I have a java application which makes webservice c...

# coroutines

[nayanjyoti]

I have a java application which makes webservice calls to another third party. Currently we notice that whenever their response time increases, all our worker thread (of the webservice call threadpool) go to wait state. I am trying to migrate that to coroutine based pool so that we can have more number of calls in parallel during high response times with the same pool size.

For that I have made small extension methods to make minimal changes to the rest of the applications.

private const val corePoolSize =  8
private val executor = Executors.newScheduledThreadPool(corePoolSize)
private val dispatcher = executor.asCoroutineDispatcher()

fun <T, R> Deferred<T>.map(block: (T) -> R): Deferred<R> {
    return async(dispatcher) {
        val target = [e-mail]()
        block(target)
    }
}

This is one of the extension method I have added to help me with the already used function composition.

Usage is like this:

// since we are calling in java codebase, we need to pass the deferred instance as the receiver

class TypeA {
    String xyz;
    String abc;
    // getter setters are here
}
Deferred<TypeA> a = thirdPartyService.foo()
return map(map(a, (a) -> {
    a.setXyz("xyz");
    return a; // yes I understand that this is more of a consume like function than a map 
}), (a) -> {
    // some more logic on a instance
    if (a.getXyz().equals("abc")) {
        // do something 
    }
});

In my understanding if I chain multiple map invocations, it should first resolve the inner map invocation in this case, which means the xyz field should not be null, however, I receive NPE in the if (a.getXyz().equals("abc")) line. I also added debug statements on the setXyz line and in the a.getXyz().equals line. I noticed the second lambda is invoked first then the first lambda.

Can anyone help me out with understanding this scenario? In my understanding it should have invoked the first lambda then the second one.