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Make Graph.adjacentNodes more transparent when a node gets deleted. #6553

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Make Graph.adjacentNodes more transparent when a node gets deleted. #6553

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5a622ab
Make `Graph.adjacentNodes` more transparent when a node gets deleted:
ineuwirth Jun 15, 2023
f05f3f9
Make `Graph.adjacentNodes` more transparent when a node gets deleted:
ineuwirth Jun 20, 2023
81e554b
Merge branch 'master' into fix-6478-confusing-adjacentnodes-content
jrtom Sep 30, 2023
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19 changes: 13 additions & 6 deletions guava-tests/test/com/google/common/graph/AbstractGraphTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -385,13 +385,20 @@ public void removeNode_nodeNotPresent() {
public void removeNode_queryAfterRemoval() {
assume().that(graphIsMutable()).isTrue();

addNode(N1);
@SuppressWarnings("unused")
Set<Integer> unused = graph.adjacentNodes(N1); // ensure cache (if any) is populated
putEdge(N1, N2);
putEdge(N2, N1);
Set<Integer> n1AdjacentNodes = graph.adjacentNodes(N1);
Set<Integer> n2AdjacentNodes = graph.adjacentNodes(N2);

assertThat(graphAsMutableGraph.removeNode(N1)).isTrue();
IllegalArgumentException e =
assertThrows(IllegalArgumentException.class, () -> graph.adjacentNodes(N1));
assertNodeNotInGraphErrorMessage(e);
assertThat(n1AdjacentNodes).isEmpty();
assertThat(n2AdjacentNodes).isEmpty();
try {
graph.adjacentNodes(N1);
fail(ERROR_NODE_NOT_IN_GRAPH);
} catch (IllegalArgumentException e) {
assertNodeNotInGraphErrorMessage(e);
}
}

@Test
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20 changes: 12 additions & 8 deletions guava-tests/test/com/google/common/graph/AbstractNetworkTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -677,15 +677,19 @@ public void removeNode_nodeNotPresent() {
public void removeNode_queryAfterRemoval() {
assume().that(graphIsMutable()).isTrue();

addNode(N1);
@SuppressWarnings("unused")
Set<Integer> unused =
networkAsMutableNetwork.adjacentNodes(N1); // ensure cache (if any) is populated
addEdge(N1, N2, E12);
Set<Integer> n1AdjacentNodes = networkAsMutableNetwork.adjacentNodes(N1);
Set<Integer> n2AdjacentNodes = networkAsMutableNetwork.adjacentNodes(N2);

assertTrue(networkAsMutableNetwork.removeNode(N1));
IllegalArgumentException e =
assertThrows(
IllegalArgumentException.class, () -> networkAsMutableNetwork.adjacentNodes(N1));
assertNodeNotInGraphErrorMessage(e);
assertThat(n1AdjacentNodes).isEmpty();
assertThat(n2AdjacentNodes).isEmpty();
try {
networkAsMutableNetwork.adjacentNodes(N1);
fail(ERROR_NODE_NOT_IN_GRAPH);
} catch (IllegalArgumentException e) {
assertNodeNotInGraphErrorMessage(e);
}
}

@Test
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11 changes: 9 additions & 2 deletions guava/src/com/google/common/graph/StandardMutableValueGraph.java
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@
import static com.google.common.graph.Graphs.checkPositive;
import static java.util.Objects.requireNonNull;

import com.google.common.collect.ImmutableList;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import javax.annotation.CheckForNull;

Expand Down Expand Up @@ -136,17 +137,23 @@ public boolean removeNode(N node) {
}
}

for (N successor : connections.successors()) {
// Since views are returned, we need to copy the successors that will be removed.
// Thus we avoid modifying the underlying view while iterating over it.
for (N successor : ImmutableList.copyOf(connections.successors())) {
// requireNonNull is safe because the node is a successor.
requireNonNull(nodeConnections.getWithoutCaching(successor)).removePredecessor(node);
requireNonNull(connections.removeSuccessor(successor));
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It's been a while since I've looked at this code, but I'm a bit suspicious of the three different ways in which we're now accessing the connections of a node in this method:

  • direct reference (or alias) for the internal data structure: nodeConnections.get(node) (via connections, line 127; nodeConnections is declared in the superclass as MapIteratorCache<N, GraphConnections<N, V>> nodeConnections)
  • direct reference without caching: nodeConnections.getWithoutCaching() (line 144)
  • (immutable) copy of the output of that structure (line 142)

We should (a) validate that we want those three different mechanisms, or use only the ones we actually want, and (b) document which one(s) we do want, and why.

There's a lot of clever stuff going on in this code, which makes it easy to make mistakes in updating it.

(To be clear, I think you've explained why you want the copy of the set in the places that you've made it, but the reason why we're using each of the above two mechanisms in different places is less clear.)

--edgeCount;
}
if (isDirected()) { // In undirected graphs, the successor and predecessor sets are equal.
for (N predecessor : connections.predecessors()) {
// Since views are returned, we need to copy the predecessors that will be removed.
// Thus we avoid modifying the underlying view while iterating over it.
for (N predecessor : ImmutableList.copyOf(connections.predecessors())) {
// requireNonNull is safe because the node is a predecessor.
checkState(
requireNonNull(nodeConnections.getWithoutCaching(predecessor)).removeSuccessor(node)
!= null);
connections.removePredecessor(predecessor);
--edgeCount;
}
}
Expand Down
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