Fork Unix
| Depends on | Processes |
|---|
fork() is the means by which a Unix process creates another
process. It is a system call which is called once but
returns twice – once in the calling process and again in a nearly
identical copy of that code (but in a separate process). It is then
usual to break this symmetry – which can be done by checking the
value returned by the fork() – and have one process evolve to run a
different program.
A typical example (in C) might look roughly like this:
new_PID = fork();
if (new_PID == -1) exit(1); // Error case
if (new_PID != 0) // This is the parent process
{
... // Record the child PID for later reference
}
else // (new_PID == 0) This is the child process
exec(<arguments>) // Load and execute other code
Here, exec() is representative of a number of variant calls.
The example above neglects any details about resynchronising and
terminating processes, which is discussed elsewhere. Here it is
sufficient to note that the parent can record the child’s PID on
creation (it may have several child processes) and the child can find
its parent (it can only have one!) as ppid.
This topic is part of this exercise.
