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<title>Parallel Workers on the Local Machine</title>
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<h1>Parallel Workers on the Local Machine</h1>
<!--
%\VignetteIndexEntry{Parallel Workers on the Local Machine}
%\VignetteAuthor{Henrik Bengtsson}
%\VignetteKeyword{R}
%\VignetteKeyword{package}
%\VignetteKeyword{vignette}
%\VignetteEngine{parallelly::selfonly}
-->
<h1>Introduction</h1>
<p>This vignettes illustrates how to launch parallel workers on the
current, local machine. This works the same on all operating systems
where R is supported, e.g. Linux, macOS, and MS Windows.</p>
<h1>Examples</h1>
<h2>Example: Launching two parallel workers</h2>
<p>The below illustrates how to launch a cluster of two parallel workers
on the current machine, run some basic calculations in paralllel, and
then shut down the cluster.</p>
<pre><code class="language-r">library(parallelly)
library(parallel)
cl <- makeClusterPSOCK(2)
print(cl)
#> Socket cluster with 2 nodes where 2 nodes are on host 'localhost'
#> (R version 4.4.2 (2024-10-31), platform x86_64-pc-linux-gnu)
y <- parLapply(cl, X = 1:100, fun = sqrt)
y <- unlist(y)
z <- sum(y)
print(z)
#> [1] 671.4629
parallel::stopCluster(cl)
</code></pre>
<p><em>Comment</em>: In the <strong>parallel</strong> package, a parallel worker is referred
to a parallel node, or short <em>node</em>, which is why we use the same term
in the <strong>parallelly</strong> package.</p>
<p>An alternative to specifying the <em>number</em> of parallel workers is to
specify a character vector with that number of <code>"localhost"</code> entries,
e.g.</p>
<pre><code class="language-r">cl <- makeClusterPSOCK(c("localhost", "localhost"))
</code></pre>
<h2>Example: Launching as many parallel workers as allotted</h2>
<p>The <code>availableCores()</code> function will return the number of workers that
the system allows. It respects many common settings that controls the
number of CPU cores that the current R process is alloted, e.g. R
options, environment variables, and CGroups settings. For details, see
<code>help("availableCores")</code>. For example,</p>
<pre><code class="language-r">library(parallelly)
cl <- makeClusterPSOCK(availableCores())
print(cl)
#> Socket cluster with 8 nodes where 8 nodes are on host 'localhost'
#> (R version 4.4.2 (2024-10-31), platform x86_64-pc-linux-gnu)
</code></pre>
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