Question

I am trying to run a thread continuously and not have it become blocked by the tcl main event loop.
Here is a simple example of what I’m trying to do:

#!/bin/sh
#\
exec tclsh "$0" "$@"

package require Thread

set ::a_thread [thread::create {thread::wait}]

proc start_a {} {
  thread::send $::a_thread {
    puts "Running a thread"
  }
  after 1000 a_start
}

proc infinite_loop {} {
  while {1} {
    puts "Loop"
    after 500
  }
}

start_a
infinite_loop

vwait forever

In this code, the infinite_loop proc is called and the main event loop runs infinitely. I would like it if the a_thread could still run in the background though. How can I achieve this?

Answer 1

The main event loop is not blocking your thread. Instead you are using the main event loop to shedule scripts to be executed in the thread. Instead, run the scheduler in the thread itself:

Code tested and works as expected:

thread::send $::a_thread {
    proc loop {} {
        puts "running a thread"
        after 1000 loop
    }
    loop
}

while 1 {
    puts "loop"
    after 500
}