Initial commit

README.md

+## Example files for the title:  
+  
+# Parallel R, by Q. McCallum
+  
+[![Parallel R, by Q. McCallum](http://akamaicovers.oreilly.com/images/9781449309916/cat.gif)](https://www.safaribooksonline.com/library/view/title/9781449317850//)
+  
+The following applies to example files from material published by O’Reilly Media, Inc. Content from other publishers may include different rules of usage. Please refer to any additional usage rights explained in the actual example files or refer to the publisher’s website.
+  
+O'Reilly books are here to help you get your job done. In general, you may use the code in O'Reilly books in your programs and documentation. You do not need to contact us for permission unless you're reproducing a significant portion of the code. For example, writing a program that uses several chunks of code from our books does not require permission. Answering a question by citing our books and quoting example code does not require permission. On the other hand, selling or distributing a CD-ROM of examples from O'Reilly books does require permission. Incorporating a significant amount of example code from our books into your product's documentation does require permission.
+  
+We appreciate, but do not require, attribution. An attribution usually includes the title, author, publisher, and ISBN.
+  
+If you think your use of code examples falls outside fair use or the permission given here, feel free to contact us at <permissions@oreilly.com>.
+  
+Please note that the examples are not production code and have not been carefully testing. They are provided "as-is" and come with no warranty of any kind.

examples/multicore/README

+This directory contains R scripts that demonstrate the "multicore"
+package, and are based on examples in chapter three of the book
+"Parallel R".
+
+The example scripts can be executed using a command such as:
+
+  % R --slave -f mclapply.R
+
+or using the "source" function within an R session:
+
+  > source('mclapply.R')
+
+Example scripts:
+
+  mclapply.R            Using mclapply to implement parallel kmeans
+  mccores.R             The mc.cores argument
+  mcsetseed.R           The mc.setseed argument
+  mcpreschedule.R       The mc.preschedule argument
+  mcpvec.R              Example use of the pvec function
+  mcparallelcollect.R   Example use of the parallel and collect functions
+  mcrng.R               Using a parallel RNG with multicore
+  mclowlevel.R          Using the low-level API to implement a stripped-
+                        down version of the mclapply function.

examples/multicore/mccores.R

+library(multicore)
+
+results <- mclapply(1:100, function(i) Sys.getpid(), mc.cores=2)
+print(unique(unlist(results)))
+
+options(cores=3)
+results <- mclapply(1:100, function(i) Sys.getpid())
+print(unique(unlist(results)))

examples/multicore/mclapply.R

+library(multicore)
+library(MASS)
+
+results <- mclapply(rep(25, 4),
+                    function(nstart) kmeans(Boston, 4, nstart=nstart))
+i <- sapply(results, function(result) result$tot.withinss)
+result <- results[[which.min(i)]]
+print(result)

examples/multicore/mclowlevel.R

+library(multicore)
+
+# Simplified version of mclapply that adds an "mc.init" argument
+mclapply.init <- function(X, FUN, ..., mc.cores=4, mc.init=NULL) {
+  cores <- max(min(mc.cores, length(X)), 1)
+  ix <- lapply(1:cores, function(i) seq(i, length(X), by=cores))
+  forkloop <- function(core) {
+    proc <- fork()
+    if (inherits(proc, "masterProcess")) {
+      sendMaster(tryCatch({
+        suppressWarnings(rm(".Random.seed", pos=.GlobalEnv))
+        if (is.function(mc.init))
+          mc.init(core, cores)
+        lapply(X[ix[[core]]], FUN, ...)
+      },
+      error=function(e) {
+        lapply(ix[[core]], function(i) e)
+      }))
+      exit(0)
+    }
+    proc$pid
+  }
+  pids <- sapply(1:cores, forkloop)
+  results <- vector("list", length(X))
+  while (! is.null(ready <- selectChildren(pids, 1))) {
+    if (is.integer(ready)) {
+      for (pid in ready) {
+        data <- readChild(pid)
+        if (is.raw(data)) {
+          core <- which(pid == pids)
+          results[ix[[core]]] <- unserialize(data)
+        }
+      }
+    }
+  }
+  names(results) <- names(X)
+  results
+}
+
+# Define an "mc.init" function that defines a worker ID variable
+set.worker.id <- function(id, cores) {
+  assign(".MC.WORKER.ID", id, pos=.GlobalEnv)
+}
+
+# Try out mclapply.init, initializing the workers with "set.worker.id"
+mclapply.init(11:13, function(i) c(i, .MC.WORKER.ID),
+              mc.cores=2, mc.init=set.worker.id)
+
+# Define an "mc.init" function that sets the RNG seed of the
+# workers in the same way as the real mclapply function.
+set.worker.seed <- function(id, cores) {
+  set.seed(Sys.getpid())
+}
+
+# Try out mclapply.init, initializing the workers with "set.worker.seed"
+mclapply.init(1:3, function(i) rnorm(1), mc.init=set.worker.seed)

examples/multicore/mcparallelcollect.R

+library(multicore)
+
+# Define our set of three contrived (but illustrative) functions
+fun1 <- function() {Sys.sleep(10); 1}
+fun2 <- function() {Sys.sleep(5);  2}
+fun3 <- function() {Sys.sleep(1);  3}
+
+# Start the three functions executing in the background
+cat('1) Starting three tasks:\n')
+f1 <- parallel(fun1())
+f2 <- parallel(fun2())
+f3 <- parallel(fun3())
+
+# Here is where you might do something useful before you
+# commit to waiting for all of the results
+
+# Wait for the results of all three computations
+cat('Calling collect with wait=TRUE:\n')
+print(collect(list(f1, f2, f3)))
+
+# Start the same three functions executing again
+cat('2) Starting three tasks:\n')
+f1 <- parallel(fun1())
+f2 <- parallel(fun2())
+f3 <- parallel(fun3())
+
+# Check for results, but don't wait, so none are ready
+cat('Calling collect with wait=FALSE:\n')
+print(collect(list(f1, f2, f3), wait=FALSE))
+
+# Pause a bit, simulating doing something useful
+cat('Sleeping for 15 seconds...\n')
+Sys.sleep(15)
+
+# Now all the results are finished, so we get them in a list
+cat('Calling collect with wait=FALSE:\n')
+print(collect(list(f1, f2, f3), wait=FALSE))
+
+# When call collect this time we get a list of three NULL's
+# indicating that each of the worker processes has exited
+cat('Calling collect with wait=FALSE:\n')
+print(collect(list(f1, f2, f3), wait=FALSE))
+
+# Finally we get a single NULL
+cat('Calling collect with wait=FALSE:\n')
+print(collect(list(f1, f2, f3), wait=FALSE))
+
+# Start the three functions one last time
+cat('3) Starting three tasks:\n')
+f1 <- parallel(fun1())
+f2 <- parallel(fun2())
+f3 <- parallel(fun3())
+
+# Because wait is FALSE and we have a timeout, we find out
+# about the events (result or process death) one at a time
+# until we get the final NULL
+cat('Calling collect with wait=FALSE, timeout=1000000:\n')
+print(collect(list(f1, f2, f3), wait=FALSE, timeout=1000000))
+cat('Calling collect with wait=FALSE, timeout=1000000:\n')
+print(collect(list(f1, f2, f3), wait=FALSE, timeout=1000000))
+cat('Calling collect with wait=FALSE, timeout=1000000:\n')
+print(collect(list(f1, f2, f3), wait=FALSE, timeout=1000000))
+cat('Calling collect with wait=FALSE, timeout=1000000:\n')
+print(collect(list(f1, f2, f3), wait=FALSE, timeout=1000000))
+cat('Calling collect with wait=FALSE, timeout=1000000:\n')
+print(collect(list(f1, f2, f3), wait=FALSE, timeout=1000000))
+cat('Calling collect with wait=FALSE, timeout=1000000:\n')
+print(collect(list(f1, f2, f3), wait=FALSE, timeout=1000000))
+cat('Calling collect with wait=FALSE, timeout=1000000:\n')
+print(collect(list(f1, f2, f3), wait=FALSE, timeout=1000000))

examples/multicore/mcpreschedule.R

+library(multicore)
+
+# Make the task time vary a lot to increase the need for load balancing
+set.seed(93564990)
+sleeptime <- abs(rnorm(10, 10, 10))
+
+cat('mclapply with prescheduling:\n')
+tm <- system.time(mclapply(sleeptime, Sys.sleep, mc.cores=4))
+print(tm)
+
+cat('mclapply without prescheduling:\n')
+tm <- system.time(mclapply(sleeptime, Sys.sleep, mc.cores=4, mc.preschedule=FALSE))
+print(tm)

examples/multicore/mcpvec.R

+library(multicore)
+
+x <- 1:10
+results <- pvec(x, '^', 1/3)
+print(results)

examples/multicore/mcrng.R

+library(multicore)
+library(snow)
+library(rsprng)
+
+nw <- 3
+seed <- 7777442
+kind <- 0
+para <- 0
+
+f1 <- parallel({initSprngNode(0, nw, seed, kind, para); rnorm(1)})
+f2 <- parallel({initSprngNode(1, nw, seed, kind, para); rnorm(1)})
+f3 <- parallel({initSprngNode(2, nw, seed, kind, para); rnorm(1)})
+results <- collect(list(f1, f2, f3))
+print(unlist(results, use.names=FALSE))
+
+cl <- makeCluster(3, type="SOCK")
+seed <- 7777442
+clusterSetupSPRNG(cl, seed=seed)
+results <- clusterEvalQ(cl, rnorm(1))
+print(unlist(results, use.names=FALSE))
+stopCluster(cl)

examples/multicore/mcsetseed.R

+# This example demonstrates the perils of using mclapply
+# with mc.set.seed=FALSE.
+
+library(multicore)
+
+cat('mc.set.seed=FALSE when .Random.seed is not set:\n')
+results <- mclapply(1:3, function(i) rnorm(3), mc.cores=3, mc.set.seed=FALSE)
+print(results)
+
+# This sets .Random.seed to a nonrepeatable value in the global environment
+ignore <- rnorm(1)
+
+cat('mc.set.seed=FALSE when .Random.seed is set:\n')
+results <- mclapply(1:3, function(i) rnorm(3), mc.cores=3, mc.set.seed=FALSE)
+print(results)
+
+# This sets .Random.seed to a repeatable value
+set.seed(7777442)
+
+cat('mc.set.seed=TRUE when .Random.seed is set:\n')
+results <- mclapply(1:3, function(i) rnorm(3), mc.cores=3, mc.set.seed=TRUE)
+print(results)

examples/parallel/README

+This directory contains R scripts that demonstrate the "parallel"
+package, and are based on examples in chapter three of the book
+"Parallel R".  Note that you must be using R 2.14.0 or later to execute
+these examples.  If you're using an older version of R you won't be able
+to load the "parallel" package.  
+
+The example scripts can be executed using a command such as:
+
+  % R --slave -f parstarted.R
+
+or using the "source" function within an R session:
+
+  > source('parstarted.R')
+
+Example scripts:
+
+  parstarted.R         Using mclapply and clusterApply to implement
+                       parallel kmeans
+  parmakecluster.R     Creating PSOCK and FORK cluster objects
+  parrng.R             Using the new L'Ecuyer-CMRG RNG with parallel

examples/parallel/parmakecluster.R

+library(parallel)
+
+type <- if (exists("mcfork", mode="function")) "FORK" else "PSOCK"
+cores <- getOption("mc.cores", detectCores())
+cl <- makeCluster(cores, type=type)
+results <- parLapply(cl, 1:10, sqrt)
+print(results)
+stopCluster(cl)

examples/parallel/parrng.R

+library(parallel)
+
+RNGkind("L'Ecuyer-CMRG")
+
+mclapply(1:2, function(i) rnorm(1))
+
+set.seed(7777442)
+mc.reset.stream()
+results <- mclapply(1:2, function(i) rnorm(1))
+print(unlist(results))
+
+set.seed(7777442)
+mc.reset.stream()
+results <- mclapply(1:2, function(i) rnorm(1))
+print(unlist(results))
+
+cl <- makeCluster(4, type="FORK")
+clusterSetRNGStream(cl, 7777442)
+unlist(clusterEvalQ(cl, rnorm(1)))
+clusterSetRNGStream(cl, 7777442)
+results <- clusterEvalQ(cl, rnorm(1))
+print(unlist(results))
+stopCluster(cl)

examples/parallel/parstarted.R

+library(parallel)
+library(MASS)  # needed to load the Boston data frame
+
+# Parallel kmeans using the "multicore-derived" API with parallel RNG
+RNGkind("L'Ecuyer-CMRG")
+mc.cores <- detectCores()
+results <- mclapply(rep(25, 4),
+                    function(nstart) kmeans(Boston, 4, nstart=nstart),
+                    mc.cores=mc.cores)
+i <- sapply(results, function(result) result$tot.withinss)
+result <- results[[which.min(i)]]
+print(result)
+
+# Parallel kmeans using the "snow-derived" API with parallel RNG
+cl <- makeCluster(detectCores())
+clusterSetRNGStream(cl)
+clusterEvalQ(cl, library(MASS))
+results <- clusterApply(cl, rep(25, 4),
+    function(nstart) kmeans(Boston, 4, nstart=nstart))
+i <- sapply(results, function(result) result$tot.withinss)
+result <- results[[which.min(i)]]
+print(result)
+stopCluster(cl)

examples/snow/README

+This directory contains R scripts that demonstrate the "snow" package,
+and are based on the examples in chapter two of the book "Parallel R".
+
+The example scripts can be executed using a command such as:
+
+  % R --slave -f kmeans.R
+
+or using the "source" function within an R session:
+
+  > source('kmeans.R')
+
+Using the "source" function allows the timing plots to be displayed
+interactively in clusterapplylb.R, loadbalancing.R and parlapply.R.
+
+Note that config.R will have to be edited, since it contains host and
+user names that very likely don't exist on your system.
+
+Example scripts:
+
+  kmeans.R             Parallel kmeans example using clusterApply
+  workerinit.R         Worker initialization
+  clusterapplylb.R     clusterApplyLB function example
+  parlapply.R          parLapply function example
+  clustersplit.R       Using clusterSplit to implement parVapply
+  loadbalancing.R      Using clusterApplyLB to implement parLapplyLB
+  env.R                Demonstrating function serialization
+  rng.R                Using clusterSetupRNG for parallel RNG
+  config.R             How to configure different workers differently
+  mpi.R                Simple example of creating and using an MPI cluster
+  batchmpi.sh          Simple PBS/TORQUE script for executing mpi.R

examples/snow/batchmpi.sh

+#!/bin/sh
+#PBS -N SNOWMPI
+#PBS -j oe
+cd $PBS_O_WORKDIR
+orterun -n 1 /usr/bin/R --slave -f mpi.R > mpi-$PBS_JOBID.out 2>&1

examples/snow/clusterapplylb.R

+library(snow)
+cl <- makeSOCKcluster(4)
+
+par(ask=TRUE)
+
+set.seed(7777442)
+sleeptime <- abs(rnorm(10, 10, 10))
+tm <- snow.time(clusterApplyLB(cl, sleeptime, Sys.sleep))
+plot(tm)
+cat(sprintf("Elapsed time for clusterApplyLB: %f\n", tm$elapsed))
+
+set.seed(7777442)
+sleeptime <- abs(rnorm(10, 10, 10))
+tm <- snow.time(clusterApply(cl, sleeptime, Sys.sleep))
+plot(tm)
+cat(sprintf("Elapsed time for clusterApply: %f\n", tm$elapsed))
+
+stopCluster(cl)

examples/snow/clustersplit.R

+library(snow)
+cl <- makeSOCKcluster(4)
+
+results <- clusterSplit(cl, 1:30)
+print(results)
+
+parVapply <- function(cl, x, fun, ...) {
+  do.call("c", clusterApply(cl, clusterSplit(cl, x), fun, ...))
+}
+results <- parVapply(cl, 1:10, '^', 1/3)
+print(results)
+
+stopCluster(cl)

examples/snow/config.R

+# WARNING: You will have to change the host and user names
+# in order to successfully run this example.
+
+library(snow)
+
+tryCatch({
+  workerList <- list(list(host='n1'),
+                     list(host='n2', user='steve'))
+  cl <- makeSOCKcluster(workerList)
+  results <- clusterEvalQ(cl, Sys.info()[['user']])
+  print(results)
+  stopCluster(cl)
+
+  workerList <- list(list(host='n1', outfile='n1.log', user='weston'),
+                     list(host='n2', outfile='n2-1.log'),
+                     list(host='n2', outfile='n2-2.log'))
+  cl <- makeSOCKcluster(workerList, user='steve')
+  results <- clusterEvalQ(cl, Sys.glob('*.log'))
+  print(results)
+  stopCluster(cl)
+},
+error=function(e) {
+  print(conditionMessage(e))
+  cat("Did you change the host and user names in this script for your system?",
+      file=stderr())
+})

examples/snow/env.R

+library(snow)
+cl <- makeCluster(4, type="SOCK")
+
+a <- 1:4
+x <- rnorm(4)
+clusterExport(cl, "x")
+mult <- function(s) s * x
+parLapply(cl, a, mult)
+
+pmult <- function(cl) {
+  a <- 1:4
+  x <- rnorm(4)
+  mult <- function(s) s * x
+  parLapply(cl, a, mult)
+}
+pmult(cl)
+
+pmult <- function(cl, a, x) {
+  x  # force x
+  mult <- function(s) s * x
+  parLapply(cl, a, mult)
+}
+scalars <- 1:4
+dat <- rnorm(4)
+pmult(cl, scalars, dat)
+
+pmult <- function(cl, a, x) {
+  mult <- function(s, x) s * x
+  environment(mult) <- .GlobalEnv
+  parLapply(cl, a, mult, x)
+}
+scalars <- 1:4
+dat <- rnorm(4)
+pmult(cl, scalars, dat)
+
+stopCluster(cl)

examples/snow/kmeans.R

+# Load MASS package to get "Boston" data frame
+library(MASS)
+
+#######################################################
+# Example use of the kmeans function
+result <- kmeans(Boston, 4, nstart=100)
+print(result)
+
+#######################################################
+# Sequential splitting using lapply function
+results <- lapply(rep(25, 4), function(nstart) kmeans(Boston, 4, nstart=nstart))
+i <- sapply(results, function(result) result$tot.withinss)
+result <- results[[which.min(i)]]
+print(result)
+
+#######################################################
+# Parallel version, converted from lapply version
+library(snow)
+cl <- makeSOCKcluster(3)
+
+ignore <- clusterEvalQ(cl, {library(MASS); NULL})
+results <- clusterApply(cl, rep(25, 4), function(nstart)
+                    kmeans(Boston, 4, nstart=nstart))
+i <- sapply(results, function(result) result$tot.withinss)
+result <- results[[which.min(i)]]
+print(result)
+
+stopCluster(cl)

examples/snow/loadbalancing.R

+library(snow)
+cl <- makeCluster(4, type="SOCK")
+
+par(ask=TRUE)
+
+# Wrapper for clusterApplyLB that sends the function and
+# the "fixed" arguments to the workers only once, rather
+# than in every task.  In some cases this can significantly
+# reduce communication, thus improving performance.
+parLapplyLB <- function(cl, x, fun, ...) {
+  clusterCall(cl, LB.init, fun, ...)
+  r <- clusterApplyLB(cl, x, LB.worker)
+  clusterEvalQ(cl, rm('.LB.fun', '.LB.args', pos=globalenv()))
+  r
+}
+
+# Worker initialization function called by parLapplyLB
+LB.init <- function(fun, ...) {
+  assign('.LB.fun', fun, pos=globalenv())
+  assign('.LB.args', list(...), pos=globalenv())
+  NULL
+}
+
+# Worker task function called by parLapplyLB
+LB.worker <- function(x) {
+  do.call('.LB.fun', c(list(x), .LB.args))
+}
+
+bigsleep <- function(sleeptime, mat) Sys.sleep(sleeptime)
+bigmatrix <- matrix(0, 2000, 2000)
+sleeptime <- rep(1, 100)
+
+# Time parLapplyLB with our contrived example
+tm <- snow.time(parLapplyLB(cl, sleeptime, bigsleep, bigmatrix))
+plot(tm)
+cat(sprintf("Elapsed time for parLapplyLB: %f\n", tm$elapsed))
+
+# Time clusterApplyLB with the same contrived example
+tm <- snow.time(clusterApplyLB(cl, sleeptime, bigsleep, bigmatrix))
+plot(tm)
+cat(sprintf("Elapsed time for clusterApplyLB: %f\n", tm$elapsed))
+
+# Cleanup
+stopCluster(cl)

examples/snow/mpi.R

+#!/usr/bin/Rscript
+library(snow)
+library(Rmpi)
+
+# This script spawns workers when creating the cluster, so make sure
+# that mpirun didn't start multiple copies of this script and that
+# there are some process slots available for spawned workers.
+if (mpi.comm.size(0) > 1 || mpi.universe.size() < 2) {
+  if (mpi.comm.rank(0) == 0)
+    cat('must use -n 1 and specify at least two slots\n', file=stderr())
+  mpi.quit()
+}
+
+# Create a cluster and make sure it works
+cl <- makeMPIcluster(mpi.universe.size() - 1)
+r <- clusterEvalQ(cl, R.version.string)
+print(unlist(r))
+
+# Stop the cluster, finalize MPI and quit
+stopCluster(cl)
+mpi.quit()

examples/snow/parlapply.R

+library(snow)
+cl <- makeCluster(4, type="SOCK")
+
+par(ask=TRUE)
+
+bigsleep <- function(sleeptime, mat) Sys.sleep(sleeptime)
+bigmatrix <- matrix(0, 2000, 2000)
+sleeptime <- rep(1, 100)
+
+tm <- snow.time(clusterApply(cl, sleeptime, bigsleep, bigmatrix))
+plot(tm)
+cat(sprintf("Elapsed time for clusterApply: %f\n", tm$elapsed))
+
+tm <- snow.time(parLapply(cl, sleeptime, bigsleep, bigmatrix))
+plot(tm)
+cat(sprintf("Elapsed time for parLapply: %f\n", tm$elapsed))
+
+stopCluster(cl)

examples/snow/rng.R

+library(snow)
+cl <- makeCluster(4, type="SOCK")
+
+results <- clusterSetupRNG(cl, type='RNGstream', seed=c(1,22,333,444,55,6))
+print(unlist(results))
+
+stopCluster(cl)

examples/snow/workerinit.R

+library(snow)
+cl <- makeSOCKcluster(3)
+
+# Define a function that loads a specified vector of packages
+worker.init <- function(packages) {
+  for (p in packages) {
+    library(p, character.only=TRUE)
+  }
+  NULL
+}
+
+# Load the MASS and boot packages on each of the workers
+results <- clusterCall(cl, worker.init, c('MASS', 'boot'))
+
+# Verify that MASS and boot are loaded on all the workers
+results <- clusterEvalQ(cl, search())
+print(results)
+
+# Assign a unique worker ID to each worker using clusterApply
+results <- clusterApply(cl, seq(along=cl), function(id) WORKER.ID <<- id)
+
+# Verify that WORKER.ID is set on each worker
+results <- clusterEvalQ(cl, paste("I am worker", WORKER.ID))
+print(results)
+
+# Cleanup
+stopCluster(cl)

multicore/README

+This directory contains R scripts that demonstrate the "multicore"
+package, and are based on examples in chapter three of the book
+"Parallel R".
+
+The example scripts can be executed using a command such as:
+
+  % R --slave -f mclapply.R
+
+or using the "source" function within an R session:
+
+  > source('mclapply.R')
+
+Example scripts:
+
+  mclapply.R            Using mclapply to implement parallel kmeans
+  mccores.R             The mc.cores argument
+  mcsetseed.R           The mc.setseed argument
+  mcpreschedule.R       The mc.preschedule argument
+  mcpvec.R              Example use of the pvec function
+  mcparallelcollect.R   Example use of the parallel and collect functions
+  mcrng.R               Using a parallel RNG with multicore
+  mclowlevel.R          Using the low-level API to implement a stripped-
+                        down version of the mclapply function.

multicore/mccores.R

+library(multicore)
+
+results <- mclapply(1:100, function(i) Sys.getpid(), mc.cores=2)
+print(unique(unlist(results)))
+
+options(cores=3)
+results <- mclapply(1:100, function(i) Sys.getpid())
+print(unique(unlist(results)))

multicore/mclapply.R

+library(multicore)
+library(MASS)
+
+results <- mclapply(rep(25, 4),
+                    function(nstart) kmeans(Boston, 4, nstart=nstart))
+i <- sapply(results, function(result) result$tot.withinss)
+result <- results[[which.min(i)]]
+print(result)

multicore/mclowlevel.R

+library(multicore)
+
+# Simplified version of mclapply that adds an "mc.init" argument
+mclapply.init <- function(X, FUN, ..., mc.cores=4, mc.init=NULL) {
+  cores <- max(min(mc.cores, length(X)), 1)
+  ix <- lapply(1:cores, function(i) seq(i, length(X), by=cores))
+  forkloop <- function(core) {
+    proc <- fork()
+    if (inherits(proc, "masterProcess")) {
+      sendMaster(tryCatch({
+        suppressWarnings(rm(".Random.seed", pos=.GlobalEnv))
+        if (is.function(mc.init))
+          mc.init(core, cores)
+        lapply(X[ix[[core]]], FUN, ...)
+      },
+      error=function(e) {
+        lapply(ix[[core]], function(i) e)
+      }))
+      exit(0)
+    }
+    proc$pid
+  }
+  pids <- sapply(1:cores, forkloop)
+  results <- vector("list", length(X))
+  while (! is.null(ready <- selectChildren(pids, 1))) {
+    if (is.integer(ready)) {
+      for (pid in ready) {
+        data <- readChild(pid)
+        if (is.raw(data)) {
+          core <- which(pid == pids)
+          results[ix[[core]]] <- unserialize(data)
+        }
+      }
+    }
+  }
+  names(results) <- names(X)
+  results
+}
+
+# Define an "mc.init" function that defines a worker ID variable
+set.worker.id <- function(id, cores) {
+  assign(".MC.WORKER.ID", id, pos=.GlobalEnv)
+}
+
+# Try out mclapply.init, initializing the workers with "set.worker.id"
+mclapply.init(11:13, function(i) c(i, .MC.WORKER.ID),
+              mc.cores=2, mc.init=set.worker.id)
+
+# Define an "mc.init" function that sets the RNG seed of the
+# workers in the same way as the real mclapply function.
+set.worker.seed <- function(id, cores) {
+  set.seed(Sys.getpid())
+}
+
+# Try out mclapply.init, initializing the workers with "set.worker.seed"
+mclapply.init(1:3, function(i) rnorm(1), mc.init=set.worker.seed)

multicore/mcparallelcollect.R

+library(multicore)
+
+# Define our set of three contrived (but illustrative) functions
+fun1 <- function() {Sys.sleep(10); 1}
+fun2 <- function() {Sys.sleep(5);  2}
+fun3 <- function() {Sys.sleep(1);  3}
+
+# Start the three functions executing in the background
+cat('1) Starting three tasks:\n')
+f1 <- parallel(fun1())