A couple of week ago I blogged about using Pygments to do live syntax highlighting in the browser using Silverlight.
A major problem with the sample was that it did the pygmentizing on the UI thread which caused most
browsers to become unresponsive. Today I wanted to fix that by using the BackgroundWorker to do the
pygmentizing in a background thread.
Firstly I refactored the pygmentizing into a method that didn't interact with the UI.
def pygmentize_text(self, text, language):
# attempt to pygmentize input with current language
try:
from pygments import highlight
from pygments.lexers import get_lexer_by_name
from pygments.formatters import HtmlFormatter
lexer = get_lexer_by_name( language, stripall=True)
formatter = HtmlFormatter(linenos=False, cssclass="source")
markup = highlight(text, lexer, formatter)
return markup
except:
return "Error Generating Markup"
I then added a method that could be passed into a DoWorkEventHandler. It gets it arguments as a tuple from
the event arguments and then sets the event argument result with the marked up HTML. The lack of explicit
typing and use of tuples is good example of how some python idioms can be used when working with the .NET framework.
def worker(self, sender, e):
# do work off UI thread.
e.Result = self.pygmentize_text(e.Argument[0],e.Argument[1])
The required BackgroundWorker and DoWorkEventHandler can be simply imported from the System.ComponentModel
namespace.
from System.ComponentModel import BackgroundWorker, DoWorkEventHandler
The BackgroundWorker can then be setup and started. Again it's syntactically nice how the tuple can be created
and passed as a RunWorkerAsync parameter.
def start_pygmentize(self):
# update application state
self.input_changed = False
self.pygmentizing = True
self.show_message("pygmentizing..")
# get paremters
input = self.input.GetProperty("value")
language = self.language.value
# setup background worker
worker = BackgroundWorker()
worker.DoWork += DoWorkEventHandler(self.worker)
worker.RunWorkerCompleted += self.complete
# start the worker
worker.RunWorkerAsync( (input,language) )
The completed event handler is the responsible for taking the markup generated by the BackgroundWorker and
updating the DOM. It also fires off another worker if the source has changed since the
last worker started.
def complete(self, sender, e):
if e.Error:
# handle errors/exceptions in worker
self.source.SetProperty("innerHTML",e.Error.Message)
else:
# show the result
self.source.SetProperty("innerHTML",e.Result)
if self.input_changed:
# input has changed, starty pygmentize again
self.start_pygmentize()
else:
# no work queued
self.pygmentizing = False
self.hide_message()
The update has made the sample much more responsive, however it appears downloading the Silverlight application is still causing some browers to become a little unresponsive
which is annoying. I will be interested to find out if this effect can be mitigated.
The actually pygmentizing processing could possibly be made a little faster by reusing the BackgroundWorker and
only doing the Pygment imports once but the responsiveness of the browser has improved the
sample enormously.
Check out the updated demo here.