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TDK 5.4 Documentation


Tutorial: Debugging Subprocesses


This tutorial shows you how to debug multiple processes by "spawning" new sessions from a main session in the Tcl Dev Kit Debugger. The new sessions are subprocesses of the main session. They are created by setting spawnpoints (similar to breakpoints) in the Tcl Dev Kit Debugger's main window. Then, when you run the debugger, a new tab displaying each spawned subprocess is launched in the Code display area.

Step One: Opening the Tutorial Program

  • Unix: Change to the directory /demos/TclDevKit/TclDebugger/Spawning/ beneath the root Tcl Dev Kit installation directory, and run:
    tcldebugger spawn.tpj
  • Windows: Click Start | Programs | ActiveState Tcl Dev Kit | Tcl Dev Kit Demos | Debugging Subprocesses

The Tcl Dev Kit Debugger will open and load the "spawn" project. The Code display portion of the debugger's main window will show the file "main.tcl".

Step Two: Modifying the Script

To debug multiple processes, your script must contain code similar to that used in this tutorial. (See Spawning a New Session for more information about modifying a script.) You must include proc spawn as well as a spawn command for each subprocess that you want to generate. The script used here launches two new sessions, "subprocess1.tcl" and "subprocess2.tcl".

Step Three: Setting Spawnpoints

In addition to including the spawn commands described in Step Two, you must set spawnpoints that tell the debugger when to launch a new session. For the purpose of this tutorial, spawnpoints (indicated by green arrows) have been preset in the project file at lines 23 and 24.

Step Four: Running the Debugger

Once the script has been modified and spawnpoints have been set, you can run the Tcl Dev Kit Debugger and spawn subprocesses.

Select Debug|Run. The Tcl Dev Kit Debugger automatically launches Code display tabs showing the subprocesses specified in Step Two. Details of the spawn are shown in the Eval Console. Note that the main session and the two subprocesses run in parallel.

Step Five: Debugging a Spawned Session

Notice that the focus in the Tcl Dev Kit Debugger's main window has shifted to the tab containing the code for "subprocess2.tcl". The yellow arrow indicates that the Tcl Dev Kit Debugger is stopped at the first executable command (proc multiply) on line 11.

To debug the subprocess2.tcl session:

  1. Set a breakpoint on line 24.
  2. Select Debug|Step In.

  3. Select Debug|Kill.

  4. A message box will be displayed advising that this command will kill the running application.
  5. Click OK to close the Tcl Dev Kit Debugger's connection with the spawned session.