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Posted to c-dev@xerces.apache.org by Jerry Napoli <jn...@iteamsolutions.com> on 2008/06/24 00:06:14 UTC

Deallocating NULL pointer in IconvLCPTranscoder

Hi,

While experimenting with memory managers, I noticed that 
IconvLCPTranscoder::transcode() passes a NULL pointer occasionally to 
MemoryManager::deallocate().  This is for version 2.8.  It looks like 
when transcoding small strings it uses a stack allocated buffer as the 
target, and dynamically allocates through the memory manager when it's 
larger:

if (maxChars >= gTempBuffArraySize)
         wideCharBuf = allocatedArray = (wchar_t*) manager->allocate
         (
             (maxChars + 1) * sizeof(wchar_t)
         );//new wchar_t[maxChars + 1];
     else
         wideCharBuf = tmpWideCharArr;

But it unconditionally calls 'manager->deallocate(allocatedArray)' at 
the end of the function.  I'm guessing it would be best to deallocate it 
only if it's non-NULL since some runtime's might complain passing a NULL 
into ::delete().

Thanks,
Jerry


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Re: Deallocating NULL pointer in IconvLCPTranscoder

Posted by Boris Kolpackov <bo...@codesynthesis.com>.
Hi David,

David Bertoni <db...@apache.org> writes:

> There are likely more places where NULL pointers end up getting passed 
> to MemoryManager::deallocate(), so I think we ought to make it a 
> requirement that deallocate() work correctly with a null pointer value.

Ok, I've added the check to deallocate. We, however, should try
to clean up as many places as possible since it is a completely
unnecessary virtual function call.

Boris

-- 
Boris Kolpackov, Code Synthesis Tools   http://codesynthesis.com/~boris/blog
Open source XML data binding for C++:   http://codesynthesis.com/products/xsd
Mobile/embedded validating XML parsing: http://codesynthesis.com/products/xsde

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Re: Deallocating NULL pointer in IconvLCPTranscoder

Posted by David Bertoni <db...@apache.org>.
Jerry Napoli wrote:
> Hi,
> 
> While experimenting with memory managers, I noticed that 
> IconvLCPTranscoder::transcode() passes a NULL pointer occasionally to 
> MemoryManager::deallocate().  This is for version 2.8.  It looks like 
> when transcoding small strings it uses a stack allocated buffer as the 
> target, and dynamically allocates through the memory manager when it's 
> larger:
> 
> if (maxChars >= gTempBuffArraySize)
>         wideCharBuf = allocatedArray = (wchar_t*) manager->allocate
>         (
>             (maxChars + 1) * sizeof(wchar_t)
>         );//new wchar_t[maxChars + 1];
>     else
>         wideCharBuf = tmpWideCharArr;
> 
> But it unconditionally calls 'manager->deallocate(allocatedArray)' at 
> the end of the function.  I'm guessing it would be best to deallocate it 
> only if it's non-NULL since some runtime's might complain passing a NULL 
> into ::delete().
There are likely more places where NULL pointers end up getting passed 
to MemoryManager::deallocate(), so I think we ought to make it a 
requirement that deallocate() work correctly with a null pointer value.

Besides, the C++ standard requires that the deallocation functions 
accept null pointer values.  Section 3.7.3.2, "Deallocation functions" 
states:

"3. The value of the first argument supplied to one of the deallocation 
functions provided in the standard library may be a null pointer value; 
if so, the call to the deallocation function has no effect. Otherwise, 
the value supplied to operator delete(void*) in the standard library 
shall be one of the values returned by a previous invocation of either 
operator new(size_t) or operator new(size_t, const std::nothrow_t&) in 
the standard library, and the value supplied to operator delete[](void*) 
in the standard library shall be one of the values returned by a 
previous invocation of either operator new[](size_t) or operator 
new[](size_t, const std::nothrow_t&) in the standard library."

That said, I think it makes sense for us to clean up any places where we 
know that pointer value is null, and doing so doesn't require extra logic.

Dave

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Re: Deallocating NULL pointer in IconvLCPTranscoder

Posted by Boris Kolpackov <bo...@codesynthesis.com>.
Hi Jerry,

Jerry Napoli <jn...@iteamsolutions.com> writes:

> I'm guessing it would be best to deallocate it only if it's non-NULL
> since some runtime's might complain passing a NULL into ::delete().

I've made the fix. Thanks for reporting this!

Boris

-- 
Boris Kolpackov, Code Synthesis Tools   http://codesynthesis.com/~boris/blog
Open source XML data binding for C++:   http://codesynthesis.com/products/xsd
Mobile/embedded validating XML parsing: http://codesynthesis.com/products/xsde

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