pnowojski commented on a change in pull request #10029:  [FLINK-14553][runtime] 
Respect non-blocking output in StreamTask#processInput
URL: https://github.com/apache/flink/pull/10029#discussion_r340033249
 
 

 ##########
 File path: 
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java
 ##########
 @@ -281,10 +289,41 @@ protected void processInput(DefaultActionContext 
context) throws Exception {
                if (status == InputStatus.END_OF_INPUT) {
                        context.allActionsCompleted();
                }
-               else if (status == InputStatus.NOTHING_AVAILABLE) {
+
+               CompletableFuture<?> jointFuture = 
getInputOutputJointFuture(status);
+               if (jointFuture != null) {
                        SuspendedMailboxDefaultAction suspendedDefaultAction = 
context.suspendDefaultAction();
-                       
inputProcessor.getAvailableFuture().thenRun(suspendedDefaultAction::resume);
+                       jointFuture.thenRun(suspendedDefaultAction::resume);
+               }
+       }
+
+       /**
+        * @return a combination of input and output futures if at-least one 
future of them is not
+        * completed, otherwise return null if all input and outputs are 
available.
+        */
+       private CompletableFuture<?> getInputOutputJointFuture(InputStatus 
status) {
+               if (status == InputStatus.MORE_AVAILABLE && 
isOutputAvailable()) {
+                       return null;
+               }
+
+               int length = recordWriters.size();
+               for (int i = 0; i < length; i++) {
+                       inputOutputFutures[i] = 
recordWriters.get(i).getAvailableFuture();
+               }
+               inputOutputFutures[length] = 
inputProcessor.getAvailableFuture();
+               return CompletableFuture.allOf(inputOutputFutures);
+       }
+
+       /**
+        * @return true if all the record writers are available.
+        */
+       private boolean isOutputAvailable() {
+               for (RecordWriter recordWriter : recordWriters) {
+                       if (!recordWriter.isAvailable()) {
 
 Review comment:
   I think there is a bug in `LocalBufferPool#requestMemorySegment` in this 
code block:
   ```
                        if (isBlocking && isUnavailable()) {
                                availabilityHelper.resetUnavailable();
                        }
   ```
   `availabilityHelper` should be marked unavailable always, not only if this 
blocking request. Or am I missing something? (If not, we need a test case for 
this)
   
   Also the non synchronised `recordWriter.isAvailable()` works here only if 
the memory request that made the buffer pool unavailable came from the 
mailbox/task thread (or established some other accidental happen before 
relationship by taking/releasing some locks)? This is just a question to think 
through, as probably such behaviour is fine.
   

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