Dear all, I may have stumbled upon a bug in the Criterion package. When running the attached Haskell program (Benchmark.hs, a simple test case) on multiple cores (with +RTS -N, +RTS -N2, +RTS -N3 etc.) it sooner or later crashes with the following exception: Benchmark: thread blocked indefinitely in an MVar operation With profiling support enabled and run with the xc flag I get the following output before the crash: *** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace: Statistics.Resampling.Bootstrap.bootstrapBCA, called from Main.main, called from Main.CAF --> evaluated by: Main.main, called from Main.CAF *** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace: Statistics.Resampling.Bootstrap.bootstrapBCA, called from Main.main *** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace: Statistics.Resampling.Bootstrap.bootstrapBCA, called from Main.main *** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace: Statistics.Resampling.Bootstrap.bootstrapBCA, called from Main.main, called from Main.CAF I have tested this with GHC versions 7.0.4 and 7.4.2 and Criterion 0.6.0.1. So I am not sure if this is a bug in Criterion itself, the Statistics package or any dependency or if I am doing something obviously wrong. I would be grateful if someone could look into this as it is holding me back from using Criterion for benchmarking my code. Regards, Till Berger