title: How to concat multiple files to a single file at the same time
body: <p>I am trying to concat multiple files (say 15 txt files) to a single file at the same time by separate ant calls.</p>
  
  <p>Say there are 15 concat() run at the same time. </p>
  
  <p>However, the output file was not expected.
  The data in the output file is corrupted.</p>
  
  <p>Does anyone have idea to solve this problem?</p>
  
  <p>Example:</p>
  
  <pre><code>Input 1:
  a=1
  b=2
  c=3
  
  Input 2:
  d=4
  e=5
  f=6
  
  Output:
  a=1
  b=2
  d=4
  e
  c=3=5
  f=6
  </code></pre>