KangweiZhu opened a new pull request, #3237:
URL: https://github.com/apache/tinkerpop/pull/3237
We observed several tests in GraphSONTypedCompatibilityTest that exhibited
flaky behavior when executed with NonDex. Specifically speaking, we can
reproduce them by using the following commands.
```
mvn clean install -DskipTests -Drat.skip=true
```
* Test shouldReadWriteEdge[expect(v2)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWriteEdge[expect(v2)]"
-Drat.skip=true
```
* Test shouldReadWriteEdge[expect(v3)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWriteEdge[expect(v3)]"
-Drat.skip=true
```
* Test shouldReadWritePath[expect(v2)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWritePath[expect(v2)]"
-Drat.skip=true
```
* Test shouldReadWritePath[expect(v3)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWritePath[expect(v3)]"
-Drat.skip=true
```
* Test shouldReadWriteProperty[expect(v2)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWriteProperty[expect(v2)]"
-Drat.skip=true
```
* Test shouldReadWriteProperty[expect(v3)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWriteProperty[expect(v3)]"
-Drat.skip=true
```
* Test shouldReadWriteTraverser[expect(v2)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWriteTraverser[expect(v2)]"
-Drat.skip=true
```
* Test shouldReadWriteTraverser[expect(v3)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWriteTraverser[expect(v3)]"
-Drat.skip=true
```
* Test shouldReadWriteVertexProperty[expect(v2)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWriteVertexProperty[expect(v2)]"
-Drat.skip=true
```
* Test shouldReadWriteVertexProperty[expect(v3)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWriteVertexProperty[expect(v3)]"
-Drat.skip=true
```
* Test shouldReadWriteVertex[expect(v2)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWriteVertex[expect(v2)]"
-Drat.skip=true
```
* Test shouldReadWriteVertex[expect(v3)]
```bash
mvn clean -pl gremlin-util edu.illinois:nondex-maven-plugin:2.2.1:nondex
-Dtest="org.apache.tinkerpop.gremlin.structure.io.graphson.GraphSONTypedCompatibilityTest#shouldReadWriteVertex[expect(v3)]"
-Drat.skip=true
```
And the error should be something like this:
```
[ERROR] Failures:
[ERROR]
GraphSONTypedCompatibilityTest>AbstractTypedCompatibilityTest.shouldReadWriteEdge:322
expected:<e[17][7-develops->10]> but was:<e[13][1-develops->10]>
[ERROR]
GraphSONTypedCompatibilityTest>AbstractTypedCompatibilityTest.shouldReadWriteEdge:322
expected:<e[17][7-develops->10]> but was:<e[13][1-develops->10]>
```
Upon our investigation, the root cause is the use of:
```
protected Map<Object, Vertex> vertices = new ConcurrentHashMap<>();
protected Map<Object, Edge> edges = new ConcurrentHashMap<>();
```
in TinkerGraph.java, which does not guarantee a deterministic order.
The simplest fix would be to replace ConcurrentHashMap with LinkedHashMap,
as we did in a previous PR. We've confirmed that this change could remove the
flakiness of these tests. However, we are concerned that such a change might
introduce unintended side effects in the code under test. Another possible fix
would be to deterministically select a fixed id, but that approach would make
the test become sensitive to future implementation changes. Thus, we decided to
use this sorting-based approach to deflake this test.
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