DN502323275

Subject: HOWTO: write C++/multithreaded extensions for Win32 + example code - DN [1]

davygrvy@bigfoot.com (David Gravereaux) - 18 Jul 1999 - comp.lang.tcl

 I thought I'd make my source code public and help the Tcl community a
 bit.  I had to write this for a recent project and thought I would
 share it.  The following link is to some free C++ source code for
 MSVC++:

   http://www.maui.net/~davygrvy/files/ghe_dirwatch.zip

 First, this is what the extension does.  It enables directory watches
 and fires a script in the origin interpreter when a file in that
 directory has been written to.

 In wish81 or wish82:
 % load ghe_dirwatch.dll
 % GHE::startwatch c:/temp {puts "got ya!"}
 watch0
 got ya!          <- dropped a file into the c:\temp folder
 got ya!          <- dropped another (immediate; no delay like polling)
 % GHE::endwatch watch0

 It uses these Win32 functions to enable the watch:
   FindFirstChangeNotification()
   FindNextChangeNotification() and
   FindCloseChangeNotification()

 The interface to Tcl is a single class instantiated in the Init
 function.  Each interp calling into it has a separate instance of this
 class.  A striped-down version of it can be found here:

   http://www.maui.net/~davygrvy/files/test.cpp

 When the GHE::startwatch command is called from Tcl, a new thread is
 created which is then "waited on" with WaitForMultipleEvents().  A
 copy of the script command and a reference to the per interp
 thread-safe workqueue is also given to the new thread.  When the event
 fires, the script Tcl_Obj is Put() to the workqueue and calls
 Tcl_AsyncMark with the token handed to it when the main per interp
 (CTclTop) class was instantiated.

 When Tcl enters the Async proc, the script to run is pulled off the
 thread-safe workqueue and queued into Tcl with Tcl_QueueEvent().
 Eventually, this comes around in the notifier and is evaluated.

 More info and detail about this 3 part Tcl thread-safe technique can
 be found here:

   http://www.maui.net/~davygrvy/tomahawk/irc_engine_oline.html

 This code follows my own convention and is not the same as what the
 tcl8.1 man pages says about threads.

 If you found this helpful, please email me some praise or better
 yet....   HIRE ME FOR YOUR MULTITHREADED TCL PROJECTS!!

 with Love and respect,

 * David Gravereaux *
 Tomahawk Software Group