1 申请Key
2打开/创建消息队列 msgget
3向消息队列发送消息 msgsnd
1打开/创建消息队列 msgget
2从消息队列接收消息 msgrcv
3 控制(删除)消息队列 msgctl
#include
#include
int msgget(key_t key, int msgflg);
成功时返回消息队列的id,失败时返回EOF
key 和消息队列关联的key IPC_PRIVATE 或 ftok
msgflg 标志位 IPC_CREAT|0666
#include
#include
int msgsnd(int msgid, const void *msgp, size_t size, int msgflg);
成功时返回0,失败时返回-1
msgid 消息队列id
msgp 消息缓冲区地址
size 消息正文长度
msgflg 标志位 0 或 IPC_NOWAIT
typedef struct{
long msg_type;
char buf[128];
}msgT;
#include
#include
int msgrcv(int msgid, void *msgp, size_t size, long msgtype,int msgflg);
成功时返回收到的消息长度,失败时返回-1
msgid 消息队列id
msgp 消息缓冲区地址
size 指定接收的消息长度
msgtype 指定接收的消息类型
- msgtype=0:收到的第一条消息,任意类型。
- msgtype>0:收到的第一条 msg_type类型的消息。
- msgtype<0:接收类型等于或者小于msgtype绝对值的第一个消息。
例子:如果msgtype=-4,只接受类型是1、2、3、4的消息
msgflg 标志位 0 或 IPC_NOWAIT
- 0:阻塞式接收消息
- IPC_NOWAIT:如果没有返回条件的消息调用立即返回,此时错误码为ENOMSG
- MSG_EXCEPT:与msgtype配合使用返回队列中第一个类型不为msgtype的消息
#include
#include
int msgctl(int msgid, int cmd, struct msqid_ds *buf);
成功时返回0,失败时返回-1
msgid 消息队列id
cmd 要执行的操作 IPC_STAT / IPC_SET / IPC_RMID
buf 存放消息队列属性的地址
发送数据-msgsnd.c
#include
#include
#include
#include
typedef struct{
long msg_type;
char buf[128];
}msgT;
#define MSGLEN (sizeof(msgT)-sizeof(long))
int main(){
key_t key;
int msgid;
int ret;
msgT msg;
key = ftok(".",100);
if(key<0){
perror("ftok");
return 0;
}
msgid = msgget(key,IPC_CREAT|0666);
if(msgid<0){
perror("msgget");
return 0;
}
msg.msg_type = 1;
strcpy(msg.buf,"this msg type 1");
ret = msgsnd(msgid,&msg,MSGLEN,0);
if(ret<0){
perror("msgsnd");
return 0;
}
msg.msg_type = 2;
strcpy(msg.buf,"this msg type 2");
ret = msgsnd(msgid,&msg,MSGLEN,0);
if(ret<0){
perror("msgsnd");
return 0;
}
msg.msg_type = 3;
strcpy(msg.buf,"this msg type 3");
ret = msgsnd(msgid,&msg,MSGLEN,0);
if(ret<0){
perror("msgsnd");
return 0;
}
msg.msg_type = 4;
strcpy(msg.buf,"this msg type 4");
ret = msgsnd(msgid,&msg,MSGLEN,0);
if(ret<0){
perror("msgsnd");
return 0;
}
msg.msg_type = 5;
strcpy(msg.buf,"this msg type 5");
ret = msgsnd(msgid,&msg,MSGLEN,0);
if(ret<0){
perror("msgsnd");
return 0;
}
}
接收数据-msgrcv.c
#include
#include
#include
#include
typedef struct{
long msg_type;
char buf[128];
}msgT;
#define MSGLEN (sizeof(msgT)-sizeof(long))
int main(){
int msgid;
key_t key;
msgT msg;
int ret;
key = ftok(".",100);
if(key<0){
perror("ftok");
return 0;
}
msgid = msgget(key,IPC_CREAT|0666);
if(msgid<0){
perror("msgget");
return 0;
}
int count=0;
while(1){
ret = msgrcv(msgid,&msg,MSGLEN,0,0);
if(ret<0){
perror("msgrcv");
return 0;
}
count++;
if(count>3){
break;
}
printf("receiv msg type=%d,buf=%s\n",(int)msg.msg_type,msg.buf);
}
ret = msgctl(msgid,IPC_RMID,NULL);
if(ret<0){
perror("msgctl");
return 0;
}
}
概念:是不同进程间或一个给定进程内部不同线程间同步的机制。类似我们的
PV操作概念:生产者和消费者场景
P(S) 含义如下:
if (信号量的值大于0)
{
申请资源的任务继续运行;
信号量的值减一;
}
else
{
申请资源的任务阻塞;
}
V(S) 含义如下:
信号量的值加一;
if (有任务在等待资源)
{
唤醒等待的任务,让其继续运行
}
sem_t *sem_open(const char *name, int oflag);
sem_t *sem_open(const char *name, int oflag,mode_t mode, unsigned int value);
参数:
name:name是给信号灯起的名字
oflag:打开方式,常用O_CREAT
mode:文件权限。常用0666
value:信号量值。二元信号灯值为1,普通表示资源数目
#include
int sem_wait(sem_t *sem); P操作
int sem_post(sem_t *sem); V操作
成功时返回0,失败时返回EOF
sem 指向要操作的信号量对象
信号灯文件位置:
/dev/shm
有名信号灯关闭
int sem_close(sem_t *sem);
有名信号灯的删除
int sem_unlink(const char* name);
sem_w.c
#include /* For O_* constants */
#include /* For mode constants */
#include
#include
#include
#include
#include
#include
#include
void delsemfile(int sig){
sem_unlink("mysem_w");
exit(0);
}
int main(){
sem_t *sem_r,*sem_w;
key_t key;
int shmid;
char *shmaddr;
struct sigaction act;
act.sa_handler = delsemfile;
act.sa_flags = 0;
sigemptyset(&act.sa_mask);
sigaction(SIGINT,&act,NULL);
key = ftok(".",100);
if(key<0){
perror("ftok");
return 0;
}
shmid = shmget(key,500,0666|IPC_CREAT);
if(shmid<0){
perror("shmget");
return 0;
}
shmaddr = shmat(shmid,NULL,0);
sem_r = sem_open("mysem_r",O_CREAT|O_RDWR,0666,0);
sem_w = sem_open("mysem_w",O_CREAT|O_RDWR,0666,1);
while(1){
sem_wait(sem_w);
printf(">");
fgets(shmaddr,500,stdin);
sem_post(sem_r);
}
}
sem_r.cr
#include /* For O_* constants */
#include /* For mode constants */
#include
#include
#include
#include
#include
#include
#include
void delsemfile(int sig){
sem_unlink("mysem_r");
exit(0);
}
int main(){
sem_t *sem_r,*sem_w;
key_t key;
int shmid;
char *shmaddr;
struct sigaction act;
act.sa_handler = delsemfile;
act.sa_flags = 0;
sigemptyset(&act.sa_mask);
sigaction(SIGINT,&act,NULL);
key = ftok(".",100);
if(key<0){
perror("ftok");
return 0;
}
shmid = shmget(key,500,0666|IPC_CREAT);
if(shmid<0){
perror("shmget");
return 0;
}
shmaddr = shmat(shmid,NULL,0);
sem_r = sem_open("mysem_r",O_CREAT|O_RDWR,0666,0);
sem_w = sem_open("mysem_w",O_CREAT|O_RDWR,0666,1);
while(1){
sem_wait(sem_r);
printf("%s\n",shmaddr);
sem_post(sem_w);
}
}
#include
int sem_init(sem_t *sem, int pshared, unsigned int val);
成功时返回0,失败时EOF
sem 指向要初始化的信号量对象
pshared 0 – 线程间 1 – 进程间
val 信号量初值
int sem_destroy(sem_t* sem);
#include /* For O_* constants */
#include /* For mode constants */
#include
#include
#include
#include
#include
#include
#include
#include
sem_t sem_r,sem_w;
char *shmaddr;
void destroysem(int sig){
// sem_unlink("mysem_w");
sem_destroy(&sem_r);
sem_destroy(&sem_w);
exit(0);
}
void *readmem(void *arg){
while(1){
sem_wait(&sem_r);
printf("%s\n",shmaddr);
sem_post(&sem_w);
}
}
int main(){
key_t key;
int shmid;
struct sigaction act;
act.sa_handler = destroysem;
act.sa_flags = 0;
sigemptyset(&act.sa_mask);
sigaction(SIGINT,&act,NULL);
key = ftok(".",100);
if(key<0){
perror("ftok");
return 0;
}
shmid = shmget(key,500,0666|IPC_CREAT);
if(shmid<0){
perror("shmget");
return 0;
}
shmaddr = shmat(shmid,NULL,0);
// sem_r = sem_open("mysem_r",O_CREAT|O_RDWR,0666,0);
// sem_w = sem_open("mysem_w",O_CREAT|O_RDWR,0666,1);
sem_init(&sem_r,0,0);
sem_init(&sem_w,0,1);
pthread_t tid;
pthread_create(&tid,NULL,readmem,NULL);
while(1){
sem_wait(&sem_w);
printf(">");
fgets(shmaddr,500,stdin);
sem_post(&sem_r);
}
}
信号灯也叫信号量,用于进程/线程同步或互斥的机制
#include
#include
int semget(key_t key, int nsems, int semflg);
成功时返回信号灯的id,失败时返回-1
key 和消息队列关联的key IPC_PRIVATE 或 ftok
nsems 集合中包含的计数信号灯个数
semflg 标志位 IPC_CREAT|0666 IPC_EXCL
#include
#include
int semctl(int semid, int semnum, int cmd, …);
成功时返回0,失败时返回EOF
semid 要操作的信号灯集id
semnum 要操作的集合中的信号灯编号
cmd 执行的操作 SETVAL IPC_RMID
union semun 取决于cmd
#include
#include
int semop(int semid, struct sembuf *sops, unsigned nsops);
成功时返回0,失败时返回-1
semid 要操作的信号灯集id
sops 描述对信号灯操作的结构体(数组)
nsops 要操作的信号灯的个数
struct sembuf
{
short sem_num;
short sem_op;
short sem_flg;
};
semnum 信号灯编号
sem_op -1:P操作 1:V操作
sem_flg 0 / IPC_NOWAIT
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define SEM_READ 0
#define SEM_WRITE 1
union semun {
int val;
};
void Poperation(int semid,int semindex){
struct sembuf sbuf;
sbuf.sem_num = semindex;
sbuf.sem_op = -1;
sbuf.sem_flg = 0;
semop(semid,&sbuf,1);
}
void Voperation(int semid,int semindex){
struct sembuf sbuf;
sbuf.sem_num = semindex;
sbuf.sem_op = 1;
sbuf.sem_flg = 0;
semop(semid,&sbuf,1);
}
int main(){
key_t key;
char *shmaddr;
int semid,shmid;
key = ftok(".",100);
if(key<0){
perror("ftok");
return 0;
}
semid = semget(key,2,IPC_CREAT |0666);
if(semid<0){
perror("semget");
return 0;
}
shmid = shmget(key,500,IPC_CREAT |0666);
shmaddr = shmat(shmid,NULL,0);
union semun mysem;
mysem.val = 0;
semctl(semid,SEM_READ,SETVAL,mysem);
mysem.val = 1;
semctl(semid,SEM_WRITE,SETVAL,mysem);
pid_t pid;
pid = fork();
if(pid<0){
perror("fork");
shmctl(shmid,IPC_RMID,NULL);
semctl(semid,0,IPC_RMID);
exit(-1);
}else if(pid == 0){
while(1){
Poperation(semid,SEM_READ);
printf("%s\n",shmaddr);
Voperation(semid,SEM_WRITE);
}
}else{
while(1){
Poperation(semid,SEM_WRITE);
printf(">");
fgets(shmaddr,32,stdin);
Voperation(semid,SEM_READ);
}
}
}