[Haskell-beginners] Nonsensical behavior with http-conduit, httpLbs

[Christopher Allen]

the function actually running the requests is:

dispatch :: String -> Method -> Maybe L.ByteString
            -> IO Reply
dispatch url method body = do
  initReq <- parseUrl url
  let reqBody = RequestBodyLBS $ fromMaybe emptyBody body
  let req = initReq { method = method
                    , requestBody = reqBody
                    , checkStatus = \_ _ _ -> Nothing}
  withManager $ httpLbs req

rest of the code is here: https://github.com/bitemyapp/bloodhound/


On Thu, Apr 10, 2014 at 1:25 AM, Christopher Allen <cma at bitemyapp.com>wrote:

> It's a step removed from that, and `seq`'ing insertData isn't fixing it,
> only a threadDelay is.
>
> The operations insertData is performing are:
> delete index, create index, add document to index
>
> the operation queryTweet is performing is:
> search index
>
> The behavior seems to indicate "search index" is happening before "add
> document to index" and after "delete index", as the document will not exist
> when the query is performed.
>
> Only adding a threadDelay as reliably worked. Even `seq`'ing insertData
> doesn't work.
>
> Are the requests somehow being performed concurrently?
>
>
>
> On Thu, Apr 10, 2014 at 1:15 AM, Michael Snoyman <michael at snoyman.com>wrote:
>
>> I can't say I fully understand your code, but it seems like it's doing
>> the following:
>>
>> 1. Send request to server to delete data.
>> 2. Send request to server to add data.
>> 3. Request data from server.
>>
>> You're saying that with a long enough delay between steps 2 and 3, then
>> (3) works, otherwise it fails. It sounds to me like there's some kind of a
>> race condition. I don't know anything about createExampleIndex, but are you
>> certain that it only returns after the data is completely ready for
>> querying?
>>
>>
>> On Thu, Apr 10, 2014 at 8:43 AM, Christopher Allen <cma at bitemyapp.com>wrote:
>>
>>> to add to my question adding a delay made it work:
>>>
>>> main :: IO ()
>>> main = do
>>>   _ <- insertData
>>>   threadDelay 1000000
>>>   myTweet <- queryTweet
>>>   print myTweet
>>>
>>>
>>>
>>> On Thu, Apr 10, 2014 at 12:41 AM, Christopher Allen <cma at bitemyapp.com>wrote:
>>>
>>>> Repro'd on GHC 7.8.1 and 7.6.3
>>>>
>>>> Original code is: https://github.com/bitemyapp/bloodhound/
>>>>
>>>> The code only works if I manually (out of band) run insertData (in a
>>>> REPL) and then run main with the insertData invocation stripped out. If I
>>>> run main with the insertData invocation included, it throws an exception
>>>> (head) because the search results are empty.
>>>>
>>>> The behavior is as if queryTweet was executing after insertData deleted
>>>> the index, but before it inserted the new data.
>>>>
>>>> The following is a stripped down example:
>>>>
>>>> insertData :: IO ()
>>>> insertData = do
>>>>   let encoded = encode exampleTweet
>>>>   _ <- deleteExampleIndex
>>>>   created <- createExampleIndex
>>>>   docCreated <- indexDocument (Server "http://localhost:9200")
>>>> "twitter" "tweet" exampleTweet "1"
>>>>   print "test"
>>>>   return ()
>>>> el
>>>> queryTweet :: IO (Either String Tweet)
>>>> queryTweet = do
>>>>   let queryFilter = BoolFilter (MustMatch (Term "user" "bitemyapp")
>>>> False)
>>>>                     <||> IdentityFilter
>>>>   let search = Search Nothing (Just queryFilter)
>>>>   reply <- searchByIndex testServer "twitter" search
>>>>   let result = eitherDecode (responseBody reply) :: Either String
>>>> (SearchResult Tweet)
>>>>   let myTweet = fmap (hitSource . head . hits . searchHits) result
>>>>   return myTweet
>>>>
>>>> main :: IO ()
>>>> main = do
>>>>   _ <- insertData
>>>>   myTweet <- queryTweet
>>>>   print myTweet
>>>>
>>>> further up the call chain, the http call is getting dispatched with
>>>> http-conduit's gear, the result returned with the expression:
>>>>
>>>> withManager $ httpLbs req
>>>>
>>>> Included this in case it affects the semantics.
>>>>
>>>> Can anybody help? This has stumped me for a couple hours and I couldn't
>>>> get anything clueful on IRC.
>>>>
>>>> Thanks to any that help.
>>>>
>>>> --- Chris
>>>>
>>>>
>>>
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>>
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