- The title given to this article is incorrect due to technical limitations. The correct title is "fork".
A fork, when applied to computing is when a process creates a copy of itself, which then acts as a "child" of the original process, now called the "parent". More generally, a fork in a multithreading environment means that a thread of execution is duplicated.
Under Unix and Unix-like operating systems, the parent and the child operations are selected by use of the return value of fork().
Example
Here is some sample C programming language code to illustrate the idea of forking. The code that is in the "Child process" and "Parent process" sections are executed simultaneously.
int i, pid;
pid = fork();
if(pid == 0)
{
/* Child process:
* When fork() returns 0, we are in
* the child process.
* Here we count up to ten, one each second.
*/
int j;
for(j=0; j < 10; j++)
{
printf("child: %d\n", j);
sleep(1);
}
_exit(0); /* Note that we do not use exit() */
}
else if(pid > 0)
{
/* Parent process:
* Otherwise, we are in the parent process.
* Again we count up to ten.
*/
int i;
for(i=0; i < 10; i++)
{
printf("parent: %d\n", i);
sleep(1);
}
}
else
{
/* Error handling. */
fprintf(stderr, "couldn't fork");
exit(1);
}
This code will print out the following:
parent: 0
child: 0
child: 1
parent: 1
parent: 2
child: 2
child: 3
parent: 3
parent: 4
child: 4
child: 5
parent: 5
parent: 6
child: 6
child: 7
parent: 7
parent: 8
child: 8
child: 9
parent: 9
The order of each output is determined by the kernel.
See also
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