How to ensure to run some code on same background thread?

Question

I am using realm in my iOS Swift project. Search involve complex filters for a big data set. So I am fetching records on background thread.

But realm can be used onl

Answer 1

You have to create your own thread with a run loop for that. Apple gives an example for a custom run loop in Objective C. You may create a thread class in Swift with that like:

class MyThread: Thread {
    public var runloop: RunLoop?
    public var done = false

    override func main() {
        runloop = RunLoop.current
        done = false
        repeat {
            let result = CFRunLoopRunInMode(.defaultMode, 10, true)
            if result == .stopped  {
                done = true
            }
        }
        while !done
    }

    func stop() {
        if let rl = runloop?.getCFRunLoop() {
            CFRunLoopStop(rl)
            runloop = nil
            done = true
        }
    }
}

Now you can use it like this:

    let thread = MyThread()

    thread.start()
    sleep(1)
    thread.runloop?.perform {
        print("task")
    }
    thread.runloop?.perform {
        print("task 2")
    }
    thread.runloop?.perform {
        print("task 3")
    }

Note: The sleep is not very elegant but needed, since the thread needs some time for its startup. It should be better to check if the property runloop is set, and perform the block later if necessary. My code (esp. runloop) is probably not safe for race conditions, and it's only for demonstration. ;-)