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Improve documentation of customStrategy #692

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merged 2 commits into from
Sep 19, 2024
Merged

Improve documentation of customStrategy #692

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86a3c35
Clarify documentation of 'customStrategy' based on #690
adamgundry Sep 19, 2024
197bcdc
Remove outdated comments on AllocationStrategy
adamgundry Sep 19, 2024
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27 changes: 14 additions & 13 deletions Data/ByteString/Builder/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -1042,14 +1042,6 @@ maximalCopySize = 2 * L.smallChunkSize
------------------------------------------------------------------------------

-- | A buffer allocation strategy for executing 'Builder's.

-- The strategy
--
-- > 'AllocationStrategy' firstBufSize bufSize trim
--
-- states that the first buffer is of size @firstBufSize@, all following buffers
-- are of size @bufSize@, and a buffer of size @n@ filled with @k@ bytes should
-- be trimmed iff @trim k n@ is 'True'.
data AllocationStrategy = AllocationStrategy
(Maybe (Buffer, Int) -> IO Buffer)
{-# UNPACK #-} !Int
Expand All @@ -1060,11 +1052,20 @@ data AllocationStrategy = AllocationStrategy
{-# INLINE customStrategy #-}
customStrategy
:: (Maybe (Buffer, Int) -> IO Buffer)
-- ^ Buffer allocation function. If 'Nothing' is given, then a new first
-- buffer should be allocated. If @'Just' (oldBuf, minSize)@ is given,
-- then a buffer with minimal size @minSize@ must be returned. The
-- strategy may reuse the @oldBuf@, if it can guarantee that this
-- referentially transparent and @oldBuf@ is large enough.
-- ^ Buffer allocation function.
--
-- * If 'Nothing' is given, then a new first buffer should be allocated.
--
-- * If @'Just' (oldBuf, minSize)@ is given, then a buffer with minimal
-- size @minSize@ must be returned. The strategy may reuse @oldBuf@ only if
-- @oldBuf@ is large enough and the consumer can guarantee that this will
-- not result in a violation of referential transparency.
--
-- /Warning:/ for multithreaded programs, it is generally unsafe to reuse
-- buffers when using the consumers of 'Builder' in this package. For
-- example, if 'toLazyByteStringWith' is called with an
-- 'AllocationStrategy' that reuses buffers, evaluating the result by
-- multiple threads simultaneously may lead to corrupted output.
-> Int
-- ^ Default buffer size.
-> (Int -> Int -> Bool)
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