iamaleksey commented on code in PR #2982:
URL: https://github.com/apache/cassandra/pull/2982#discussion_r1453622777
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src/java/org/apache/cassandra/service/accord/AccordJournal.java:
##########
@@ -699,6 +1003,246 @@ private static int msVersion(int version)
}
}
+ /*
+ * Record framing logic
+ */
+
+ private final class FrameAggregator implements Interruptible.Task
+ {
+ /* external MPSC pending request queue */
+ private final ManyToOneConcurrentLinkedQueue<PendingRequest>
unframedRequests = new ManyToOneConcurrentLinkedQueue<>();
+
+ private final LongArrayList waitForEpochs = new LongArrayList();
+ private final Long2ObjectHashMap<ArrayList<PendingRequest>>
delayedRequests = new Long2ObjectHashMap<>();
+
+ private volatile Interruptible executor;
+
+ // a signal and flag that callers outside the aggregator thread can use
+ // to signal they want the aggregator to run again
+ private final Semaphore haveWork = newSemaphore(1);
+
+ void onWrite(Pointer pointer, RequestContext context)
+ {
+ unframedRequests.add(new PendingRequest(pointer, context));
+ haveWork.release(1);
+ }
+
+ void notifyOfEpoch()
+ {
+ haveWork.release(1);
+ }
+
+ void start()
+ {
+ executor =
executorFactory().infiniteLoop("AccordJournal#FrameAggregator", this, SAFE,
NON_DAEMON, SYNCHRONIZED);
+ }
+
+ void shutdown()
+ {
+ executor.shutdown();
+ }
+
+ /* internal reusable buffers used for frame generation */
+ private final ArrayList<PendingRequest> requestBuffer = new
ArrayList<>();
+ private final ArrayList<Pointer> pointersBuffer = new ArrayList<>();
+ private final ArrayList<RequestContext> contextsBuffer = new
ArrayList<>();
+
+ @Override
+ public void run(Interruptible.State state) throws InterruptedException
+ {
+ if (unframedRequests.isEmpty() && delayedRequests.isEmpty())
+ return;
+
+ try
+ {
+ doRun();
+ }
+ finally
+ {
+ requestBuffer.clear();
+ pointersBuffer.clear();
+ contextsBuffer.clear();
+ }
+
+ haveWork.acquire(1);
+ }
+
+ private void doRun()
+ {
+ /*
+ * Deal with delayed requests
+ */
+
+ waitForEpochs.sort(null);
+
+ for (int i = 0; i < waitForEpochs.size(); i++)
+ {
+ long waitForEpoch = waitForEpochs.getLong(i);
+ if (!node.topology().hasEpoch(waitForEpoch))
+ break;
+ requestBuffer.addAll(delayedRequests.remove(waitForEpoch));
+ }
+
+ waitForEpochs.removeIfLong(epoch ->
!delayedRequests.containsKey(epoch));
+
+ /*
+ * Deal with regular pending requests
+ */
+
+ PendingRequest request;
+ while (null != (request = unframedRequests.poll()))
+ {
+ long waitForEpoch = request.context.waitForEpoch;
+ if (!node.topology().hasEpoch(waitForEpoch))
+ {
+ delayedRequests.computeIfAbsent(waitForEpoch, ignore ->
new ArrayList<>()).add(request);
+ if (!waitForEpochs.containsLong(waitForEpoch))
+ {
+ waitForEpochs.addLong(waitForEpoch);
+ node.withEpoch(waitForEpoch, this::notifyOfEpoch);
+ }
+ }
+ else
+ {
+ requestBuffer.add(request);
+ }
+ }
+
+ for (PendingRequest req : requestBuffer)
+ {
+ pointersBuffer.add(req.pointer);
+ contextsBuffer.add(req.context);
+ }
+
+ if (!requestBuffer.isEmpty())
+ {
+ FrameRecord frame = new FrameRecord(node.uniqueNow(),
pointersBuffer.toArray(new Pointer[0]));
Review Comment:
I still needed to copy somewhere, as the original buffer was needed for
later reuse. But I simplified the logic a little by switching to lists and not
keeping additional buffer state between runs of aggregator.
P.S. As for escaping new empty arrays there, this is from 2016, regarding
`toArray()`: https://shipilev.net/blog/2016/arrays-wisdom-ancients/
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