If you start the new thread *after* the file is closed, no race 
condition should exist. I'm sorry but I'm unable to follow the code you 
use to create threads and write the makefile; but you should verify 
that your original assertion "Once a makefile is generated, launch a 
separate process..." is true.

Alternatively, when using a Queue like in my last example, make sure 
the new job enters the queue *after* closing the file.