Completion handlers defaulting to main thread #9276
Description
[REQUIRED] Step 1: Describe your environment
- Xcode version:
13.2 (13C90) - Firebase SDK version:
8.12.0 - Installation method:
Swift Package Manager(select one) - Firebase Component:
Firestore - Target platform(s):
All
[REQUIRED] Step 2: Describe the problem
Steps to reproduce:
Full disclosure beforehand, this may not be a bug, this may be intentional but I can't find anything saying so.
The main methods in Firestore automatically reenter the main thread when completed. So any work that may be intended to be on a background thread (eg, the getDocuments method was called on the background thread) will be put on the main thread instead.
This can cause confusion when a method like Firestore.firestore().getDocuments was called on a background thread already, and wastes time reentering the main thread. This also produces a small amount of spaghetti code to bring the work back onto the original thread the method was called from.
Intended Functionality
When a method is called, it reenters the thread from before when completing the work Firestore had to do. Example in the Relevant Code section
Relevant Code:
The current method to make this happen as intended.
// Enter the background thread
DispatchQueue.global(qos: .background).async { [weak self] in
// Make a query (in this example querying some Employees documents)
Firestore.firestore().collection("Employees").getDocuments { [weak self] (snapshot, error) in
// Ugly extra DispatchQueue call just to reenter the thread we were already on
DispatchQueue.global(qos: .background).async { [weak self] in
// do the work now on the background thread
}
}
}The intended method:
DispatchQueue.global(qos: .background).async { [weak self] in
Firestore.firestore().collection("Employees").getDocuments { [weak self] (snapshot, error) in
// Do the work on the background thread it was called from
}
}