future and future.apply – Some Recent Improvements

This article is originally published at https://www.jottr.org/

There are new versions of future and future.apply - your friends in the parallelization business - on CRAN. These updates are mostly maintenance updates with bug fixes, some improvements, and preparations for upcoming changes. It’s been some time since I blogged about these packages, so here is the summary of the main updates this far since early 2020:

• future:

  • values() for lists and other containers was renamed to value() to simplify the API [future 1.17.0]

  • When future results in an evaluation error, the result() object of the future holds also the session information when the error occurred [future 1.17.0]

  • value() can now detect and warn if a future(..., seed=FALSE) call generated random numbers, which then might give unreliable results because non-parallel safe, non-statistically sound random number generation (RNG) was used [future 1.16.0]

  • Progress updates by progressr are relayed in a near-live fashion for multisession and cluster futures [future 1.16.0]

  • makeClusterPSOCK() gained argument rscript_envs for setting or copying environment variables during the startup of each worker, e.g. rscript_envs=c(FOO="hello world", "BAR") [future 1.17.0]. In addition, on Linux and macOS, it also possible to set environment variables prior to launching the workers, e.g. rscript=c("TMPDIR=/tmp/foo", "FOO='hello world'", "Rscript") [future 1.18.0]

  • Error messages of severe cluster future failures are more informative and include details on the affected worker include hostname and R version [future 1.17.0 and 1.18.0]

• future.apply:

  • future_apply() gained argument simplify, which has been added to base::apply() R-devel (to become R 4.1.0) [future.apply 1.6.0]

  • Added future_.mapply() corresponding to base::.mapply() [future.apply 1.5.0]

  • future_lapply() and friends set a label on each future that reflects the name of the function and the index of the chunk, e.g. ‘future_lapply-3’ [future.apply 1.4.0]

  • The assertion of the maximum size of globals per chunk is significantly faster for future_apply() [future.apply 1.4.0]

There have also been updates to doFuture and future.batchtools. Please see their NEWS files for the details.

What’s next?

I’m working on cleaning up and harmonization the Future API even further. This is necessary so I can add some powerful features later on. One example of this cleanup is making sure that all types of futures are resolved in a local environment, which means that the local argument can be deprecated and eventually removed. Another example is to deprecate argument persistent for cluster futures, which is an “outlier” and remnant from the past. I’m aware that some of you use plan(cluster, persistent=TRUE), which, as far as I understand, is because you need to keep persistent variables around throughout the lifetime of the workers. I’ve got a prototype of “sticky globals” that solves this problem differently, without the need for persistent=FALSE. I’ll try my best to make sure everyone’s needs are met.

I’ve also worked with the maintainers of foreach to harmonize the end-user and developer experience of foreach with that of the future framework. For example, in y <- foreach(...) %dopar% { ... }, the { ... } expression is now always evaluated in a local environment, just like futures. This helps avoid some quite common beginner mistakes that happen when moving from sequential to parallel processing. You can read about this change in the ‘foreach 1.5.0 now available on CRAN’ blog post by Hong Ooi. There is also a discussion on updating how foreach identifies global variables and packages so that it works the same as the future framework.

Happy futuring!

Links

• future package: CRAN, GitHub
• future.apply package: CRAN, GitHub
• doFuture package: CRAN, GitHub (a foreach adapter)
• future.batchtools package: CRAN, GitHub
• future.callr package: CRAN, GitHub
• future.tests package: CRAN, GitHub
• progressr package: GitHub

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