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      1 /*
      2  * Copyright  2012  Google, Inc.
      3  *
      4  *  This is part of HarfBuzz, a text shaping library.
      5  *
      6  * Permission is hereby granted, without written agreement and without
      7  * license or royalty fees, to use, copy, modify, and distribute this
      8  * software and its documentation for any purpose, provided that the
      9  * above copyright notice and the following two paragraphs appear in
     10  * all copies of this software.
     11  *
     12  * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
     13  * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
     14  * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
     15  * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
     16  * DAMAGE.
     17  *
     18  * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
     19  * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
     20  * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
     21  * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
     22  * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
     23  *
     24  * Google Author(s): Behdad Esfahbod
     25  */
     26 
     27 #include "hb-private.hh"
     28 #include "hb-shaper-private.hh"
     29 #include "hb-atomic-private.hh"
     30 
     31 
     32 static const hb_shaper_pair_t all_shapers[] = {
     33 #define HB_SHAPER_IMPLEMENT(name) {#name, _hb_##name##_shape},
     34 #include "hb-shaper-list.hh"
     35 #undef HB_SHAPER_IMPLEMENT
     36 };
     37 
     38 
     39 /* Thread-safe, lock-free, shapers */
     40 
     41 static const hb_shaper_pair_t *static_shapers;
     42 
     43 #ifdef HB_USE_ATEXIT
     44 static
     45 void free_static_shapers (void)
     46 {
     47   if (unlikely (static_shapers != all_shapers))
     48     free ((void *) static_shapers);
     49 }
     50 #endif
     51 
     52 const hb_shaper_pair_t *
     53 _hb_shapers_get (void)
     54 {
     55 retry:
     56   hb_shaper_pair_t *shapers = (hb_shaper_pair_t *) hb_atomic_ptr_get (&static_shapers);
     57 
     58   if (unlikely (!shapers))
     59   {
     60     char *env = getenv ("HB_SHAPER_LIST");
     61     if (!env || !*env) {
     62       (void) hb_atomic_ptr_cmpexch (&static_shapers, NULL, &all_shapers[0]);
     63       return (const hb_shaper_pair_t *) all_shapers;
     64     }
     65 
     66     /* Not found; allocate one. */
     67     shapers = (hb_shaper_pair_t *) calloc (1, sizeof (all_shapers));
     68     if (unlikely (!shapers)) {
     69       (void) hb_atomic_ptr_cmpexch (&static_shapers, NULL, &all_shapers[0]);
     70       return (const hb_shaper_pair_t *) all_shapers;
     71     }
     72 
     73     memcpy (shapers, all_shapers, sizeof (all_shapers));
     74 
     75      /* Reorder shaper list to prefer requested shapers. */
     76     unsigned int i = 0;
     77     char *end, *p = env;
     78     for (;;) {
     79       end = strchr (p, ',');
     80       if (!end)
     81 	end = p + strlen (p);
     82 
     83       for (unsigned int j = i; j < ARRAY_LENGTH (all_shapers); j++)
     84 	if (end - p == (int) strlen (shapers[j].name) &&
     85 	    0 == strncmp (shapers[j].name, p, end - p))
     86 	{
     87 	  /* Reorder this shaper to position i */
     88 	 struct hb_shaper_pair_t t = shapers[j];
     89 	 memmove (&shapers[i + 1], &shapers[i], sizeof (shapers[i]) * (j - i));
     90 	 shapers[i] = t;
     91 	 i++;
     92 	}
     93 
     94       if (!*end)
     95 	break;
     96       else
     97 	p = end + 1;
     98     }
     99 
    100     if (!hb_atomic_ptr_cmpexch (&static_shapers, NULL, shapers)) {
    101       free (shapers);
    102       goto retry;
    103     }
    104 
    105 #ifdef HB_USE_ATEXIT
    106     atexit (free_static_shapers); /* First person registers atexit() callback. */
    107 #endif
    108   }
    109 
    110   return shapers;
    111 }
    112