Threading - Follow-up Question to Ticket #40

ID	Created	Type	mocl Version	Dev OS	Target	Status
#89	by TSchulte on 2015-12-11 (2013 days ago)	question	14.08	Mac OS X	iOS	closed

Description

Summary:

In Ticket #40, Wukix responded in part as follows:

"As a caveat, multiple mocl threads should not be running simultaneously, so it is up to you to coordinate that somehow, such as with locks."

I would like to understand whether this limitation has to do with accessing shared data in our own code only, or whether it is a limitation of the mocl runtime itself.    

Referencing shared data would appear to be unsafe without some type of manual locking if functions one and two below are invoked repeatedly in simultaneous background threads.   

(defvar *shared* 3)
(defun one () (+ *shared* 1)
(defun two () (+ *shared* 2)

If two Lisp functions are defined with no reference to any shared data, is it still unsafe to invoke them simultaneously in multiple background threads?  Is there something in the mocl runtime that might cause an error in the examples below (assuming they took a little longer to run and were likely to be swapped for other threads at some point?)

(defun one () 1)
(defun two () 2)  


Steps to Reproduce:
n/a
Expected Results:
n/a
Actual Results:
n/a
Notes:

Comments

It is a limitation of the mocl runtime. mocl uses a single stack that is shared across threads. Therefore simultaneous Lisp threads of *any* kind may interfere with each other by overwriting the stack of the other.

- Wukix, 2011 days ago