Hello, The paper "Extending the Haskell FFI with Concurrency" mentioned the following in Section 6.3: "GHC's run-time system employs one OS thread for every bound thread; additionally, there is a variable number of so-called "worker" OS threads that are used to execute the unbounded (lightweight) threads." How does the runtime system determine the number of worker threads? Is the number hardcoded in the RTS or dynamically adjustable? Can a programmer specify it as an RTS option or change it using an API? I would like to use a large number (say, 2000) of unbounded threads, each calling a blocking, safe foreign function via FFI import. What is supposed to happen if all the worker threads are used up? I tried this in the recent GHC 6.5 and got some kind of "runaway worker threads?" RTS failure message when more than 32 threads are used. Is it a current limitation of the RTS, or should I file a bug report for it? Thanks, Peng