[PATCH] man3/getaddrinfo_a.3: New manual page

[PATCH] man3/getaddrinfo_a.3: New manual page

[Petr Baudis]

This patch adds original documentation for the getaddrinfo_a(3)
glibc function and the associated suite of gai_suspend(3),
gai_error(3) and gai_cancel(3), including two example programs.

The notification facility is not demonstrated in the interactive
frontend since I judged the would-be extra machinery as too
obscuring (and producing potentially messy results if using
signal notification). Maybe a third pthread example would be due?

Please review and comment.

Signed-off-by: Petr Baudis <pasky-AlSwsSmVLrQ@public.gmane.org>

diff --git a/man3/gai_cancel.3 b/man3/gai_cancel.3
index e69de29..1b0f392 100644
--- a/man3/gai_cancel.3
+++ b/man3/gai_cancel.3
@@ -0,0 +1 @@
+.so man3/getaddrinfo_a.3
diff --git a/man3/gai_error.3 b/man3/gai_error.3
index e69de29..1b0f392 100644
--- a/man3/gai_error.3
+++ b/man3/gai_error.3
@@ -0,0 +1 @@
+.so man3/getaddrinfo_a.3
diff --git a/man3/gai_suspend.3 b/man3/gai_suspend.3
index e69de29..1b0f392 100644
--- a/man3/gai_suspend.3
+++ b/man3/gai_suspend.3
@@ -0,0 +1 @@
+.so man3/getaddrinfo_a.3
diff --git a/man3/getaddrinfo.3 b/man3/getaddrinfo.3
index 0917006..c02866c 100644
--- a/man3/getaddrinfo.3
+++ b/man3/getaddrinfo.3
@@ -801,6 +801,7 @@ main(int argc, char *argv[])
 .SH "SEE ALSO"
 .\" .BR getipnodebyaddr (3),
 .\" .BR getipnodebyname (3),
+.BR getaddrinfo_a (3),
 .BR gethostbyname (3),
 .BR getnameinfo (3),
 .BR inet (3),
diff --git a/man3/getaddrinfo_a.3 b/man3/getaddrinfo_a.3
index e69de29..c32331f 100644
--- a/man3/getaddrinfo_a.3
+++ b/man3/getaddrinfo_a.3
@@ -0,0 +1,478 @@
+.\" Copyright (c) 2009 Petr Baudis <pasky-AlSwsSmVLrQ@public.gmane.org>
+.\"
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of this
+.\" manual under the conditions for verbatim copying, provided that the
+.\" entire resulting derived work is distributed under the terms of a
+.\" permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume no
+.\" responsibility for errors or omissions, or for damages resulting from
+.\" the use of the information contained herein.  The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\"
+.\" References: http://people.redhat.com/drepper/asynchnl.pdf,
+.\" 	http://www.imperialviolet.org/page25.html#e498
+.\"
+.TH GETADDRINFO_A 3 2009-04-08 "GNU" "Linux Programmer's Manual"
+.SH NAME
+getaddrinfo_a, gai_suspend, gai_error, gai_cancel \- asynchronous
+network address and service translation
+.SH SYNOPSIS
+.nf
+.B #define _GNU_SOURCE
+.B #include <sys/types.h>
+.B #include <sys/socket.h>
+.B #include <signal.h>
+.B #include <netdb.h>
+.sp
+.BI "int getaddrinfo_a(int " "mode" ", struct gaicb *" "list[]" ,
+.BI "                int " "ent" ", struct sigevent *" "sig" );
+.sp
+.BI "int gai_suspend(struct gaicb *" "list[]" ", int " "ent" ,
+.BI "                struct timespec *" "timeout" );
+.sp
+.BI "int gai_error(struct gaicb *" "req" );
+.sp
+.BI "int gai_cancel(struct gaicb *" "req" );
+.sp
+Link with \fI\-lanl\fP.
+.fi
+.SH DESCRIPTION
+The function
+.BR getaddrinfo_a ()
+will process in parallel the given list of requests,
+either synchronously or asynchronously
+with optional notification. The
+.I mode
+parameter can be either
+.B GAI_WAIT
+for synchronous lookup or
+.B GAI_NOWAIT
+if the function shall return immediately
+while the requests are being resolved on background;
+in that case, notifications about resolved requests
+can be sent based on the
+.I sig
+parameter (see
+.BR sigevent (7)
+for details).
+.PP
+The requests to process are given in the
+.I list
+array of
+.I ent
+entries and are fired in parallel - if any element
+of the list is NULL, this element is ignored.
+Each request is described by the
+.I gaicb
+structure that is defined as follows:
+.sp
+.in +4n
+.nf
+struct gaicb {
+    const char *ar_name;
+    const char *ar_service;
+    const struct addrinfo *ar_request;
+    struct addrinfo *ar_result;
+};
+.fi
+.in
+.PP
+The elements of this structure simply correspond
+to arguments of
+.BR getaddrinfo (3).
+Thus,
+.I ar_name
+corresponds to the
+.I node
+parameter and
+.I ar_service
+to the
+.I service
+parameter, identifying an Internet host and a service.
+The
+.I ar_request
+element represents the
+.I hints
+parameter, specifying the criteria for selecting
+the returned socket address structures.
+Finally,
+.I ar_result
+is the same as the
+.I res
+parameter; you do not need to initialize this element,
+it will be automatically set when the request
+is resolved.
+The
+.I addrinfo
+structure referenced by the last two elements is described
+along the documentation of
+.BR getaddrinfo (3).
+.PP
+The
+.BR gai_suspend ()
+routine will suspend execution of the calling thread
+until at least one of the requests (given in the
+.I list
+array of
+.I ent
+elements; NULL pointers are ignored) is completed,
+a signal is received, or the time interval specified in
+.I timeout
+elapses (if the argument is not NULL).
+No explicit indication of which request was completed
+is given - you must determine that by iterating with
+.BR gai_error ()
+over the list of requests.
+.PP
+The
+.BR gai_error ()
+function will return the status of the given request - either
+.B 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.
+.PP
+The
+.BR gai_cancel ()
+function will cancel the given request
+.IR req .
+If the request has been cancelled successfully,
+the error status of the request will be set to
+.B EAI_CANCELLED
+and normal asynchronous notification will be performed;
+the request cannot be cancelled if it is currently being
+processed - in that case, it will be handled as if
+this function has never been called.
+If
+.I req
+is NULL, all outstanding requests the process has made
+are attempted to be cancelled.
+
+.SH "RETURN VALUE"
+.BR getaddrinfo_a ()
+returns 0 if all the requests have been enqueued successfully,
+or one of the following non-zero error codes:
+.TP
+.B EAI_AGAIN
+The resources necessary to enqueue the lookup requests were not
+available. The application may check the error status of each
+request to determine which ones failed.
+.TP
+.B EAI_MEMORY
+Out of memory.
+.PP
+.BR gai_suspend ()
+returns 0 if at least one of the listed requests has been completed.
+Otherwise, it returns one of the following non-zero error codes:
+.TP
+.B EAI_AGAIN
+The given timeout expired before any of the requests could be completed.
+.TP
+.B EAI_ALLDONE
+There were no actual requests given to the function.
+.TP
+.B EAI_INTR
+A signal has interrupted the function. Note that this interruption might
+be potentially caused by signal notification of some completed request.
+.PP
+.BR gai_error ()
+can return
+.B EAI_INPROGRESS
+for unfinished request, zero for successfully completed one
+(as described above), one of the error codes that could be returned by
+.BR getaddrinfo (3)
+or the error code
+.B EAI_CANCELLED
+if the request has been cancelled explicitly before it could be finished.
+.PP
+The
+.BR gai_cancel ()
+function can return one of these values:
+.TP
+.B EAI_CANCELLED
+The request has been cancelled successfully.
+.TP
+.B EAI_NOTCANCELLED
+The request has not been cancelled.
+.TP
+.B EAI_ALLDONE
+The request has already completed.
+.P
+The
+.BR gai_strerror (3)
+function translates these error codes to a human readable string,
+suitable for error reporting.
+.SH "CONFORMING TO"
+These functions are GNU extensions;
+they first appeared in glibc in version 2.2.3.
+.SH "NOTES"
+The interface of
+.BR getaddrinfo_a ()
+was modelled after the
+.BR lio_listio (3)
+pthreads interface.
+.SH EXAMPLE
+Two examples are provided - simple example showing just resolving
+several requests in parallel synchronously, and complex example
+showing some of the asynchronous capabilities.
+.SS Synchronous Example
+The program will simply resolve several hostnames in parallel,
+giving a speed-up compared to resolving the hostnames sequentially
+using the classical interfaces. It might be used like this:
+.in +4n
+.nf
+
+$ \fB./a.out ftp.us.kernel.org enoent.linuxfoundation.org gnu.cz\fP
+ftp.us.kernel.org: 128.30.2.36
+enoent.linuxfoundation.org: Name or service not known
+gnu.cz: 87.236.197.13
+.fi
+.in
+.PP
+This is the example source code:
+.nf
+
+#define _GNU_SOURCE
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <signal.h>
+#include <netdb.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int
+main(int argc, char *argv[])
+{
+    int i;
+
+    if (argc < 2) {
+        fprintf(stderr, "Usage: %s HOST...\\n", argv[0]);
+        exit(EXIT_FAILURE);
+    }
+
+    struct gaicb *reqs[argc - 1];
+    for (i = 0; i < argc - 1; i++) {
+        reqs[i] = alloca(sizeof(*reqs[0]));
+        memset(reqs[i], 0, sizeof(*reqs[0]));
+        reqs[i]->ar_name = argv[i + 1];
+    }
+
+    int ret;
+    ret = getaddrinfo_a(GAI_WAIT, reqs, argc - 1, NULL);
+    if (ret) {
+        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);
+        int ret = gai_error(reqs[i]);
+        if (!ret) {
+            char host[NI_MAXHOST];
+            struct addrinfo *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);
+}
+.fi
+
+.SS Asynchronous Example
+This example shows a simple interactive
+.BR getaddrinfo_a ()
+frontend. The notification facility is not demonstrated.
+.PP
+An example session might go like this:
+.in +4n
+.nf
+
+$ \fB./a.out\fP
+> 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
+.fi
+.in
+.PP
+The program source goes as follows:
+
+\&
+.nf
+#define _GNU_SOURCE
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <signal.h>
+#include <netdb.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct gaicb **reqs = NULL;
+int nreqs = 0;
+
+char *
+getcmd(void)
+{
+    static char buf[256];
+    fputs("> ", stdout); fflush(stdout);
+    if (!fgets(buf, sizeof(buf), stdin))
+        return NULL;
+    if (buf[strlen(buf) - 1] == '\\n')
+        buf[strlen(buf) - 1] = 0;
+    return buf;
+}
+
+/** Add requests for specified hostnames */
+void
+add_requests(void)
+{
+    int nreqs_base = nreqs;
+
+    char *host;
+    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. */
+    int ret;
+    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 */
+void
+wait_requests(void)
+{
+    /* NULL elements are ignored by gai_suspend(). */
+    struct gaicb const **wait_reqs = calloc(nreqs, sizeof(*wait_reqs));
+
+    char *id;
+    while ((id = strtok(NULL, " "))) {
+        wait_reqs[atoi(id)] = reqs[atoi(id)];
+    }
+
+    int ret = gai_suspend(wait_reqs, nreqs, NULL);
+    if (ret) {
+        printf("gai_suspend(): %s\\n", gai_strerror(ret));
+        return;
+    }
+
+    int i;
+    for (i = 0; i < nreqs; i++) {
+        if (!wait_reqs[i])
+            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 */
+void
+cancel_requests(void)
+{
+    char *id;
+    while ((id = strtok(NULL, " "))) {
+        int ret = gai_cancel(reqs[atoi(id)]);
+        printf("[%s] %s: %s\\n", id, reqs[atoi(id)]->ar_name,
+               gai_strerror(ret));
+    }
+}
+
+/** List all requests */
+void
+list_requests(void)
+{
+    int i;
+    for (i = 0; i < nreqs; i++) {
+        printf("[%02d] %s: ", i, reqs[i]->ar_name);
+        int ret = gai_error(reqs[i]);
+        if (!ret) {
+            char host[NI_MAXHOST];
+            struct addrinfo *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));
+        }
+    }
+}
+
+int
+main(int argc, char *argv[])
+{
+    char *cmdline;
+
+    while ((cmdline = getcmd())) {
+        char *cmd = strtok(cmdline, " ");
+        if (!cmd) {
+            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;
+        }
+    }
+    exit(EXIT_SUCCESS);
+}
+.fi
+.SH "SEE ALSO"
+.BR getaddrinfo (3),
+.BR inet (3),
+.BR lio_listio (3),
+.BR hostname (7),
+.BR ip (7)
diff --git a/man3/strtok.3 b/man3/strtok.3
index dde40d8..c55e397 100644
--- a/man3/strtok.3
+++ b/man3/strtok.3
@@ -193,6 +193,11 @@ main(int argc, char *argv[])
     exit(EXIT_SUCCESS);
 } /* main */
 .fi
+.PP
+Another example program using
+.BR strtok ()
+is shown in the manual page of
+.BR getaddrinfo_a (3).
 .SH "SEE ALSO"
 .BR index (3),
 .BR memchr (3),
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Re: [PATCH] man3/getaddrinfo_a.3: New manual page

[Petr Baudis]

On Wed, Apr 22, 2009 at 02:53:15AM +0200, Petr Baudis wrote:
> This patch adds original documentation for the getaddrinfo_a(3)
> glibc function and the associated suite of gai_suspend(3),
> gai_error(3) and gai_cancel(3), including two example programs.
> 
> The notification facility is not demonstrated in the interactive
> frontend since I judged the would-be extra machinery as too
> obscuring (and producing potentially messy results if using
> signal notification). Maybe a third pthread example would be due?
> 
> Please review and comment.
> 
> Signed-off-by: Petr Baudis <pasky-AlSwsSmVLrQ@public.gmane.org>

Ping...

Maybe just commit if you don't have time to review and let possible
bugreports flow in...?

				Petr "Pasky" Baudis
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Re: [PATCH] man3/getaddrinfo_a.3: New manual page

[Petr Baudis]

On Sun, Sep 20, 2009 at 05:05:46PM +0200, Petr Baudis wrote:
> On Wed, Apr 22, 2009 at 02:53:15AM +0200, Petr Baudis wrote:
> > This patch adds original documentation for the getaddrinfo_a(3)
> > glibc function and the associated suite of gai_suspend(3),
> > gai_error(3) and gai_cancel(3), including two example programs.
> > 
> > The notification facility is not demonstrated in the interactive
> > frontend since I judged the would-be extra machinery as too
> > obscuring (and producing potentially messy results if using
> > signal notification). Maybe a third pthread example would be due?
> > 
> > Please review and comment.
> > 
> > Signed-off-by: Petr Baudis <pasky-AlSwsSmVLrQ@public.gmane.org>
> 
> Ping...
> 
> Maybe just commit if you don't have time to review and let possible
> bugreports flow in...?

Ping...

-- 
				Petr "Pasky" Baudis
A great many people think they are thinking when they are merely
rearranging their prejudices. -- William James
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Re: [PATCH] man3/getaddrinfo_a.3: New manual page

[Michael Kerrisk]

Hello Petr,

Again, apologies for the long delay in processing this mail...

On Wed, Apr 22, 2009 at 2:53 AM, Petr Baudis <pasky-AlSwsSmVLrQ@public.gmane.org> wrote:
> This patch adds original documentation for the getaddrinfo_a(3)
> glibc function and the associated suite of gai_suspend(3),
> gai_error(3) and gai_cancel(3), including two example programs.
>
> The notification facility is not demonstrated in the interactive
> frontend since I judged the would-be extra machinery as too
> obscuring (and producing potentially messy results if using
> signal notification). Maybe a third pthread example would be due?

I've made various language tweaks, added a few pieces (sigevent), and
added made some tweaks to your example programs (changed some idioms
to be more consistent with existing examples, added error checking in
a few places). Could you please review the version below? Also, you
could double check the new versions of the programs: I tested them,
and they seemed to work okay, but an independent check would be good.

I've also applied the various other changes in this patch, and you can
find them in the current git. They;ll be released with man-pages-3.28.
And, of course, thank you for documenting this API!

Thanks,

Michael


.\" Copyright (c) 2009 Petr Baudis <pasky-AlSwsSmVLrQ@public.gmane.org>
.\" and clean-ups and additions (C) 2010 Michael Kerrisk
<mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" References: http://people.redhat.com/drepper/asynchnl.pdf,
.\"     http://www.imperialviolet.org/2005/06/01/asynchronous-dns-lookups-with-glibc.html
.\"
.TH GETADDRINFO_A 3 2010-09-27 "GNU" "Linux Programmer's Manual"
.SH NAME
getaddrinfo_a, gai_suspend, gai_error, gai_cancel \- asynchronous
network address and service translation
.SH SYNOPSIS
.nf
.B #define _GNU_SOURCE
.B #include <netdb.h>
.sp
.BI "int getaddrinfo_a(int " "mode" ", struct gaicb *" "list[]" ,
.BI "                int " "nitems" ", struct sigevent *" "sevp" );
.sp
.BI "int gai_suspend(struct gaicb *" "list[]" ", int " "nitems" ,
.BI "                struct timespec *" "timeout" );
.sp
.BI "int gai_error(struct gaicb *" "req" );
.sp
.BI "int gai_cancel(struct gaicb *" "req" );
.sp
Link with \fI\-lanl\fP.
.fi
.SH DESCRIPTION
The
.BR getaddrinfo_a ()
function performs the same task as
.BR getaddrinfo (3),
but allows multiple name look-ups to be performed asynchronously,
with optional notification on completion of look-up operations.

The
.I mode
argument has one of the following values:
.TP
.B GAI_WAIT
Perform the look-ups synchronously;
the call blocks until the look-ups have completed.
.TP
.B GAI_NOWAIT
Perform the look-ups asynchronously.
The call returns immediately,
and the requests are resolved in the background.
See the discussion of the
.I sevp
argument below.
.PP
The array
.I list
specifies the look-up requests to process.
The
.I nitems
argument specifies the number of elements in
.IR list .
The requested look-up operations are started in parallel.
NULL elements in
.I list
are ignored.
Each request is described by a
.I gaicb
structure, defined as follows:
.sp
.in +4n
.nf
struct gaicb {
    const char            *ar_name;
    const char            *ar_service;
    const struct addrinfo *ar_request;
    struct addrinfo       *ar_result;
};
.fi
.in

The elements of this structure correspond to the arguments of
.BR getaddrinfo (3).
Thus,
.I ar_name
corresponds to the
.I node
argument and
.I ar_service
to the
.I service
argument, identifying an Internet host and a service.
The
.I ar_request
element corresponds to the
.I hints
argument, specifying the criteria for selecting
the returned socket address structures.
Finally,
.I ar_result
corresponds to the
.I res
argument; you do not need to initialize this element,
it will be automatically set when the request
is resolved.
The
.I addrinfo
structure referenced by the last two elements is described in
.BR getaddrinfo (3).

When
.I mode
is specified as
.BR GAI_NOWAIT,
notifications about resolved requests
can be obtained by employing the
.I sigevent
structure pointed to by the
.I sevp
argument.
For the definition and general details of this structure, see
.BR sigevent (7).
The
.I sevp\->sigev_notify
field can have the following values:
.TP
.BR SIGEV_NONE
Don't provide any notification.
.TP
.BR SIGEV_SIGNAL
When a look-up completes, generate the signal
.I sigev_signo
for the process.
See
.BR sigevent (7)
for general details.
The
.I si_code
field of the
.I siginfo_t
structure will be set to
.BR SI_ASYNCNL .
.\" si_pid and si_uid are also set, to the values of the calling process,
.\" which doesn't provide useful information, so we'll skip mentioning it.
.TP
.BR SIGEV_THREAD
When a look-up completes, invoke
.I sigev_notify_function
as if it were the start function of a new thread.
See
.BR sigevent (7)
for details.
.PP
For
.BR SIGEV_SIGNAL
and
.BR SIGEV_THREAD ,
it may be useful to point
.IR sevp\->sigev_value.sival_ptr
to
.IR list .

The
.BR gai_suspend ()
function suspends execution of the calling thread,
waiting for the completion of one or more requests in the array
.ID list .
The
.I nitems
argument specifies the size of the array
.IR list .
The call blocks until one of the following occurs:
.IP * 3
One or more of the operations in
.I list
completes.
.IP *
The call is interrupted by a signal that is caught.
.IP *
The time interval specified in
.I timeout
elapses.
This argument specifies a timeout in seconds plus nanoseconds (see
.BR nanosleep (2)
for details of the
.I timespec
structure).
If
.I timeout
is NULL, then the call blocks indefinitely
(until one of the events above occurs).
.PP
No explicit indication of which request was completed is given;
you must determine which request(s) have completed by iterating with
.BR gai_error ()
over the list of requests.

The
.BR gai_error ()
function returns the status of the request
.IR req :
either
.B 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
.BR gai_cancel ()
function cancels the request
.IR req .
If the request has been canceled successfully,
the error status of the request will be set to
.B EAI_CANCELLED
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
.BR gai_cancel ()
has never been called.
If
.I req
is NULL, an attempt is made to cancel all outstanding requests
that the process has made.
.SH "RETURN VALUE"
The
.BR getaddrinfo_a ()
function returns 0 if all of the requests have been enqueued successfully,
or one of the following nonzero error codes:
.TP
.B 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.
.TP
.B EAI_MEMORY
Out of memory.
.TP
.B EAI_SYSTEM
.I mode
is invalid.
.PP
The
.BR 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:
.TP
.B EAI_AGAIN
The given timeout expired before any of the requests could be completed.
.TP
.B EAI_ALLDONE
There were no actual requests given to the function.
.TP
.B 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.
.PP
The
.BR gai_error ()
function can return
.B 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
.BR getaddrinfo (3),
or the error code
.B EAI_CANCELLED
if the request has been canceled explicitly before it could be finished.

The
.BR gai_cancel ()
function can return one of these values:
.TP
.B EAI_CANCELLED
The request has been canceled successfully.
.TP
.B EAI_NOTCANCELLED
The request has not been canceled.
.TP
.B EAI_ALLDONE
The request has already completed.
.PP
The
.BR gai_strerror (3)
function translates these error codes to a human readable string,
suitable for error reporting.
.SH "CONFORMING TO"
These functions are GNU extensions;
they first appeared in glibc in version 2.2.3.
.SH NOTES
The interface of
.BR getaddrinfo_a ()
was modeled after the
.BR lio_listio (3)
interface.
.SH 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.
.SS Synchronous Example
The program below simply resolves several hostnames in parallel,
giving a speed-up compared to resolving the hostnames sequentially using
.BR getaddrinfo (3).
The program might be used like this:
.in +4n
.nf

$ \fB./a.out ftp.us.kernel.org enoent.linuxfoundation.org gnu.cz\fP
ftp.us.kernel.org: 128.30.2.36
enoent.linuxfoundation.org: Name or service not known
gnu.cz: 87.236.197.13
.fi
.in
.PP
Here is the program source code
.nf

#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);
}
.fi

.SS Asynchronous Example
This example shows a simple interactive
.BR getaddrinfo_a ()
front-end.
The notification facility is not demonstrated.
.PP
An example session might look like like this:
.in +4n
.nf

$ \fB./a.out\fP
> 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
.fi
.in
.PP
The program source goes as follows:

\&
.nf
#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] == \(aq\\n\(aq)
        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 \(aqa\(aq:
                add_requests();
                break;
            case \(aqw\(aq:
                wait_requests();
                break;
            case \(aqc\(aq:
                cancel_requests();
                break;
            case \(aql\(aq:
                list_requests();
                break;
            default:
                fprintf(stderr, "Bad command: %c\\n", cmd[0]);
                break;
            }
        }
    }
    exit(EXIT_SUCCESS);
}
.fi
.SH "SEE ALSO"
.BR getaddrinfo (3),
.BR inet (3),
.BR lio_listio (3),
.BR hostname (7),
.BR ip (7),
.BR sigevent (7)

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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