msgsnd() -- send message to a queue

SYNOPSIS

#include <sys/msg.h>

int msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg);

DESCRIPTION

The msgsnd() function sends a message to the queue associated with message queue identifier msqid.

If the call completes successfully, the following actions are taken with respect to the data structure (msqid_ds) associated with msqid:

msg_qnum is incremented by 1.

msg_lspid is set to the process ID of the calling process.

msg_stime is set to the current time.

The argument msgp must point to a user-defined buffer that must contain first a field of type long int that specifies the type of the message, and then a data portion that holds the data bytes of the message. The following structure is an example of how a user-defined buffer might be declared:

struct mymsg {
	long int mtype;
	char mtext[1];
}

The structure member mtype is the message type, and the structure member mtext contains any text of length msgsz bytes. The argument msgsz can range from 0 to a system-imposed maximum.

PARAMETERS

msqid

Is a unique positive integer, created by msgget(), that identifies a message queue and its associated data structure.

msgp

Points to a user-defined buffer.

msgsz

Is the length of the message to be sent.

msgflg

Specifies the action to be taken if one or more of the following are true:

The number of bytes already on the queue is equal to msg_qbytes from the msqid_ds data structure.

The total number of messages on all queues system-wide is equal to the system-imposed limit.

If (msgflg & IPC_NOWAIT) is non-zero, the message is not sent and the calling process returns immediately. If (msgflg & IPC_NOWAIT) is zero, the calling process suspends execution until one of the following occurs:

The condition responsible for the suspension no longer exists, in which case the message is sent.

msqid is removed from the system. When this occurs, errno is set to EIDRM, and -1 is returned.

The calling process receives a signal that is to be caught. In this case, the message is not sent and the calling process resumes execution as appropriate for the signal.

RETURN VALUES

If successful, msgsnd() returns a value of zero. On failure, msgsnd() returns a value of -1 and sets errno to one of the following values:

EACCES

Operation permission is denied to the calling process.

EFAULT

msgp is an invalid pointer.

EIDRM

msqid was removed.

EINTR

A signal interrupted the call.

EINVAL

msgsz is less than 0 or greater than the system-imposed limit.

msqid is not a valid message queue identifier.

mtype is less than 1.

ENOMSG

The message cannot be sent and (msgflg & IPC_NOWAIT) is non-zero.

msgsnd()
send message to a queue

Function

SYNOPSIS

DESCRIPTION

PARAMETERS

RETURN VALUES

CONFORMANCE

MULTITHREAD SAFETY LEVEL

PORTING ISSUES

AVAILABILITY

SEE ALSO

msgsnd() send message to a queue

Function

msgsnd()
send message to a queue