unpin a mutable byte array

Sometimes, it necessary to allocate a mutable byte array as pinned. This commonly happens when the mutable byte array will immidiately be handed over to a safe FFI routine to be initialized. However, after it has been initialized, it might not be useful for it to be pinned anymore. If it's a little byte array, it may contribute to a fragmented heap. Even if it's large, the fact that the user explicitly asked pin it prohibits it from ever being added to a compact region (pinned bytearrays that were pinned simply because they are over 3KB can be added to compact regions). A workaround for either of these problems is to copy the pinned bytearray into an unpinned byte array afterwards. But that's kind of wasteful. Is it possible to have a primop

unpinMutableByteArray :: MutableByteArray s -> State# s -> State# s

After this, the mutable byte array could be moved in memory. This would require isMutableByteArrayPinned# to undergo a similar transition as sizeofMutableByteArray# (which was superceeded by getSizeofMutableByteArray#) underwent.

Is this possible? Or are pinned things allocated in a special place that makes unpinning impossible?

Trac metadata

Trac field	Value
Version	8.6.2
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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