System freezes on "Applying Effects" caused by too many threads

[sassman]

Describe the bug
System gets unresponsive when too many frames are there to be processed for the effects

To Reproduce
Steps to reproduce the behavior:

1. t-rec on a big terminal for example
2. End Recording
3. Observe the threads count when "Applying Effects" hits
4. System gets unresponsive for a while

Expected behavior
System should stay responsive all the time

Version Numbers of your System:

• OS: any