| recvmmsg() | |
|---|---|
| receive multiple messages on a socket | |
| #define _GNU_SOURCE #include 'sys/socket.h' int recvmmsg (int sockfd, struct mmsghdr *msgvec, unsigned_int vlen , unsigned int flags , struct timespec *timeout ); |
The recvmmsg() system call is an extension of recvmsg(2) that allows the caller to receive multiple messages from a socket using a single system call. (This has performance benefits for some applications.) A further extension over recvmsg(2) is support for a timeout on the receive operation.
The sockfd argument is the file descriptor of the socket to receive data from.
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 recvmsg(2). The msg_len field is the number of bytes returned for the message in the entry. This field has the same value as the return value of a single recvmsg(2) on the header.
The flags argument contains flags ORed together. The flags are the same as documented for recvmsg(2), with the following addition:
The timeout argument points to a struct timespec (see clock_gettime(2)) defining a timeout (seconds plus nanoseconds) for the receive operation. (This interval will be rounded up to the system clock granularity, and kernel scheduling delays mean that the blocking interval may overrun by a small amount.) If timeout is NULL then the operation blocks indefinitely.
A blocking recvmmsg() call blocks until vlen messages have been received or until the timeout expires. A nonblocking call reads as many messages as are available (up to the limit specified by vlen) and returns immediately.
On return from recvmmsg(), successive elements of msgvec are updated to contain information about each received message: msg_len con‐ tains the size of the received message; the subfields of msg_hdr are updated as described in recvmsg(2). The return value of the call indicates the number of elements of msgvec that have been updated.
On success, recvmmsg() returns the number of messages received in msgvec; on error, -1 is returned, and errno is set to indicate the error.