refactor: make nextListenerDelay local to Listener module

Right now stateNextListenerDelay is only used in Listener module.
This change is a small refactoring moving nextListenerDelay to Listener to increase cohesion and decrease coupling.

src/PostgREST/AppState.hs

@@ -11,13 +11,11 @@ module PostgREST.AppState
   , getMainThreadId
   , getPgVersion
   , getNextDelay
-  , getNextListenerDelay
   , getTime
   , getJwtCacheState
   , init
   , initWithPool
   , putConfig -- For tests TODO refactoring
-  , putNextListenerDelay
   , putSchemaCache
   , putPgVersion
   , putIsListenerOn
@@ -72,33 +70,31 @@ import Protolude
 
 data AppState = AppState
   -- | Database connection pool
-  { statePool              :: SQL.Pool
+  { statePool             :: SQL.Pool
   -- | Database server version
-  , statePgVersion         :: IORef PgVersion
+  , statePgVersion        :: IORef PgVersion
   -- | Schema cache
-  , stateSchemaCache       :: IORef (Maybe SchemaCache)
+  , stateSchemaCache      :: IORef (Maybe SchemaCache)
   -- | The schema cache status
-  , stateSCacheStatus      :: SchemaCacheStatus
+  , stateSCacheStatus     :: SchemaCacheStatus
   -- | State of the LISTEN channel
-  , stateIsListenerOn      :: IORef Bool
+  , stateIsListenerOn     :: IORef Bool
   -- | starts the connection worker with a debounce
-  , debouncedSCacheLoader  :: IO ()
+  , debouncedSCacheLoader :: IO ()
   -- | Config that can change at runtime
-  , stateConf              :: IORef AppConfig
+  , stateConf             :: IORef AppConfig
   -- | Time used for verifying JWT expiration
-  , stateGetTime           :: IO UTCTime
+  , stateGetTime          :: IO UTCTime
   -- | Used for killing the main thread in case a subthread fails
-  , stateMainThreadId      :: ThreadId
+  , stateMainThreadId     :: ThreadId
   -- | Keeps track of the next delay for db connection retry
-  , stateNextDelay         :: IORef Int
-  -- | Keeps track of the next delay for the listener
-  , stateNextListenerDelay :: IORef Int
+  , stateNextDelay        :: IORef Int
   -- | Observation handler
-  , stateObserver          :: ObservationHandler
+  , stateObserver         :: ObservationHandler
   -- | JWT Cache
-  , stateJwtCache          :: JwtCache.JwtCacheState
-  , stateLogger            :: Logger.LoggerState
-  , stateMetrics           :: Metrics.MetricsState
+  , stateJwtCache         :: JwtCache.JwtCacheState
+  , stateLogger           :: Logger.LoggerState
+  , stateMetrics          :: Metrics.MetricsState
   }
 
 -- | Schema cache status.
@@ -131,7 +127,6 @@ initWithPool pool conf loggerState metricsState observer = mdo
     <*> mkAutoUpdate defaultUpdateSettings { updateAction = getCurrentTime }
     <*> myThreadId
     <*> newIORef 0
-    <*> newIORef 1
     <*> pure observer
     <*> JwtCache.init conf observer
     <*> pure loggerState
@@ -248,12 +243,6 @@ schemaCacheLoader = debouncedSCacheLoader
 getNextDelay :: AppState -> IO Int
 getNextDelay = readIORef . stateNextDelay
 
-getNextListenerDelay :: AppState -> IO Int
-getNextListenerDelay = readIORef . stateNextListenerDelay
-
-putNextListenerDelay :: AppState -> Int -> IO ()
-putNextListenerDelay = atomicWriteIORef . stateNextListenerDelay
-
 getConfig :: AppState -> IO AppConfig
 getConfig = readIORef . stateConf
 

src/PostgREST/Listener.hs

@@ -18,6 +18,8 @@ import qualified PostgREST.Config   as Config
 import           Control.Arrow              ((&&&))
 import           Data.Bitraversable         (bisequence)
 import           Data.Either.Combinators    (whenRight)
+import           Data.IORef                 (IORef, newIORef,
+                                             readIORef, writeIORef)
 import qualified Data.Text                  as T
 import qualified Database.PostgreSQL.LibPQ  as LibPQ
 import qualified Hasql.Session              as SQL
@@ -29,13 +31,14 @@ import           Protolude
 runListener :: AppState -> IO ()
 runListener appState = do
   AppConfig{..} <- getConfig appState
-  when configDbChannelEnabled $
-    void . forkIO . void $ retryingListen appState False
+  when configDbChannelEnabled $ do
+    nextDelay <- newIORef 1
+    void . forkIO . void $ retryingListen appState nextDelay False
 
 -- | Starts a LISTEN connection and handles notifications. It recovers with exponential backoff with a cap of 32 seconds, if the LISTEN connection is lost.
 -- | This function never returns (but can throw) and return type enforces that.
-retryingListen :: AppState -> Bool -> IO Void
-retryingListen appState hasDbListenerBug = do
+retryingListen :: AppState -> IORef Int -> Bool -> IO Void
+retryingListen appState nextDelay hasDbListenerBug = do
   cfg@AppConfig{..} <- AppState.getConfig appState
   let
     dbChannel = toS configDbChannel
@@ -48,13 +51,13 @@ retryingListen appState hasDbListenerBug = do
         killThread mainThreadId
 
       -- retry the listener
-      delay <- AppState.getNextListenerDelay appState
+      delay <- readIORef nextDelay
       observer $ DBListenRetry delay
       threadDelay (delay * oneSecondInMicro)
       unless (delay == maxDelay) $
-        AppState.putNextListenerDelay appState (delay * 2)
+        writeIORef nextDelay (delay * 2)
       -- loop running the listener
-      retryingListen appState (isDbListenerBug err)
+      retryingListen appState nextDelay (isDbListenerBug err)
 
   -- Execute the listener with error handling
   handle onError $ do
@@ -75,12 +78,12 @@ retryingListen appState hasDbListenerBug = do
 
           AppState.putIsListenerOn appState True
 
-          delay <- AppState.getNextListenerDelay appState
+          delay <- readIORef nextDelay
           when (delay > 1) $ do -- if we did a retry
             -- assume we lost notifications, refresh the schema cache
             AppState.schemaCacheLoader appState
             -- reset the delay
-            AppState.putNextListenerDelay appState 1
+            writeIORef nextDelay 1
 
           observer $ DBListenStart pqHost pqPort pgFullName dbChannel