Hi Michael,
You are absolutely correct about the memory leak, and also about the reason
why it was done.
When I added this code I was fully aware I was adding a leak, but judged it
was negligible because it's not a critical function at all. It'll be called
only as many times as the number of distinct tables that you load.
I wasn't aware of the StringArray solution. I'll have a look and see
whether I can use it.
Thanks!
2016-08-02 17:29 GMT+02:00 Michael Whapples <dmarc-noreply@xxxxxxxxxxxxx>:
I think I have identified a potential memory leak around the use of a
table resolver in LibLouis.
The function resolveTable looks like:
char** resolveTable(const char *tableList, const char *base)
{
return copyStringArray((*tableResolver)(tableList, base));
}
I think I may understand why this was done. In liblouis-java I notice that
the resolver there returns String[] and according to the JNA documents this
will only last whilst the String[] object is not garbage collected (IE.
reliably only whilst a reference is held) and as the method is just
returning it then no reference is being held so you are copying it before
garbage collection frees it.
Why I think this is a memory leak. If a resolver was to do things in the
more normal way of expecting the caller who recieves the returned value to
free the memory, then the returned array will never be freed.
I am not a C expert so may be I miss something, but I am uncertain how a C
application with a custom table resolver would get that memory of the
returned array freed.
If changing it so that LibLouis does free the memory of the returned
array, you may have the question of how liblouis-java should overcome the
issue of garbage collection freeing the memory as well. The answer I think
is to use JNA's StringArray class. StringArray creates a string array in
native memory and is easy to create from a Java String[] object, there is
the constructor StringArray(String[]).
So is my thought of there being a memory leak correct, particularly when
thinking about languages like C without garbage collection?
Do I need to explain more about JNA;s StringArray class and how
liblouis-java could be fixed?
Michael Whapples
For a description of the software, to download it and links to
project pages go to http://liblouis.org
