GNU bug report logs - #13530
head: memory exhausted when printing all from stdin but last P/E bytes

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From: Bernhard Voelker <mail <at> bernhard-voelker.de>
To: Pádraig Brady <P <at> draigBrady.com>
Cc: Lei Zhang <lei.zhang <at> uwaterloo.ca>, 13530 <at> debbugs.gnu.org
Subject: bug#13530: head: memory exhausted when printing all from stdin but last P/E bytes
Date: Wed, 23 Jan 2013 13:53:47 +0100

On 01/23/2013 01:34 PM, Pádraig Brady wrote:
> There is the argument that we _should_ allocate
> everything up front to indicate immediately
> that the system can't (currently) support the requested operation,
> but given the 'currently' caveat above I guess it's
> more general to fail when we actually run out of mem?

head doesn't "allocate everything up front" - instead, it only
allocates the pointer array which would hold the actual data.
The strategy in elide_tail_lines_pipe() seems more robust:
it allocates memory when needed.

Or another (probably martian) idea:
what about a tmpfile()?

>       free_mem:
> -      for (i = 0; i < n_bufs; i++)
> +      for (i = 0; i < n_alloc; i++)
>           free (b[i]);
>         free (b);

BTW: both in the old and the new version, the loop can break
if (b[i] == 0) because the array is filled from the beginning.

-      for (i = 0; i < n_bufs; i++)
+      for (i = 0; i < n_bufs && b[i]; i++)

This makes "echo 123 | head -c -T" ~40% faster here on my PC.

Have a nice day,
Berny

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