Will OCaml 5+ multicore be fragile?

[cvine]

@dbuenzli

Pre-multicore the reasoning behind this kind of code was always of the form:

1. A single thread is running OCaml code and I’m this thread at the moment.
2. I know which operations can trigger a gc. If no such operation happens the pointers to the values I have cannot move so I don’t need to keep roots on them.

In the case above I started to worry that t could actually start moving under my feets since 1. is obviousy no longer true with multicore. @sadiq answered me that this was not the case because:

GC work can only happen at poll points or allocations […] the only thing that can be happening concurrently is marking and sweeping, neither of which could cause a problem there. […] Minor collections require all domains to be stopped (and that can only happen at poll and allocation points)

The same point arose on this forum here: A tutorial on parallel programming in OCaml 5 - #6 by kayceesrk