Database locked using FMDB for iOS - ios

Question

First of all, I'd like to say that I'm really having a bad time trying to configure and use my SQLite DB in a background thread so that the main thread is not blocked.
After I found a little guide somewhere on the Internet, I've decided to go for the FMDB wrapper.
All the methods related to the DB operations are in the same class and this is where I'm getting errors:
I've set the static variables like this:
static FMDatabaseQueue *_queue;
static NSOperationQueue *_writeQueue;
static NSRecursiveLock *_writeQueueLock;
Then in my init method I have:
- (id)init {
self = [super init];
if (self) {
_queue = [FMDatabaseQueue databaseQueueWithPath:[self GetDocumentPath]];
_writeQueue = [NSOperationQueue new];
[_writeQueue setMaxConcurrentOperationCount:1];
_writeQueueLock = [NSRecursiveLock new];
}
return self;
}
And this is the method that gives me the error:
- (void)UpdateTime:(NSString *)idT :(int)userId {
[_writeQueue addOperationWithBlock:^{
[_writeQueueLock lock];
[_queue inDatabase:^(FMDatabase *dbase) {
AppDelegate *deleg = (AppDelegate *)[[UIApplication sharedApplication] delegate];
if (![dbase executeUpdate:#"update orari set orario=datetime(orario, '? minutes') where nome=? and dataid>=? and idutente=?"
withArgumentsInArray:#[[NSNumber numberWithFloat:deleg.diff], deleg.nome, [NSNumber numberWithInt:deleg.idMed], [NSNumber numberWithInt: userId]]]) {
NSLog(#"error");
}
}];
[_writeQueueLock unlock];
}];
[_writeQueue addOperationWithBlock:^{
[_writeQueueLock lock];
[_queue inDatabase:^(FMDatabase *dbase) {
AppDelegate *deleg = (AppDelegate *)[[UIApplication sharedApplication] delegate];
if (![dbase executeUpdate:#"UPDATE orari SET presa=1 where dataid=? and idutente=?"
withArgumentsInArray:#[[NSNumber numberWithInt:deleg.identific], [NSNumber numberWithInt: userId]]]) {
NSLog(#"error");
}
}];
[_writeQueueLock unlock];
}];
[self AddNotification];
}
These are the errors I'm getting:
*** -[NSRecursiveLock dealloc]: lock (<NSRecursiveLock: 0xc38b350> '(null)') deallocated while still in use
DB Error: 5 "database is locked"
*** -[NSRecursiveLock unlock]: lock (<NSRecursiveLock: 0x13378d20> '(null)') unlocked when not locked
From the guide I've read, I supposed that the access to my DB would have been "serialized", and each update would have been added to a queue and executed one at a time.
As you can see, I have a lot to learn about this topic, so any help would really be appreciated.

Answer 1

As I can See you have not created shared instance or singleton instance of this init call
- (id)init {
self = [super init];
if (self) {
_queue = [FMDatabaseQueue databaseQueueWithPath:[self GetDocumentPath]];
_writeQueue = [NSOperationQueue new];
[_writeQueue setMaxConcurrentOperationCount:1];
_writeQueueLock = [NSRecursiveLock new];
}
return self;
}
This should be a singleton call as you will create multiple instance of NSOperationQueue which will make DB vulnurable in a multi-threaded environment, try making it singleton call for your database either using GCD or
static DBManager *sharedInstance = nil;
+(DBManager*)getSharedInstance{
if (!sharedInstance) {
sharedInstance = [[super allocWithZone:NULL]init];
_queue = [FMDatabaseQueue databaseQueueWithPath:[self GetDocumentPath]];
_writeQueue = [NSOperationQueue new];
[_writeQueue setMaxConcurrentOperationCount:1];
_writeQueueLock = [NSRecursiveLock new];
}
return sharedInstance;
}
It might solve your problem and this is first time I am answering here and I am new to the environment so please be little bit forgiving :) Thanks