有名信号量的创建

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#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <errno.h> #include <string.h> #include <fcntl.h> #include <semaphore.h>   const int maxline=4096;   int main(int argc, char **argv) {     int c, flags;     sem_t *sem;     unsigned int value;     char errbuff[maxline];       flags = O_RDWR | O_CREAT;     value=1;       while((c=getopt(argc, argv, "ei:"))!=-1) {         switch(c) {         case 'e':             flags|=O_EXCL;             break;         case 'i':             value=atoi(optarg);             break;         }     }           if(optind!=argc-1) {         fprintf(stderr, "usage: ./a.out [-e] [-i initalvalue] <name>.\n");         exit(-1);     }       if((sem=sem_open(argv[optind], flags, 0644, value))==SEM_FAILED) {         strerror_r(errno, errbuff, maxline);         fprintf(stderr, "sem_open error: %s\n", errbuff);         exit(-1);     }       sem_close(sem);       exit(0); }

查看创建结果：

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$ ./a.out jia $ cd /dev/shm/ $ ls -l total 4 -rw-r--r--. 1 dmin dmin 32 Oct 11 14:19 sem.jia

 获取信号量的值：

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#include <stdio.h> #include <stdlib.h> #include <semaphore.h>   int main(int argc, char **argv) {     sem_t *sem;     int val;       if(argc!=2) {         fprintf(stderr, "usage: ./a.out <name>.\n");         exit(-1);     }       sem=sem_open(argv[1], 0);     sem_getvalue(sem, &val);       printf("value=%d\n", val);       exit(0); }

结果如下：

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1 2	$ ./a.out jia value=1