Re: [vim/vim] fix: ":for" over a tuple leaks memory on every iteration (PR #20914)

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SamuelSchlesinger left a comment (vim/vim#20914)

```vimscript
" Demonstrates the ":for" over a tuple memory leak.
" Run with:  vim -N -u NONE -i NONE -es -S tuple_leak_demo.vim
"
" Each round runs 100,000 iterations of a ":for" loop over a two-string
" tuple and then prints the process RSS.  On an unpatched Vim the RSS grows
" by ~26 MB every round (the copied tuple items are never freed).  On a
" patched Vim the RSS is flat after the first round's allocator warm-up.

func s:Rss()
  return str2nr(system('ps -o rss= -p ' . getpid()))
endfunc

func s:Print(msg)
  call writefile([a:msg], '/dev/stdout', 'a')
endfunc

let s:str = repeat('abcdefghij', 20)
call s:Rss()    " warm up the ps invocation itself

call s:Print('start:         RSS ' . s:Rss() . ' KB')
for s:round in range(1, 5)
  for s:i in range(100000)
    for s:x in (s:str, 'short')
    endfor
  endfor
  call s:Print('after round ' . s:round . ': RSS ' . s:Rss() . ' KB')
endfor
qa!
```

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<div style=3D"display: flex; flex-wrap: wrap; white-space: pre-wrap; align-=
items: center; "><img height=3D"20" width=3D"20" style=3D"border-radius:50%=
; margin-right: 4px;" decoding=3D"async" src=3D"https://avatars.githubuserc=
ontent.com/u/10200200" /><strong>SamuelSchlesinger</strong> left a comment =
<a href=3D"https://github.com/vim/vim/pull/20914#issuecomment-5157497193">(=
vim/vim#20914)</a></div>
<div class=3D"highlight highlight-source-viml" dir=3D"auto"><pre class=3D"n=
otranslate"><span class=3D"pl-c"><span class=3D"pl-c">"</span> Demonstrates=
 the ":for" over a tuple memory leak.</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span> Run with:  vim -N -u NON=
E -i NONE -es -S tuple_leak_demo.vim</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span></span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span> Each round runs 100,000 =
iterations of a ":for" loop over a two-string</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span> tuple and then prints th=
e process RSS.  On an unpatched Vim the RSS grows</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span> by ~26 MB every round (t=
he copied tuple items are never freed).  On a</span>
<span class=3D"pl-c"><span class=3D"pl-c">"</span> patched Vim the RSS is f=
lat after the first round's allocator warm-up.</span>

<span class=3D"pl-k">func</span> <span class=3D"pl-en"><span class=3D"pl-k"=
>s:</span>Rss</span>()
  <span class=3D"pl-k">return</span> <span class=3D"pl-en">str2nr</span>(<s=
pan class=3D"pl-en">system</span>(<span class=3D"pl-s"><span class=3D"pl-pd=
s">'</span>ps -o rss=3D -p <span class=3D"pl-pds">'</span></span> . <span c=
lass=3D"pl-en">getpid</span>()))
<span class=3D"pl-k">endfunc</span>

<span class=3D"pl-k">func</span> <span class=3D"pl-en"><span class=3D"pl-k"=
>s:</span>Print</span>(msg)
  <span class=3D"pl-c1">call</span> <span class=3D"pl-en">writefile</span>(=
[<span class=3D"pl-smi"><span class=3D"pl-k">a:</span>msg</span>], <span cl=
ass=3D"pl-s"><span class=3D"pl-pds">'</span>/dev/stdout<span class=3D"pl-pd=
s">'</span></span>, <span class=3D"pl-s"><span class=3D"pl-pds">'</span>a<s=
pan class=3D"pl-pds">'</span></span>)
<span class=3D"pl-k">endfunc</span>

<span class=3D"pl-k">let</span> <span class=3D"pl-smi"><span class=3D"pl-k"=
>s:</span>str</span> <span class=3D"pl-k">=3D</span> <span class=3D"pl-en">=
repeat</span>(<span class=3D"pl-s"><span class=3D"pl-pds">'</span>abcdefghi=
j<span class=3D"pl-pds">'</span></span>, <span class=3D"pl-c1">20</span>)
<span class=3D"pl-c1">call</span> <span class=3D"pl-en"><span class=3D"pl-k=
">s:</span>Rss</span>()<span class=3D"pl-c">    <span class=3D"pl-c">"</spa=
n> warm up the ps invocation itself</span>

<span class=3D"pl-c1">call</span> <span class=3D"pl-en"><span class=3D"pl-k=
">s:</span>Print</span>(<span class=3D"pl-s"><span class=3D"pl-pds">'</span=
>start:         RSS <span class=3D"pl-pds">'</span></span> . <span class=3D=
"pl-en"><span class=3D"pl-k">s:</span>Rss</span>() . <span class=3D"pl-s"><=
span class=3D"pl-pds">'</span> KB<span class=3D"pl-pds">'</span></span>)
<span class=3D"pl-k">for</span> <span class=3D"pl-smi"><span class=3D"pl-k"=
>s:</span>round</span> <span class=3D"pl-k">in</span> <span class=3D"pl-en"=
>range</span>(<span class=3D"pl-c1">1</span>, <span class=3D"pl-c1">5</span=
>)
  <span class=3D"pl-k">for</span> <span class=3D"pl-smi"><span class=3D"pl-=
k">s:</span>i</span> <span class=3D"pl-k">in</span> <span class=3D"pl-en">r=
ange</span>(<span class=3D"pl-c1">100000</span>)
    <span class=3D"pl-k">for</span> <span class=3D"pl-smi"><span class=3D"p=
l-k">s:</span>x</span> <span class=3D"pl-k">in</span> (<span class=3D"pl-sm=
i"><span class=3D"pl-k">s:</span>str</span>, <span class=3D"pl-s"><span cla=
ss=3D"pl-pds">'</span>short<span class=3D"pl-pds">'</span></span>)
    <span class=3D"pl-k">endfor</span>
  <span class=3D"pl-k">endfor</span>
  <span class=3D"pl-c1">call</span> <span class=3D"pl-en"><span class=3D"pl=
-k">s:</span>Print</span>(<span class=3D"pl-s"><span class=3D"pl-pds">'</sp=
an>after round <span class=3D"pl-pds">'</span></span> . <span class=3D"pl-s=
mi"><span class=3D"pl-k">s:</span>round</span> . <span class=3D"pl-s"><span=
 class=3D"pl-pds">'</span>: RSS <span class=3D"pl-pds">'</span></span> . <s=
pan class=3D"pl-en"><span class=3D"pl-k">s:</span>Rss</span>() . <span clas=
s=3D"pl-s"><span class=3D"pl-pds">'</span> KB<span class=3D"pl-pds">'</span=
></span>)
<span class=3D"pl-k">endfor</span>
<span class=3D"pl-c1">qa</span><span class=3D"pl-k">!</span></pre></div>

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