Github user NicoK commented on a diff in the pull request:
https://github.com/apache/flink/pull/4509#discussion_r141673902
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/io/network/partition/consumer/RemoteInputChannel.java
---
@@ -390,7 +390,63 @@ public BufferProvider getBufferProvider() throws
IOException {
return inputGate.getBufferProvider();
}
- public void onBuffer(Buffer buffer, int sequenceNumber) {
+ /**
+ * Requests buffer from input channel directly for receiving network
data.
+ * It should always return an available buffer in credit-based mode.
+ *
+ * @return The available buffer.
+ */
+ public Buffer requestBuffer() {
+ synchronized (availableBuffers) {
+ return availableBuffers.poll();
+ }
+ }
+
+ /**
+ * Receives the backlog from producer's buffer response. If the number
of available
+ * buffers is less than the backlog length, it will request floating
buffers from buffer
+ * pool, and then notify unannounced credits to the producer.
+ *
+ * @param backlog The number of unsent buffers in the producer's sub
partition.
+ */
+ private void onSenderBacklog(int backlog) {
+ int numRequestedBuffers = 0;
+
+ synchronized (availableBuffers) {
+ // Important: the isReleased check should be inside the
synchronized block.
+ if (!isReleased.get()) {
+ senderBacklog.set(backlog);
+
+ while (senderBacklog.get() >
availableBuffers.size() && !isWaitingForFloatingBuffers.get()) {
--- End diff --
By taking all buffers until none are available any more, we do not really
ensure a fair distribution where large backlogs on one channel may actually
"starve" another (except for the exclusive buffers). Floating buffers should be
assigned round-robin among the channels.
Also, actually, the total number of required buffers should be `backlog +
initialCredit - currentCredit` with `currentCredit` being the credit that was
guaranteed, i.e. `availableBuffers.size()`.
Let me think about this a bit more to sort out the details - I'll come back
to you.
---
