Re: [xml] Memory leak / cleanup missing after node creation.

[Jose Commins <axora myrealbox com>]

	I see!  So in effect xmlBufferCreateSize does indeed allocate the 
amount of memory I specify (my xml output buffers never go beyond 4K, 
so I allocate 8192 just in case).
	In my app I keep the buffers persistent throughout threads, so I don't 
constantly create/destroy buffers, just re-use them on the next pass.  
Seeing as I have to use xmlBufferEmpty or xmlBufferShrink after each 
use, am I right in thinking that xmlBufferShrink is more optimal since 
it doesn't clear the data (I am guessing here)?

	By the way, I have to reiterate Igor that you have been of invaluable 
help and knowledge on these matters and I send my thanks again.

Regards,
                Jose.

On 25 May 2004, at 1:04 pm, Igor Zlatkovic wrote:

> On 25.05.2004 04:00, Jose Commins wrote:
> >     Thanks again Igor!  During the process I also found some more 
> > memory oddness - the following below doesn't register as a leak using 
> > 'leaks' in FreeBSD Terminal, but I see the memory go up:
> >
> >     In my (multithreaded) app I have x amount of buffers allocated 
> > with:
> >     theFinalXML = xmlBufferCreateSize(8192);
> >     If, for example, I perform a 'xmlBufferLength(theFinalXML)' I get 
> > back zero.  Er, OK, weird, since I thought 'xmlBufferCreateSize' can 
> > pre-allocate a known size so the buffer doesn't need to be constantly 
> > re-malloc'ed (or whatever scheme it uses).
> >     So if I dump the buffer (this is in my main thread loop):
> >     theFinalXMLSize = xmlNodeDump(theFinalXML, doc, root_element, 0, 
> > 0);
> >     I *have* to perform:
> >     xmlBufferEmpty(theFinalXML);
> >     afterwards, otherwise the buffers grow and grow.  Um, I am fine 
> > with using BufferEmpty (apart from the performace hit of constant 
> > allocs and reallocs), but then what use has 'xmlBufferCreateSize' ?
>
> No reallocation has happened unless your nodes, in the serialised 
> form, were bigger than 8k. More, xmlBufferEmpty does not free any 
> memory, it just erases the content, so it cannot be that calling this 
> function makes your buffer memory smaller.
>
> xmlBufferCreateSize creates a buffer with the specified initial size 
> and allocates its memory. xmlBufferLength returns the length of the 
> content. After you created the buffer, you haven't written any data in 
> it yet, so the content length is 0. But the memory of the specified 
> size has been allocated. If you write no more than the initial size 
> into the buffer, no reallocation will occur.
>
> When you write more data into a buffer than it can hold, the buffer 
> will grow automatically. It will however never shrink automatically, 
> that you must tell it to do explicitly (xmlBufferShrink) but this 
> operation probably does not do what you think it does.
>
> Ciao,
> Igor