Commit a05406e6 authored by Martin Mareš's avatar Martin Mareš

Implemented deletion/insertion/asynchronous-walk lists.

For example of their use, look at comments in lib/slists.h.
parent 29ad2c9e
......@@ -20,3 +20,5 @@ xmalloc.c
printf.c
string.h
patmatch.c
slists.c
slists.h
/*
* 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.
*/
#define _BIRD_SLISTS_C_
#include "nest/bird.h"
#include "lib/slists.h"
static inline void
s_merge(snode *from, snode *to)
{
siterator *f, *g;
if (!(f = from->readers))
return;
if (!(g = to->readers))
{
/* Fast path */
to->readers = f;
f->prev = (siterator *) to;
fixup:
while (f && f->node)
{
f->node = NULL;
f = f->next;
}
return;
}
/* Really merging */
while (g->next)
g = g->next;
g->next = f;
f->prev = g;
goto fixup;
}
snode *
s_get(siterator *i)
{
siterator *f, *g;
snode *n;
if (!(n = i->node))
{
/*
* No node found. We have to walk the iterator list backwards
* to find where are we linked.
*/
f = i;
while (!f->null)
f = f->prev;
n = (snode *) f;
}
f = i->prev; /* Maybe the snode itself */
g = i->next;
f->next = g;
if (g)
g->prev = f;
return n;
}
void
s_put(siterator *i, snode *n)
{
siterator *f;
i->node = n;
if (f = n->readers)
f->prev = i;
i->next = f;
n->readers = i;
i->prev = (siterator *) n;
i->null = NULL;
}
void
s_add_tail(slist *l, snode *n)
{
snode *z = l->tail;
n->next = (snode *) &l->null;
n->prev = z;
z->next = n;
l->tail = n;
n->readers = NULL;
}
void
s_add_head(slist *l, snode *n)
{
snode *z = l->head;
n->next = z;
n->prev = (snode *) &l->head;
z->prev = n;
l->head = n;
n->readers = NULL;
}
void
s_insert_node(snode *n, snode *after)
{
snode *z = after->next;
n->next = z;
n->prev = after;
after->next = n;
z->prev = n;
n->readers = NULL;
}
void
s_rem_node(snode *n)
{
snode *z = n->prev;
snode *x = n->next;
z->next = x;
x->prev = z;
s_merge(n, x);
}
void
s_init_list(slist *l)
{
l->head = (snode *) &l->null;
l->null = NULL;
l->tail = (snode *) &l->head;
l->tail_readers = NULL;
}
void
s_add_tail_list(slist *to, slist *l)
{
snode *p = to->tail;
snode *q = l->head;
p->next = q;
q->prev = p;
q = l->tail;
q->next = (snode *) &to->null;
to->tail = q;
s_merge((snode *) &l->null, (snode *) &to->null);
}
#ifdef TEST
#include "lib/resource.h"
#include <stdio.h>
void dump(char *c, slist *a)
{
snode *x;
puts(c);
for(x=SHEAD(*a); x; x=x->next)
{
siterator *i, *j;
printf("%p", x);
j = (siterator *) x;
for(i=x->readers; i; i=i->next)
{
if (i->prev != j)
printf(" ???");
j = i;
printf(" [%p:%p]", i, i->node);
}
putchar('\n');
}
puts("---");
}
int main(void)
{
slist a, b;
snode *x, *y;
siterator i, j;
s_init_list(&a);
s_init_list(&b);
x = xmalloc(sizeof(*x));
s_add_tail(&a, x);
x = xmalloc(sizeof(*x));
s_add_tail(&a, x);
x = xmalloc(sizeof(*x));
s_add_tail(&a, x);
dump("1", &a);
s_init(&i, &a);
s_init(&j, &a);
dump("2", &a);
x = s_get(&i);
printf("Got %p\n", x);
dump("3", &a);
s_put(&i, x->next);
dump("4", &a);
y = s_get(&j);
while (y)
{
s_put(&j, y);
dump("5*", &a);
y = s_get(&j)->next;
}
dump("5 done", &a);
s_rem_node(a.head->next);
dump("6 (deletion)", &a);
s_put(&i, s_get(&i)->next);
dump("6 (relink)", &a);
x = xmalloc(sizeof(*x));
s_add_tail(&b, x);
dump("7 (second list)", &b);
s_add_tail_list(&b, &a);
dump("8 (after merge)", &b);
return 0;
}
#endif
/*
* 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
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment