added configurable cache expiration handling

MapView/Map/RMDatabaseCache.h

@@ -43,5 +43,6 @@
 - (void)setPurgeStrategy:(RMCachePurgeStrategy)theStrategy;
 - (void)setCapacity:(NSUInteger)theCapacity;
 - (void)setMinimalPurge:(NSUInteger)thePurgeMinimum;
+- (void)setExpiryPeriod:(NSTimeInterval)theExpiryPeriod;
 
 @end

MapView/Map/RMDatabaseCache.m

@@ -57,6 +57,7 @@ @implementation RMDatabaseCache
 	RMCachePurgeStrategy purgeStrategy;
 	NSUInteger capacity;
 	NSUInteger minimalPurge;
+	NSTimeInterval expiryPeriod;
 }
 
 @synthesize databasePath;
@@ -169,6 +170,13 @@ - (void)setMinimalPurge:(NSUInteger)theMinimalPurge
 	minimalPurge = theMinimalPurge;
 }
 
+- (void)setExpiryPeriod:(NSTimeInterval)theExpiryPeriod
+{
+    expiryPeriod = theExpiryPeriod;
+
+    srand(time(NULL));
+}
+
 - (UIImage *)cachedImage:(RMTile)tile withCacheKey:(NSString *)aCacheKey
 {
 //	RMLog(@"DB cache check for tile %d %d %d", tile.x, tile.y, tile.zoom);
@@ -203,6 +211,28 @@ - (UIImage *)cachedImage:(RMTile)tile withCacheKey:(NSString *)aCacheKey
     if (capacity != 0 && purgeStrategy == RMCachePurgeStrategyLRU)
         [self touchTile:tile withKey:aCacheKey];
 
+    if (expiryPeriod > 0)
+    {
+        if (rand() % 100 == 0)
+        {
+            [writeQueueLock lock];
+
+            [queue inDatabase:^(FMDatabase *db)
+             {
+                 BOOL result = [db executeUpdate:@"DELETE FROM ZCACHE WHERE last_used < ?", [NSDate dateWithTimeIntervalSinceNow:-expiryPeriod]];
+
+                 if (result == NO)
+                     RMLog(@"Error expiring cache");
+
+                 [[db executeQuery:@"VACUUM"] close];
+             }];
+
+            [writeQueueLock unlock];
+
+            tileCount = [self countTiles];
+        }
+    }
+
 //    RMLog(@"DB cache     hit    tile %d %d %d (%@)", tile.x, tile.y, tile.zoom, [RMTileCache tileHash:tile]);
 
 	return cachedImage;
@@ -217,7 +247,7 @@ - (void)addImage:(UIImage *)image forTile:(RMTile)tile withCacheKey:(NSString *)
     {
         NSUInteger tilesInDb = [self count];
 
-        if (capacity <= tilesInDb)
+        if (capacity <= tilesInDb && expiryPeriod == 0)
             [self purgeTiles:MAX(minimalPurge, 1+tilesInDb-capacity)];
 
 //        RMLog(@"DB cache     insert tile %d %d %d (%@)", tile.x, tile.y, tile.zoom, [RMTileCache tileHash:tile]);

MapView/Map/RMTileCache.h

@@ -65,8 +65,11 @@ typedef enum {
     // This one has its own variable because we want to propagate cache hits down in
     // the cache hierarchy up to the memory cache
     RMMemoryCache *memoryCache;    
+    NSTimeInterval expiryPeriod;
 }
 
+- (id)initWithExpiryPeriod:(NSTimeInterval)period;
+
 + (NSNumber *)tileHash:(RMTile)tile;
 
 // Add another cache to the chain

MapView/Map/RMTileCache.m

@@ -41,13 +41,14 @@ @interface RMTileCache (Configuration)
 
 @implementation RMTileCache
 
-- (id)init
+- (id)initWithExpiryPeriod:(NSTimeInterval)period
 {
 	if (!(self = [super init]))
 		return nil;
 
 	caches = [[NSMutableArray alloc] init];
     memoryCache = nil;
+    expiryPeriod = period;
 
 	id cacheCfg = [[RMConfiguration configuration] cacheConfiguration];	
 	if (!cacheCfg)
@@ -87,6 +88,14 @@ - (id)init
 	return self;
 }
 
+- (id)init
+{
+    if (!(self = [self initWithExpiryPeriod:0]))
+        return nil;
+
+    return self;
+}
+
 - (void)dealloc
 {
     [memoryCache release]; memoryCache = nil;
@@ -230,11 +239,16 @@ @implementation RMTileCache (Configuration)
             RMLog(@"minimalPurge must be at least one and at most the cache capacity");
         }
     }
+
+    NSNumber *expiryPeriodNumber = [cfg objectForKey:@"expiryPeriod"];
+    if (expiryPeriodNumber != nil)
+        expiryPeriod = [expiryPeriodNumber intValue];
 
     RMDatabaseCache *dbCache = [[[RMDatabaseCache alloc] initUsingCacheDir:useCacheDir] autorelease];
     [dbCache setCapacity:capacity];
     [dbCache setPurgeStrategy:strategy];
     [dbCache setMinimalPurge:minimalPurge];
+    [dbCache setExpiryPeriod:expiryPeriod];
 
     return dbCache;
 }