Adding background thread

[crenelle]

I've been using GRDB in a Swift/SwiftUI app since late 2019, and haven't been encountering any serious or wacky issues in that time (I think I asked about something in 2020). My app was simple, everything running in main and there were no issues to speak of.

Now I'm adding a background thread and having most of the database reads (there are no writes) and computations being done in that, in order to brighten up the UI. I have stuff like:
if (dbPool != nil) {
do {
try dbPool.read { db in
let expData = try Row.fetchOne(db, sql:query, arguments:[symbol, contractYear, contractMonth])
exp = toString(expData?["expiration"])
expRec["expiration"] = exp
let boundryData = try Row.fetchOne(db,
sql:"""
SELECT DATE(?,?) as cutoff_date
""",
arguments:[exp, sub8day]
)
...

moved to the background thread. This code seems to run fine for a while and then it starts to take up the majority of runtime. It seems to spend most of the time doing a DatabasePool.read(:) myapp in a closure running OS_dispatch_queue.sync(execute:) libswiftDispatch.dylib, and the second DatabasePool.read(:) myapp in a closure running SerializedDatabase.sync(_:) myapp. This looks like thrashing.

I'd normally stew over something like this for a while (days) before asking about it, but then I noticed that the async / await support in GRBD is labeled experimental. SInce I'm just now making some sense with GCD vs async / await, I thought maybe I'd better ask early.

I'm not currently seeing warnings about updating published from background (I was earlier).

[groue]

Hello @crenelle,

GRDB support for Swift Concurrency, precisely async/await, is marked as "experimental" because any new version of the library may introduce a breaking change in those apis. This experimental flag does not mean "probably buggy". There's a FAQ about it: What Are Experimental Features?

You do not share any information about the way you are "adding a background thread", so it is impossible to guess what's wrong in your application. Please consider checking the Concurrency guide.