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002f206faf
There are a few places in Git that would benefit from a fast most-recently-used cache (e.g., the list of packs, which we search linearly but would like to order based on locality). This patch introduces a generic list that can be used to store arbitrary pointers in most-recently-used order. The implementation is just a doubly-linked list, where "marking" an item as used moves it to the front of the list. Insertion and marking are O(1), and iteration is O(n). There's no lookup support provided; if you need fast lookups, you are better off with a different data structure in the first place. There is also no deletion support. This would not be hard to do, but it's not necessary for handling pack structs, which are created and never removed. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
51 lines
968 B
C
51 lines
968 B
C
#include "cache.h"
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#include "mru.h"
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void mru_append(struct mru *mru, void *item)
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{
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struct mru_entry *cur = xmalloc(sizeof(*cur));
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cur->item = item;
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cur->prev = mru->tail;
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cur->next = NULL;
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if (mru->tail)
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mru->tail->next = cur;
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else
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mru->head = cur;
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mru->tail = cur;
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}
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void mru_mark(struct mru *mru, struct mru_entry *entry)
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{
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/* If we're already at the front of the list, nothing to do */
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if (mru->head == entry)
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return;
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/* Otherwise, remove us from our current slot... */
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if (entry->prev)
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entry->prev->next = entry->next;
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if (entry->next)
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entry->next->prev = entry->prev;
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else
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mru->tail = entry->prev;
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/* And insert us at the beginning. */
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entry->prev = NULL;
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entry->next = mru->head;
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if (mru->head)
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mru->head->prev = entry;
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mru->head = entry;
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}
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void mru_clear(struct mru *mru)
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{
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struct mru_entry *p = mru->head;
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while (p) {
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struct mru_entry *to_free = p;
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p = p->next;
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free(to_free);
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}
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mru->head = mru->tail = NULL;
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}
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