On 26 April 2016 at 22:36, Merijn Verstraaten
I would propose adding a Bool value to base that indicates whether the code was compiled/linked with the threaded or single threaded runtime system. A library might want to implement certain functionality differently depending on whether the threaded runtime system is used (i.e. avoid blocking C FFI calls in single-threaded).
There is currently no good way to do this. StackExchange currently suggests using "Control.Concurrent.rtsSupportsBoundThreads" for this, which is defined as:
HsBool rtsSupportsBoundThreads(void) { #if defined(THREADED_RTS)
return HS_BOOL_TRUE; #else return HS_BOOL_FALSE; #endif }
But it seems undesirable to conflate support for bound threads and use of the threaded runtime system? Especially since this would be a trivial addition to Control.Concurrent (i.e. simply an ifdef'ed True/False constant).
I may very well be wrong with this, but off the top of my head if the library is installed globally (either manually, non-sandboxed cabal-install or using stack in some fashion), then I don't think whether a particular _executable_ is compiled with a multi-/single-threaded runtime system would affect the value from a constant that's already been compiled (unless INLINE is used to prevent it being pre-computed).
Cheers, Merijn
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