title: How to use CUDA stream in Pytorch?
body: <p>I wanna use CUDA stream in Pytorch to parallel some computations, but I don't know how to do it.
  For instance, if there's 2 tasks, A and B, need to be parallelized, I wanna do the following things:</p>
  
  <pre><code>stream0 = torch.get_stream()
  stream1 = torch.get_stream()
  with torch.now_stream(stream0):
      // task A
  with torch.now_stream(stream1):
      // task B
  torch.synchronize()
  // get A and B's answer
  </code></pre>
  
  <p>How can I achieve the goal in real python code?</p>