Re: [ft-devel] How to free the memory of evicted font faces when using cache system?

[Werner LEMBERG]

[Please don't write HTML emails to this list!  It greatly reduces your
chances to get a reply.]

Sorry for the late reply.

> Hello.  I have a question regarding the FreeType cache system.  I do
> not know if I'm doing the right things with the cache.  Please help
> me.
>
> In my main function, I render text with different fonts.  I extract
> the essential attributes of the current font to a structure, put it
> into a set (so that duplicate fonts will not be requested twice),
> and call FTC_Manager_LookupFace with face_id equals to the pointer
> of the structure.  In the Font Requester function, I convert the
> face_id back to the structure, use it to load font file into memory,
> and construct FT_Face with FT_New_Memory_Face.  In the function, the
> font file data is buffered in memory, and not freed when the
> function returns, because in the doc, the note under
> FT_New_Memory_Face says "You must not deallocate the memory before
> calling FT_Done_Face.".  Certainly I can record the buffer address
> in somewhere in my program, and could free them when the face is not
> needed anymore.
>
> My question is, since the created faces are completely managed by
> the cache system, and there is no callback function to notify the
> eviction of a cached face, what is the appropriate time to free the
> font file data buffer?  In my experiment, I set the max_faces of
> FTC_Manager_New() to 1, and render text with different fonts.  The
> memory usage increases sharply.
>
> I also searched the mailing list.  In
> http://lists.nongnu.org/archive/html/freetype/2006-08/msg00000.html,
> Kristján asked about the similar question about node, not face, and
> David answered "first of all, nobody seemed to use this 'feature'".
> Does this answer also apply to the face case?  And I found another
> implementation of using the cache system with FT_Stream (there is
> virtually nothing about these things in doc).  If I change my "char
> *buf = new buf[file_len];" and FT_New_Memory_Face with FT_Stream and
> FT_Open_Face, will FT_Stream free the buffer automatically?

It's really difficult to answer your question without seeing actual
code.  Please provide a small compilable code snippet (without
graphics output) which demonstrates your problems.

Note, however, that the cache subsystem is my weakest point; maybe I
can't answer your question at all in a satisfying way...


    Werner