Swift: Performing operation in background using GCD

[parvez....@decurtis.com]

For an iOS application using Couchbase lite version 1.3.1 (build 6), I need to move all things related to couchbase on a background queue as UI is not directly consuming the data from database. I tried below code snippet to start the things in background but it is printing warning in console as:

-[CBLDatabase waitFor:] cannot be used with dispatch queues, only runloops {at -[CBLDatabase waitFor:]:183}

The code for dispatchQueue setup is as below:

var manager:CBLManager! //global variable

var serialQueue: DispatchQueue! //global variable

manager = CBLManager.sharedInstance().copy()

serialQueue = DispatchQueue(label: "com.background.process")

manager.dispatchQueue = serialQueue

After above setup, I call a function from main thread:

public func setupDatabase(){

        

        var databaseError: Error?

        

        serialQueue.async {

            do{

                self.database = try self.manager.databaseNamed(name)

                self.setupDatabaseReplication()

                self.registerModelClasses()

                self.setupViews()                

            }catch{

                print("Encountered error: \(error) while setting up database")

            }

        }        

}

All the function called inside the do block like database replication, register model classes etc are not dispatching on other queues but are instead simple functions. Why am I getting warning in this case?

What is wrong with above?

Is their any other way to accomplish things in background? I want to maintain a single queue to perform all database operations.

Thanks

[Jens Alfke]

On Jul 26, 2017, at 7:40 AM, parvez....@decurtis.com wrote:

What is wrong with above?

You’re calling -[CBLLiveQuery waitForRows]. This isn’t supported on GCD queues (for complicated reasons.) Instead of blocking, use KVO to observe the .rows property and do your stuff when it changes.

—Jens