Implement an initial version of reference counting.

include/refcount.h

@@ -0,0 +1,79 @@
+#ifndef LIBABACUS_REFCOUNT_H
+#define LIBABACUS_REFCOUNT_H
+
+#include "result.h"
+
+/**
+ * A struct for holding
+ * the number of references
+ * to a value, as well as the function required
+ * to free the value.
+ */
+struct libab_ref_count_s {
+    /**
+     * The fucntion to free the value.
+     * Can be NULL for no-op.
+     */
+    void (*free_func)(void* data);
+    /**
+     * The number of references that
+     * prevent the deallocation of the value.
+     */
+    int strong;
+    /**
+     * The number of references
+     * that still exist, even to a freed instance.
+     */
+    int weak;
+};
+
+/**
+ * A reference to a value.
+ */
+struct libab_ref_s {
+    /**
+     * Whether this reference is a strong reference.
+     */
+    int strong;
+    /**
+     * The reference count struct keeping track
+     * of how many references are pointing to the value.
+     */
+    struct libab_ref_count_s* count;
+    /**
+     * The value this reference holds.
+     */
+    void* data;
+};
+
+typedef struct libab_ref_s libab_ref;
+typedef struct libab_ref_count_s libab_ref_count;
+
+/**
+ * Creates a new referene, using the given data and free function.
+ * @param ref the reference to initialize with the given data.
+ * @param data the data to reference count.
+ * @param free_func the function to use to realease the data when refcount reaches 0.
+ * @return the result of the construction of the reference.
+ */
+libab_result libab_ref_new(libab_ref* ref, void* data, void (*free_func)(void* data));
+/**
+ * Turns the given reference into a weak reference,
+ * making it not keep the data allocated.
+ */
+void libab_ref_weaken(libab_ref* ref);
+/**
+ * Releases this particular reference to the data.
+ * This doesn't necessarily free the underlying data.
+ */
+void libab_ref_free(libab_ref* ref);
+/**
+ * Copies this reference, thereby increasing the reference count.
+ */
+void libab_ref_copy(libab_ref* ref, libab_ref* into);
+/**
+ * Gets the value of the reference.
+ */
+void* libab_ref_get(libab_ref* ref);
+
+#endif