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GETADDRINFO_A(3) | Linux Programmer's Manual | GETADDRINFO_A(3) |
NAME¶
getaddrinfo_a, gai_suspend, gai_error, gai_cancel - asynchronous network address and service translationSYNOPSIS¶
#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(struct gaicb *list[], int nitems, 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.- 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.
struct gaicb { const char *ar_name; const char *ar_service; const struct addrinfo *ar_request; struct addrinfo *ar_result; };
- 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.
- *
- 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).
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.
- 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.
- EAI_CANCELLED
- The request has been canceled successfully.
- EAI_NOTCANCELLED
- The request has not been canceled.
- EAI_ALLDONE
- The request has already completed.
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.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 goes 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 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.2010-09-27 | GNU |