同期型の例¶

以下のプログラムは単に複数のホスト名の解決を並行で行う。 getaddrinfo(3) を使って順番にホスト名の解決を行うのに比べて速度が向上する。 このプログラムは以下のように使う。

$ ./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

プログラムのソースコードは以下のとおりである。

#define _GNU_SOURCE
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
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 (int 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 (int 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);
}

非同期型の例¶

この例は getaddrinfo_a() の簡単な対話式のフロントエンドである。 通知機能は使っていない。

セッションの実行例は以下のようになる。

$ ./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

プログラムのソースは以下のとおりである。

#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, sizeof(reqs[0]) * nreqs);


        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 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 (int 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 ret;


    char host[NI_MAXHOST];


    struct addrinfo *res;


    for (int 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);
}