Re: Can we go GTK-only?

[YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>]

>>>>> On Wed, 02 Nov 2016 17:46:26 +0200, Eli Zaretskii <eliz@gnu.org> said:

>> 1489	              dispatch_group_async (group, queue, ^{
>> 1490	                  int nkeys;
>> 1491	                  uintptr_t key;
>> 1492	                  nkeys = nkeys_or_perm;
>> 1493	                  for (key = row * (256 / NGLYPHS_IN_VALUE); ; key++)
>> 1494	                    if (CFDictionaryContainsKey (dictionary,
>> 1495	                                                 (const void *) key))
>> 1496	                      {
>> 1497	                        CFDictionaryRemoveValue (dictionary,
>> 1498	                                                 (const void *) key);
>> 1499	                        if (--nkeys == 0)
>> 1500	                          break;
>> 1501	                      }
>> 1502	                });
>> 
>> I can disable this for NS if it does not fit with the current policy
>> of GNU Emacs mainline source code.

> I know next to nothing about NS.  These are system APIs, right?  If
> so, calling them could be okay, and I defer to NS and OS X people here
> to make that call.

They internally use malloc/free.  What if the code like above were
using malloc/free instead of CF functions?

BTW, I just remember the current implementation of xfree should not be
used from a non-main thread if XMALLOC_BLOCK_INPUT_CHECK is defined.
The Mac port contains a code that calls "free" off the main thread for
some data that were allocated in the main thread.

void
mac_free_gc (GC gc)
{
  CGColorRelease (gc->cg_fore_color);
  CGColorRelease (gc->cg_back_color);
  if (gc->clip_rects_data)
    CFRelease (gc->clip_rects_data);
#if defined (XMALLOC_BLOCK_INPUT_CHECK) && DRAWING_USE_GCD
  /* Don't use xfree here, because this might be called in a non-main
     thread.  */
  free (gc);
#else
  xfree (gc);
#endif
}

> One things bothers me, though: can't this arrangement, where data is
> allocated in one thread and deallocated in another, cause races?  Or
> do these threads have means to synchronize between them?

For CFDictionary itself, its fundamental operations are thread-safe,
as well as malloc/free.  For the font data structure that use
CFDictionary, the main thread waits for the other thread after doing
some independent tasks that do not use CFDictionary.

  1543	          if (group)
  1544	            {
  1545	              dispatch_group_wait (group, DISPATCH_TIME_FOREVER);
  1546	              dispatch_release (group);
  1547	            }
  1548	        }

				     YAMAMOTO Mitsuharu
				mituharu@math.s.chiba-u.ac.jp