key_t键和ftok()函数
* 消息队列、信号量和共享内存具有内核持续性(与具体进程周期不相关),故需要在内核用一个全局唯一的Key来标识。
* 这个Key的类型为整数key_t (#include<sys/types.h>),可以在代码写死,也可以用ftok()函数生成- 使用例子:
#include <stdio.h> #include <sys/types.h> #include <sys/ipc.h> int main() { const char *pMsgPath = "/data/home/andyawang/code/ipc/MsgQueue"; key_t key = ftok(pMsgPath, 1); printf("Key : %d\n", key); return 0; }
2个命令:ipcs和ipcrm
* ipcs用于显示当前内核这3种IPC的各种信息,ipcrm为删除
* 使用例子:
# ipcs ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0x00000000 0 root 666 12000 6 dest 0x00005fe7 32769 root 666 524288 2 0x00005fe8 65538 root 666 2097152 12 ------ Semaphore Arrays -------- key semid owner perms nsems 0x00008708 32769 root 666 1 0x000086f8 589826 root 666 1 ------ Message Queues -------- key msqid owner perms used-bytes messages 0x5ca04f5b 3473408 root 666 0 0
数据结构msqid_ds (#include<sys/msg.h>)
struct msqid_ds { struct msqid_ds { struct ipc_perm msg_perm; struct msg *msg_first; /* first message on queue,unused */ struct msg *msg_last; /* last message in queue,unused */ __kernel_time_t msg_stime; /* last msgsnd time */ __kernel_time_t msg_rtime; /* last msgrcv time */ __kernel_time_t msg_ctime; /* last change time */ unsigned long msg_lcbytes; /* Reuse junk fields for 32 bit */ unsigned long msg_lqbytes; /* ditto */ unsigned short msg_cbytes; /* current number of bytes on queue */ unsigned short msg_qnum; /* number of messages in queue */ unsigned short msg_qbytes; /* max number of bytes on queue */ __kernel_ipc_pid_t msg_lspid; /* pid of last msgsnd */ __kernel_ipc_pid_t msg_lrpid; /* last receive pid */ };
* 相关函数
#include <sys/ipc.h> #include <sys/msg.h> // 创建或打开一个消息队列 int msgget(key_t key, int msgflg); // 往消息队列发送消息 int msgsnd(int msqid, const void *msgp, size_t msgsz, int msgflg); // 往消息队列取出消息 ssize_t msgrcv(int msqid, void *msgp, size_t msgsz, long msgtyp, int msgflg); // 控制操作,如删除等 int msgctl ( int msgqid, int cmd, struct msqid_ds *buf );
* 使用例子:
[服务端:MsgQueSvr,cpp,循环 { 接收消息类型为1的消息之后,就发送消息类型为2的消息 } ]
#include <iostream> #include <string.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> using namespace std; const int MAXSIZE = 100; // 消息的数据结构: // * 最前必须有一个long来作为消息的类型,剩下的可自定义 struct SMsgUnit { long type; int len; char data[MAXSIZE]; }; int main() { struct SMsgUnit sMsg; key_t iKey; int iMsgId; // Get MsgQue Key const char *pMsgPath = "/data/home/andyawang/code/ipc/MsgQueue"; if ((iKey = ftok(pMsgPath, 1)) == -1) { cout << "Ftok Err" << endl; return -1; } // 1.msgget if ((iMsgId = msgget(iKey, IPC_CREAT|IPC_EXCL|0666)) == -1) { cout << "Msgget Err" << endl; return -1; } // 2.msgrcv & msgsnd for(int i = 0; i < 5; i ++) { msgrcv(iMsgId, &sMsg, sizeof(struct SMsgUnit), 1, 0); cout << "Svr Recv Msg, type=" << sMsg.type << ", len=" << sMsg.len << ", data=" << sMsg.data << endl; sMsg.type = 2; strcpy(sMsg.data, "I Am Svr.."); sMsg.len = strlen(sMsg.data); msgsnd(iMsgId, &sMsg, sizeof(struct SMsgUnit), 0); } // 3.msgctl if (msgctl(iMsgId, IPC_RMID, NULL) == -1) { cout << "Msgctl Err" << endl; return -1; } return 0; }[客户端:MsgQueCli.cpp,发送消息类型为1的消息之后,就接收消息类型为2的消息 ]
#include <iostream> #include <string.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> using namespace std; const int MAXSIZE = 100; struct SMsgUnit { long type; int len; char data[MAXSIZE]; }; int main() { struct SMsgUnit sMsg; key_t iKey; int iMsgId; // Get MsgQue Key const char *pMsgPath = "/data/home/andyawang/code/ipc/MsgQueue"; if ((iKey = ftok(pMsgPath, 1)) == -1) { cout << "Ftok Err" << endl; return -1; } // 1.msgget if ((iMsgId = msgget(iKey, IPC_CREAT|0666)) == -1) { cout << "Msgget Err" << endl; return -1; } // 2.msgsnd sMsg.type = 1; strcpy(sMsg.data, "I Am Cli.."); sMsg.len = strlen(sMsg.data); msgsnd(iMsgId, &sMsg, sizeof(struct SMsgUnit), 0); // 3.msgrcv msgrcv(iMsgId, &sMsg, sizeof(struct SMsgUnit), 2, 0); cout << "Cli Recv Msg, type=" << sMsg.type << ", len=" << sMsg.len << ", data=" << sMsg.data << endl; return 0; }