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recvmmsg.2: Add an example program 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Elie De Brauwer 2012-12-22 19:54:30 +01:00 committed by Michael Kerrisk
parent e3b419fae8
commit f2246260a9
1 changed files with 92 additions and 2 deletions
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man2/recvmmsg.2
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@ -21,8 +21,6 @@
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" FIXME: This page could be improved with an example program.
.\"
.TH RECVMMSG 2 2012-05-02 "Linux" "Linux Programmer's Manual"
.SH NAME
recvmmsg \- receive multiple messages on a socket
@ -165,6 +163,98 @@ Support in glibc was added in version 2.12.
.SH CONFORMING TO
.BR recvmmsg ()
is Linux-specific.
.SH EXAMPLE
.PP
The following program uses
.BR recvmmsg ()
to receive multiple messages on a socket and stores
them in multiple buffers.
The call returns if all buffers are filled or if the
timeout specified is expired.
The following snippet periodically generates UDP datagrams
containing a random number:
.in +4n
.nf
.RB "$" " while true; do echo $RANDOM > /dev/udp/127.0.0.1/1234; sleep 0.25; done"
.fi
.in
These datagrams are read by the example application which
can give the following output:
.in +4n
.nf
.RB "$" " ./a.out"
5 messages received
1 11782
2 11345
3 304
4 13514
5 28421
.fi
.in
.SS Program source
\&
.nf
#define _GNU_SOURCE
#include <netinet/ip.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
int
main()
{
#define VLEN 10
#define BUFSIZE 200
#define TIMEOUT 1
int sockfd, retval, i;
struct sockaddr_in sa;
struct mmsghdr msgs[VLEN];
struct iovec iovecs[VLEN];
char bufs[VLEN][BUFSIZE+1];
struct timespec timeout;
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd == \-1) {
perror("socket()");
exit(EXIT_FAILURE);
}
sa.sin_family = AF_INET;
sa.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
sa.sin_port = htons(1234);
if (bind(sockfd, (struct sockaddr *) &sa, sizeof(sa)) == \-1) {
perror("bind()");
exit(EXIT_FAILURE);
}
memset(msgs, 0, sizeof(msgs));
for (i = 0; i < VLEN; i++) {
iovecs[i].iov_base = bufs[i];
iovecs[i].iov_len = BUFSIZE;
msgs[i].msg_hdr.msg_iov = &iovecs[i];
msgs[i].msg_hdr.msg_iovlen = 1;
}
timeout.tv_sec = TIMEOUT;
timeout.tv_nsec = 0;
retval = recvmmsg(sockfd, msgs, VLEN, 0, &timeout);
if (retval == \-1) {
perror("recvmmsg()");
exit(EXIT_FAILURE);
}
printf("%d messages received\\n", retval);
for (i = 0; i < retval; i++) {
bufs[i][msgs[i].msg_len] = 0;
printf("%d %s", i+1, bufs[i]);
}
exit(EXIT_SUCCESS);
}
.fi
.SH SEE ALSO
.BR clock_gettime (2),
.BR recvmsg (2),