Question

Consider a process which is creating multiple application domains. Do these Application domains share same thread pool? If yes, how is it coordinated between multiple application domains?

Answer 1

The ThreadPool is shared across all appdomains – since that means threads might end up switching between appdomains (potentially often!) there’s been perf work around that:

Link

[…] In fact, we violate this “rule”
already: since .NET 3.5, the CLR
thread pool has maintained separate
FIFO queues for each AppDomain in the
process, and an additional independent
FIFO queue for “native” work items
such as those queued by a host
(ASP.net being the prime user of this
feature). We round-robin between
these work queues, allowing each to
execute work for some time before
moving on to the next.[…]

BTW, note that strictly speaking the ThreadPool isn’t shared across the entire process anymore, since the v4 CLR allows loading side-by-side with V2, and each will have its own threadpool.