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diff --git a/src/common/ref.h b/src/common/ref.h
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+/*  Copyright (C) 2011 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+/*!
+ * \file ref.h
+ *
+ * \author Marek Vavrusa <marek.vavrusa@nic.cz>
+ *
+ * \brief Atomic reference counting structures.
+ *
+ * Reference counting allows implicit sharing of objects
+ * between threads with custom destructor functions.
+ *
+ * \addtogroup common_lib
+ * @{
+ */
+
+#ifndef _KNOTD_REF_H_
+#define _KNOTD_REF_H_
+
+#include <stddef.h>
+
+struct ref_t;
+
+/*! \brief Prototype for object destructor callback. */
+typedef void (*ref_destructor_t)(struct ref_t * p);
+
+/*!
+ * \brief Structure for reference counting.
+ *
+ * Size equals to two sizes of pointer size.
+ * Structure may be embedded to the structures which
+ * we want to use for reference counting.
+ *
+ * \code
+ * struct mystruct {
+ *    ref_t ref;
+ *    int mydata;
+ *    char *mystr;
+ * }
+ * \endcode
+ */
+typedef struct ref_t {
+	size_t count;          /*! \brief Reference counter. */
+	ref_destructor_t dtor; /*! \brief Object destructor function. */
+} ref_t;
+
+/*!
+ * \brief Initialize reference counter.
+ *
+ * Set reference counter to 0 and initialize destructor callback.
+ *
+ * \param p Reference-counted object.
+ * \param dtor Destructor function.
+ */
+void ref_init(ref_t *p, ref_destructor_t dtor);
+
+/*!
+ * \brief Mark object as used by the caller.
+ *
+ * Reference counter will be incremented.
+ *
+ * \param p Reference-counted object.
+ */
+void ref_retain(ref_t *p);
+
+/*!
+ * \brief Marks object as unused by the caller.
+ *
+ * Reference counter will be decremented.
+ *
+ * \param p Reference-counted object.
+ */
+void ref_release(ref_t *p);
+
+#endif /* _KNOTD_REF_H_ */
+
+/*! @} */