[HarfBuzz] [Feature Request] Custom allocator support

Behdad Esfahbod behdad.esfahbod at gmail.com
Sat Oct 3 05:20:15 PDT 2015


On 15-10-02 10:00 PM, Jamie Dale wrote:
> That's similar to what I originally had, so I'm fine with something like that.
> My only question is, what would hb_malloc_impl, hb_calloc_impl,
> hb_realloc_impl, and hb_free_impl be defined to in your example?

Define it to the name of your external function.  I don't want to fix a name
in HarfBuzz itself.  Updated patch to add externs:

diff --git a/src/hb-private.hh b/src/hb-private.hh
index 07550cb..826e41a 100644
--- a/src/hb-private.hh
+++ b/src/hb-private.hh
@@ -54,6 +54,23 @@
 #include <stdarg.h>


+/* Compile-time custom allocator support. */
+
+#if defined(hb_malloc_impl) \
+ && defined(hb_calloc_impl) \
+ && defined(hb_realloc_impl) \
+ && defined(hb_free_impl)
+extern void* hb_malloc_impl(size_t size);
+extern void* hb_calloc_impl(size_t nmemb, size_t size);
+extern void* hb_realloc_impl(void *, size_t size);
+extern void  hb_free_impl(void *ptr);
+#define malloc hb_malloc_impl
+#define calloc hb_calloc_impl
+#define realloc hb_realloc_impl
+#define free hb_free_impl
+#endif
+

I'll go ahead and commit this.  Let me know if it doesn't work.

> I went with the extern function approach so I could inject my own allocator
> functions into HarfBuzz at link time, rather than have to include any of our
> code into HarfBuzz at compile time (since any local code changes we make have
> to be re-applied against new versions).
> 
> For your reference, this was my original implementation:
> 
> /* Override the allocation functions when 
>  * HAVE_EXTERNAL_ALLOCATOR is defined. */
> #ifdef HAVE_EXTERNAL_ALLOCATOR
> extern void* _hb_malloc(size_t);
> extern void* _hb_calloc(size_t, size_t);
> extern void* _hb_realloc(void*, size_t);
> extern void _hb_free(void*);
> #define malloc _hb_malloc
> #define calloc _hb_calloc
> #define realloc _hb_realloc
> #define free _hb_free
> #endif
> 
> Failure to define those functions in something that linked to HarfBuzz would
> produce an unresolved external symbol error at link time.
> 
> -Jamie.
> 
> On 2 October 2015 at 08:08, Behdad Esfahbod <behdad.esfahbod at gmail.com
> <mailto:behdad.esfahbod at gmail.com>> wrote:
> 
>     Hi Jamie,
> 
>     I'm opposed to runtime custom allocators, but am fine with something like what
>     you suggest.  However, that has two down sides:
> 
>       1. It touches a lot of callsites,
> 
>       2. I have to add macros to make sure stock malloc etc are not used by
>     mistake.
> 
>     If doing 2., I might as well just define them to their custom behavior.  Ie,
>     would this patch work for you:
> 
>     diff --git a/src/hb-private.hh b/src/hb-private.hh
>     index 07550cb..167c067 100644
>     --- a/src/hb-private.hh
>     +++ b/src/hb-private.hh
>     @@ -54,6 +54,19 @@
>      #include <stdarg.h>
> 
> 
>     +/* Compile-time custom allocator support. */
>     +
>     +#if defined(hb_malloc_impl) \
>     + && defined(hb_calloc_impl) \
>     + && defined(hb_realloc_impl) \
>     + && defined(hb_free_impl)
>     +#define malloc hb_malloc_impl
>     +#define calloc hb_calloc_impl
>     +#define realloc hb_realloc_impl
>     +#define free hb_free_impl
>     +#endif
>     +
>     +
>      /* Compiler attributes */
> 
> 
> 
> 
>     On 15-09-30 03:49 PM, Jamie Dale wrote:
>     > Since there was no movement here I went ahead and hacked in our allocator by
>     > redefining malloc, calloc, realloc, and free to point to extern'd functions
>     > that I define in our application. This yielded some performance benefits for
>     > us, so I'm hoping that a more standard HarfBuzz solution might appear at
>     some
>     > point :)
>     >
>     > If you're not keen on the idea of allowing the allocator to be swapped
>     out at
>     > runtime, would you at least allow it to be extern'd at compile time? I'm not
>     > familiar with HarfBuzz coding standards, but I'd propose adding
>     something like
>     > a HAVE_EXTERNAL_ALLOCATOR define to control this, and then define your own
>     > allocator functions that you'd use in place of malloc, etc.
>     >
>     > Basically, something like this (I currently have this code in
>     hb-private.hh):
>     >
>     > /* Define our allocation functions. These may be provided by an
>     >  * external source when HAVE_EXTERNAL_ALLOCATOR is defined. */
>     > #ifdef HAVE_EXTERNAL_ALLOCATOR
>     > extern void* _hb_malloc(size_t);
>     > extern void* _hb_calloc(size_t, size_t);
>     > extern void* _hb_realloc(void*, size_t);
>     > extern void _hb_free(void*);
>     > #define hb_malloc _hb_malloc
>     > #define hb_calloc _hb_calloc
>     > #define hb_realloc _hb_realloc
>     > #define hb_free _hb_free
>     > #else
>     > #define hb_malloc malloc
>     > #define hb_calloc calloc
>     > #define hb_realloc realloc
>     > #define hb_free free
>     > #endif
>     >
>     > You'd then replace calls to malloc, calloc, realloc, and free from within
>     > HarfBuzz to use hb_malloc, hb_calloc, hb_realloc, and hb_free.
>     >
>     > This is basically the code I already have, except I
>     > redefined malloc, calloc, realloc, and free rather than create the
>     > hb_*variants, as I didn't want to change too much HarfBuzz code.
>     >
>     > Thoughts?
>     >
>     > On 31 August 2015 at 22:17, Jamie Dale <jamiedale88+harfbuzz at gmail.com <mailto:jamiedale88%2Bharfbuzz at gmail.com>
>     > <mailto:jamiedale88+harfbuzz at gmail.com <mailto:jamiedale88%2Bharfbuzz at gmail.com>>>
>     wrote:
>     >
>     >     Hey,
>     >
>     >     I'm not sure if this is correct place to post/discuss feature requests...
>     >     hopefully it is.
>     >
>     >     Our project makes use of a custom memory allocator, and we like to ensure
>     >     that our third-party libraries are using this where possible, as our
>     >     allocator can offer significantly better performance, and can also allow
>     >     us better memory profiling and debugging support.
>     >
>     >     A look through the HarfBuzz source code would suggest that it doesn't
>     >     currently support custom memory allocators, and instead just directly
>     >     calls the standard malloc/free/etc functions. I was wondering if you'd
>     >     ever considered (or would consider) adding a way to override this behaviour?
>     >
>     >     In my case, I'd just need a single global override to be set before my
>     >     first call to any other HarfBuzz code... basically something like
>     >     the FT_Memory struct from FreeType:
>     >     http://www.freetype.org/freetype2/docs/reference/ft2-system_interface.html#FT_Memory
>     >
>     >     Thanks,
>     >     Jamie.
>     >
>     >
>     >
>     >
>     > _______________________________________________
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>     > HarfBuzz at lists.freedesktop.org <mailto:HarfBuzz at lists.freedesktop.org>
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>     >
> 
> 


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