Message Queue function, queue Function

Message Queue function, queue Function

1. Definition of Message Queue struct

Typedef struct {
Uid_t uid;/* owner's user id */
Gid_t gid;/* owner's group id */
Udi_t cuid;/* creator's user id */
Gid_t cgid;/* creator's group id */
Mode_t mode;/* read-write permissions 0400 MSG_R 0200 MSG_W */
Ulong_t seq;/* slot usage sequence number */
} Ipc_perm;

Typedef stuct {
Struct ipc_perm msg_perm;/* read_write perms */
Struct msg * msg_first;/* ptr to first message on queue */
Struct msg * msg_last;/* ptr to last message on queue */
Msglen_t msg_cbytes;/* used bytes current on queue */
Msgqnum_t msg_qnum;/* current num of message on queue */
Msglen_t msg_qbytes;/* max # of bytes allowed on queue */
Pid_t msg_lspid;/* pid of last msgsnd ()*/
Pid_t msg_lrpid;/* pid of last msgrcv ()*/
Time_t msg_stime;/* time of last msgsnd ()*/
Time_t msg_rtime;/* time of last msgrcv ()*/
Time_t msg_ctime;/* time of last msgctl ()*/
} Msqid_ds;

Typedef struct
{
Long mtype;
Char mbuf [MSGLEN];
} Message;

2. Create a message queue:

/*************************************** ************
Function:
Int msgget (ket_t key, int oflag );
Explain:
Create or view a message queue
Return:
A int indemo-
Include:
Sys/msg. h
Introduction:
Oflag: 0400 msg_r
0200 msg_w
0600 msg_wr
Ipc_creat: NO exist and then creat a queue
Exist: reference a queue
Ipc_creat | ipc_excl: NO exist and then creat a queue
Exist: return error
**************************************** ************/
# Include <stdio. h>
# Include <sys/msg. h>
# Include <stdlib. h>

Int MsgGet (int key)
{
Int ret;
Ret = msgget (key, 0600 | IPC_CREAT );
// Ret = msgget (key, 0600 | IPC_CREAT | IPC_EXCL );
If (ret <0)
Perror ("creat msgid error ");
Printf ("msgid = % d/n", ret );
System ("ipcs-q-I ret ");
Return ret;
}
Int main (int argc, char * agrv [])
{
Int key;
Printf ("pleasse input msgkey :");
Scanf ("% d", & key );
MsgGet (key );
Return 0;
}

3. Send the message msgsnd to the Message Queue

/*************************************** **************************************** ****
Function:
Int msgsnd (int msqid, const void * ptr, size_t length, int flag)
Explain:
Send a message to a queue
Return:
Len: send message len;
Include:
Sys/msg. h
Introduction:
Flag: 0: if queue full wait: 1> space for storing new messages
2> message queues identified by msqid are deleted from the system (EIDRM error is returned)
3> the call thread is interrupted by a captured signal (an EINTR error is returned)
IPC_NOWAIT: If there is no space to store new messages, the function returns immediately
1> the specified queue contains too many bytes.
2> too many messages exist in the system scope
**************************************** **************************************** *********/
# Include "typemsg. h"
Int MsgSnd (int msqid, char * buf, int len, int flag)
{
Int ret;
Ret = msgsnd (msqid, buf, len, flag );
If (ret <0)
Perror ("msgsnd error ");
System ("ipcs-q ");
Return ret;
}

Int main ()
{
Int msqid, len, stype;
Message msgb;
Memset (& msgb, 0, sizeof (Message ));
Printf ("msgsnd: please input msqid :");
Scanf ("% d", & msqid );
Printf ("please input msgtype :");
Scanf ("% d", & stype );
Msgb. mtype = stype;
Strcpy (msgb. mbuf, "zhangweia ");
MsgSnd (msqid, (char *) & msgb, sizeof (Message), 0 );
Return 0;
}

4. Get the message msgrcv from the queue

/*************************************** ******************************
Function:
Int msgrcv (int msqid, const void * ptr, size_t msglen, long type, int flag)
Explain:
Recv message order by type
Msgrcv error: Argument list too long --> the length of msglen is smaller than the length of the message in the message body.
Para:
Ptr: point to message struct
Msglen: the size of the Data Part in the buffer directed by ptr. This is the maximum data volume that the function can return.
Type: message type;

1> 0: return the earliest message in the queue.
2> greater than 0: return the first message of type in the message queue.
3> less than 0: return the first message of the smallest type in the message queue whose type is smaller than or equal to the absolute value of type.
Flag: 0 <wait> when there is no message or the message type does not match, the thread waits
Response: 1> A message of the requested type can be obtained.
2> the msqid message queue is deleted by the system and an EIDRM is returned.
3> the call thread is interrupted by a captured signal.
IPC_NOWAIT: If no data exists, an ENOMSG error is returned immediately.
MSGNOERROR: When the received message data is longer than msglen, the system obtains the truncated data. Otherwise, the E2BIG error is returned.
Return:
Message len
**************************************** *****************************/
# Include "typemsg. h"
Int MsgRcv (int msqid, char * buf, int msglen, long type, int flag)
{
Int ret;
Ret = msgrcv (msqid, buf, msglen, type, flag );
If (ret <0)
Perror ("msgrcv error ");
System ("ipcs-q ");
Return ret;

}

Int main ()
{
Int msqid, len;
Long ttype;
Message mbuf;
Printf ("msgrcv: please input recv msqid :");
Scanf ("% d", & msqid );
MsgRcv (msqid, (char *) & mbuf, 8900,0, IPC_NOWAIT );
Printf ("recv message = % s/n", mbuf. mbuf );
Put_String (unsigned char *) & mbuf, sizeof (Message ));
Return 0;
}

6. Message Queue control msgctl

/*************************************** *******************
Function:
Int msgctl (int msqid, int cmd, struct msqid_ds * buff)
Explain:
Cdm: IPC_RMID; delete msqid
IPC_SET:
IPC_STAT: return msqid stat

**************************************** *****************/
# Include "typemsg. h"
Int MsgCtl (int msqid, int cmd, struct msqid_ds * buff)
{
Int ret;
Ret = msgctl (msqid, cmd, buff );
If (ret <0)
{
Perror ("msgctl error ");
Return-1;
}
Return 0;
}

Int main ()
{
Int msqid, type;
Struct msqid_ds info;
Printf ("please input msqid/nand type (1: icp_rmid; 2: ipc_stat )");
Scanf ("% d", & msqid, & type );
If (type = 1)
{
MsgCtl (msqid, IPC_RMID, NULL );
Printf ("delete queue success: % d/n", msqid );
} Else if (type = 2)
{
MsgCtl (msqid, IPC_STAT, & info );
Printf ("get queue stat: % d/n", msqid );
}
Return 0;

}