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

[Christopher Allen]

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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