when calling a `suspend` function within `runBlocking` the f

Question

when calling a `suspend` function within `runBlocking` the following code should not be executed until the function completes correct I am seeing some flakiness in a test that doesn t make sense to me

wasyl · Answer

Can you paste the function `runBlocking` doesn t change all suspend functions into blocking ones

Kris Wong · Answer

the test function or the suspending function

wasyl · Answer

You can still run things in parallel for example

wasyl · Answer

gt the test function or the suspending function The test function

Kris Wong · Answer

``` Test fun someTest = runBlocking someSuspendingFunction assertTrue shouldBeTrue expects above function to have returned ```

Kris Wong · Answer

it s working most of the time

louiscad · Answer

< Kris Wong> Which platform Can you reproduce it with any code or only an expectation is missed for a particular function you have written

Kris Wong · Answer

i am currently seeing a failure running junit tests from the command line via ` gradlew testDebugUnitTest` it s a common test and passes on iOS and also when run in the IDE

louiscad · Answer

Failure is too broad you know it

Kris Wong · Answer

it s only 1 test that is failing other tests are exercising the same code in similar ways the suspending function ends up calling Ktor `HttpClient post`

louiscad · Answer

Define failing please

Kris Wong · Answer

a boolean gets set to true in a callback that is called from the suspending function

Kris Wong · Answer

which is not happening the callback is not called in this one case

wasyl · Answer

My guess is that `someSuspendingFunction` does thing asynchronously launches a coroutine in a separate scope for example And the test is simply flaky sometimes the asynchronous thing manages to complete and sometimes it doesn t

Kris Wong · Answer

also my guess just not what I expected and I m not quite sure how to fix it

Kris Wong · Answer

unfortunately I am limited to APIs in stdlib common

wasyl · Answer

gt I m not quite sure how to fix it It really depends on what `someSuspendingFunction ` does

louiscad · Answer

You said it works all the time on iOS and in the IDE If so then on which platform is it sometimes failing

Kris Wong · Answer

android junit tests

Kris Wong · Answer

which is of course just JVM

louiscad · Answer

AGP 7

louiscad · Answer

Running in the JVM or in an emulator or device Because Android is not just JVM despite it being almost it

Kris Wong · Answer

android unit tests run in the JVM unlike connected tests AGP 4 1 2

louiscad · Answer

Alright Weird then blob thinking upside down

Kris Wong · Answer

I believe something like `withContext` might do the trick but I don t think that API is available

louiscad · Answer

It is

louiscad · Answer

You can also use `Dispatchers Default ` or just `coroutineScope ` if you fear you broke structured concurrency in a way or another at the immediate level

louiscad · Answer

If you have a class implementing `CoroutineScope` it s very likely you re breaking structured concurrency BTW

Kris Wong · Answer

the only scope my code is creating is provided by `runBlocking` however I am sure Ktor is creating one or more scopes

Kris Wong · Answer

`withContext` didn t fix it

louiscad · Answer

Then we cannot help without a reproducer

louiscad · Answer

It might be a ktor specific issue

Kris Wong · Answer

oh snap I notice the test execution order is not the same between the IDE and the command line I think I may be on to something with that

louiscad · Answer

Shared mutable state thinking face

Kris Wong · Answer

yes it succeeds when isolate the failing test

Kris Wong · Answer

nothing to see here sorry for the trouble

Kris Wong · Answer

I have tracked this down to what appears to be a very strange IllegalMonitorStateException with ReentrantLock that was being swallowed

Kris Wong · Answer

man yet another red herring the root of the problem was that I was passing too small of a grace period timeout to stop the Ktor server I was using for the tests

Kris Wong · Answer

moral of the story `runBlocking` is working as expected

louiscad · Answer

Why don t you stop the server only when all the tests are done

gildor · Answer

Why start stop server on every test otherwise it breaks test isolation

Kris Wong · Answer

test isolation is exactly why i start and stop it on every test

gildor · Answer

yep makes sense but I don t see why stop timeout is required for tests

Kris Wong · Answer

the API requires it

Kris Wong · Answer

stopping the server does a bit of asynchronous work within `runBlocking`

Kris Wong · Answer

I was passing 1 ms for both values grace period and timeout bumped to 10 and 100

Kris Wong · Answer

simple fix but it took me nearly all day to get to the root of the issue