There are a lot of different issues with this threading discussion.
1) live code execution like LightBox and the lisp music demo - any
useful live code execution mode would have to parse the code (ast
trees?), execute it expression by expression, and display the results,
probably in a specific environment. It would be an interesting
experiment, but probably separate from how Leo executes scripts and
whether Leo "hangs" when it is executing scripts.
2) Leo hanging on scripts that don't interact with Leo - there could be
a new run-script command to execute scripts in the background, although
it doesn't take too much to do it explicitly:
from threading import Thread
def do_something():
....
t = Thread(target=do_something)
t.start()
3) Scripts that interact with Leo - these are probably better
implemented using hooks / callbacks including onIdle.
How threads can bite unexpectedly - a slow running script that changes
the tree is going to be very hard to run in a separate thread, because
as it continues to run it will keep invalidating positions in the main
thread, making it impossible to do anything - not unexpected. But even
a script that simply runs without touching Leo (c, g, the interface)
until it's done and then does `c._slow_answer = foo` may cause trouble.
When you assign to c._slow_answer you're updating c.__dict__. Another
thread (the main thread) might be iterating c.__dict__ to find an
attribute of c, or adding an attribute, and get interrupted by the
sub-thread such that one of them ends up with an inconsistent view of
c.__dict__.
There are ways around this, but you have to write the code to
anticipate the problems. queue.Queue is thread safe for example, you
could do `c._slow_answer` = queue.Queue() *in the main thread*, your
background thread can stick its answer there when its done, and Leo can
check for new answers in c._slow_answer onIdle or on user demand.
Queue does behind the scenes stuff to ensure that threads don't trip
each other up working with the same data.
Cheers -Terry
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