在内存映射文件中给计数器＋1

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#include <stdio.h> #include <fcntl.h> #include <errno.h> #include <string.h> #include <semaphore.h> #include <stdlib.h> #include <sys/mman.h>   #define SEM_NAME "mysem"   const int maxline=4096;   int main(int argc, char **argv) {     int fd, i, nloop, zero=0;     int *ptr;     sem_t *mutex;     char errbuff[maxline];       if(argc!=3) {         fprintf(stderr, "usage: ./a.out <pathname> <#nloops>\n");         exit(-1);     }       nloop=atoi(argv[2]);       fd=open(argv[1], O_RDWR|O_CREAT, 0644);     if(write(fd, &zero, sizeof(int)) != sizeof(int)) {         fprintf(stderr, "write error.\n");         exit(-1);     }       if((ptr=mmap(NULL, sizeof(int), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0))==MAP_FAILED) {         fprintf(stderr, "mmap error.\n");         exit(-1);     }     close(fd);       if((mutex=sem_open(SEM_NAME, O_CREAT|O_EXCL, 0644, 1))==SEM_FAILED) {         strerror_r(errno, errbuff, maxline);         fprintf(stderr, "sem_open error: %s\n", errbuff);         exit(-1);     }     sem_unlink(SEM_NAME);       setbuf(stdout, NULL);       if(fork()==0) {         for(i=0;i<nloop;i++) {             sem_wait(mutex);             printf("child: %d\n", (*ptr)++);             sem_post(mutex);         }         exit(0);     }       for(i=0;i<nloop;i++) {         sem_wait(mutex);         printf("parent: %d\n", (*ptr)++);         sem_post(mutex);     }     exit(0); }

运行结果如下：

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$ gcc  incr2.c -pthread $ ./a.out tmp 5 parent: 0 parent: 1 parent: 2 child: 3 child: 4 child: 5 child: 6 parent: 7 parent: 8 child: 9