title: How to fork/parallelize process in purrr::pmap
body: <p>I have the following code that does serial processing with <a href="http://purrr.tidyverse.org/reference/map2.html" rel="noreferrer">purr::pmap</a></p>
  
  <p>
  <br/></p>
  
  <pre class="lang-r prettyprint-override"><code>library(tidyverse)
  
  set.seed(1)
  params &lt;- tribble(
    ~mean, ~sd, ~n,
    5,     1,  1,
    10,     5,  3,
    -3,    10,  5
  )
  params %&gt;% 
    pmap(rnorm)
  #&gt; [[1]]
  #&gt; [1] 4.373546
  #&gt; 
  #&gt; [[2]]
  #&gt; [1] 10.918217  5.821857 17.976404
  #&gt; 
  #&gt; [[3]]
  #&gt; [1]   0.2950777 -11.2046838   1.8742905   4.3832471   2.7578135
  </code></pre>
  
  <p>How can I parallelize (fork) the process above so that it runs faster and produces identical result?</p>
  
  <p>Here, I use <code>rnorm</code> for illustration purpose, in reality I have a function that does heavy duty work. It needs parallelizing.</p>
  
  <p>I'm open to non-purrr (non-tidyverse) solution, as long as it produces identical result given the <code>rnorm</code> function and <code>params</code> as input.</p>