Below are all R options that are currently used by the future package and packages enhancing it.
WARNING: Note that the names and the default values of these options may change in future versions of the package. Please use with care until further notice.
Default future strategy plan used unless otherwise specified via plan(). This will also be the future plan set when calling plan("default"). If not specified, this option may be set when the future package is loaded if command-line option --parallel=ncores (short -p ncores) is specified; if ncores > 1, then option future.plan is set to multiprocess otherwise sequential (in addition to option mc.cores being set to ncores, if ncores >= 1). If system environment variable R_FUTURE_PLAN is set, then that overrides the future plan set by the command-line option. (Default: sequential)
Action to take when non-existing global variables ("globals" or "unknowns") are identified when the future is created. If "error", an error is generated immediately. If "ignore", no action is taken and an attempt to evaluate the future expression will be made. The latter is useful when there is a risk for false-positive globals being identified, e.g. when future expression contains non-standard evaluation (NSE). (Default: "ignore")
Method used to identify globals. For details, see globalsOf(). (Default: "ordered")
Maximum allowed total size (in bytes) of global variables identified. Used to prevent too large exports. If set of +Inf, then the check for large globals is skipped. (Default: 500 * 1024 ^ 2 = 500 MiB)
If TRUE, globals that are Future objects (typically created as explicit futures) will be resolved and have their values (using value()) collected. Because searching for unresolved futures among globals (including their content) can be expensive, the default is not to do it and instead leave it to the run-time checks that assert proper ownership when resolving futures and collecting their values. (Default: FALSE)
Controls whether the identified globals should be scanned for so called references (e.g. external pointers and connections) or not. It is unlikely that another R process ("worker") can use a global that uses a internal reference of the master R process - we call such objects non-exportable globals.
If this option is "error", an informative error message is produced if a non-exportable global is detected.
If "warning", a warning is produced, but the processing will continue; it is likely that the future will be resolved with a run-time error unless processed in the master R process (e.g. plan(sequential) and plan(multicore)).
If "ignore", no scan is performed.
(Default: "ignore" but may change)
An integer specifying the maximum recursive depth to which futures should be resolved. If negative, nothing is resolved. If 0, only the future itself is resolved. If 1, the future and any of its elements that are futures are resolved, and so on. If +Inf, infinite search depth is used. (Default: 0)
Maximum waiting time (in seconds) for a free worker before a timeout error is generated. (Default: 30 * 24 * 60 * 60 (= 30 days))
Initial interval (in seconds) between polls. (Default: 0.2 = 0.2 seconds)
Positive scale factor used to increase the interval after each poll. (Default: 1.01)
If TRUE, extensive debug messages are generated. (Default: FALSE)
If TRUE, progress is displayed while blocked waiting for futures to be resolved. (Default: FALSE)
If FALSE, any .future.R startup scripts, which may exist in the current directory and / or the user's home directory, are ignored. Such startup scripts are otherwise sourced when the future package is attached. Importantly, this option is always set to FALSE if the future package is loaded as part of a future expression being evaluated, e.g. in a background process. In order words, they are sourced in the main R process but not in future processes. (Default: TRUE in main R process and FALSE in future processes / during future evaluation)
Overrides commandArgs() when the future package is loaded.
Default lookup methods for availableCores(). (Default: c("system", "mc.cores", "_R_CHECK_LIMIT_CORES_", "PBS", "SGE", "Slurm", "fallback"))
Default lookup methods for availableWorkers(). (Default: c("mc.cores", "_R_CHECK_LIMIT_CORES_", "PBS", "SGE", "Slurm", "system", "fallback"))
Number of cores to use when no core-specifying settings are detected other than "system". If not specified, this option is set according to system environment variable R_FUTURE_AVAILABLECORES_FALLBACK when the future package is loaded. This options makes it possible to set the default number of cores returned by availableCores() / availableWorkers() yet allow users and schedulers to override it. In multi-tenant environment, such as HPC clusters, it is useful to set R_FUTURE_AVAILABLECORES_FALLBACK=1.
Number of "system" cores used instead of what is reported by availableCores(which = "system"). If not specified, this option is set according to system environment variable R_FUTURE_AVAILABLECORES_SYSTEM when the future package is loaded. This option allows you to effectively override what parallel::detectCores() reports the system has.
Either a named list of mandelbrot() arguments or an integer in {1, 2, 3} specifying a predefined Mandelbrot region. (Default: 1L)
Number of rows and columns of tiles. (Default: 3L)
To set R options when R starts (even before the future package is loaded), see the Startup help page. The startup package provides a friendly mechanism for configurating R's startup process.