Question

I need to have two way communication between threads in Tcl and all I can get is one way with parameters passing in as my only master->helper communication channel. Here is what I have:

proc ExecProgram { command } {     if { [catch {open '| $command' RDWR} fd ] } {         #         # Failed, return error indication         #         error '$fd'     } } 

To call the tclsh83, for example ExecProgram ‘tclsh83 testCases.tcl TestCase_01’

Within the testCases.tcl file I can use that passed in information. For example:

set myTestCase [lindex $argv 0]  

Within testCases.tcl I can puts out to the pipe:

puts '$myTestCase' flush stdout 

And receive that puts within the master thread by using the process ID:

gets $app line 

…within a loop.

Which is not very good. And not two-way.

Anyone know of an easy 2-way communication method for tcl in Windows between 2 threads?

Answer 1

Here is a small example that shows how two processes can communicate. First off the child process (save this as child.tcl):

gets stdin line puts [string toupper $line] 

and then the parent process that starts the child and comunicates with it:

set fd [open '| tclsh child.tcl' r+]  puts $fd 'This is a test' flush $fd  gets $fd line puts $line 

The parent uses the value returned by open to send and receive data to/from the child process; the r+ parameter to open opens the pipeline for both read and write.

The flush is required because of the buffering on the pipeline; it is possible to change this to line buffering using the fconfigure command.

Just one other point; looking at your code you aren’t using threads here you are starting a child process. Tcl has a threading extension which does allow proper interthread communications.