4.11. Using Concurrent Haskell
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## 4.11. Using Concurrent Haskell

GHC supports Concurrent Haskell by default, without requiring a special option or libraries compiled in a certain way. To get access to the support libraries for Concurrent Haskell, just import `Control.Concurrent`. More information on Concurrent Haskell is provided in the documentation for that module.

The following RTS option(s) affect the behaviour of Concurrent Haskell programs:

`-C`s``

  Sets the context switch interval to `s` seconds. A context switch will occur at the next heap block allocation after the timer expires (a heap block allocation occurs every 4k of allocation). With `-C0` or `-C`, context switches will occur as often as possible (at every heap block allocation). By default, context switches occur every 20ms. Note that GHC's internal timer ticks every 20ms, and the context switch timer is always a multiple of this timer, so 20ms is the maximum granularity available for timed context switches.

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