How to properly call SQLite functions from background thread on iPhone?

Question

I\'m using an SQLite database in my iPhone app. At startup, there are some database actions that I want to perform in a separate thread. (I\'m doing this mainly to minimize

Answer 1

SQLite handles (sqlite3_stmt * for sure, and sqlite3 * I think) are thread-specific. The correct way to call them from multiple threads is to maintain a separate set of handles for each thread.

Answer 2

I would use NSOperation and just do everything there during startup. NSOperation rocks. Did I say how much NSOperation rocks? It does. Rock, that is.

Answer 3

If you are still not having any luck with above, you could try using this wrapper by EnormEGO https://github.com/jdp-global/egodatabase

They use asynchronous callbacks which may kill two birds with one stone.

Have a look at my Readme section for EGODatabaseRequest - asynchronous requests to db

Answer 4

If you want to use SQLite on multiple threads with no restrictions, do the following before opening your connection:

sqlite3_shutdown();
sqlite3_config(SQLITE_CONFIG_SERIALIZED);
sqlite3_initialize();

http://www.sqlite.org/threadsafe.html

Answer 5

My solution is to delete the app on my device (I want to delete the database that I created). This solves the problem for me.

Answer 6

I've tried these two solutions and they worked perfectly. You can either use critical sections or NSOperationQueue and I prefer the first one, here is the code for both of them:

define some class "DatabaseController" and add this code to its implementation:

static NSString * DatabaseLock = nil;
+ (void)initialize {
    [super initialize];
    DatabaseLock = [[NSString alloc] initWithString:@"Database-Lock"];
}
+ (NSString *)databaseLock {
    return DatabaseLock;
}

- (void)writeToDatabase1 {
    @synchronized ([DatabaseController databaseLock]) {
        // Code that writes to an sqlite3 database goes here...
    }
}
- (void)writeToDatabase2 {
    @synchronized ([DatabaseController databaseLock]) {
        // Code that writes to an sqlite3 database goes here...
    }
}

OR to use the NSOperationQueue you can use:

static NSOperationQueue * DatabaseQueue = nil;
+ (void)initialize {
    [super initialize];

    DatabaseQueue = [[NSOperationQueue alloc] init];
    [DatabaseQueue setMaxConcurrentOperationCount:1];
}
+ (NSOperationQueue *)databaseQueue {
    return DatabaseQueue;
}

- (void)writeToDatabase {
    NSInvocationOperation * operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(FUNCTION_THAT_WRITES_TO_DATABASE) object:nil];
    [operation setQueuePriority:NSOperationQueuePriorityHigh];
    [[DatabaseController databaseQueue] addOperations:[NSArray arrayWithObject:operation] waitUntilFinished:YES];
    [operation release];
}

these two solutions block the current thread until the writing to database is finished which you may consider in most of the cases.