PJSIP random crashing in Swift - ios

Question

I'm build a softphone for iOS using Swift and PJSIP.
The PJSIP documentation states: "PJLIB API should be called from a registered thread, otherwise it will raise assertion such as "Calling pjlib from unknown/external thread...". With GCD, we cannot really be sure of which thread executing the PJLIB function. Registering that thread to PJLIB seems to be a simple and easy solution, however it potentially introduces a random crash which is harder to debug. Here are few possible crash scenarios:
PJLIB's pj_thread_desc should remain valid until the registered thread stopped, otherwise crash of invalid pointer access may occur, e.g: in pj_thread_check_stack().
Some compatibility problems between GCD and PJLIB, see #1837 for more info.
If you want to avoid any possibility of blocking operation by PJLIB (or any higher API layer such as PJMEDIA, PJNATH, PJSUA that usually calls PJLIB), instead of dispatching the task using GCD, the safest way is to create and manage your own thread pool and register that thread pool to PJLIB. Or alternatively, simply use PJSUA timer mechanism (with zero delay), see pjsua_schedule_timer()/pjsua_schedule_timer2() docs for more info."
So what I did was to use the class below found here on another thread in Stack Overflow:
class Worker {
private var thread: Thread?
private let semaphore = DispatchSemaphore(value: 0)
private let lock = NSRecursiveLock()
private var queue = [() -> Void]()
public func enqueue(_ block: #escaping () -> Void) { locked { queue.append(block) }
semaphore.signal()
if thread == nil { thread = Thread(block: work) thread?.start()
}
}
private func work() { while true { semaphore.wait()
let block = locked { queue.removeFirst() } block()
}
}
return block()
}
}
So every time I have to call any function from pjsip I use
worker.enqueue { }
For example:
worker.enqueue {
var threadError: NSError = NSError()
if !createPjSipThread(error: &threadError) {
print(threadError)
}
}
worker.enqueue { var error = NSError()
if !PjApp.shared().start(appDir: "", error: &error {
print(error)
}
}
Without the worker thread, the app crashes constantly (specially on TestFlight/Production Build).
Any ideias on what I'm missing or doing wrong? Thanks in advance.