TIP #335: AN API FOR DETECTING ACTIVE INTERPRETERS 
====================================================
 Version:      $Revision: 1.8 $
 Author:       Joe Mistachkin <joe_at_mistachkin.com>
 State:        Final
 Type:         Project
 Tcl-Version:  8.6
 Vote:         Done
 Created:      Monday, 13 October 2008
 URL:          https://tip.tcl-lang.org335.html
 Post-History: 

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 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 
 [<URL:http://wiki.tcl.tk/6580>] [<URL: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. 

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