1 /* 2 * Copyright © 2019 Facebook, 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 * Facebook Author(s): Behdad Esfahbod 25 */ 26 27 #ifndef HB_POOL_HH 28 #define HB_POOL_HH 29 30 #include "hb.hh" 31 32 /* Memory pool for persistent allocation of small objects. 33 * 34 * Some AI musings on this, not necessarily true: 35 * 36 * This is a very simple implementation, but it's good enough for our 37 * purposes. It's not thread-safe. It's not very fast. It's not 38 * very memory efficient. It's not very cache efficient. It's not 39 * very anything efficient. But it's simple and it works. And it's 40 * good enough for our purposes. If you need something more 41 * sophisticated, use a real allocator. Or use a real language. */ 42 43 template <typename T, unsigned ChunkLen = 32> 44 struct hb_pool_t 45 { hb_pool_thb_pool_t46 hb_pool_t () : next (nullptr) {} ~hb_pool_thb_pool_t47 ~hb_pool_t () 48 { 49 next = nullptr; 50 51 + hb_iter (chunks) 52 | hb_apply (hb_free) 53 ; 54 } 55 allochb_pool_t56 T* alloc () 57 { 58 if (unlikely (!next)) 59 { 60 if (unlikely (!chunks.alloc (chunks.length + 1))) return nullptr; 61 chunk_t *chunk = (chunk_t *) hb_malloc (sizeof (chunk_t)); 62 if (unlikely (!chunk)) return nullptr; 63 chunks.push (chunk); 64 next = chunk->thread (); 65 } 66 67 T* obj = next; 68 next = * ((T**) next); 69 70 hb_memset (obj, 0, sizeof (T)); 71 72 return obj; 73 } 74 releasehb_pool_t75 void release (T* obj) 76 { 77 * (T**) obj = next; 78 next = obj; 79 } 80 81 private: 82 83 static_assert (ChunkLen > 1, ""); 84 static_assert (sizeof (T) >= sizeof (void *), ""); 85 static_assert (alignof (T) % alignof (void *) == 0, ""); 86 87 struct chunk_t 88 { threadhb_pool_t::chunk_t89 T* thread () 90 { 91 for (unsigned i = 0; i < ARRAY_LENGTH (arrayZ) - 1; i++) 92 * (T**) &arrayZ[i] = &arrayZ[i + 1]; 93 94 * (T**) &arrayZ[ARRAY_LENGTH (arrayZ) - 1] = nullptr; 95 96 return arrayZ; 97 } 98 99 T arrayZ[ChunkLen]; 100 }; 101 102 T* next; 103 hb_vector_t<chunk_t *> chunks; 104 }; 105 106 107 #endif /* HB_POOL_HH */ 108