fromPtr should have a more explicit name that points out use of mask_

[nh2]

fromPtr $ do ... uses mask_, thus making anything it wraps uninterruptible.

This means that common code such as

fromPtr $ [C.block|Mat * {
  // long-running C++ computation here
  }|]

will hang, not properly reacting to Ctrl+C, timeout, async cancellation, or other async exceptions.

Of course the C/C++ part itself cannot be interrupted anyway because it is a foreign call (unless foreign import ccall interruptible is used, which it isn't and which would need the called code to provide the necessary guarantees).

But the user of fromPtr should be made more explicitly aware that mask_ is going on, so that they ensure to not write any unnecessary Haskell code under it.

Solution

• fromPtr is in OpenCV.Internal.C.Types and doesn't seem to be re-exported to public APIs, so I think we should rename it to fromPtrWithMask, and deprecate the old name (but keep it forever).