Adding notification for when a YapDatabase instance is deallocated, a…

…nd thus has closed all references to the underlying sqlite files. Fixes issue #139

YapDatabase/YapDatabase.h

@@ -97,6 +97,44 @@ typedef id __nonnull (^YapDatabaseDeserializer)(NSString *collection, NSString *
 typedef id __nonnull (^YapDatabasePreSanitizer)(NSString *collection, NSString *key, id obj);
 typedef void (^YapDatabasePostSanitizer)(NSString *collection, NSString *key, id obj);
 
+/**
+ * This notification is posted when a YapDatabase instance is deallocated,
+ * and has thus closed all references to the underlying sqlite files.
+ * 
+ * If you intend to delete the sqlite file(s) from disk,
+ * it's recommended you use this notification as a hook to do so.
+ * 
+ * More info:
+ * The YapDatabase class itself is just a retainer for the filepath, blocks, config, etc.
+ * And YapDatabaseConnection(s) open a sqlite connection to the database file,
+ * and rely on the blocks & config in the parent YapDatabase class.
+ * Thus a YapDatabaseConnection instance purposely retains the YapDatabase instance.
+ * This means that in order to fully close all references to the underlying sqlite file(s),
+ * you need to deallocate YapDatabase and all associated YapDatabaseConnections.
+ * While this may be simple in concept, it's generally difficult to know exactly when all
+ * the instances have been deallocated. Especially when there may be a bunch of asynchronous operations going.
+ * 
+ * Therefore the best approach is to do the following:
+ * - destroy your YapDatabase instance (set it to nil)
+ * - destroy all YapDatabaseConnection instances
+ * - wait for YapDatabaseClosedNotification
+ * - use notification as hook to delete all associated sqlite files from disk
+ *
+ * The userInfo dictionary will look like this:
+ * @{
+ *     YapDatabasePathKey    : <NSString of full filePath to db.sqlite file>,
+ *     YapDatabasePathWalKey : <NSString of full filePath to db.sqlite-wal file>,
+ *     YapDatabasePathShmKey : <NSString of full filePath to db.sqlite-shm file>,
+ * }
+ *
+ * This notification is always posted to the main thread.
+**/
+extern NSString *const YapDatabaseClosedNotification;
+
+extern NSString *const YapDatabasePathKey;
+extern NSString *const YapDatabasePathWalKey;
+extern NSString *const YapDatabasePathShmKey;
+
 /**
  * This notification is posted following a readwrite transaction where the database was modified.
  * 
@@ -108,10 +146,10 @@ typedef void (^YapDatabasePostSanitizer)(NSString *collection, NSString *key, id
  *
  * The userInfo dictionary will look something like this:
  * @{
- *     YapDatabaseSnapshotKey = <NSNumber of snapshot, incremented per read-write transaction w/modification>,
- *     YapDatabaseConnectionKey = <YapDatabaseConnection instance that made the modification(s)>,
- *     YapDatabaseExtensionsKey = <NSDictionary with individual changeset info per extension>,
- *     YapDatabaseCustomKey = <Optional object associated with this change, set by you>,
+ *     YapDatabaseSnapshotKey   : <NSNumber of snapshot, incremented per read-write transaction w/modification>,
+ *     YapDatabaseConnectionKey : <YapDatabaseConnection instance that made the modification(s)>,
+ *     YapDatabaseExtensionsKey : <NSDictionary with individual changeset info per extension>,
+ *     YapDatabaseCustomKey     : <Optional object associated with this change, set by you>,
  * }
  *
  * This notification is always posted to the main thread.

YapDatabase/YapDatabase.m

@@ -28,6 +28,12 @@
   static const int ydbLogLevel = YDB_LOG_LEVEL_WARN;
 #endif
 
+NSString *const YapDatabaseClosedNotification = @"YapDatabaseClosedNotification";
+
+NSString *const YapDatabasePathKey    = @"databasePath";
+NSString *const YapDatabasePathWalKey = @"databasePath_wal";
+NSString *const YapDatabasePathShmKey = @"databasePath_shm";
+
 NSString *const YapDatabaseModifiedNotification = @"YapDatabaseModifiedNotification";
 
 NSString *const YapDatabaseSnapshotKey   = @"snapshot";
@@ -549,6 +555,16 @@ - (void)dealloc
 {
 	YDBLogVerbose(@"Dealloc <%@ %p: databaseName=%@>", [self class], self, [databasePath lastPathComponent]);
 
+	NSDictionary *userInfo = @{
+		YapDatabasePathKey    : self.databasePath     ?: @"",
+		YapDatabasePathWalKey : self.databasePath_wal ?: @"",
+		YapDatabasePathShmKey : self.databasePath_shm ?: @""
+	};
+	NSNotification *notification =
+	  [NSNotification notificationWithName:YapDatabaseClosedNotification
+	                                object:nil // Cannot retain self within dealloc method
+	                              userInfo:userInfo];
+
 	while ([connectionPoolValues count] > 0)
 	{
 		sqlite3 *aDb = (sqlite3 *)[[connectionPoolValues objectAtIndex:0] pointerValue];
@@ -583,6 +599,11 @@ - (void)dealloc
 	if (checkpointQueue)
 		dispatch_release(checkpointQueue);
 #endif
+
+	dispatch_async(dispatch_get_main_queue(), ^{
+
+		[[NSNotificationCenter defaultCenter] postNotification:notification];
+	});
 }
 
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