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[OpenSmalltalk/opensmalltalk-vm] code smell (IntelliSense C6308): realloc could cause a memory leak (#335)

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David T Lewis

[OpenSmalltalk/opensmalltalk-vm] code smell (IntelliSense C6308): realloc could cause a memory leak (#335)

In this pattern:

ptr = realloc( ptr , new_size );

realloc may fail when HEAP memory is exhausted, then return 0, and overwrite ptr with a NULL pointer...
But realloc did not free(ptr), it rather leaves it untouched!

OK, we rarely exhaust HEAP nowadays, and consequences might be catastrophic anyway.
But it is a code smell. It should be written like this:

aux = realloc( ptr , new_size );
if( aux == NULL ) /* handle_the_error */ {};
else ptr = aux;

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David T Lewis

Re: [OpenSmalltalk/opensmalltalk-vm] code smell (IntelliSense C6308): realloc could cause a memory leak (#335)

See: 82d1c33#diff-ea77aa3cf89ad27f0980e8a8b857fb1cR585

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timrowledge

Re: [OpenSmalltalk/opensmalltalk-vm] code smell (IntelliSense C6308): realloc could cause a memory leak (#335)

In reply to this post by David T Lewis

> On 2019-01-01, at 1:39 PM, Nicolas Cellier <[hidden email]> wrote:
>
> In this pattern:
>
> ptr = realloc( ptr , new_size );
>
> realloc may fail when HEAP memory is exhausted, then return 0, and overwrite ptr with a NULL pointer...
> But realloc did not free(ptr), it rather leaves it untouched!

That's just... awful. If it can't realloc it should damn well leave the original alone

tim
--
tim Rowledge; [hidden email]; http://www.rowledge.org/tim
Useful random insult:- Not much to show for four billion years of evolution.

David T Lewis

Re: [OpenSmalltalk/opensmalltalk-vm] code smell (IntelliSense C6308): realloc could cause a memory leak (#335)

In reply to this post by David T Lewis

Tim, to be sure about understanding: realloc does the right thing, it leaves the original alone.
It's we, programmers that do not do the right thing: we overwrite a valid pointer with a NULL pointer. And now, there is no references to the valid pointer anymore => memory leak (+ eventually other side effects of having a NULL pointer hanging).

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timrowledge

Re: [OpenSmalltalk/opensmalltalk-vm] code smell (IntelliSense C6308): realloc could cause a memory leak (#335)

> On 2019-01-02, at 7:12 AM, Nicolas Cellier <[hidden email]> wrote:
>
> Tim, to be sure about understanding: realloc does the right thing, it leaves the original alone.
> It's we, programmers that do not do the right thing: we overwrite a valid pointer with a NULL pointer.

Yeah, I thought I had cancelled my email once I realised that was what was going on. Apparently I overwrote the pointer with nil....

tim
--
tim Rowledge; [hidden email]; http://www.rowledge.org/tim
Strange OpCodes: ESBD: Erase System and Burn Documentation