Hi, my coroutine job immediately gets cancelled even before staring. Now I am not sure what could be...

# coroutines

[Rohan Maity]

Hi, my coroutine job immediately gets cancelled even before staring. Now I am not sure what could be reasons for this. What could be reasons for coroutine to get cancelled even before it is cancelled

private fun CoroutineScope?.launchWithNullCheck(
        block: suspend () -> Unit
    ) {
        this?.let {
            Log.d("FUI", "Scope not null")
            val job = launch {
                Log.d("FUI", "executing block not null")
                block()
            }
            Log.d("FUI", "job isActive ${job.isActive}, isCompleted: ${job.isCompleted}, isCancelled: ${job.isCancelled}")
        }
}

[Sam]

One possible reason is if the CoroutineScope that you’re launching it in contains an already-cancelled Job. Launching a job as a child of a cancelled job will immediately return a cancelled job and won’t start the coroutine. Hard to say if that’s what’s happening here, though. Can you give any more information about how it’s behaving? Do you see any output, for example?

[Rohan Maity]

Launching a job as a child of a cancelled job will immediately return a cancelled job

Let me verify this and give more information

[Rohan Maity]

Is there any way to see any cancelled job for the particular scope?

[Sam]

this?.coroutineContext?.job should work (where this is the coroutine scope receiver from your example)

[Rohan Maity]

I printed out whether scope is active or not and existing job is Cancelled or not

private fun CoroutineScope?.launchWithNullCheck(
        block: suspend () -> Unit
    ) {
        this?.let {
            Log.d("FUI", "scope isActive: ${this.isActive}")
            Log.d("FUI", "existing job cancelled: ${coroutineContext.job.isCancelled}")
            Log.d("FUI", "Scope not null")
            val job = launch {
                Log.d("FUI", "executing block not null")
                block()
            }
            Log.d("FUI", "job isActive ${job.isActive}, isCompleted: ${job.isCompleted}, isCancelled: ${job.isCancelled}")
        }
}

For me it says job was not cancelled but scope became inactive

[Rohan Maity]

Screenshot 2023-03-03 at 15.54.33.png

[Sam]

Okay, that explains why the job does not start. The scope’s job is already finished, so it can’t launch new child jobs. If it’s not active, but not cancelled, that means it just completed normally. How did you create this scope?

[Rohan Maity]

I passed this scope from another class android's viewmodel
This is actually viewmodelscope and I am holding reference to that in this class

[Sam]

In that case I guess it just means that the associated ViewModel has already been cleared?

[Rohan Maity]

Thats the issue, Its not cleared. This happens while the viewmodel is active

[Sam]

Okay, I haven’t used ViewModelScope myself so I’m not sure know what could cause it to be inactive. Hopefully someone with more Android knowledge can help 🤞

[Rohan Maity]

I figured it out. Instead of passing viewModelScope I was passing its childScope which caused the issue
ChildScope was getting completed before my further operations
Passing viewModelScope solved the issue

[Rohan Maity]

Although while figuring this issue, I found out its best to manage my the coroutineScope for the class (which was receiving coroutine) on its own instead of receiving from another class