...
| Code Block | ||
|---|---|---|
| ||
char c;
int pid;
int fd = open(filename,O_RDWR,0);
if (fd == -1) {
/* Handle error */
}
read(fd,&c,1);
printf("root process:%c\n",c);
pid = fork();
if(pid == 0){/*child*/
read(fd,&c,1);
printf("child:%c\n",c);
}else{ /*parent*/
read(fd,&c,1);
printf("parent:%c\n",c);
}
|
...
| Code Block | ||
|---|---|---|
| ||
char c; int pid; int fd = open(filename,O_RDWR,0); if (fd == -1) { /* Handle error */ } read(fd,&c,1); printf("root process:%c\n",c); close(fd); pid = fork(); if(pid == 0){/*child*/ fd = open(filename,O_RDONLY,0); read(fd,&c,1); read(fd,&c,1); printf("child:%c\n",c); ; close(fd); }else{ /*parent*/ fd = open(filename,O_RDWR,0); read(fd,&c,1); read(fd,&c,1); printf("parent:%c\n",c); close(fd); } |
The output of this code is :
root process:a
child:b
parent:b
Because file descriptors access files in a sequential manner, the order in which the parent and child run can affect the order of access to the file, and because file descriptors are shared across multiple processes, this allows multiple processes to read/write from a file concurrently in a semi-random order.