Today at the GNET Michael Kennedy, Jason Whittington and I discovered a pretty interesting change in .NET 2.0 SP1 (included in .NET 3.5).

We knew they increased the thread pool limit from 25 threads/cpu to 250 threads/cpu, but we also found they changed the heuristics for creating threads to avoid creating a bunch of threads in a short period of time. In previous versions of .NET, threads were allocated at a rate of 1 every 500ms assuming there were queued items. This is documented behavior in MSDN.

In .NET 3.5, it appears to have been changed to a sliding scale where they slow down thread creation as more demand is placed on the pool. This is a change even from the beta and must have been slipped in at the last minute.

Michael documented the whole change on his blog here.. recommended reading.

Thanks to all of you who attended the Boston WPF class last week. You can get the demos we built in class here -- Class.zip.