p10-5.c

SUN Solaris8平台下进程间通信

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include "err_exit.h"
#include "filelock.h"
int main(void)
{
    int fd;
    off_t fdpos;
    /*打开文件 */
    if((fd = open("tempfile",O_RDWR|O_CREAT,0666)) < 0)
       err_exit("open error");
    /* 对文件尾及其之后的扩充部分置写锁 */
    if (WRITE_LOCK(fd,0,SEEK_END,0) == -1) 
       err_exit("WRITE_LOCK error");
    else
       printf("%d: call WRITE_LOCK(fd,0,SEEK_END,0) success\n",getpid());
    /* 定位文件位置于当前文件尾，并写入8个字符 */
    fdpos = lseek(fd,0L,SEEK_END);
    write(fd,"8 bytes.",8);               
    /* 企图释放前面设置的写锁，但实际并未释放，因为文件尾的位置已后移 */
    if (UN_LOCK(fd,0L,SEEK_END,0) == -1) 
       err_exit("UN_LOCK error");
    else
       printf("%d: call UN_LOCK(fd,0,SEEK_END,0) success\n",getpid());
    /* 让子进程在该区域设置读锁验证父进程是否已正确释放其写锁 */
    if (vfork()== 0){   /* 子进程 */
       if((fd = open("tempfile",O_RDWR|O_CREAT,0666)) < 0)
          err_exit("open error");
        /* 对整个文件读置锁，不能设置读锁表明父进程有锁区域未释放 */
       if (READ_LOCK(fd, 0,SEEK_SET,0) == -1)
          printf("%d: READ_LOCK failed \n",getpid());
       else
          printf("%d: READ_LOCK success\n",getpid());
       exit(0);
    }
    /* 父进程 */
    sleep(10);       /* 保证父进程后退出 */
    exit(0);
}