Writing multi-threaded applications in Python is often a headache because of
the Global Interpreter Lock - only one Python thread can run at any given
moment, which makes multi-threading useful only in the case where all modules
but one actually run C code. However, thanks to the impressive new Python
Magazine, I’ve stumbled across a package called
processing, paraphrasing python’s built-in threading package. Essentially,
the package provides an API identical to Python’s threading, but uses processes
and pipes (or other mechanisms on non-posix operating systems) instead. What
the magazine does not cover is the fact that this can also benefit GUI
applications; updating a progressbar in the application doesn’t need to slow
down heavy computations being done in a separate thread. To show how easy the
integration is, take the following example which shows usage of either threads
or processes at the user’s choice:
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| import processing
import threading
import Queue
import time
import gtk
import gobject
gtk.gdk.threads_init()
USE_PROCESSING = False
WORKER_DELAY = 1.0
GUI_DELAY = 0.5
def f(q, sq):
print "Init other thread"
i = 0
while sq.empty():
time.sleep(WORKER_DELAY)
q.put(i)
print "Other thread: %d" % i
i += 1
def update_label((l, q, sq)):
print "Updating label"
try:
i = q.get_nowait()
l.set_text("Number in thread: %d" % i)
except Queue.Empty:
l.set_text("Queue is empty!")
except processing.Queue.Empty:
l.set_text("Queue is empty!")
return sq.empty()
def close(window, sq):
sq.put(True)
gtk.main_quit()
if __name__ == '__main__':
if USE_PROCESSING:
q = processing.Queue()
sq = processing.Queue()
p = processing.Process(target = f,
args = [q, sq])
else:
q = Queue.Queue()
sq = Queue.Queue()
p = threading.Thread(target = f,
args = [q, sq])
p.start()
w = gtk.Window()
l = gtk.Label()
gobject.timeout_add(int(1000*GUI_DELAY),
update_label, (l,q,sq))
w.add(l)
w.connect('destroy', close, sq)
w.show_all()
print "Mainloop!"
gtk.main()
|