Add hb_pool_t<> for pooled memory allocation

src/Makefile.sources

@@ -129,6 +129,7 @@ HB_BASE_sources = \
 	hb-ot-var-mvar-table.hh \
 	hb-ot-var.cc \
 	hb-ot-vorg-table.hh \
+	hb-pool.hh \
 	hb-sanitize.hh \
 	hb-serialize.hh \
 	hb-set-digest.hh \

src/hb-pool.hh

@@ -0,0 +1,98 @@
+/*
+ * Copyright © 2019  Facebook, Inc.
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ * Facebook Author(s): Behdad Esfahbod
+ */
+
+#ifndef HB_POOL_HH
+#define HB_POOL_HH
+
+#include "hb.hh"
+
+/* Memory pool for persistent allocation of small objects. */
+
+template <typename T, unsigned ChunkLen = 16>
+struct hb_pool_t
+{
+  hb_pool_t () : next (nullptr) {}
+
+  ~hb_pool_t ()
+  {
+    next = nullptr;
+    + hb_iter (chunks)
+    | hb_apply ([] (chunk_t *_) { ::free (_); })
+    ;
+  }
+
+  T* alloc ()
+  {
+    if (unlikely (!next))
+    {
+      if (unlikely (!chunks.alloc (chunks.length + 1))) return nullptr;
+      chunk_t *chunk = (chunk_t *) malloc (sizeof (chunk_t));
+      if (unlikely (!chunk)) return nullptr;
+      chunks.push (chunk);
+      next = chunk->thread ();
+    }
+
+    T* obj = next;
+    next = * ((T**) next);
+
+    *obj = Null (T);
+
+    return obj;
+  }
+
+  void free (T* obj)
+  {
+    * (T**) obj = next;
+    next = obj;
+  }
+
+  private:
+
+  static_assert (ChunkLen > 1, "");
+  static_assert (sizeof (T) >= sizeof (void *), "");
+  static_assert (alignof (T) % sizeof (void *) == 0, "");
+
+  struct chunk_t
+  {
+    T* thread ()
+    {
+      for (unsigned i = 0; i < ARRAY_LENGTH (arrayZ) - 1; i++)
+        * (T**) &arrayZ[i] = &arrayZ[i + 1];
+
+      * (T**) &arrayZ[ARRAY_LENGTH (arrayZ) - 1] = nullptr;
+
+      return arrayZ;
+    }
+
+    T arrayZ[ChunkLen];
+  };
+
+  T* next;
+  hb_vector_t<chunk_t *> chunks;
+};
+
+
+#endif /* HB_POOL_HH */