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fa2fad3c06
Previously one had to use slist_delete(), implying an additional scan of the list, making this infrastructure considerably less efficient than traditional Lists when deletion of element(s) in a long list is needed. Modify the slist_foreach_modify() macro to support deleting the current element in O(1) time, by keeping a "prev" pointer in addition to "cur" and "next". Although this makes iteration with this macro a bit slower, no real harm is done, since in any scenario where you're not going to delete the current list element you might as well just use slist_foreach instead. Improve the comments about when to use each macro. Back-patch to 9.3 so that we'll have consistent semantics in all branches that provide ilist.h. Note this is an ABI break for callers of slist_foreach_modify(). Andres Freund and Tom Lane
115 lines
2.5 KiB
C
115 lines
2.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* ilist.c
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* support for integrated/inline doubly- and singly- linked lists
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*
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* Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/backend/lib/ilist.c
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*
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* NOTES
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* This file only contains functions that are too big to be considered
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* for inlining. See ilist.h for most of the goodies.
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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/* See ilist.h */
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#define ILIST_INCLUDE_DEFINITIONS
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#include "lib/ilist.h"
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/*
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* Delete 'node' from list.
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*
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* It is not allowed to delete a 'node' which is is not in the list 'head'
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*
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* Caution: this is O(n); consider using slist_delete_current() instead.
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*/
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void
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slist_delete(slist_head *head, slist_node *node)
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{
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slist_node *last = &head->head;
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slist_node *cur;
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bool found PG_USED_FOR_ASSERTS_ONLY = false;
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while ((cur = last->next) != NULL)
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{
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if (cur == node)
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{
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last->next = cur->next;
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#ifdef USE_ASSERT_CHECKING
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found = true;
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#endif
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break;
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}
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last = cur;
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}
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Assert(found);
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slist_check(head);
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}
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#ifdef ILIST_DEBUG
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/*
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* Verify integrity of a doubly linked list
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*/
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void
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dlist_check(dlist_head *head)
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{
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dlist_node *cur;
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if (head == NULL)
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elog(ERROR, "doubly linked list head address is NULL");
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if (head->head.next == NULL && head->head.prev == NULL)
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return; /* OK, initialized as zeroes */
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/* iterate in forward direction */
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for (cur = head->head.next; cur != &head->head; cur = cur->next)
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{
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if (cur == NULL ||
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cur->next == NULL ||
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cur->prev == NULL ||
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cur->prev->next != cur ||
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cur->next->prev != cur)
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elog(ERROR, "doubly linked list is corrupted");
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}
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/* iterate in backward direction */
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for (cur = head->head.prev; cur != &head->head; cur = cur->prev)
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{
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if (cur == NULL ||
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cur->next == NULL ||
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cur->prev == NULL ||
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cur->prev->next != cur ||
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cur->next->prev != cur)
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elog(ERROR, "doubly linked list is corrupted");
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}
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}
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/*
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* Verify integrity of a singly linked list
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*/
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void
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slist_check(slist_head *head)
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{
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slist_node *cur;
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if (head == NULL)
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elog(ERROR, "singly linked list head address is NULL");
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/*
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* there isn't much we can test in a singly linked list except that it
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* actually ends sometime, i.e. hasn't introduced a cycle or similar
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*/
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for (cur = head->head.next; cur != NULL; cur = cur->next)
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;
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}
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#endif /* ILIST_DEBUG */
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