Why I fail so bad to check for memory leak with this code?

[MRAB]

On 21/07/2022 23:39, Marco Sulla wrote:
> I've done this other simple test:
>
> #!/usr/bin/env python3
>
> import tracemalloc
> import gc
> import pickle
>
> tracemalloc.start()
>
> snapshot1 = tracemalloc.take_snapshot().filter_traces(
>     (tracemalloc.Filter(True, __file__), )
> )
>
> for i in range(10000000):
>     pickle.dumps(iter([]))
>
> gc.collect()
>
> snapshot2 = tracemalloc.take_snapshot().filter_traces(
>     (tracemalloc.Filter(True, __file__), )
> )
>
> top_stats = snapshot2.compare_to(snapshot1, 'lineno')
> tracemalloc.stop()
>
> for stat in top_stats:
>     print(stat)
>
> The result is:
>
> /home/marco/sources/test.py:14: size=3339 B (+3339 B), count=63 (+63), 
> average=53 B
> /home/marco/sources/test.py:9: size=464 B (+464 B), count=1 (+1), 
> average=464 B
> /home/marco/sources/test.py:10: size=456 B (+456 B), count=1 (+1), 
> average=456 B
> /home/marco/sources/test.py:13: size=28 B (+28 B), count=1 (+1), 
> average=28 B
>
> It seems that, after 10 million loops, only 63 have a leak, with only 
> ~3 KB. It seems to me that we can't call it a leak, no? Probably 
> pickle needs a lot more cycles to be sure there's actually a real leakage.
If it was a leak, then the amount of memory used or the counts would 
increase with increasing iterations. If that's not happening, if the 
memory used and the counts stay the roughly the same, then it's probably 
not a leak, unless it's a leak of something that happens only once, such 
as creating a cache or buffer on first use.