|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
GETADDRINFO_A(3) Linux Programmer's Manual GETADDRINFO_A(3)
getaddrinfo_a, gai_suspend, gai_error, gai_cancel - asynchronous net‐
work address and service translation
#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.
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.
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() │ │ │
└────────────────────────────────┴───────────────┴─────────┘
These functions are GNU extensions; they first appeared in glibc in
version 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 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);
}
getaddrinfo(3), inet(3), lio_listio(3), hostname(7), ip(7),
sigevent(7)
This page is part of release 4.12 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)
Pages that refer to this page: getaddrinfo(3), strtok(3), sigevent(7)