[GitHub] [pulsar] Shawyeok commented on a change in pull request #14687: [pulsar-client] Fix race condition in consumer redelivery

[GitBox <gi...@apache.org>]

Shawyeok commented on a change in pull request #14687:
URL: https://github.com/apache/pulsar/pull/14687#discussion_r826705555



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File path: pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConsumerImpl.java
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@@ -1916,20 +1916,20 @@ protected void completeOpBatchReceive(OpBatchReceive<T> op) {
         if (messageIds == null || messageIds.isEmpty()) {
             return CompletableFuture.completedFuture(Collections.emptyList());
         }
-        List<MessageIdData> data = new ArrayList<>(messageIds.size());
-        List<CompletableFuture<Void>> futures = new ArrayList<>(messageIds.size());
-        messageIds.forEach(messageId -> {
+        List<CompletableFuture<MessageIdData>> futures = messageIds.stream().map(messageId -> {
             CompletableFuture<Boolean> future = processPossibleToDLQ(messageId);
-            futures.add(future.thenAccept(sendToDLQ -> {
+            return future.thenApply(sendToDLQ -> {
                 if (!sendToDLQ) {
-                    data.add(new MessageIdData()
+                    return new MessageIdData()
                             .setPartition(messageId.getPartitionIndex())
                             .setLedgerId(messageId.getLedgerId())
-                            .setEntryId(messageId.getEntryId()));
+                            .setEntryId(messageId.getEntryId());
                 }
-            }));
-        });
-        return FutureUtil.waitForAll(futures).thenCompose(v -> CompletableFuture.completedFuture(data));
+                return null;
+            });
+        }).collect(Collectors.toList());
+        return FutureUtil.waitForAll(futures).thenApply(v ->
+                futures.stream().map(CompletableFuture::join).filter(Objects::nonNull).collect(Collectors.toList()));

Review comment:
       Actually using CompletableFuture::join here is safe cause the `futures` are already **completed**, it return immediately instead of block waiting for result.




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