| sendmmsg() | |
|---|---|
| send multiple messages on a socket | |
| #define _GNU_SOURCE #include 'sys/socket.h' sendmmsg (int sockfd, struct mmsghdr *msgvec, unsigned_int vlen , unsigned int flags ); |
The sendmmsg() system call is an extension of sendmsg(2) that allows the caller to transmit multiple messages on a socket using a sin‐ gle system call. (This has performance benefits for some applications.)
The sockfd argument is the file descriptor of the socket on which data is to be transmitted.
The msgvec argument is a pointer to an array of mmsghdr structures. The size of this array is specified in vlen.
The msg_hdr field is a msghdr structure, as described in sendmsg(2). The msg_len field is used to return the number of bytes sent from the message in msg_hdr (i.e., the same as the return value from a single sendmsg(2) call).
The flags argument contains flags ORed together. The flags are the same as for sendmsg(2).
A blocking sendmmsg() call blocks until vlen messages have been sent. A nonblocking call sends as many messages as possible (up to the limit specified by vlen) and returns immediately.
On return from sendmmsg(), the msg_len fields of successive elements of msgvec are updated to contain the number of bytes transmitted from the corresponding msg_hdr. The return value of the call indicates the number of elements of msgvec that have been updated.
On success, sendmmsg() returns the number of messages sent from msgvec; if this is less than vlen, the caller can retry with a further sendmmsg() call to send the remaining messages.
On error, -1 is returned, and errno is set to indicate the error.