Re: Add a new function 'FcPatternRefCount'

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On Mon, Jun 5, 2023 at 10:26 AM Akira TAGOH <akira@xxxxxxxxx> wrote:
> Another point is, there is no way to know what objects are really used
> or not. introducing such functions may introduce unexpected behavior.
> freeing all the FcPattern instances at exiting, as you proposed at
> doesn't fix anything
> for users because unwanted memory still keeps allocated as long as it
> keeps running. What if it is huge and often happens? Do you suggest
> restarting apps so often and many times?

When people talk about a 'resource leak' or a 'memory leak', they are
typically talking about a leak that gets progressively worse as the
program runs for more and more time. So let's say a program allocates
a buffer of 512 kilobytes every time you click an item in a tree view
on screen, and so every time you click it, the memory usage increases
and increases. So if you run the program on a server PC for two weeks
straight then it could allocate a gig of RAM. These are the kinds of
memory leak that we really need to fix.

The other kind of memory leak is where memory is allocated only once
and is supposed to remain accessible until the program ends. We don't
need to free these allocations because the operating system frees all
heap allocations when a program ends. However, these kinds of leaks
can be cumbersome for debugging. If you build a wxWidgets program for
Linux with GTK3, and if you use Address Sanitiser, then when the
program ends you get a report of memory leaks from libpango. To get
rid of this clutter, and also to be 100% certain that the leaks aren't
accumulative, the debug build of the program should free these
once-off allocations, perhaps by making use of the Standard C function

The patch I proposed to libpango uses the 'atexit' function to free
all the once-off allocations when the program ends. It keeps calling
FcPatternDestroy on an FcPattern until the internal counter reaches
zero. So maybe there should be a function in libfontconfig that keeps
destroying an FcPattern until the count is zero?

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