Random behavior of mclapply

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Random behavior of mclapply

Thibault Vatter-2
Hi,

I wondered about the behavior described in the following stackoverflow
question:

https://stackoverflow.com/questions/20674538/mclapply-returns-null-randomly

More specifically, I would like to know if you ever considered the
suggestion made in the comments of the first answer, namely to somehow warn
the user if one of the processes has been killed by the out-of-memory
killer ?

I am always surprised to see the random NULLs without message/warning/error
of any kind, and I think that it could be a useful feature to know whether
the function executed by mclapply returned a NULL or if the process was
killed for some reason.

In the following gist, I have an example of this (in this case non-random)
behavior:

https://gist.github.com/tvatter/2fcf3a9a99c256f9b9360f596b300715

For the record, I generate the list of NULLs in the 4th mclapply in the
girst above with a late 2013 macbook pro with macOS High Sierra, 16GB of
memory, and my sessionInfo() is:

R version 3.5.0 (2018-04-23)
Platform: x86_64-apple-darwin16.7.0 (64-bit)
Running under: macOS High Sierra 10.13.6

Matrix products: default
BLAS:
/System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK:
/System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libLAPACK.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] parallel  stats     graphics  grDevices utils     datasets  methods
 base

loaded via a namespace (and not attached):
[1] compiler_3.5.0 tools_3.5.0    yaml_2.1.19

------------------------------------------------------------
Thibault Vatter
Department of Statistics
Columbia University

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