JobQueue is a simple job queue library based on prioritized FCFS scheduling. This is useful when you want to write a reliable batch system.
Execute the cabal install command and the library and example programs will be placed into your .cabal directory.
> cd haskell-jobqueue/
> cabal install jobqueue/ --only-dependencies --extra-include-dirs=/usr/local/include/zookeeper # if you use brew on Mac OSX
> cabal install jobqueue/ jobqueue-examples/
Various backends can be plugged in for use with this library. You can select the backend you wish to use depending on your needs. For example, one may choose Zookeeper for the backend if high availability is a requirement, or one may choose sqlite3 as their backend for a standalone tool.
- Zookeeper
- Sqlite3
Import JobQueue module in your source file.
{-# LANGUAGE LambdaCase #-}
import Control.Monad
import System.Environment hiding (getEnv)
import Network.JobQueueDefine your environment data type.
data JobEnv = JobEnv {
jeHello :: String
} deriving (Eq, Show)
instance Env JobEnv where -- You need Env instance when you define environment.
instance Aux JobEnv where -- You need Aux instance when you run the job queue.Define states that describe your state machine.
data JobUnit = HelloStep | WorldStep deriving (Show, Read, Eq, Ord)
instance Unit JobUnit where
getPriority _ju = 1
getRecovery _ju = HelloStep
instance Desc JobUnit whereDefine actions and run the state machine.
main :: IO ()
main = do
args <- getArgs
case args of
(loc:name:args') -> do
let withJobQueue = buildJobQueue loc name $ process $ \case
WorldStep -> commitIO (putStrLn "world") >> fin
HelloStep -> do
env <- getEnv
commitIO (putStr $ (jeHello env) ++ ", ")
next WorldStep
case args' of
("run":[]) -> withJobQueue $ loop (JobEnv "hello")
("init":[]) -> withJobQueue $ \jq -> scheduleJob jq HelloStep
[] -> putStrLn $ "command not specified."
(cmd:_) -> putStrLn $ "unknown command: " ++ cmd
_ -> return ()
where
loop env jq = do
executeJob jq env
count <- countJobQueue jq
when (count > 0) $ loop env jqThe "hello" example demonstrates a simple sequential state transition. It consists of just two states, a "Hello" step and a "World" step.
To initialize the state machine, execute it with the "init" command.
> jobqueue-sample-hello sqlite3://hello.sqlite3 test init
To run the state machine, execute it with the "run" command.
> jobqueue-sample-hello sqlite3://hello.sqlite3 test run
hello, world
If you wish to use a Zookeeper cluster, you can specify a Zookeeper address (e.g. "zookeeper://localhost:2181/") instead of the sqlite3 address.
The "fibonacci" example demonstrates a slightly more complex case with a loop in the state machine. It consists of an initialization step and a computation step.
To initialize the state machine, execute it with the "init" command.
> jobqueue-sample-fibonacci sqlite3://fibonacci.sqlite3 test init
To run the state machine, execute it with the "run" command.
> jobqueue-sample-fibonacci sqlite3://fibonacci.sqlite3 test run
[0,1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,1597,2584,4181,6765,10946,17711,28657,46368,75025,121393,196418,317811,514229,832040,1346269,2178309,3524578,5702887,9227465,14930352,24157817,39088169,63245986,102334155,165580141,267914296,433494437,701408733,1134903170,1836311903,2971215073,4807526976,7778742049,12586269025,20365011074,32951280099,53316291173,86267571272,139583862445,225851433717,365435296162,591286729879,956722026041,1548008755920,2504730781961,4052739537881,6557470319842,10610209857723,17167680177565,27777890035288,44945570212853,72723460248141,117669030460994,190392490709135,308061521170129,498454011879264,806515533049393,1304969544928657,2111485077978050,3416454622906707,5527939700884757,8944394323791464,14472334024676221,23416728348467685,37889062373143906,61305790721611591,99194853094755497,160500643816367088,259695496911122585,420196140727489673,679891637638612258,1100087778366101931,1779979416004714189,2880067194370816120,4660046610375530309,7540113804746346429,12200160415121876738,19740274219868223167,31940434634990099905,51680708854858323072,83621143489848422977,135301852344706746049,218922995834555169026,354224848179261915075]