calloc");
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 ret;
size_t n;
struct gaicb const **wait_reqs;
wait_reqs = CALLOC(nreqs, const struct gaicb *);
if (wait_reqs == NULL)
err(EXIT_FAILURE, "calloc");
/* 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 (size_t i = 0; i < nreqs; i++) {
if (wait_reqs[i] == NULL)
continue;
ret = gai_error(reqs[i]);
if (ret == EAI_INPROGRESS)
continue;
printf("[%02zu] %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;
size_t 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 ret;
char host[NI_MAXHOST];
struct addrinfo *res;
for (size_t i = 0; i < nreqs; i++) {
printf("[%02zu] %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(void)
{
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);
}
getaddrinfo(3), inet(3), lio_listio(3), hostname(7), ip(7),
sigevent(3type)
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user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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Linux man-pages 6.9.1 2024-06-15 getaddrinfo_a(3)
Pages that refer to this page: getaddrinfo(3), sigevent(3type), strtok(3)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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