[work-pool] Add work-pool subproject

* This is an extraction from my mutant-manager project.

stack-9.4.yaml

@@ -71,6 +71,8 @@ flags:
     development: true
   tasty-mgolden:
     development: true
+  work-pool:
+    development: true
   xray:
     development: true
 packages:
@@ -97,4 +99,5 @@ packages:
 - source-constraints
 - stack-deploy
 - tasty-mgolden
+- work-pool
 - xray

stack-9.6.yaml

@@ -63,6 +63,8 @@ flags:
     development: true
   tasty-mgolden:
     development: true
+  work-pool:
+    development: true
   xray:
     development: true
 packages:
@@ -89,4 +91,5 @@ packages:
 - source-constraints
 - stack-deploy
 - tasty-mgolden
+- work-pool
 - xray

work-pool/README.md

@@ -0,0 +1,3 @@
+# work-pool
+
+Minimal fixed max size, fixed worker count work pool with per worker boot and dynamic job production.

work-pool/package.yaml

@@ -0,0 +1,25 @@
+_common/package: !include "../common/package.yaml"
+
+name:     work-pool
+synopsis: Simple work pool with max queue size, dynamic resupply and explicit worker boot.
+homepage: https://github.com/mbj/mhs#readme
+github:   mbj/mhs
+version:  0.0.1
+
+<<: *defaults
+
+dependencies:
+- base
+- mprelude
+- text
+- unliftio
+
+tests:
+  test:
+    <<: *test
+    dependencies:
+    - containers
+    - devtools
+    - tasty
+    - tasty-hunit
+    - work-pool

work-pool/src/WorkPool.hs

@@ -0,0 +1,78 @@
+module WorkPool
+  ( Config(..)
+  , Pool
+  , pushJob
+  , runPool
+  )
+where
+
+import MPrelude
+import Prelude (succ)
+
+import qualified UnliftIO.Async as UnliftIO
+import qualified UnliftIO.STM   as UnliftIO
+
+-- | Worker pool configuration
+data Config a = Config
+  { produceJobs :: forall m . MonadUnliftIO m => Pool a -> m ()
+  -- ^ function called from the main thread producing work, use `pushJob` to
+  -- create workable jobs.
+  , queueSize   :: Natural
+  -- ^ maximum size of the jobs queued
+  , workerCount :: Natural
+  -- ^ number of workers to boot
+  , workerRun   :: forall m . MonadUnliftIO m => Natural -> m (a -> m ())
+  -- ^ function called when a worker is booted, argument is the worker index,
+  -- returns an action to be called per job assigned to this worker.
+  }
+
+-- Internal queue event, supplying job or quitting the worker
+data Event a = Quit | Job a
+
+-- | Running pool
+newtype Pool a = Pool
+  { queue :: UnliftIO.TBQueue (Event a)
+  }
+
+-- | Add (dynamically) created a job to the pool
+--
+-- This function will block if the max queue size would be overflown.
+-- As the workers create space in the queue this function will unblock.
+pushJob :: MonadIO m => Pool a -> a -> m ()
+pushJob Pool{..} item
+  = UnliftIO.atomically
+  $ UnliftIO.writeTBQueue queue (Job item)
+
+-- | Run worker pool with specified config
+--
+-- The function will return if either:
+-- * the `produceJobs` function returns
+-- * a worker or throws an error
+-- * the producer throws an error.
+--
+-- Care is taken to not leak threads via the use if `withAsync` from the `async` package.
+runPool :: forall a m . MonadUnliftIO m => Config a -> m ()
+runPool Config{..} = do
+  pool@Pool{..} <- UnliftIO.atomically $ do
+    queue <- UnliftIO.newTBQueue queueSize
+    pure Pool{..}
+
+  boot pool $ \handlers -> do
+    produceJobs pool                                       -- supply jobs
+    UnliftIO.atomically $ UnliftIO.writeTBQueue queue Quit -- signal workers to gracefully exit
+    traverse_ UnliftIO.wait handlers                       -- wait for workers to gracefully exit
+  where
+    boot Pool{..} withAsyncHandlers = go 0 []
+      where
+        go index asyncHandlers =
+          if index == workerCount
+            then withAsyncHandlers asyncHandlers
+            else
+              UnliftIO.withAsync
+                (workLoop =<< workerRun index)
+                (\async -> go (succ index) (async:asyncHandlers))
+
+        workLoop action =
+          UnliftIO.atomically (UnliftIO.readTBQueue queue) >>= \case
+            (Job item) -> action item >> workLoop action
+            Quit       -> UnliftIO.atomically $ UnliftIO.writeTBQueue queue Quit

work-pool/test/Test.hs

@@ -0,0 +1,86 @@
+import Control.Arrow (left)
+import Control.Monad (when)
+import MPrelude
+import Test.Tasty
+import Test.Tasty.HUnit
+
+import qualified Data.List           as List
+import qualified Data.Set            as Set
+import qualified Data.String         as String
+import qualified Devtools
+import qualified UnliftIO.Concurrent as UnliftIO
+import qualified UnliftIO.Exception  as UnliftIO
+import qualified WorkPool
+
+main :: IO ()
+main
+  = defaultMain
+  $ testGroup "work-pool"
+  [ Devtools.testTree $$(Devtools.readDependencies [Devtools.Target "work-pool"])
+  , mkSuccess 1 1
+  , mkSuccess 1 100
+  , mkSuccess 100 1
+  , mkSuccess 100 100
+  , mkSuccess 1000 1000
+  , producerFailure
+  , workerFailure
+  ]
+  where
+    mkSuccess :: Natural -> Natural -> TestTree
+    mkSuccess queueSize workerCount =
+      testCase ("queue size: " <> show queueSize <> ", workerCount: " <> show workerCount) $ do
+        output <- UnliftIO.newMVar []
+        WorkPool.runPool $ config output
+        assertEqual "" (Set.fromList values) =<< UnliftIO.readMVar output
+      where
+        config output = WorkPool.Config{..}
+          where
+            workerRun :: MonadUnliftIO m => Natural -> m (Natural -> m ())
+            workerRun _index = pure $ \value -> do
+              void $ UnliftIO.modifyMVar output $ \set -> pure (Set.insert value set, ())
+
+    workerFailure :: TestTree
+    workerFailure = testCase "worker failure" $ do
+      result <- UnliftIO.try (WorkPool.runPool config)
+      assertEqual "" (Left "intentional error\n") (left formatException result)
+      where
+        config = WorkPool.Config{queueSize = 100, workerCount = 100, ..}
+
+        workerRun :: MonadIO m => Natural -> m (Natural -> m ())
+        workerRun _index = pure $ \value ->
+          when (value == 100) $ UnliftIO.throwString "intentional error"
+
+    producerFailure :: TestTree
+    producerFailure = testCase "producer failure" $ do
+      result <- UnliftIO.try (WorkPool.runPool config)
+      assertEqual "" (Left "intentional error\n") (left formatException result)
+      where
+        config
+          = WorkPool.Config
+          { produceJobs = produceJobsFailing
+          , queueSize   = 100
+          , workerCount = 100
+          , ..
+          }
+
+        produceJobsFailing :: MonadIO m => WorkPool.Pool Natural -> m ()
+        produceJobsFailing pool = do
+          WorkPool.pushJob pool 1
+          UnliftIO.throwString "intentional error"
+
+        workerRun :: MonadIO m => Natural -> m (Natural -> m ())
+        workerRun _index = pure . const $ pure ()
+
+    formatException :: UnliftIO.SomeException -> String
+    formatException
+      = String.unlines
+      . List.drop 2
+      . List.take 3
+      . String.lines
+      . UnliftIO.displayException
+
+    produceJobs :: MonadIO m => WorkPool.Pool Natural -> m ()
+    produceJobs pool = traverse_ (WorkPool.pushJob pool) values
+
+    values :: [Natural]
+    values = [0..1000]

work-pool/test/stack-9.4-dependencies.txt

@@ -0,0 +1,122 @@
+Diff 0.4.1
+OneTuple 0.4.1.1
+QuickCheck 2.14.3
+StateVar 1.2.2
+aeson 2.1.2.1
+alex 3.3.0.0
+ansi-terminal 0.11.5
+ansi-terminal-types 0.11.5
+ansi-wl-pprint 0.6.9
+array 0.5.4.0
+assoc 1.1
+async 2.2.5
+attoparsec 0.14.4
+base 4.17.2.1
+base-compat 0.12.3
+base-compat-batteries 0.12.3
+base-orphans 0.9.1
+bifunctors 5.5.15
+binary 0.8.9.1
+bitvec 1.1.5.0
+bytestring 0.11.5.3
+call-stack 0.4.0
+clock 0.8.4
+cmdargs 0.10.22
+colour 2.3.6
+comonad 5.0.8
+conduit 1.3.5
+containers 0.6.7
+contravariant 1.5.5
+cpphs 1.20.9.1
+data-default 0.7.1.1
+data-default-class 0.1.2.0
+data-default-instances-containers 0.0.1
+data-default-instances-dlist 0.0.1
+data-default-instances-old-locale 0.0.1
+data-fix 0.3.2
+deepseq 1.4.8.0
+deriving-aeson 0.2.9
+devtools 0.2.0
+directory 1.3.7.1
+distributive 0.6.2.1
+dlist 1.0
+exceptions 0.10.5
+extra 1.7.14
+file-embed 0.0.15.0
+filepath 1.4.2.2
+filepattern 0.1.3
+foldable1-classes-compat 0.1
+generically 0.1.1
+ghc 9.4.8
+ghc-bignum 1.3
+ghc-boot 9.4.8
+ghc-boot-th 9.4.8
+ghc-heap 9.4.8
+ghc-lib-parser 9.4.8.20231111
+ghc-lib-parser-ex 9.4.0.0
+ghc-prim 0.9.1
+ghci 9.4.8
+happy 1.20.1.1
+hashable 1.4.3.0
+hlint 3.5
+hpc 0.6.1.0
+hscolour 1.24.4
+indexed-traversable 0.1.3
+indexed-traversable-instances 0.1.1.2
+integer-logarithms 1.0.3.1
+libyaml 0.1.2
+mono-traversable 1.0.15.3
+mprelude 0.2.3
+mtl 2.2.2
+old-locale 1.0.0.7
+optparse-applicative 0.17.1.0
+parsec 3.1.16.1
+polyparse 1.13
+pretty 1.1.3.6
+primitive 0.8.0.0
+process 1.6.18.0
+random 1.2.1.1
+refact 0.3.0.2
+resourcet 1.2.6
+rts 1.0.2
+safe-exceptions 0.1.7.4
+scientific 0.3.7.0
+semialign 1.3
+semigroupoids 5.3.7
+source-constraints 0.0.5
+split 0.2.3.5
+splitmix 0.1.0.5
+stm 2.5.1.0
+strict 0.5
+syb 0.7.2.4
+tagged 0.8.7
+tasty 1.4.3
+tasty-expected-failure 0.12.3
+tasty-hunit 0.10.1
+tasty-mgolden 0.0.2
+template-haskell 2.19.0.0
+terminfo 0.4.1.5
+text 2.0.2
+text-short 0.1.5
+th-abstraction 0.4.5.0
+th-lift 0.8.4
+these 1.2
+time 1.12.2
+time-compat 1.9.6.1
+transformers 0.5.6.2
+transformers-compat 0.7.2
+typed-process 0.2.11.1
+unbounded-delays 0.1.1.1
+uniplate 1.6.13
+unix 2.7.3
+unliftio 0.2.25.0
+unliftio-core 0.2.1.0
+unordered-containers 0.2.19.1
+utf8-string 1.0.2
+uuid-types 1.0.5.1
+vector 0.13.1.0
+vector-algorithms 0.9.0.1
+vector-stream 0.1.0.0
+witherable 0.4.2
+work-pool 0.0.1
+yaml 0.11.11.2