Inlined FrameworkMarshallers.create spawns more classes in Metaspace than you could imagine

[jreznot]

object FrameworkMarshallers {
    inline fun <reified T : Any> create(crossinline reader: (AbstractBuffer) -> T, crossinline writer: (AbstractBuffer, T) -> Unit, predefinedId: Int? = null): UniversalMarshaller<T> {
        return UniversalMarshaller(T::class, { _, stream -> reader(stream) }, { _, stream, v -> writer(stream, v) }, predefinedId)
    }

Check this:

 { _, stream -> reader(stream) }

This means that for every callsite of FrameworkMarshallers.create there will be separate class created. Our JVM classloading logs for IntelliJ IDA shows clearly:

[1.35760] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$39
[1.35764] Loading class: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$40 (2724 bytes)
[1.35772] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$40
[1.35778] Loading class: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$41 (2583 bytes)
[1.35786] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$41
[1.35790] Loading class: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$42 (2726 bytes)
[1.35797] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$42
[1.35803] Loading class: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$43 (2585 bytes)
[1.35810] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$43
[1.35814] Loading class: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$44 (2728 bytes)
[1.35820] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$44
[1.35826] Loading class: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$45 (2581 bytes)
[1.35832] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$45
[1.35836] Loading class: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$46 (2724 bytes)
[1.35844] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$46
[1.35849] Loading class: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$47 (2587 bytes)
[1.35856] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$47
[1.35859] Loading class: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$48 (2730 bytes)
[1.35866] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$48
[1.35900] Loading class: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$49 (2667 bytes)
[1.35907] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$49
[1.35911] Loading class: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$50 (2794 bytes)
[1.35917] Class prepared: com/jetbrains/rd/framework/FrameworkMarshallers$special$$inlined$create$50

[jreznot]

I would recommend noinline for lambdas, we cannot eliminate them fully anyway, as UniversalMarshaller needs to store some instances:

    inline fun <reified T : Any> create(noinline reader: (AbstractBuffer) -> T, 
                                        noinline writer: (AbstractBuffer, T) -> Unit, 
                                        predefinedId: Int? = null): UniversalMarshaller<T> {
        return UniversalMarshaller(T::class, { _, stream -> reader(stream) }, { _, stream, v -> writer(stream, v) }, predefinedId)
    }

[ForNeVeR]

A proposed solution that should work in Kotlin 1.9 (currently, it generates exactly the same number of classes):

    inline fun <reified T : Any> create(
        noinline reader: (AbstractBuffer) -> T,
        noinline writer: (AbstractBuffer, T) -> Unit,
        predefinedId: Int? = null
    ): UniversalMarshaller<T> {
        return create(T::class, reader, writer, predefinedId)
    }

    /**
     * This is a non-inline companion of the above function, to avoid creating too many class files for crossinline
     * lambdas.
     */
    fun <T : Any> create(
        kClass: KClass<T>,
        reader: (AbstractBuffer) -> T,
        writer: (AbstractBuffer, T) -> Unit,
        predefinedId: Int? = null
    ): UniversalMarshaller<T> {
        return UniversalMarshaller(
            kClass,
            { _, stream -> reader(stream) },
            { _, stream, v -> writer(stream, v) },
            predefinedId
        )
    }

So, to fix this issue, we'll have to wait for Kotlin 1.9 with extended invokedynamic usage.

We will be waiting.