comm IPC example with 'callbacks'

# A
package require comm

# it behaves almost like a normal interactive session :P
# invoke 'eventloop' to enter the event loop
proc stdin {} {
	global stdin
	if {[info complete [append stdin [gets stdin]]]} {
		if {$stdin=="exit"} {
			unset ::eventloop; unset stdin
		} {
			catch {uplevel #0 $stdin} stdin
			puts -nonewline "$stdin\n% "
			flush stdout
			set stdin ""
		}
	} {
		append stdin "\n"
	}
}
proc eventloop {} {
	if {[info exists eventloop]} {
		puts -nonewline "You're already in the event loop :)\n%"
		flush stdout
	} {
		fileevent stdin readable stdin
		set ::eventloop 1
		puts -nonewline "Entering the event loop...\n% "
		flush stdout
		vwait eventloop
		puts "Exiting the event loop..."
		fileevent stdin readable {}
	}
}

proc done {id results} {
  puts "$id is done -> $results"
}

proc do {id cmd} {
   comm::comm send -async $id [list do [comm::comm self] $cmd]
   return {}
}

eventloop


# B

package require comm
puts "I am [comm::comm id]"

proc do {from cmd} {
   puts "executing \"$cmd\" from $from"
   catch {uplevel #0 $cmd} result
   comm::comm send -async $from [list done [comm::comm self] $result]
}

vwait forever


# Output A

Entering the event loop...
% do 2109 {expr {4+5}}

% 2109 is done -> 9
# wait some time in B

% do 2109 {puts "calculating" ; after 5000 ; puts "calculation done" ; expr {4+5}}

% 2109 is done -> 9


# Output B

I am 2109
executing "expr {4+5}" from 2108
executing "puts "calculating" ; after 5000 ; puts "calculation done" ; expr {4+5}" from 2108
calculating
calculation done