title: C++ Threads writing to different parts of array of vector
body: <p>I have an <code>std::array&lt;std::vector, NUM_THREADS&gt;</code> and I basically want each thread to go get some data, and store it in its own <code>std::vector</code>, and also to read from its vector.</p>
  
  <p>Is this safe?  Or am I going to have to use a mutex or something?</p>