For hard realtime systems it actually doesn't matter anymore. These are mostly implemented with a "don't allocate at all" strategy, since every allocation is not determistic. Therefore things are mostly statically allocated and bounded. And maybe there are some objects pools are around. You can do this in Go in the same way as in C. The only question there is if the GC will still run in the respective languages if no allocations happen through the user (e.g. because the runtime could do allocations in the background for it's housekeeping).

This is known, but it's always possible to overcome these situations and its part of the language maturing. Golang has already had its run with optimizing their GC for real-time systems. Twitch uses Golang for their IRC chat, and they've taken the Golang GC on a journey which you can read about here: https://blog.twitch.tv/gos-march-to-low-latency-gc-a6fa96f06...

Crystal will at some point also be forced to optimize their GC for these cases, although it currently uses an out-of-the-box GC called Boehm-Demers-Weiser conservative garbage collector http://www.hboehm.info/gc/ which they have acknowledged they need to replace sooner or later.

Any program running on any non-realtime OS can stop for any number of milliseconds. There are a billion reasons for such interruptions like other processes wanting to run, cleanup phases internal to the OS, memory paging...

If your program stops for 50 ms, do you really care if it was because of a GC cycle or something else? If you really do care, then you are not allowed to target Linux, Windows or OS X all of which are decidedly not real time operating systems.