mclapply returns NULL randomly

Question

When I am using mclapply, from time to time (really randomly) it gives incorrect results. The problem is quite thoroughly described in other posts across the Internet, e.g.

Answer 1

I'm adding this answer so others hitting this question won't have to wade through the long thread of comments (I am the bounty granter but not the OP).

mclapply initially populates the list it creates with NULLS. As the worker processes return values, these values overwrite the NULLS. If a process dies without ever returning a value, mclapply will return a NULL.

When memory becomes low, the Linux out of memory killer (oom killer)

https://lwn.net/Articles/317814/

will start silently killing processes. It does not print anything to the console to let you know what it's doing, although the oom killer activities show up in the system log. In this situation the output of mclapply will appear to have been randomly contaminated with NULLS.