I've seen a few questions go by recently about threads in VW - so I thought it might be useful to publicize the existing information. Have a look at this page for information on controlling the thread pool. In your image, look at class ProcessorScheduler - in particular, look at these methods:
- primGetThreadLevels - returns an array with the current values for various thread settings - see the method comment for details
- primSetThreadLimit: limit lowTide: lowTide - Set the OE's thread limit and low tide. A less-than-zero value is ignored, allowing each level to be set independently. Note that these values must be at least 1 since there is one thread devoted to Smalltalk
Those two methods will tell you what's going on, and how to control how your external API threads are managed. There's a wealth of information available on that page and in the method comments - go take a look!