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man pages section 3: Basic Library Functions

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Updated: Friday, August 13, 2021
 
 

sendmmsg(3C)

Name

sendmmsg - send multiple messages from a socket

Synopsis

#include <sys/socket.h>

int sendmmsg(int s, struct mmsghdr *msgvec, unsigned int vlen,
	unsigned int flags);

Parameters

s

The socket descriptor. For more information, see the socket(3C) man page.

msgvec

Pointer to an array of mmsghdr structures

vlen

The number of elements in the array of mmsghdr structures

flags

Flags for sending as in the sendmsg(3C) function.

Description

The sendmmsg() function is an extension to the sendmsg(3C) function that allows the caller to transmit multiple messages on a socket in a single invocation.

A blocking sendmmsg() function call blocks until vlen messages have been sent.

A non-blocking call sends as many messages as possible, up to vlen, and returns immediately.

The mmsghdr structure is defined as:

struct mmsghdr {
    struct msghdr   msg_hdr;  /* Message header */
    ssize_t         msg_len;  /* Number of bytes transmitted */
};
msg_hdr

msghdr structure as described in socket.h(3HEAD)

msg_len

Is used to return the number of bytes sent from the message in msg_hdr. This is equivalent to the return value from a single sendmsg() function call.

The contents of the msghdr structure differ depending on whether or not __USE_SUNOS_SOCKETS__ is defined before including the <sys/socket.h> header. All source files accessing msghdr structures or calling the sendmmsg() function must be compiled with either __USE_SUNOS_SOCKETS__ defined or all with it undefined — mixing and matching will not work. See the socket.h(3HEAD) manual page for details.

Return Values

Upon successful completion, the sendmmsg() function returns the number of messages sent. The number of bytes sent is the arithmetic sum of the msg_len members of each mmsghdr structure.

The functions returns -1 if an error occurs and errno is set to indicate the error.

Errors

Errors are the same as per the sendmsg() function.

For more information, see the sendmsg(3C) man page.

Attributes

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
Async-Signal-Safe

See Also

fcntl(2), poll(2), recvmmsg(3C), select(3C), socket(3C), sendmsg(3C), socket.h(3HEAD), attributes(7)

History

The sendmmsg() function was added to Oracle Solaris in the 11.3 SRU 32 release.