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[ base ] Add non-blocking and timeout variants for channelGet #3435

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@Matthew-Mosior Matthew-Mosior commented Dec 4, 2024

Description

This PR adds a two new functions in System.Concurrency, channelGetNonBlocking and channelGetWithTimeout (only for the chez backend).

This PR closes #3424.

Should this change go in the CHANGELOG?

  • If this is a fix, user-facing change, a compiler change, or a new paper
    implementation, I have updated CHANGELOG_NEXT.md (and potentially also
    CONTRIBUTORS.md).

…g with return values of blodwen-channel-get-non-blocking.
@Matthew-Mosior Matthew-Mosior changed the title [ lib] Add Non-Blocking and Timeout variants for channelGet [ lib ] Add Non-Blocking and Timeout variants for channelGet Dec 4, 2024
@Matthew-Mosior Matthew-Mosior changed the title [ lib ] Add Non-Blocking and Timeout variants for channelGet [ libs ] Add Non-Blocking and Timeout variants for channelGet Dec 4, 2024
@Matthew-Mosior Matthew-Mosior changed the title [ libs ] Add Non-Blocking and Timeout variants for channelGet [ base ] Add Non-Blocking and Timeout variants for channelGet Dec 4, 2024
@Matthew-Mosior Matthew-Mosior changed the title [ base ] Add Non-Blocking and Timeout variants for channelGet [ base ] Add non-blocking and timeout variants for channelGet Dec 4, 2024
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I'm not really a member of this project, so I can't approve it, but I'll at least provide some initial feedback.

Hopefully this will get some other folks to chime in.

Comment on lines +184 to +194
data ChannelSchemeObj : Type where
Null : ChannelSchemeObj
Cons : ChannelSchemeObj -> ChannelSchemeObj -> ChannelSchemeObj
IntegerVal : Integer -> ChannelSchemeObj
FloatVal : Double -> ChannelSchemeObj
StringVal : String -> ChannelSchemeObj
CharVal : Char -> ChannelSchemeObj
Symbol : String -> ChannelSchemeObj
Box : ChannelSchemeObj -> ChannelSchemeObj
Vector : Integer -> List ChannelSchemeObj -> ChannelSchemeObj
Procedure : ChannelObj -> ChannelSchemeObj
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Minor nit: since this type isn't indexed, it could be converted to the simpler data syntax.

data ChannelSchemeObj
 = Null
 | Cons ChannelSchemeObj ChanelSchemeObj
 ...


Procedure : ChannelObj -> ChannelSchemeObj

export
interface Scheme a where
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nit: rename the interface to FromScheme, for consistency with FromString, FromInteger, etc.

Comment on lines +377 to +388
if prim_isInteger obj == 1 then IntegerVal (unsafeGetInteger obj)
else if prim_isVector obj == 1 then Vector (unsafeGetInteger (unsafeVectorRef obj 0))
(readVector (unsafeVectorLength obj) 1 obj)
else if prim_isPair obj == 1 then Cons (decodeObj (unsafeFst obj))
(decodeObj (unsafeSnd obj))
else if prim_isFloat obj == 1 then FloatVal (unsafeGetFloat obj)
else if prim_isString obj == 1 then StringVal (unsafeGetString obj)
else if prim_isChar obj == 1 then CharVal (unsafeGetChar obj)
else if prim_isSymbol obj == 1 then Symbol (unsafeReadSymbol obj)
else if prim_isProcedure obj == 1 then Procedure obj
else if prim_isBox obj == 1 then Box (decodeObj (unsafeUnbox obj))
else Null
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I wonder if there's a better way to express this. I generally think of long conditionals as a code smell.

Not to mention you have essentially the same conditional in the WithTimeout variant below. Could the runtime type checks be be folded into the FromScheme interface implementation, so that you only need to call fromScheme here?

(begin
(sleep (make-time 'time-duration 1000000 0))
(loop start-time)))))))

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Someone familiar with scheme internals really needs to look this whole function over carefully.

Comment on lines 1 to 23
import System
import System.Concurrency

-- Test that using channelGetNonBlocking works as expected.
main : IO ()
main = do
chan <- makeChannel
threadID <- fork $ do
channelPut chan "Hello"
channelPut chan "Goodbye"
sleep 1
case !(channelGetNonBlocking chan) of
Nothing =>
putStrLn "Nothing"
Just val' =>
putStrLn val'
case !(channelGetNonBlocking chan) of
Nothing =>
putStrLn "Nothing"
Just val' =>
putStrLn val'
sleep 1

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Formatting nits: don't need to split these cases over multiple lines.

Nothing => putStrLn "Nothing"
Just val   => putStrLn val

This entire case statement can be collapsed to putStrLn $ fromMaybe "Nothing" !(channelGetNonBlocking chan)

or

putStrLn $ show !(channelGetNonBlocking chan), with the caveat that the output will be pretty-printed, but that's probably fine here so long as you adjust your expected values to match

do c <- makeChannel
tids <- for [0..11] $ \n => fork $ producer c n
vals <- for [0..11] $ \_ => channelGetWithTimeout c 5
ignore $ traverse (\t => threadWait t) tids
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lambda is redundant here: ignore $ traverse threadWait tids

Comment on lines +21 to +27
let vals' = map (\val => case val of
Nothing =>
0
Just val' =>
val'
) vals
s = sum vals'
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style nit:

lambda can be replaced with partial application of library routine, map with <$>.

sum $ fromMaybe 0 <$> vals

The whole thing can then be:

putStrLn $ sum $ fromMaybe 0 <$> vals

Adjust expected case to simply read 55.

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System.Concurrency.channelGet is hard to use and too coupled into scheme support code
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