Fix #5331 and #5332.

lib/upcoming/asyncdispatch.nim

@@ -1233,9 +1233,14 @@ else:
           newList.add(cb)
 
     withData(p.selector, ident, adata) do:
+      # descriptor still present in queue.
       adata.rwlist = newList & adata.rwlist
       rLength = len(adata.readList)
       wLength = len(adata.writeList)
+    do:
+      # descriptor was unregistered in callback via `unregister()`.
+      rLength = -1
+      wLength = -1
 
   template processCustomCallbacks(ident: untyped) =
     # Process pending custom event callbacks. Custom events are
@@ -1254,11 +1259,16 @@ else:
     var cb = curList[0]
     if not cb(fd.AsyncFD):
       newList.add(cb)
-    else:
-      p.selector.unregister(fd)
 
     withData(p.selector, ident, adata) do:
+      # descriptor still present in queue.
       adata.readList = newList & adata.readList
+      if len(adata.readList) == 0:
+        # if no callbacks registered with descriptor, unregister it.
+        p.selector.unregister(fd)
+    do:
+      # descriptor was unregistered in callback via `unregister()`.
+      discard
 
   proc poll*(timeout = 500) =
     var keys: array[64, ReadyKey]
@@ -1302,15 +1312,10 @@ else:
         # because state `data` can be modified in callback we need to update
         # descriptor events with currently registered callbacks.
         if not custom:
-          var update = false
           var newEvents: set[Event] = {}
-          if rLength > 0:
+          if rLength != -1 and wLength != -1:
-            update = true
+            if rLength > 0: incl(newEvents, Event.Read)
-            incl(newEvents, Event.Read)
+            if wLength > 0: incl(newEvents, Event.Write)
-          if wLength > 0:
-            update = true
-            incl(newEvents, Event.Write)
-          if update:
             p.selector.updateHandle(SocketHandle(fd), newEvents)
         inc(i)
 

tests/async/tupcoming_async.nim

@@ -61,6 +61,17 @@ when defined(upcoming):
       discard
     e.close()
 
+  proc eventTest5331() =
+    # Event must not raise any exceptions while was unregistered inside of
+    # own callback.
+    # Issue #5331.
+    let e = newAsyncEvent()
+    addEvent(e) do (fd: AsyncFD) -> bool:
+      e.unregister()
+      e.close()
+    e.setEvent()
+    poll()
+
   when ioselSupportedPlatform or defined(windows):
 
     import osproc
@@ -124,6 +135,7 @@ when defined(upcoming):
     eventTest()
     eventTest5304()
     eventTest5298()
+    eventTest5331()
     processTest()
     signalTest()
     echo "OK"
@@ -132,12 +144,14 @@ when defined(upcoming):
     eventTest()
     eventTest5304()
     eventTest5298()
+    eventTest5331()
     processTest()
     echo "OK"
   else:
     eventTest()
     eventTest5304()
     eventTest5298()
+    eventTest5331()
     echo "OK"
 else:
   echo "OK"