Foreign.Marshal.Pool functions use inefficient O(n) operations

Foreign.Marshal.Pool uses Data.List.delete and Data.List.elem to determine whether a pointer is already in the pool and to delete them, as a result of newtype Pool = Pool (IORef [Ptr ()]).

Thus repeated operations on pools with many entries can become very slow.

If possible, we might consider using Ord on the Ptr and an O(log n) data structure instead of a [Ptr] list.

Alternatively, we should warn in the docs that this is the case, but it seems better to just fix the implementation.

Trac metadata

Trac field	Value
Version	8.2.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
Test case
Differential revisions
BlockedBy
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Blocking
CC	nh2
Operating system
Architecture