12-21-2006
Position? It's a pipe.
I've thought of lots of applications for this idea, but the original one was a sort of temporary automatic buffer. One process produces data and writes it to the next, the next buffers it, the third reads from the buffer. When the buffer bottoms out, the process joins the input and output pipes together then quits.
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getpid(2) System Calls Manual getpid(2)
NAME
getpid(), getpgid(), getpgrp(), getpgrp2(), getppid() - get process, process group and parent process ID.
SYNOPSIS
DESCRIPTION
These functions return process, process group and parent process IDs, as follows:
Process group ID of the specified process.
If pid is zero, the call applies to the calling process. Same result as
Process group ID of the calling process.
Process group ID of the specified process.
If pid is zero, the call applies to the calling process. Same result as
Process ID of the calling process.
Parent process ID of the calling process.
If the parent process is the initialization process (known as the call returns 1.
Security Restrictions
The system call is subject to compartmental restrictions. See compartments(5) for more information about compartmentalization on systems
that support that feature.
Compartmental restrictions can be overridden if the process possesses the privilege (PRIV_COMMALLOWED). Processes owned by the superuser
may not have this privilege. Processes owned by any user may have this privilege, depending on system configuration. See privileges(5)
for more information about privileged access on systems that support fine-grained privileges.
RETURN VALUE
The functions return the following values:
Successful completion.
n is a nonnegative process ID, as described above.
Failure:
and only. is set to indicate the error.
ERRORS
If or fails, is set to one of the following values:
[EPERM] The current process and pid are not in the same session (see setsid(2)).
[ESRCH] No process can be found corresponding to that specified by pid.
AUTHOR
and were developed by HP, AT&T, and the University of California, Berkeley.
SEE ALSO
exec(2), fork(2), setpgid(2), setsid(2), signal(5).
STANDARDS CONFORMANCE
getpid(2)