From a05406e69c699c8b6f43bf58f47b8b0385113083 Mon Sep 17 00:00:00 2001
From: Martin Mares <mj@ucw.cz>
Date: Sun, 20 Dec 1998 13:56:27 +0000
Subject: Implemented deletion/insertion/asynchronous-walk lists. For example
 of their use, look at comments in lib/slists.h.

---
 lib/slists.h | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 lib/slists.h

(limited to 'lib/slists.h')

diff --git a/lib/slists.h b/lib/slists.h
new file mode 100644
index 00000000..27520c9f
--- /dev/null
+++ b/lib/slists.h
@@ -0,0 +1,88 @@
+/*
+ *	BIRD Library -- Safe Linked Lists
+ *
+ *	(c) 1998 Martin Mares <mj@ucw.cz>
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ */
+
+#ifndef _BIRD_SLISTS_H_
+#define _BIRD_SLISTS_H_
+
+/*
+ *  These linked lists work in a way similar to standard lists defined
+ *  in lib/lists.h, but in addition to all usual list functions they
+ *  provide fast deletion/insertion/everything-safe asynchronous
+ *  walking.
+ *
+ *  Example:
+ *		slist l;
+ *		siterator i;
+ *		snode *n;
+ *
+ *	       	s_init(&i, &l);		// Initialize iteration
+ *		...
+ *		n = s_get(&i);		// Some time later, fetch present
+ *					// value of the iterator and unlink it
+ *					// from the list.
+ *		while (n->next) {
+ *		     ...
+ *		     if (decided_to_stop) {
+ *			s_put(&i, n);	// Store current position (maybe even
+ *					// that we stay at list end)
+ *			return;		// and return
+ *		     }
+ *		     ...
+ *		}
+ *		// After finishing, don't link the iterator back
+ */
+
+typedef struct snode {
+  struct snode *next, *prev;
+  struct siterator *readers;
+} snode;
+
+typedef struct slist {			/* In fact two overlayed snodes */
+  struct snode *head, *null, *tail;
+  struct siterator *tail_readers;
+} slist;
+
+typedef struct siterator {
+  /*
+   * Caution: Layout of this structure depends hard on layout of the
+   *	      snode. Our `next' must be at position of snode `readers'
+   *	      field, our `null' must be at position of `prev' and it must
+   *	      contain NULL in order to distinguish between siterator
+   *	      and snode (snodes with NULL `prev' field never carry
+   *	      iterators). You are not expected to understand this.
+   */
+  struct siterator *prev, *null, *next;
+  /*
+   * For recently merged nodes this can be NULL, but then it's NULL
+   * for all successors as well. This is done to speed up iterator
+   * merging when there are lots of deletions.
+   */
+  snode *node;
+} siterator;
+
+#define SNODE (snode *)
+#define SHEAD(list) ((void *)((list).head))
+#define STAIL(list) ((void *)((list).tail))
+#define WALK_SLIST(n,list) for(n=SHEAD(list);(SNODE (n))->next; \
+				n=(void *)((SNODE (n))->next))
+#define WALK_SLIST_DELSAFE(n,nxt,list) \
+     for(n=SHEAD(list); nxt=(void *)((SNODE (n))->next); n=(void *) nxt)
+#define EMPTY_SLIST(list) (!(list).head->next)
+
+void s_add_tail(slist *, snode *);
+void s_add_head(slist *, snode *);
+void s_rem_node(snode *);
+void s_add_tail_list(slist *, slist *);
+void s_init_list(slist *);
+void s_insert_node(snode *, snode *);
+
+snode *s_get(siterator *);
+void s_put(siterator *, snode *n);
+static inline void s_init(siterator *i, slist *l) { s_put(i, SHEAD(*l)); }
+
+#endif
-- 
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