Memory leak in a long running application

Hello,

I'm using openhtf as the core module tester in my application. It consists of a long running process.
I'm encountering a huge memory leak. To validate my speculation, I took the hello world example and ran it in a loop which is similar of what I need in my application (create a thread per test and dispatch it...). The memory usage is indeed increasing. Here's a snapshot of the memory after a couple of iterations of the hello world example.

*** Logs (see the SummaryTracker print_diff at the end of each 100 iterations)
[hello_world_mm_leak.log](https://github.com/google/openhtf/files/2923648/hello_world_mm_leak.log)

*** Script (as a text file to be uploaded)
[hello_world_openhtf.py.txt](https://github.com/google/openhtf/files/2923642/hello_world_openhtf.py.txt)

I'd like to add that by using Processes, I've no longer encountered a memory leak. However, the use of them is a bit overkill in my application and creates other ones.

Thoughts?