weakref, memory management and execution slow down in PyQt4

kjs bfb at riseup.net
Sun Sep 7 21:11:25 CEST 2014

Antoine Pitrou:
> kjs <bfb <at> riseup.net> writes:
>> I have come to believe that the growing number of weakrefs is slowing
>> down execution. Is my analysis misguided? How can I introspect further?
>> If the slowdown can be attributed to weakref escalation, what are some
>> next steps?
> The way to analyze this is to build some gradually smaller subsets of your
> application until you can isolate what is causing the growth in number of
> objects (if any). I would suggest first remove the GUI and replace it with
> some dummy functions, to stress your core logic.

Thanks for the advice. I commented out the graph generation and PyQt call

>>> self.app.processEvents()

where in the class __init__

>>> self.app = QtGui.QApplication(sys.argv)

This stopped the weakref proliferation. All other objects grow and
shrink in number as expected.

> Note that "top" isn't a very reliable tool, as memory fragmentation and
> other factors can cause your process' visible size to grow even though
> Python's memory consumption may be stable. There are dedicated Python tools
> for finer analysis, such as tracemalloc, which is standard on 3.4 and available
> as a backport for older versions:
> https://docs.python.org/3/library/tracemalloc.html
> http://pytracemalloc.readthedocs.org/
> But regardless of such tools, the approach above (try to decompose your
> workload into separate parts until your find the culprit) is highly recommended.
> Regards
> Antoine.
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