TIP #88 Version 1.1: Extend Tcl Process Id Control via 'pid'

This is not necessarily the current version of this TIP.

Abstract

This TIP proposes extended the [pid] command to provide more control over native processes in Tcl.

Rationale

Certain process control functions have shown themselves to be portable and of high usefulness to Tcl programmers. Most of these already exist in TclX, but simply requiring that extension isn't always acceptable. The [pid] command in Tcl is a command that is often overlooked, and so simple that it lends itself easily to being enhanced with new syntax. This TIP proposes adding subcommands to [pid] that extend the process control functionality of pure Tcl.

Specification

   pid ?fileId?
   pid id ?-uid uid? ?-gid gid? ?-parent parentId?
   pid kill ?-group bool? ?-signal signalType? fileIdOrPid ?fileIdOrPid ...?
   pid wait ?-nohang bool? ?-untraced bool? ?-group bool? ?fileIdOrPid?

The first line is the current definition for [pid], which is to return the name of the current process id, or that attached to a fileId (as returned by [open] or [socket]). I propose to add kill, id, and wait. These commands are adapted almost directly from TclX, but changed to work as a subcommand of [pid], with changes to the options to specify booleans to keep name/value option pairing. The [pid id] command would be for Unix only. The -parent option would be read-only (like -longname for [file attributes]).

Reference Implementation

Although TclX's current documentation denies it, the kill is already implemented for Windows as well as Unix, and wait has been available on both for a while. Macintosh implementations for OS 9 and below would need to be created, or the documentation would need to stress that these are not available there (OS X is Unix based).

File: tcl/mac/tclMacChan.c

File: tcl/unix/tclUnixPipe.c

File: tcl/win/tclWinPipe.c

Function: Tcl_PidObjCmd

Future Potential

What this also provides is a blueprint for future process management functions like these:

   pid nice ?-level niceLevel? fileIdOrPid
   pid list ?pattern?
   pid signal ...

[pid nice] is easy to implement, while [pid list] is very much platform sensitive. [pid signal] is of course another oft-requested feature for the core. These aren't to be addressed in this TIP, but are just ideas for the future.

Copyright

This document has been placed in the public domain.

This is not necessarily the current version of this TIP.