Profiling Meld?

[Magnus Ihse Bursie <magnus ihse net>]

Hi,

When viewing large (> 1 MB) files with Meld, it takes a noticable amount 
of time for the diff to show up. (My current example is a 2 MB file 
which, on my machine takes ~8 seconds).

I have always naively assumed that it was the underlying diff algorithm 
that was slow, perhaps due to (my perceived) slowness of python. This 
turned out to be completely incorrect. When I created a unit test to 
just read the files into an array and feed it directly to 
MyersSequenceMatcher, it's so blazingly fast I can't even get a reliable 
measurement on it.

So it's something else that causes the delays.

I tried running 'python -m cProfile -s time  bin/meld' but this only 
gives the following un-helpful result:

         457930 function calls (454080 primitive calls) in 9.639 seconds

   Ordered by: internal time

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    7.278    7.278    9.639    9.639 meld:19(<module>)
      476    0.227    0.000    0.348    0.001 diffgrid.py:232(do_draw)
      976    0.209    0.000    0.210    0.000 Gtk.py:676(insert)
     6647    0.174    0.000    0.188    0.000 
meldbuffer.py:57(do_apply_tag)
       42    0.143    0.003    0.293    0.007 
meldbuffer.py:212(__getitem__)
        3    0.139    0.046    0.149    0.050 gnomeglade.py:39(__init__)
       80    0.119    0.001    0.119    0.001 {method 'splitlines' of 
'unicode' objects}
     3540    0.098    0.000    0.321    0.000 
diffgrid.py:182(child_allocate)
        2    0.085    0.042    0.096    0.048 
matchers.py:128(index_matching)
     8496    0.080    0.000    0.140    0.000 
diffgrid.py:168(get_child_prop_int)
      236    0.078    0.000    0.114    0.000 
diffgrid.py:214(_get_min_sizes)
<cut>

So the complete run took more than 9 seconds, of which 7 was spend in 
"meld:19". The rest of the calls contributes to negligeble times and is 
clearly not the culprit here. (Note that the timing includes a split 
second for me to close the meld Window after the diff has finished 
rendering.)

I assume that "meld" refers to the bin/meld.py script. Line 19 is 
obviosly bogus (that's the first non-comment line, an import statement). 
I guess the problem here is
    status = meld.meldapp.app.run(sys.argv)
and that cProfile and Gtk.Application does not play well together.

I have tried googling on how to profile a Gtk.Application-based python 
program, but ended up with no usable results.

Have anyone here tried profiling Meld before? If so, how did you do?

/Magnus