fix: shutdown should wait for in flight requests

Author: mkleczek

CHANGELOG.md

@@ -21,6 +21,9 @@ All notable changes to this project will be documented in this file. From versio
 - Log error when `db-schemas` config contains schema `pg_catalog` or `information_schema` by @taimoorzaeem in #4359
   + Now fails at startup. Prior to this, it failed with `PGRST205` on requests related to these schemas.
 
+### Fixed
+- Shutdown should wait for in flight requests by @mkleczek in #4702
+
 ## [14.7] - 2026-03-20
 
 ### Fixed

src/PostgREST/App.hs

@@ -22,6 +22,7 @@ import GHC.IO.Exception (IOErrorType (..))
 import System.IO.Error  (ioeGetErrorType)
 
 import Control.Monad.Except     (liftEither)
+import Control.Monad.Extra      (whenJust)
 import Data.Either.Combinators  (mapLeft, whenLeft)
 import Data.Maybe               (fromJust)
 import Data.String              (IsString (..))
@@ -79,8 +80,10 @@ run appState = do
 
   AppState.schemaCacheLoader appState -- Loads the initial SchemaCache
   (mainSocket, adminSocket) <- initSockets conf
-
-  Unix.installSignalHandlers observer (AppState.getMainThreadId appState) (AppState.schemaCacheLoader appState) (AppState.readInDbConfig False appState)
+  let closeSockets = do
+        whenJust adminSocket NS.close
+        NS.close mainSocket
+  Unix.installSignalHandlers observer closeSockets (AppState.schemaCacheLoader appState) (AppState.readInDbConfig False appState)
 
   Listener.runListener appState
 
@@ -92,6 +95,10 @@ run appState = do
     address <- resolveSocketToAddress mainSocket
     observer $ AppServerAddressObs address
 
+  -- Hardcoding maximum graceful shutdown timeout (arbitrary set to 5 seconds)
+  -- This is unfortunate but necessary becase graceful shutdowns don't work with HTTP keep-alive
+  -- causing Warp to handle requests on already opened connections even if the listen socket is closed
+  -- See: https://github.com/yesodweb/wai/issues/853
   Warp.runSettingsSocket (serverSettings conf & setOnException onWarpException) mainSocket app
   where
     observer = AppState.getObserver appState

src/PostgREST/Unix.hs

@@ -19,10 +19,9 @@ import           System.Directory      (removeFile)
 import           System.IO.Error       (isDoesNotExistError)
 
 -- | Set signal handlers, only for systems with signals
-installSignalHandlers :: Observation.ObservationHandler -> ThreadId -> IO () -> IO () -> IO ()
+installSignalHandlers :: Observation.ObservationHandler -> IO () -> IO () -> IO () -> IO ()
 #ifndef mingw32_HOST_OS
-installSignalHandlers observer tid usr1 usr2 = do
-  let interrupt = throwTo tid UserInterrupt
+installSignalHandlers observer interrupt usr1 usr2 = do
   install Signals.sigINT  $ observer (Observation.TerminationUnixSignalObs "SIGINT") >> interrupt
   install Signals.sigTERM $ observer (Observation.TerminationUnixSignalObs "SIGTERM") >> interrupt
   install Signals.sigUSR1 usr1

test/io/test_io.py

@@ -105,7 +105,6 @@ def sleep():
         t.join()
 
 
-@pytest.mark.xfail(reason="Graceful shutdown is currently failing", strict=True)
 def test_graceful_shutdown_waits_for_in_flight_request(defaultenv):
     "SIGTERM should allow in-flight requests to finish before exiting"