Presumably you will have a safe and an unsafe variant of each function, the safe one calling its corresponding unsafe variant guarded by an appropriate locking mechanism. Just export both and note why the unsafe variants are marked "unsafe". Separating policy from implementation is always nice for callers. Presumably they know their application and what they are willing to pay for each call. Best, Ben On Tue, 12 Apr 2016 at 08:57 Thomas Koster wrote:

Hi friends,

I am writing a library that has Handle-like values for resources that are not thread-safe (foreign state from a non-thread-safe C library). In other words, a resource can only be "used" by one Haskell thread at a time. Unless I take steps, if one shares the resource between concurrent Haskell threads, bad things will happen at runtime (even with a single-threaded runtime).

Naturally, I want consumers to use my library safely, so I am considering making it safe for all by pessimistically enforcing safe usage with MVars.

Is it common/expected that Haskell libraries enforce safe access like this?

MVars are not free from cost, but are they cheap (i.e. almost as fast as no forced synchronization) as long as no blocking/rescheduling occurs?

Thanks, -- Thomas Koster

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