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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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94
man2/recvmmsg.2
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@ -21,8 +21,6 @@
.\" Formatted or processed versions of this manual, if unaccompanied by .\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work. .\" 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" .TH RECVMMSG 2 2012-05-02 "Linux" "Linux Programmer's Manual"
.SH NAME .SH NAME
recvmmsg \- receive multiple messages on a socket recvmmsg \- receive multiple messages on a socket
@ -165,6 +163,98 @@ Support in glibc was added in version 2.12.
.SH CONFORMING TO .SH CONFORMING TO
.BR recvmmsg () .BR recvmmsg ()
is Linux-specific. 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 .SH SEE ALSO
.BR clock_gettime (2), .BR clock_gettime (2),
.BR recvmsg (2), .BR recvmsg (2),