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pg_include/lib/dllist.h

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+/*-------------------------------------------------------------------------
+ *
+ * dllist.h
+ *		simple doubly linked list primitives
+ *		the elements of the list are void* so the lists can contain anything
+ *		Dlelem can only be in one list at a time
+ *
+ *
+ *	 Here's a small example of how to use Dllists:
+ *
+ *	 Dllist *lst;
+ *	 Dlelem *elt;
+ *	 void	*in_stuff;	  -- stuff to stick in the list
+ *	 void	*out_stuff
+ *
+ *	 lst = DLNewList();				   -- make a new dllist
+ *	 DLAddHead(lst, DLNewElem(in_stuff)); -- add a new element to the list
+ *											 with in_stuff as the value
+ *	  ...
+ *	 elt = DLGetHead(lst);			   -- retrieve the head element
+ *	 out_stuff = (void*)DLE_VAL(elt);  -- get the stuff out
+ *	 DLRemove(elt);					   -- removes the element from its list
+ *	 DLFreeElem(elt);				   -- free the element since we don't
+ *										  use it anymore
+ *
+ *
+ * It is also possible to use Dllist objects that are embedded in larger
+ * structures instead of being separately malloc'd.  To do this, use
+ * DLInitElem() to initialize a Dllist field within a larger object.
+ * Don't forget to DLRemove() each field from its list (if any) before
+ * freeing the larger object!
+ *
+ *
+ * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/lib/dllist.h
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef DLLIST_H
+#define DLLIST_H
+
+struct Dllist;
+struct Dlelem;
+
+typedef struct Dlelem
+{
+	struct Dlelem *dle_next;	/* next element */
+	struct Dlelem *dle_prev;	/* previous element */
+	void	   *dle_val;		/* value of the element */
+	struct Dllist *dle_list;	/* what list this element is in */
+} Dlelem;
+
+typedef struct Dllist
+{
+	Dlelem	   *dll_head;
+	Dlelem	   *dll_tail;
+} Dllist;
+
+extern Dllist *DLNewList(void); /* allocate and initialize a list header */
+extern void DLInitList(Dllist *list);	/* init a header alloced by caller */
+extern void DLFreeList(Dllist *list);	/* free up a list and all the nodes in
+										 * it */
+extern Dlelem *DLNewElem(void *val);
+extern void DLInitElem(Dlelem *e, void *val);
+extern void DLFreeElem(Dlelem *e);
+extern void DLRemove(Dlelem *e);	/* removes node from list */
+extern void DLAddHead(Dllist *list, Dlelem *node);
+extern void DLAddTail(Dllist *list, Dlelem *node);
+extern Dlelem *DLRemHead(Dllist *list); /* remove and return the head */
+extern Dlelem *DLRemTail(Dllist *list);
+extern void DLMoveToFront(Dlelem *e);	/* move node to front of its list */
+
+/* These are macros for speed */
+#define DLGetHead(list)  ((list)->dll_head)
+#define DLGetTail(list)  ((list)->dll_tail)
+#define DLGetSucc(elem)  ((elem)->dle_next)
+#define DLGetPred(elem)  ((elem)->dle_prev)
+#define DLGetListHdr(elem)	((elem)->dle_list)
+
+#define DLE_VAL(elem)	((elem)->dle_val)
+
+#endif   /* DLLIST_H */