[twitter.server] offload ShutdownHandler

# Problem
ShutdownHandler is executed on a netty IO thread and calls app.close which can easily block this thread.

# Solution
Offload execution to a thread.

JIRA Issues: STOR-1705

Differential Revision: https://phabricator.twitter.biz/D1109579

server/src/main/scala/com/twitter/server/handler/ShutdownHandler.scala

@@ -2,11 +2,18 @@ package com.twitter.server.handler
 
 import com.twitter.app.App
 import com.twitter.finagle.Service
-import com.twitter.finagle.http.{Method, Request, Response, Status, Uri}
+import com.twitter.finagle.http.Method
+import com.twitter.finagle.http.Request
+import com.twitter.finagle.http.Response
+import com.twitter.finagle.http.Status
+import com.twitter.finagle.http.Uri
 import com.twitter.io.Buf
-import com.twitter.server.util.HttpUtils.{newOk, newResponse}
+import com.twitter.server.util.HttpUtils.newOk
+import com.twitter.server.util.HttpUtils.newResponse
 import com.twitter.util.logging.Logger
-import com.twitter.util.{Duration, Future}
+import com.twitter.util.Duration
+import com.twitter.util.Future
+import com.twitter.util.Local
 
 class ShutdownHandler(app: App) extends Service[Request, Response] {
   private[this] val log = Logger[ShutdownHandler]
@@ -38,7 +45,22 @@ class ShutdownHandler(app: App) extends Service[Request, Response] {
         s"[${req.uri}] from ${req.remoteAddress.getHostAddress} " +
           s"quitting with grace period $grace"
       )
-      app.close(grace)
+
+      // Isolate a current thread (likely netty IO thread)
+      // from probable blocking calls inside app.close.
+      val ctx = Local.save()
+      new Thread(
+        () =>
+          try {
+            Local.restore(ctx)
+            app.close(grace)
+          } catch {
+            case th: Throwable =>
+              log.error("Exception when asking an app to close", th)
+          },
+        "shutdown-handler" // thread name
+      ).start()
+
       newOk("quitting\n")
     } else {
       log.info(

server/src/test/scala/com/twitter/server/handler/ShutdownHandlerTest.scala

@@ -1,10 +1,21 @@
 package com.twitter.server.handler
 
 import com.twitter.conversions.DurationOps._
-import com.twitter.finagle.http.{Method, Request, Status}
+import com.twitter.finagle.http.Method
+import com.twitter.finagle.http.Request
+import com.twitter.finagle.http.Status
 import com.twitter.server.TwitterServer
-import com.twitter.util.{Await, Awaitable, Closable, Duration, Future, Time}
+import com.twitter.util.Await
+import com.twitter.util.Awaitable
+import com.twitter.util.Closable
+import com.twitter.util.Duration
+import com.twitter.util.Future
+import com.twitter.util.Time
+import org.scalatest.concurrent.Eventually.eventually
+import org.scalatest.concurrent.PatienceConfiguration.Timeout
 import org.scalatest.funsuite.AnyFunSuite
+import org.scalatest.time.Seconds
+import org.scalatest.time.Span
 
 class ShutdownHandlerTest extends AnyFunSuite {
 
@@ -38,7 +49,9 @@ class ShutdownHandlerTest extends AnyFunSuite {
     val handler = new ShutdownHandler(closer)
     val rsp = await(handler(Request(Method.Post, "/foo")))
     assert(rsp.status == Status.Ok)
-    assert(closer.closed)
+    eventually(Timeout(Span(5, Seconds))) {
+      assert(closer.closed)
+    }
   })
 
   test("close without a grace period, but closer overrides default grace")(
@@ -53,7 +66,9 @@ class ShutdownHandlerTest extends AnyFunSuite {
       val handler = new ShutdownHandler(closer)
       val rsp = await(handler(Request(Method.Post, "/foo")))
       assert(rsp.status == Status.Ok)
-      assert(closer.closed)
+      eventually(Timeout(Span(5, Seconds))) {
+        assert(closer.closed)
+      }
     })
 
   test("close with a grace period") {
@@ -66,7 +81,9 @@ class ShutdownHandlerTest extends AnyFunSuite {
     val handler = new ShutdownHandler(closer)
     val rsp = await(handler(Request(Method.Post, "/foo?grace=" + grace.toString)))
     assert(rsp.status == Status.Ok)
-    assert(closer.closed)
+    eventually(Timeout(Span(5, Seconds))) {
+      assert(closer.closed)
+    }
   }
 
   test("fail when an invalid grace parameter is specified") {