有时候不小心开启同一个程序两次会造成意想不到的错误，下面介绍一种方法，可以防止出现这种情况，测试可用。
在程序中添加如下代码
1 #include <unistd.h> 2 #include <signal.h> 3 #include <sys/types.h> 4 #include <sys/stat.h> 5 #include <errno.h> 6 #include <fcntl.h> 7 #include <fstream> 8 9 10 #define PIDFILE "/daemon_shouhu.pid" //定义你自己的file名 11 #define write_lock(fd, offset, whence, len) \ 12 lock_reg(fd, F_SETLK, F_WRLCK, offset, whence, len) 13 14 int lock_reg(int fd, int cmd, int type, off_t offset, int whence, off_t len) 15 { 16 struct flock lock; 17 18 lock.l_type = type; /* F_RDLCK, F_WRLCK, F_UNLCK */ 19 lock.l_start = offset; /* byte offset, relative to l_whence */ 20 lock.l_whence = whence; /* SEEK_SET, SEEK_CUR, SEEK_END */ 21 lock.l_len = len; /* #bytes (0 means to EOF) */ 22 23 return( fcntl(fd, cmd, &lock) ); /* -1 upon error */ 24 } 25 26 27 28 int Check_Running() 29 { 30 int fd, val; 31 32 if ((fd = open(PIDFILE, O_WRONLY|O_CREAT, "at")) < 0) 33 { 34 printf(" Open file error \n"); 35 } 36 37 if (write_lock(fd, 0, SEEK_SET, 0) < 0) 38 { 39 if (errno == EACCES || errno == EAGAIN) 40 { 41 printf(" Server Already running! \n"); 42 _exit(-1); 43 return -1; 44 } 45 else 46 { 47 printf(" Write_lock error! \n"); 48 } 49 } 50 51 if (ftruncate(fd, 0) < 0) 52 { 53 printf(" ftruncate error \n"); 54 } 55 56 char buf[10] = {0}; 57 sprintf(buf, "%d\n", getpid()); 58 if (write(fd, buf, strlen(buf)) != (int)strlen(buf)) 59 printf(" Write error \n"); 60 61 if ((val = fcntl(fd, F_GETFD, 0)) < 0) 62 printf(" fcntl F_GETFD error \n"); 63 64 val |= FD_CLOEXEC; 65 if (fcntl(fd, F_SETFD, val) < 0) 66 printf(" fcntl F_SETFD error \n"); 67 68 return 0; 69 }
然后在程序入口添加Check_Running()就可以了，重新编译后执行，当第二次打开程序时会输出" Server Already running! "，第二个进程无法打开。
