fix: DH-18433: SourcePartitionedTable needs to check the size of pend…

…ing locations even if there are no added or removed locations (#6570) (#6571)

engine/table/src/main/java/io/deephaven/engine/table/impl/SourcePartitionedTable.java

@@ -250,27 +250,42 @@ private void processPendingLocations(final boolean notifyListeners) {
             try (final TableLocationSubscriptionBuffer.LocationUpdate locationUpdate =
                     subscriptionBuffer.processPending()) {
                 if (locationUpdate == null) {
-                    return;
+                    removed = null;
+                } else {
+                    removed = processRemovals(locationUpdate);
+                    processAdditions(locationUpdate);
                 }
-                removed = processRemovals(locationUpdate);
-                added = processAdditions(locationUpdate);
+                added = checkPendingLocations();
             }
 
-            resultRows.update(added, removed);
+            if (removed == null) {
+                if (added == null) {
+                    return;
+                }
+                resultRows.insert(added);
+            } else if (added == null) {
+                resultRows.remove(removed);
+            } else {
+                resultRows.update(added, removed);
+            }
             if (notifyListeners) {
                 result.notifyListeners(new TableUpdateImpl(
-                        added,
-                        removed,
+                        added == null ? RowSetFactory.empty() : added,
+                        removed == null ? RowSetFactory.empty() : removed,
                         RowSetFactory.empty(),
                         RowSetShiftData.EMPTY,
                         ModifiedColumnSet.EMPTY));
             } else {
-                added.close();
-                removed.close();
+                if (added != null) {
+                    added.close();
+                }
+                if (removed != null) {
+                    removed.close();
+                }
             }
         }
 
-        private RowSet processAdditions(final TableLocationSubscriptionBuffer.LocationUpdate locationUpdate) {
+        private void processAdditions(final TableLocationSubscriptionBuffer.LocationUpdate locationUpdate) {
             /*
              * This block of code is unfortunate, because it largely duplicates the intent and effort of similar code in
              * RegionedColumnSourceManager. I think that the RegionedColumnSourceManager could be changed to
@@ -280,13 +295,18 @@ private RowSet processAdditions(final TableLocationSubscriptionBuffer.LocationUp
              * population in STM ColumnSources.
              */
             // TODO (https://github.com/deephaven/deephaven-core/issues/867): Refactor around a ticking partition table
-            locationUpdate.getPendingAddedLocationKeys().stream()
-                    .map(LiveSupplier::get)
-                    .filter(locationKeyMatcher)
-                    .map(tableLocationProvider::getTableLocation)
-                    .peek(this::manage)
-                    .map(PendingLocationState::new)
-                    .forEach(pendingLocationStates::offer);
+            if (locationUpdate != null) {
+                locationUpdate.getPendingAddedLocationKeys().stream()
+                        .map(LiveSupplier::get)
+                        .filter(locationKeyMatcher)
+                        .map(tableLocationProvider::getTableLocation)
+                        .peek(this::manage)
+                        .map(PendingLocationState::new)
+                        .forEach(pendingLocationStates::offer);
+            }
+        }
+
+        private RowSet checkPendingLocations() {
             for (final Iterator<PendingLocationState> iter = pendingLocationStates.iterator(); iter.hasNext();) {
                 final PendingLocationState pendingLocationState = iter.next();
                 if (pendingLocationState.exists()) {
@@ -296,7 +316,7 @@ private RowSet processAdditions(final TableLocationSubscriptionBuffer.LocationUp
             }
 
             if (readyLocationStates.isEmpty()) {
-                return RowSetFactory.empty();
+                return null;
             }
 
             final RowSet added = sortAndAddLocations(readyLocationStates.stream().map(PendingLocationState::release));

engine/table/src/main/java/io/deephaven/engine/table/impl/locations/impl/TableLocationSubscriptionBuffer.java

@@ -129,7 +129,8 @@ public void close() {
      * reset). No order is maintained internally. If a pending exception is thrown, this signals that the subscription
      * is no longer valid and no subsequent location keys will be returned.
      *
-     * @return The collection of pending location keys.
+     * @return A {@link LocationUpdate} collecting pending added and removed location keys, or {@code null} if there are
+     *         none; the caller must {@link LocationUpdate#close() close} the returned object when done.
      */
     public synchronized LocationUpdate processPending() {
         if (!subscribed) {

engine/table/src/test/java/io/deephaven/engine/table/impl/SourcePartitionedTableTest.java

@@ -62,35 +62,42 @@ public void tearDown() throws Exception {
     private QueryTable p2;
     private QueryTable p3;
     private QueryTable p4;
+    private QueryTable p5;
 
     private DependentRegistrar registrar;
     private TableBackedTableLocationProvider tlp;
 
     private SourcePartitionedTable setUpData() {
-        p1 = testRefreshingTable(i(0, 1, 2, 3).toTracking(),
+        p1 = testRefreshingTable(ir(0, 3).toTracking(),
                 stringCol("Sym", "aa", "bb", "aa", "bb"),
                 intCol("intCol", 10, 20, 40, 60),
                 doubleCol("doubleCol", 0.1, 0.2, 0.4, 0.6));
         p1.setAttribute(Table.APPEND_ONLY_TABLE_ATTRIBUTE, true);
 
-        p2 = testRefreshingTable(i(0, 1, 2, 3).toTracking(),
+        p2 = testRefreshingTable(ir(0, 3).toTracking(),
                 stringCol("Sym", "cc", "dd", "cc", "dd"),
                 intCol("intCol", 100, 200, 400, 600),
                 doubleCol("doubleCol", 0.1, 0.2, 0.4, 0.6));
         p2.setAttribute(Table.APPEND_ONLY_TABLE_ATTRIBUTE, true);
 
-        p3 = testRefreshingTable(i(0, 1, 2, 3).toTracking(),
+        p3 = testRefreshingTable(ir(0, 3).toTracking(),
                 stringCol("Sym", "ee", "ff", "ee", "ff"),
                 intCol("intCol", 1000, 2000, 4000, 6000),
                 doubleCol("doubleCol", 0.1, 0.2, 0.4, 0.6));
         p3.setAttribute(Table.APPEND_ONLY_TABLE_ATTRIBUTE, true);
 
-        p4 = testRefreshingTable(i(0, 1, 2, 3).toTracking(),
+        p4 = testRefreshingTable(ir(0, 3).toTracking(),
                 stringCol("Sym", "gg", "hh", "gg", "hh"),
                 intCol("intCol", 10000, 20000, 40000, 60000),
                 doubleCol("doubleCol", 0.1, 0.2, 0.4, 0.6));
         p4.setAttribute(Table.APPEND_ONLY_TABLE_ATTRIBUTE, true);
 
+        p5 = testRefreshingTable(i().toTracking(), // Initially empty
+                stringCol("Sym"),
+                intCol("intCol"),
+                doubleCol("doubleCol"));
+        p5.setAttribute(Table.APPEND_ONLY_TABLE_ATTRIBUTE, true);
+
         registrar = new DependentRegistrar();
         tlp = new TableBackedTableLocationProvider(
                 registrar,
@@ -238,7 +245,7 @@ public void testAddAndRemoveLocations() {
          */
         final TableLocation location5;
         try (final SafeCloseable ignored = LivenessScopeStack.open(new LivenessScope(), true)) {
-            final QueryTable p5 = testRefreshingTable(i(0, 1, 2, 3).toTracking(),
+            final QueryTable p5 = testRefreshingTable(ir(0, 3).toTracking(),
                     stringCol("Sym", "ii", "jj", "ii", "jj"),
                     intCol("intCol", 10000, 20000, 40000, 60000),
                     doubleCol("doubleCol", 0.1, 0.2, 0.4, 0.6));
@@ -407,4 +414,27 @@ public void testCantReadPrev() {
                         TableLocationRemovedException.class).isPresent()));
         getUpdateErrors().clear();
     }
+
+    @Test
+    public void testInitiallyEmptyLocation() {
+        final SourcePartitionedTable spt = setUpData();
+        final Table ptSummary = spt.merge().selectDistinct("Sym");
+        verifyStringColumnContents(ptSummary, "Sym", "aa", "bb", "cc", "dd");
+        tlp.add(p5);
+        updateGraph.getDelegate().runWithinUnitTestCycle(() -> {
+            updateGraph.refreshSources();
+            // We refreshed the source first, so it won't see a new size for the location backed by p5 on this cycle.
+            addToTable(p5, ir(0, 3),
+                    stringCol("Sym", "ii", "jj", "kk", "ll"),
+                    intCol("intCol", 10000, 20000, 40000, 60000),
+                    doubleCol("doubleCol", 0.1, 0.2, 0.4, 0.6));
+        }, true);
+        verifyStringColumnContents(ptSummary, "Sym", "aa", "bb", "cc", "dd");
+        updateGraph.getDelegate().runWithinUnitTestCycle(() -> {
+            updateGraph.refreshSources();
+            // Now the source has been refreshed, so it should see the new size of the location backed by p5, and
+            // include it in the result.
+        }, true);
+        verifyStringColumnContents(ptSummary, "Sym", "aa", "bb", "cc", "dd", "ii", "jj", "kk", "ll");
+    }
 }

engine/test-utils/src/main/java/io/deephaven/engine/testutil/TstUtils.java

@@ -136,6 +136,17 @@ public static WritableRowSet i(long... keys) {
         return RowSetFactory.fromKeys(keys);
     }
 
+    /**
+     * A shorthand for {@link RowSetFactory#fromRange(long, long)} for use in unit tests.
+     *
+     * @param firstRowKey the first key of the new RowSet
+     * @param lastRowKey the last key (inclusive) of the new RowSet
+     * @return a new RowSet with the given key range
+     */
+    public static WritableRowSet ir(final long firstRowKey, final long lastRowKey) {
+        return RowSetFactory.fromRange(firstRowKey, lastRowKey);
+    }
+
     public static void addToTable(final Table table, final RowSet rowSet, final ColumnHolder<?>... columnHolders) {
         if (rowSet.isEmpty()) {
             return;