Run lapply in parallel

Uses lapply_async2, but allows better parallel scheduling via with_future_parallel. On 'Unix', the function will fork processes. On 'Windows', the function uses strategies specified by on_failure

Usage

lapply_async(
  x,
  FUN,
  FUN.args = list(),
  callback = NULL,
  ncores = NULL,
  on_failure = "multisession",
  ...
)

Arguments

x

iterative elements

FUN

function to apply to each element of x

FUN.args

named list that will be passed to FUN as arguments

callback

callback function or NULL. When passed as function, the function takes one argument (elements of x) as input, and it suppose to return one string character.

ncores

number of cores to use, constraint by the max_worker option (see raveio_getopt); default is the maximum number of workers available

on_failure

alternative strategy if fork process is disallowed (set by users or on 'Windows')

...

passed to lapply_async2

Examples

if(!is_on_cran()) {
library(raveio)

# ---- Basic example ----------------------------
lapply_async(1:16, function(x) {
  # function that takes long to fun
  Sys.sleep(1)
  x
})

# With callback
lapply_async(1:16, function(x){
  Sys.sleep(1)
  x + 1
}, callback = function(x) {
  sprintf("Calculating|%s", x)
})

# With ncores
pids <- lapply_async(1:16, function(x){
  Sys.sleep(0.5)
  Sys.getpid()
}, ncores = 2)

# Unique number of PIDs (cores)
unique(unlist(pids))

# ---- With scheduler ----------------------------
# Scheduler pre-initialize parallel workers and temporary
# switches parallel context. The workers ramp-up
# time can be saved by reusing the workers.
#
with_future_parallel({

  # lapply_async block 1
  pids <- lapply_async(1:16, function(x){
    Sys.sleep(1)
    Sys.getpid()
  }, callback = function(x) {
    sprintf("lapply_async without ncores|%s", x)
  })
  print(unique(unlist(pids)))

  # lapply_async block 2
  pids <- lapply_async(1:16, function(x){
    Sys.sleep(1)
    Sys.getpid()
  }, callback = function(x) {
    sprintf("lapply_async with ncores|%s", x)
  }, ncores = 4)
  print(unique(unlist(pids)))

})


}
#> NOT_CRAN is TRUE/true (not on CRAN)
#> [1] 7199 7200
#> [1] 7263 7264
#> [1] 7263 7264