[Haskell-cafe] What does unpacking an MVar really mean?

[Leon Smith]

On Tue, Jul 31, 2012 at 7:37 AM, Bertram Felgenhauer <
bertram.felgenhauer at googlemail.com> wrote:

> Note that MVar# itself cannot be unpacked -- the StgMVar record will
> always be a separate heap object.


One could imagine a couple of techniques to unpack the MVar# itself,  and
was curious if GHC might employ one of them.

So, really,  unpacking the MVar does not eliminate a layer of indirection,
 it just eliminates the need to check a pointer tag (and possibly execute a
thunk or follow some redirects if you don't have a pointer to an MVar#).
 I think this is what I was ultimately after.

Best,
Leon
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