Linux IPC System V 消息隊(duì)列

模型

#include #include #include ftok() //獲取key值 msgget() //創(chuàng)建/獲取消息隊(duì)列 msgsnd()/msgrcv() //發(fā)消息到消息隊(duì)列/從消息隊(duì)列收信息 msgctl() //刪除消息隊(duì)列

ftok()

//獲取key值, key值是System V IPC的標(biāo)識(shí)符，成功返回key，失敗返回-1設(shè)errno//同pathname+同 proj_id==>同key_t;key_t ftok(const char *pathname, int proj_id);

pathname?:文件名
proj_id: 1~255的一個(gè)數(shù)，表示project_id

key_t key=ftok(".",100); //“.”就是一個(gè)存在且可訪問的路徑, 100是假設(shè)的proj_id if(-1==key) perror("ftok"),exit(-1);

msgget()

//創(chuàng)建/獲取消息隊(duì)列，成功返回shmid，失敗返回-1int msgget(key_t key, int msgflg); //ATTENTION:用int msqid=msgget()比較好看

msgflg:具體的操作標(biāo)志

• IPC_CREAT?若不存在則創(chuàng)建, 需要在msgflg中＂|權(quán)限信息＂; 若存在則打開
• IPC_EXCL若存在則創(chuàng)建失敗
• 0?獲取已經(jīng)存在的消息隊(duì)列

消息隊(duì)列的容量由msg_qbytes控制，在消息隊(duì)列被創(chuàng)建的過程中，這個(gè)大小被初始化為MSGMNB，這個(gè)限制可以通過msgctl()修改

int msqid=msgget(key,IPC_CREAT|IPC_EXCL|0664);if(-1==msqid) perror("msgget"),exit(-1);

msgsnd()

//向指定的消息隊(duì)列發(fā)送指定的消息，如果消息隊(duì)列已經(jīng)滿了，默認(rèn)的行為是堵塞，直到隊(duì)列有空間容納新的消息，成功返回0,失敗返回-1設(shè)errnoint msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg);

msqid?msgget()返回的消息隊(duì)列的ID
msgp消息的的首地址, 消息的參考數(shù)據(jù)類型如下

struct msgbuf { long mtype; /* message type, must be > 0 */ //消息的類型 char mtext[1]; /* message data */ //消息的內(nèi)容};ATTENTION:The mtext field is an array (or other structure) whose size is specified by msgsz, a nonnegative integer value.

msgsz消息的大小, 該參數(shù)用于指定消息內(nèi)容的大小, 不包括消息的類型。只能sizeof(Msgbuf.mtext),不能sizeof(Msgbuf)
msgflg發(fā)送的標(biāo)志, 默認(rèn)給0即可

Msg msg1={1,"hello"};//消息的類型是1,內(nèi)容是helloint res=msgsnd(msqid,&msg2,sizeof(msg2.buf),0);if(-1==res) perror("msgsnd"),exit(-1);

msgrcv()

//向指定的消息隊(duì)列取出指定的消息，成功返回實(shí)際接受到的byte數(shù)，失敗返回-1設(shè)errnossize_t msgrcv(int msqid, void *msgp, size_t msgsz, long msgtyp, int msgflg);

msqid: 消息隊(duì)列的ID(returned by msgget)
msgp: 存放接收到消息的緩沖區(qū)首地址
msgsz: 消息的最大大小, 不包括消息的類型==>只能sizeof(Msgbuf.mtext),不能sizeof(Msgbuf)

• 如果消息的長(zhǎng)度>msgsz且msgflg里有MSG_NOERROR，則消息會(huì)被截?cái)?，被截?cái)嗟牟糠謺?huì)丟失
• 如果消息的長(zhǎng)度>msgsz且msgflg里沒有MSG_NOERROR，那么會(huì)出錯(cuò)，報(bào)E2BIG。

msgtyp: 消息的類型

• 0:讀取消息隊(duì)列中的第一個(gè)消息
• >0:讀取消息隊(duì)列中第一個(gè)type為msgtype的消息, 除非msg_flg里有MSG_EXCEPT，此時(shí)隊(duì)列中的第一個(gè)不是msgtyp的消息會(huì)被讀取
• <0讀取消息隊(duì)列中type<=|msgtype|的消息, 這里再優(yōu)先讀取最小的

msgflg: 發(fā)送的標(biāo)志, 默認(rèn)給0即可

Msg msg1;int res=msgrcv(msqid,&msg1,sizeof(msg1.buf),1,0);if(-1==res) perror("msgrcv"),exit(-1);

msgctl()

// 消息操作，成功返回0,失敗返回-1設(shè)errnoint msgctl(int msqid, int cmd, struct msqid_ds *buf);

msqid?:消息隊(duì)列的ID,由msgget()
buf?結(jié)構(gòu)體指針

struct msqid_ds { struct ipc_perm msg_perm; /* Ownership and permissions */ time_t msg_stime; /*Time of last msgsnd(2) */ time_t msg_rtime; /* Time of last msgrcv(2) */ time_t msg_ctime; /* Time of last change */ unsigned long __msg_cbytes; /* Current number of bytes in queue (nonstandard) */ msgqnum_t msg_qnum; /* Current number of messages in queue */ msglen_t msg_qbytes; /* Maximum number of bytes allowed in queue */ pid_t msg_lspid; /* PID of last msgsnd(2) */ pid_t msg_lrpid; /* PID of last msgrcv(2) */};struct ipc_perm { key_t __key; /* Key supplied to msgget(2) */ uid_t uid; /* Effective UID of owner */ gid_t gid; /* Effective GID of owner */ uid_t cuid; /* Effective UID of creator */ gid_t cgid; /* Effective GID of creator */ unsigned short mode; /* Permissions */ unsigned short __seq; /* Sequence number */};

cmd

• IPC_STAT從內(nèi)核相關(guān)結(jié)構(gòu)體中拷貝消息隊(duì)列相關(guān)的信息到buf指向的結(jié)構(gòu)體中
• IPC_SET把buf指向的結(jié)構(gòu)體的內(nèi)容寫入到內(nèi)核相關(guān)的結(jié)構(gòu)體中，同時(shí)更顯msg_ctimer成員，同時(shí)以下成員也會(huì)被更新：msg_qbytes, msg_perm.uid, msg_perm.gid, msg_perm.mode。調(diào)用隊(duì)列的進(jìn)程的effective UID必須匹配隊(duì)列所有者或創(chuàng)建者的msg_perm.uid或msg_perm.cuid或者該進(jìn)程擁有特權(quán)級(jí)別，
• IPC_RMID立即銷毀消息隊(duì)列，喚醒所有正在等待讀取或?qū)懭朐撓㈥?duì)列進(jìn)程，調(diào)用的進(jìn)程的UID必須匹配隊(duì)列所有者或創(chuàng)建者或者該進(jìn)程擁有足夠的特權(quán)級(jí)別

• IPC_INFO?(Linux-specific)返回整個(gè)系統(tǒng)對(duì)與消息隊(duì)列的限制信息到buf指向的結(jié)構(gòu)體中

  //_GNU_SOURCE//struct msginfo { int msgpool;/*Size in kibibytes of buffer pool used to hold message data; unused within kernel*/ int msgmap; /*Maximum number of entries in message map; unused within kernel*/ int msgmax; /*Maximum number of bytes that can be written in a single message*/ int msgmnb; /*Maximum number of bytes that can be written to queue; used to initialize msg_qbytes during queue creation*/ int msgmni; /*Maximum number of message queues*/ int msgssz; /*Message segment size; unused within kernel*/ int msgtql; /*Maximum number of messages on all queues in system; unused within kernel*/ unsigned short int msgseg; /*Maximum number of segments; unused within kernel*/};

  int res=msgctl(msqid,IPC_RMID,NULL);if(-1==res)perror("msgctl"),exit(-1);

例子

//Sys V IPC msg#include#include#include#include#includetypedef struct{ long mtype; //消息的類型 char buf[20]; //消息的內(nèi)容}Msg;int msqid; //使用全局變量,這樣就可以在fa中使用msqid了void fa(int signo){ printf("deleting..\n"); sleep(3); int res=msgctl(msqid,IPC_RMID,NULL); if(-1==res) perror("msgctl"),exit(-1); exit(0);}int main(){ //ftok() key_t key=ftok(".",150); if(-1==key) perror("ftok"),exit(-1); printf("key%#x\n",key); //msgget() msqid=msgget(key,IPC_CREAT|IPC_EXCL|0664); if(-1==msqid) perror("msgget"),exit(-1); printf("msqid%d\n",msqid); //msgsnd() Msg msg1={1,"hello"};//消息的類型是1,內(nèi)容是hello Msg msg2={2,"world"}; int res=msgsnd(msqid,&msg2,sizeof(msg2.buf),0); if(-1==res) perror("msgsnd"),exit(-1); res=msgsnd(msqid,&msg1,sizeof(msg1.buf),0); if(-1==res) perror("msgsnd"),exit(-1); //msgctl() //Ctrl+C delete msq printf("Press CTRL+C to delete msq\n"); if(SIG_ERR==signal(SIGINT,fa)) perror("signal"),exit(-1); while(1); return 0;}