TIP:		335
Title:		An API for Detecting Active Interpreters
Version:	$Revision: 1.8 $
Author:		Joe Mistachkin <joe@mistachkin.com>
State:		Final
Type:		Project
Vote:		Done
Created:	13-Oct-2008
Keywords:	numLevels,embedding,terminate,async,thread,safe,gc
Tcl-Version:	8.6
Post-History:	

~ Abstract

This TIP introduces the ability to quickly and safely decide whether a Tcl
script is evaluating in an interpreter, allowing an external system to
determine whether it is safe to delete that interpreter.

~ Rationale

For applications written in garbage-collected languages, such as C#, it is not
always desirable to rely upon the '''Tcl_Preserve''' / '''Tcl_Release'''
mechanism to protect an against deletion of an interpreter while it is in use.
For details of how this is used, see [http://wiki.tcl.tk/6580]
[http://eagle.to/] and Joe Mistachkin's talk at Tcl 2008.

Additionally, an application may want to proactively forbid attempts to delete
an interpreter while it is in use. Unfortunately, there is currently no
publicly exposed method to determine if a given Tcl interpreter is in use
(i.e. one or more calls to '''Tcl_Eval''' are active). This TIP proposes to
correct that deficiency.

~ Specification

This TIP introduces a single function to Tcl's public API:

 > int '''Tcl_InterpActive'''(Tcl_Interp *''interp'')

The '''Tcl_InterpActive''' function returns non-zero if the interpreter is in
use, and zero if it is idle (i.e. not evaluating any script).

~ Reference Implementation

|/*
| *----------------------------------------------------------------------
| *
| * Tcl_InterpActive --
| *
| *	Returns non-zero if the specified interpreter is in use.
| *
| * Results:
| *	See above.
| *
| * Side effects:
| *	None.
| *
| *----------------------------------------------------------------------
| */
|
|int
|Tcl_InterpActive(Tcl_Interp *interp)
|{
|    return (((Interp *) interp)->numLevels > 0);
|}

~ Copyright

This document has been placed in the public domain.