Better handling of zeromq connection close

modules/shared/channels/src/main/scala/almond/channels/zeromq/ZeromqConnection.scala

@@ -1,6 +1,6 @@
 package almond.channels.zeromq
 
-import java.nio.channels.{ClosedByInterruptException, Selector}
+import java.nio.channels.{ClosedByInterruptException, ClosedSelectorException, Selector}
 import java.nio.charset.StandardCharsets.UTF_8
 
 import almond.channels._
@@ -137,7 +137,8 @@ final class ZeromqConnection(
       case Channel.Input    => stdin0
     }
 
-  @volatile private var selectorOpt = Option.empty[Selector]
+  @volatile private var selectorClosing = false
+  @volatile private var selectorOpt     = Option.empty[Selector]
 
   private def withSelector[T](f: Selector => T): T =
     selectorOpt match {
@@ -190,18 +191,29 @@ final class ZeromqConnection(
           (channel, new PollItem(socket.channel, Poller.POLLIN))
         }
 
-      withSelector { selector =>
-        ZMQ.poll(selector, pollItems.map(_._2).toArray, pollingDelay.toMillis)
+      val doRead = withSelector { selector =>
+        try {
+          ZMQ.poll(selector, pollItems.map(_._2).toArray, pollingDelay.toMillis)
+          true
+        }
+        catch {
+          case _: ClosedSelectorException if selectorClosing || selectorOpt.isEmpty =>
+            // channel was closed
+            false
+        }
       }
 
-      pollItems
-        .collectFirst {
-          case (channel, pi) if pi.isReadable =>
-            channelSocket0(channel)
-              .read
-              .map(_.map((channel, _)))
-        }
-        .getOrElse(IO.pure(None))
+      if (doRead)
+        pollItems
+          .collectFirst {
+            case (channel, pi) if pi.isReadable =>
+              channelSocket0(channel)
+                .read
+                .map(_.map((channel, _)))
+          }
+          .getOrElse(IO.pure(None))
+      else
+        IO.pure(None)
     }.evalOn(threads.pollingEc).flatMap(identity)
 
   def close(partial: Boolean, lingerDuration: Duration): IO[Unit] = {
@@ -222,8 +234,13 @@ final class ZeromqConnection(
       if (!partial)
         heartBeatThreadOpt.foreach(_.interrupt())
 
-      selectorOpt.foreach(_.close())
-      selectorOpt = None
+      try {
+        selectorClosing = true
+        selectorOpt.foreach(_.close())
+        selectorOpt = None
+      }
+      finally
+        selectorClosing = false
 
       log.debug(s"Closed channels for $params" + (if (partial) " (partial)" else ""))
     }.evalOn(threads.selectorOpenCloseEc)