tcllauncher

tcllauncher is a way to have Tcl programs launch out of /usr/local/bin, or wherever, like any binary application on your system.

Moved

Moved to github tcllauncher project

Now you might think, why bother? I'll just put my Tcl script in there and do a #! thing to invoke Tcl.

Well, OK, but this has certain problems:

• everything will show in "ps" as tclsh
• everything will show in "top" as tclsh

You'd like to be able to have stuff show up as its script name.

You could just copy or even link tclsh to the name of your program. (Say, for instance, trackserver.)

But then you have to invoke trackserver with arguments and do stuff to prep it, like:

    cd ...somewhere...
    /usr/local/bin/trackserver main.tcl

That's the original purpose for tcllauncher, just to make that reasonable.

    cp /usr/local/bin/tcllauncher /usr/local/bin/trackserver

    trackserver

How does it find its files? It cd's to the corresponding lib directory and a directory underneath that of the same name as the application, and sources main.tcl with tcl_interactive set to 0.

run

        trackserver

what happens

• usr/local/bin/trackserver, a copy of /usr/local/bin/tcllauncher, sources in /usr/local/lib/trackserver/main.tcl.

Also, a global variable called launchdir is set containing the "launch directory." In the above example, /usr/local/lib/trackserver.

What Directory?

Tcllauncher doesn't change your directory behind your back, so whatever directory you're in when you run a tcllauncher app, you're still in that directory.

But a lot of times you want to go to your application directory. In that case you can just

        cd $::launchdir

Then you can source in all of your various files and stuff like that.

Or you can source your files from an explicit path based on launchdir without changing directories, something like

    source $::launchdir/processing.tcl

or more formally

source [file join $::launchdir processing.tcl]

In the above case if you set launchdir, when it doesn't exist, to "." or your development dir, when developing you can source in your main.tcl and get all the same load behavior as when the tcllauncher app runs, facilitating development and debugging by giving you tclsh command line access to all of your procs and stuff.

Process Group

If you are going to fork off children, exec them, or whatever, you should probably become your own process group so hopefully your children might inherit your signals and Do The Right Thing.

    package require Tclx
    id process group set

PID File

Lots of apps write a file with the server's process ID in it. Upon relaunch, the program can come along and look in its own pid file to see if it's already alive or not, and also to potentially kill it.

We need this functionality.

Something like

• pidfile
• pidfile app.pid
• pidfile -kill app.pid

Should tcllauncher have standard semantics for killing, like

apachectl graceful