In WinVector/rquery: Relational Query Generator for Data Manipulation at Scale

library("prrd")
td <- tempdir()
package = "rquery"
date()
packageVersion(package)

parallelCluster <- NULL
ncores <- parallel::detectCores()
# prrd back to bombing out with database locked
#if(ncores > 1) {
#  parallelCluster <- parallel::makeCluster(ncores)
#}

orig_dir <- getwd()
print(orig_dir)
setwd(td)
print(td)

options(repos = c(CRAN="https://cloud.r-project.org"))
jobsdfe <- enqueueJobs(package=package, directory=td)

mk_fn <- function(package, directory) {
  force(package)
  force(directory)
  function(i) {
    library("prrd")
    setwd(directory)
    Sys.sleep(1*i)
    dequeueJobs(package=package, directory=directory)
  }
}
f <- mk_fn(package=package, directory=td)

if(!is.null(parallelCluster)) {
  parallel::parLapply(parallelCluster, seq_len(ncores), f)
} else {
  f(0)
}

summariseQueue(package=package, directory=td)

setwd(orig_dir)
if(!is.null(parallelCluster)) {
  parallel::stopCluster(parallelCluster)
}