Speaking as an experienced programmer: all the time, in subtle ways, sometimes that you don't notice for a long time. Sometime benign, sometimes your data has been being corrupted for months before you notice.
My standard advice on concurrency is, quite simply, don't. It always looks way simpler than it actually is. If you're doing something that _requires_ it, get all the help you can. Type-level enforcement sounds _excellent_ to me.
Yep. I deal with a platform that has some sort of race and accesses a destroyed object. It's incredibly tricky to find it, and customers only hit it at the worst time, with certain traffic loads. It's a subtle bug that's lasted years and is in a codepath used millions of times a day.
I haven't checked Erlang too well, but is it so that the concurrency in Erlang software is basically actors only? Of course in this space you can also use Akka and even Rust and C++ have actor libraries available.
But there are definitely use cases where you don't want to use actors, where you might want to compose several futures together without the overhead of actor mailboxes.
> it so that the concurrency in Erlang software is basically actors only?
Erlang's concurrency is "don't communicate by sharing, share by communicating" enforced at the language level: an Erlang system is composed of processes which each have their own heap (and stack) and an incoming "mailbox", an Erlang process can only interact with the world by calling BIFs (built-in "native" functions, Erlang syscalls if you will) or sending messages to other processes, and messages can only contain immutable data structures (mutation happens only at the process level).
Of course one of the sources for this design is that Erlang comes from a world where 1 = 0 (if you don't have redundancy you don't have a system) thus two processes may live on different nodes (erlang VMs) on different physical machines and shouldn't behave any differently than if they were on the same node.
So basically it's like Scala/Akka, except in Erlang you can send functions which is a nice feature. One thing that has kept me from using it in production is its dynamic typing. Once you've been spoiled with a good type system, it's quite hard to go back to dynamic typing.
Akka is modeled on Erlang but the JVM has very different characteristics. The Erlang VM is optimized for immutable languages and message passing. GC is very different (almost a non-issue) because of the process model.
And pattern matching in Erlang is a joy every developer should experience. I've not been impressed with my limited exposure to Scala, which also bears the burden of trying to be a kitchen sink language.
My standard advice on concurrency is, quite simply, don't. It always looks way simpler than it actually is. If you're doing something that _requires_ it, get all the help you can. Type-level enforcement sounds _excellent_ to me.