Version 4 of automatically generating socket based Tcl / C connection code, 1

started by Theo Verelst

To make use a pipe or as here a general socket [L1 ] [L2 ] to connect a user interface with a progam or to link programs together is a long used and tried solution since at least X windows. Not that that always worked perfectly, but its pretty ok.

Also web servers/browsers, ftp, etc are examples of existing progams making use of socket IPC. The principle is clear enough: one makes a stream connection, and sends messages across with commands and data [L3 ].

In practice, this doesn't work out all too easy, usually. This page presents an example to do most work completely automatically to make a tcl program connect with a C program, and have the C program execute functions under control of the tcl program (alternatively: C compiled image processing on an interactive Bwise canvas).

Also, an example is easily created, where Tk is used to have a stack of buttons for testing this.

On this page I used a recent windows XP running KDE (on an X simulator), and my own compiled tcl/tk 8.4 (but like on linux) in kde windows. Also, I used the cygwin unix-like environment including gcc compiler for windows. Most or all of the materials presented here should run equally well on linux/unix, and probably other os-es, provided they have a C compiler with unix flavour sockets.

Major issues when making a socket link and programming code around it are:

newlines (one or two characters, newline or carriage return)
end of line (don't forhet '\0' to terminate C strings)
end of message (how do you know the whole message is in)
flow control (no dead/live lock, buffer sizes)
process issues (creation, referencing, security, joint load)
connection control (setup, re-setup, connection with protocol, leakless cleanup, eof issues)
error correction/sensitivity (incomplete messages,resyncing)

The approach taken for this test version consists of the following steps:

define a list of message names, which are also used as corresponding C function names
make the socket connection possible both on C and Tcl side
generate automatically the C message handler and the frame of the C functions
generate Tcl/Tk code to make a button for each message
save and compile the generated C file
link it with the socket code
run the resulting C program
connect the tcl program
test the buttons to see if the corresponding C functions get called.

Motivations and subsequent work include:

real time sound synthesis/analysis C code I have can be runtime tcl/tk controlled [L4 ] [L5 ] [L6 ]
idem for 3D graphics [L7 ]
webserver extensions in c or tcl Web pages with images
BWise-ification of the various blocks here [L8 ]
distributed applications (protocol based [L9 ] [L10 ]) [L11 ] distributed linked bwise [L12 ]