信号量概要：http://www.kernel.org/doc/man-pages/online/pages/man7/sem_overview.7.html
以下实例通过信号量使两个无亲缘关系的进程进行同步通信
HOST:
#include <sys/mman.h>#include <sys/types.h>#include <fcntl.h>#include <unistd.h>#include <stdio.h>#include <string.h>#include <semaphore.h>#include <sys/stat.h>#include <sys/ipc.h>#define MAP_SHARED_FILE "./test"//共享内存映射的文件char SEM_NAME[]= "uart_test";//信号名称typedef struct{char name[4];int age;}people;int main(int argc, char** argv){int fd,i;people *p_map;char temp;sem_t *mutex; fd = open(MAP_SHARED_FILE, O_CREAT | O_RDWR | O_TRUNC, 777);if (fd < 0){perror("Open ");return 0;}/* 设置映射文件的大小，如果不设置的话第一次引用共享内存会产生SIGBUS错误 */if (lseek(fd, sizeof(people)*10 - 1, SEEK_SET) == -1){perror("lseek ");return 0;}if (write(fd, "", 1) != 1){perror("write ");return 0;} //create & initialize existing semaphore mutex = sem_open(SEM_NAME, O_CREAT, 0644, 0); if(mutex == SEM_FAILED) { perror("Create semaphore "); sem_unlink(SEM_NAME); return 0; } p_map = (people *)mmap(NULL, sizeof(people)*10, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);close(fd);//关闭文件描述符不会使内存映射I/O失效temp = 'a';for(i = 0; i < 10; i++){memcpy((*(p_map+i)).name, &temp, 1);(*(p_map+i)).age = 10 + i;printf("Write %c\n", temp);temp++;sem_wait(mutex);//lock}sem_close(mutex);//close semaphoresem_unlink(SEM_NAME);//remove semaphore from systemmunmap(p_map, sizeof(people)*10);//解除映射区 return 0;}
CLIENT:
#include <sys/mman.h>#include <sys/types.h>#include <fcntl.h>#include <unistd.h>#include <stdio.h>#include <semaphore.h>#include <sys/stat.h>#include <sys/ipc.h>#define MAP_SHARED_FILE "./test" //共享内存映射的文件char SEM_NAME[]= "uart_test";typedef struct{char name[4];int age;}people;int main(int argc, char** argv){int fd,i;people *p_map;sem_t *mutex;fd = open(MAP_SHARED_FILE, O_CREAT | O_RDWR, 777);if (fd < 0){perror("Open ");return 0;}//create & initialize existing semaphore mutex = sem_open(SEM_NAME, 0, 0644, 0); if(mutex == SEM_FAILED) { perror("Execute semaphore "); sem_close(mutex); return 0; }p_map = (people*)mmap(NULL, sizeof(people)*10, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);for(i = 0; i < 10; i++){printf("name: %s age %d\n", (*(p_map+i)).name, (*(p_map+i)).age);sem_post(mutex);//unlocksleep(1);}sem_post(mutex);sem_close(mutex);munmap(p_map, sizeof(people)*10); return 0;}
编译时记得加 -lrt 参数！
莫找借口失败，只找理由成功。(不为失败找理由，要为成功找方法)
