Flagsmith Lambda not working inside `suspendCoroutine`

[MamboBryan]

I've been trying to check if a featureFlag exists inside suspendCoroutine with runblocking but the resulting lambda doesn't execute. Something like the one below.

fun isWalletEnabled(): Boolean = runBlocking {
        Log.d(TAG, "isWalletEnabled: starting")
        suspendCoroutine { continuation ->
            Log.d(TAG, "isWalletEnabled: suspending")
            flagsmith.hasFeatureFlag("is_wallet_enabled") {
                Log.d(TAG, "isWalletEnabled: resulting -> ${it.getOrNull()}")
                continuation.resumeWith(Result.success(it.getOrNull() ?: false))
            }
        }
    }

Interestingly if I run it outside the suspendCoroutine it works and runs the lambda.

fun isWalletEnabled(): Boolean = runBlocking {
        Log.d(TAG, "isWalletEnabled: starting")
        flagsmith.hasFeatureFlag("is_wallet_enabled") {
            Log.d(TAG, "isWalletEnabled: resulting -> ${it.getOrNull()}")
        }
        true
    }

Anyway I could solve this?

[matthewelwell]

Hey @MamboBryan, thanks for raising this, and apologies for the delay in responding. I hope that you were able to find your own solution here, but if not and for future readers of this issue, I've added some details below.

This is actually a deadlock caused by runBlocking blocking the main thread while Retrofit (which we use under the hood) tries to deliver its callback back on that same main thread — so neither can proceed.

If possible, the fix is to drop runBlocking and make your function suspend instead:

suspend fun isWalletEnabled(): Boolean = suspendCoroutine { continuation ->
    flagsmith.hasFeatureFlag("is_wallet_enabled") {
        continuation.resumeWith(Result.success(it.getOrNull() ?: false))
    }
}

This should allow Retrofit to deliver its callback and resume execution normally and you can call this from a coroutine scope like viewModelScope.launch { ... }.

That being said, this does highlight that the SDK would probably benefit from first-class suspend function support to avoid this kind of friction — it's something that we'd like to add in due course. If you're willing to help out with a PR, we'd love to receive any contributions.