Add ForeignPtr type and builtins for finalizing external resources - #6192
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Share tests pass (aside from a couple expected failures). Benchmarks look good. I must not completely understand the new checking framework to get past CI, though. |
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We're working out some issues with it, sorry. I'll try making it pass. |
pchiusano
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LGTM assuming conflicts are fixed and CI passes. Can you prep a PR to base after this gets merged, too?
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This PR adds a
ForeignPtrtype and various related builtins for managing foreign resources in conjunction with garbage collection. This is based on GHC's support for this feature.ForeignPtrscan be created in two waysPtr awith a finalizer, which is useful for memory allocated and returned from foreign functionsallocatefunctions. These are similar to the existing functions forPtr, except they come equipped with finalizers that automatically release the memory (I think actually the memory is automatically collected because it's pinned memory in the Haskell heap, but that doesn't really matter)There are also two types of finalizers available
Func (Ptr a ->{IO} ()). These are foreign functions loaded from a DLL via a new builtin that returns a 'function pointer' rather than a callable unison function.'{IO} ()These can't actually be combined, because GHC doesn't allow it. However, anything you could do with the first could be done by the second by calling the foreign function in the thunk.
I didn't add any builtins for dereferencing the function pointers, since the only use we really have for them right now are these finalizers. There is enough information in the representation to get out a callable function if that becomes desirable in the future.
Tests of the new features have been added in transcripts. I didn't exhaustively test all the allocation builtins, but they're implemented uniformly, so testing one (which I did) should be sufficient.
I also had to tweak one of the git hook scripts to actually be able to push this, so that's included.
I have most of the docs written up for inclusion in base if/once this gets merged and released.
Haven't run share tests and benchmarks yet. I'll get on that.