Howdy, Have a beginner question around coroutines...

# coroutines

[Conor Fennell]

Howdy,

Have a beginner question around coroutines.
I am using coroutines in a ktor project. And multiple coroutines can increment the same prometheus counter at the same time io.prometheus.client.Counter
The prometheus Counter is a Java library.

Is there any concurrency issues people would foresee?

The prometheus implementation uses Compare and Swap operations so should be coroutine safe.
But saying that, there is a thread hash code used for some accounting ThreadLocal() .

static final ThreadLocal<int[]> threadHashCode = new ThreadLocal();
    static final Random rng = new Random();
    static final int NCPU = Runtime.getRuntime().availableProcessors();
    transient volatile Striped64.Cell[] cells;
    transient volatile long base;
    transient volatile int busy;
    private static final AtomicLongFieldUpdater<Striped64> CAS_BASE = AtomicLongFieldUpdater.newUpdater(Striped64.class, "base");
    private static final AtomicIntegerFieldUpdater<Striped64> CAS_BUSY = AtomicIntegerFieldUpdater.newUpdater(Striped64.class, "busy");

[TwoClocks]

If promrtheus is thread safe, then it's coroutine safe. If prometheus is not thread safe then it's might not be coroutine safe depending on which dispatcher/coroutineScope you are using.

[uli]

@TwoClocks not true 🙂
I have not looked at the code. But if the code relies on ThreadLocal there is a chance of this ThreadLocal to change because the dispatcher thread of the coroutine might change.

[TwoClocks]

ahhh. I see. Yeah, that could be a problem, again depending on which dispatcher you used.