Realm incorrect thread access crash - ios

Question

I am late to this party and newbie to Realm
I have created a signleton class having following method to write but it crashes at times because incorrect thread access
Let me know what I am doing wrong here.
func save<T:Object>(_ realmObject:T) {
let backgroundQueue = DispatchQueue(label: ".realm", qos: .background)
backgroundQueue.async {
let realm = try! Realm()
try! realm.write {
realm.add(realmObject)
}
}
}

Answer 1

Thanks for asking this question! The incorrect thread access exception is a result of the Realm object being passed through a thread boundary. I recommend reading the documentation on Passing Instances Across Threads and this blog post (specifically the section on thread confinement).
In order to avoid that exception, you'll need to change your code to:
func save<T:Object>(_ realmObject:T) {
let realmObjectRef = ThreadSafeReference(to: realmObject)
let backgroundQueue = DispatchQueue(label: ".realm", qos: .background)
backgroundQueue.async {
guard let realmObject = realm.resolve(realmObjectRef) else {
return // although proper error handling should happen
}
let realm = try! Realm()
try! realm.write {
realm.add(realmObject)
}
}
}
The ThreadSafeReference object, documented here provides you with a thread safe reference for a given Realm object that can be passed through a thread boundary and then resolved back to a thread-confined object once you're safely inside a different thread. I hope this helps and let me know if you need anything else. Cheers!