Fine thread control, Run only n bytecodes

[Christopher T King]

On Fri, 16 Jul 2004, David Pokorny wrote:

> I'd like to be able to take a function or other chunk of code (that someone
> else has written), run it for, say 50 byte codes, and then return control
> back to my program/controlling thread until my program/controlling thread
> indicates that it wants to run the next 50 bytes codes of the foreign
> program, etc...
> 
> Is there an extension to the python threading module that supports such fine
> control?

Not that I know of (Python doesn't support per-bytecode hooks), but you 
can get a similar effect after every X lines using settrace() and Lock 
objects (untested):

count=0
main_lock=Lock()
thread_lock=Lock()

def local_tracer(f,e,a):
    global main_lock, thread_lock, count
    count-=1
    if not count:
        main_lock.release()
        thread_lock.acquire()
    return local_tracer

def global_tracer(f,e,a):
    return local_tracer

def mythread():
    global thread_lock
    sys.settrace(tracer)
    thread_lock.acquire()
    do_stuff()

def waitfor(n):
    global main_lock, thread_lock, count
    count=n
    thread_lock.release()
    main_lock.acquire()

def main():
    thread_lock.acquire()
    main_lock.acquire()

    start_thread(mythread)

    while True:
        waitfor(50)
        do_stuff()

There's probably a more direct way about this, though.