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perf: Add semaphore to limit threads using the pool #4507

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perf: Add semaphore to limit threads using the pool #4507

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9 changes: 6 additions & 3 deletions src/PostgREST/AppState.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,8 @@ import Protolude
data AppState = AppState
-- | Database connection pool
{ statePool :: SQL.Pool
-- | Semaphore to limit threads using the pool
, statePoolSemaphore :: QSem
-- | Database server version
, statePgVersion :: IORef PgVersion
-- | Schema cache
Expand Down Expand Up @@ -133,10 +135,11 @@ init conf@AppConfig{configLogLevel, configDbPoolSize} = do
pure state' { stateSocketREST = sock, stateSocketAdmin = adminSock}

initWithPool :: AppSockets -> SQL.Pool -> AppConfig -> Logger.LoggerState -> Metrics.MetricsState -> ObservationHandler -> IO AppState
initWithPool (sock, adminSock) pool conf loggerState metricsState observer = do
initWithPool (sock, adminSock) pool conf@AppConfig{configDbPoolSize} loggerState metricsState observer = do

appState <- AppState pool
<$> newIORef minimumPgVersion -- assume we're in a supported version when starting, this will be corrected on a later step
<$> newQSem configDbPoolSize
<*> newIORef minimumPgVersion -- assume we're in a supported version when starting, this will be corrected on a later step
<*> newIORef Nothing
<*> newIORef SCPending
<*> newIORef False
Expand Down Expand Up @@ -216,7 +219,7 @@ usePool :: AppState -> SQL.Session a -> IO (Either SQL.UsageError a)
usePool AppState{stateObserver=observer, stateMainThreadId=mainThreadId, ..} sess = do
observer PoolRequest

res <- SQL.use statePool sess
res <- bracket_ (waitQSem statePoolSemaphore) (signalQSem statePoolSemaphore) (SQL.use statePool sess)

observer PoolRequestFullfilled

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