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Optimize Chunk#to{Byte,Char}Buffer, add note about mutability #3147

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merged 3 commits into from
Feb 19, 2023
Merged

Optimize Chunk#to{Byte,Char}Buffer, add note about mutability #3147

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a3969c0
`toByteBuffer` optimizations
armanbilge Feb 19, 2023
03885df
Smae for `toCharBuffer`
armanbilge Feb 19, 2023
583b09a
Add scaladoc note about buffer mutability
armanbilge Feb 19, 2023
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16 changes: 12 additions & 4 deletions core/shared/src/main/scala/fs2/Chunk.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -306,30 +306,38 @@ abstract class Chunk[+O] extends Serializable with ChunkPlatform[O] with ChunkRu
case _ => Chunk.ArraySlice(toArray, 0, size)
}

/** Converts this chunk to a `java.nio.ByteBuffer`. */
/** Converts this chunk to a `java.nio.ByteBuffer`.
* @note that even "read-only" interaction with a `ByteBuffer` may increment its `position`,
* so this method should be considered as unsafely allocating mutable state.
*/
def toByteBuffer[B >: O](implicit ev: B =:= Byte): JByteBuffer =
this match {
case c: Chunk.ArraySlice[_] if c.values.isInstanceOf[Array[Byte]] =>
JByteBuffer.wrap(c.values.asInstanceOf[Array[Byte]], c.offset, c.length)
case c: Chunk.ByteBuffer =>
val b = c.buf.asReadOnlyBuffer
val b = c.buf.duplicate // share contents, independent position/limit
Comment on lines -315 to +318
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asReadOnlyBuffer and duplicate are similar in that the returned buffer has independent position/limit.

The difference is that a read-only buffer denies access to its underlying Array, while a duplicated buffer does not. Being able to get at that array is an important optimization.

if (c.offset == 0 && b.position() == 0 && c.size == b.limit()) b
else {
(b: JBuffer).position(c.offset.toInt)
(b: JBuffer).limit(c.offset.toInt + c.size)
b
}
case c: Chunk.ByteVectorChunk =>
c.bv.toByteBuffer
case _ =>
JByteBuffer.wrap(this.asInstanceOf[Chunk[Byte]].toArray, 0, size)
}

/** Converts this chunk to a `java.nio.CharBuffer`. */
/** Converts this chunk to a `java.nio.CharBuffer`.
* @note that even "read-only" interaction with a `CharBuffer` may increment its position,
* so this method should be considered as unsafely allocating mutable state.
*/
def toCharBuffer[B >: O](implicit ev: B =:= Char): JCharBuffer =
this match {
case c: Chunk.ArraySlice[_] if c.values.isInstanceOf[Array[Char]] =>
JCharBuffer.wrap(c.values.asInstanceOf[Array[Char]], c.offset, c.length)
case c: Chunk.CharBuffer =>
val b = c.buf.asReadOnlyBuffer
val b = c.buf.duplicate // share contents, independent position/limit
if (c.offset == 0 && b.position() == 0 && c.size == b.limit()) b
else {
(b: JBuffer).position(c.offset.toInt)
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