title: How to prevent Numba from parallelizing a particular loop when parallel=True is used?
body: <p>I have a test code like so:</p>
  <pre><code>import numpy as np
  from numba import njit, prange
  import random
  
  
  def func():
      a = np.empty(0)
      for i in range(10):
          b = np.arange(np.random.randint(10))
          a = np.concatenate((a, b))
          print(len(b), ' / ', len(a))
  
  
  func()
  </code></pre>
  <p>It works as expected:</p>
  <pre><code>3  /  3
  6  /  9
  5  /  14
  8  /  22
  9  /  31
  6  /  37
  9  /  46
  5  /  51
  3  /  54
  9  /  63
  </code></pre>
  <p>If I compile with Numba by adding <code>@njit(parallel=True)</code> decorator, it stops working because Numba parallelizes this loop which causes issues:</p>
  <pre><code>2  /  0
  1  /  0
  2  /  0
  7  /  0
  0  /  0
  3  /  0
  2  /  0
  5  /  0
  7  /  0
  2  /  0
  </code></pre>
  <p>In my real code there is another loop in this function which uses prange, so I want parallel=True on the whole function. But I don't want it for this loop.</p>
  <p>How to prevent this?</p>