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Is the map returned by mutableMapOf(...) multihread-capable? E.g. is it a ConcurrentHashMap or something similiar?
If not, what map should I use in multithreading environment. e.g ConcurrentHashMap?

It is not thread safe. Yes use ConcurrentHashMap.

Probably better asked in <#C0B8MA7FA|>, incidentally.
Also - you can just CTL/CMD click through to see its definition in IntelliJ, which will show you it's a `kotlin.collections.LinkedHashMap`, which is an `expect class`.

Unfortunately IntelliJ doesn't make it easy to go from an `expect class` to an `actual class` (as far as I can see) but if you look in `kotlin-stdlib-1.6.10.jar!/kotlin/collections/TypeAliases.kt` you'll see that `public actual typealias LinkedHashMap&lt;K, V&gt; = java.util.LinkedHashMap&lt;K, V&gt;`.

&gt; Unfortunately IntelliJ doesn't make it easy to go from an `expect class` to an `actual class`
A good trick I've used is to Ctrl-Shift-F (Search everywhere) and then Scope -&gt; All Places and search for a `actual class ClassName` or `actual typealias ClassName`

Yup, that's how I found that one! But it's not nearly as convenient as navigating from, e.g., interface -&gt; implementations.

Having said that there's no easy way to get from `kotlin.collections.MutableMap` to its implementations either... looks like some of the hierarchy navigation doesn't work inside dependency sources?