Re: Memory leak in flex generated file

On 20 Oct 2005 00:14:55 -0400, "pavel.orehov@gmail.com"
<pavel.orehov@gmail.com> wrote:


>I am using flex and bison to parse HTTP headers. After some
>investigation i found a memory leak in flex generated file with
>valgrind tool.
>
<snip huge listing>


It's possible the verifier tool is misleading you - Flex makes some
allocations the first time it is called which will be reused by
subsequent calls. If you haven't created a reentrant scanner, those
allocations will be global and valgrind might be considering them to
be a leak.


OTOH,
I haven't used either Flex or Bison for a while, but in the past they
had a number of ways to leak memory. Flex had several issues related
to buffering which made it problematic to use multiple input streams
or to scan input from memory rather than from traditional files. When
used with the %pure_parser option Bison's own memory use was sound,
but when a parse error occurred any scanner allocations made for the
unmatched tokens would be lost.


I used Flex and Bison to scan input from memory in an embedded system
where no leaks could be tolerated. I ended up manually controlling
Flex's buffering and reading, and using a custom allocator to
guarantee that any dangling allocations would be freed in the event of
a parse failure.


George

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