[tracker/lru-stmt-cache] libtracker-data: LRU ring for the TrackerDBStatement cache

[Philip Van Hoof <pvanhoof src gnome org>]

commit ddd6bf8a034afe136ec4c442fa07cad4e4e919a6
Author: Philip Van Hoof <philip codeminded be>
Date:   Tue Sep 21 13:59:41 2010 +0200

    libtracker-data: LRU ring for the TrackerDBStatement cache

 src/libtracker-data/tracker-db-interface-sqlite.c |   47 +++++++++++++++++++++
 1 files changed, 47 insertions(+), 0 deletions(-)
---
diff --git a/src/libtracker-data/tracker-db-interface-sqlite.c b/src/libtracker-data/tracker-db-interface-sqlite.c
index acb768f..e4bb71e 100644
--- a/src/libtracker-data/tracker-db-interface-sqlite.c
+++ b/src/libtracker-data/tracker-db-interface-sqlite.c
@@ -38,6 +38,8 @@
 
 #include "tracker-db-interface-sqlite.h"
 
+#define TRACKER_STMT_LRU_SIZE	1000
+
 struct TrackerDBInterface {
 	GObject parent_instance;
 
@@ -83,8 +85,15 @@ struct TrackerDBStatement {
 	TrackerDBInterface *db_interface;
 	sqlite3_stmt *stmt;
 	gboolean stmt_is_sunk;
+	TrackerDBStatement *next, *prev;
 };
 
+static struct {
+	TrackerDBStatement *head;
+	TrackerDBStatement *tail;
+	guint size;
+} stmt_lru = { NULL, NULL, 0 };
+
 struct TrackerDBStatementClass {
 	GObjectClass parent_class;
 };
@@ -878,9 +887,47 @@ tracker_db_interface_create_statement (TrackerDBInterface  *db_interface,
 			g_hash_table_replace (db_interface->dynamic_statements,
 			                      (gpointer) sqlite3_sql (sqlite_stmt),
 			                      stmt);
+
+			if (stmt_lru.size > TRACKER_STMT_LRU_SIZE) {
+				/* Destroy old stmt_lru.head and fix the ring */
+				stmt->prev = stmt_lru.head->prev;
+				stmt_lru.head->prev->next = stmt;
+				g_hash_table_remove (db_interface->dynamic_statements,
+				                     (gpointer) sqlite3_sql (stmt_lru.head->stmt));
+			} else {
+				if (stmt_lru.size == 0) {
+					stmt_lru.head = stmt;
+					stmt_lru.tail = stmt;
+				}
+				/* Put stmt as new head (new least recent used) */
+				stmt->prev = stmt_lru.head;
+				stmt_lru.head->next = stmt;
+				stmt_lru.size++;
+			}
+
+			/* Shared by both of above */
+			stmt_lru.tail->prev = stmt;
+			stmt->next = stmt_lru.tail;
+			stmt_lru.head = stmt;
 		}
 	} else {
 		tracker_db_statement_sqlite_reset (stmt);
+
+		if (stmt == stmt_lru.head) {
+			/* Current stmt is least used, shift the ring */
+			stmt_lru.head = stmt_lru.head->next;
+			stmt_lru.tail = stmt_lru.tail->next;
+		} else if (stmt != stmt_lru.tail) {
+			/* Take stmt out of the list */
+			stmt->prev->next = stmt->next;
+			stmt->next->prev = stmt->prev;
+			/* Put stmt as tail (most recent used) */
+			stmt->next = stmt_lru.head;
+			stmt_lru.head->prev = stmt;
+			stmt->prev = stmt_lru.tail;
+			stmt_lru.tail->next = stmt;
+			stmt_lru.tail = stmt;
+		} /* if (stmt == tail), do nothing, of course */
 	}
 
 	g_free (full_query);