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Performance improvement by fixing hashCode() #849

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Jun 14, 2021
Merged

Performance improvement by fixing hashCode() #849

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8 changes: 6 additions & 2 deletions src/main/java/org/testng/internal/BaseTestMethod.java
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Original file line number Diff line number Diff line change
Expand Up @@ -70,7 +70,7 @@ public abstract class BaseTestMethod implements ITestNGMethod {
private int m_priority;

private XmlTest m_xmlTest;
private Object m_instance;
private final Object m_instance;

/**
* Constructs a <code>BaseTestMethod</code> TODO cquezel JavaDoc.
Expand Down Expand Up @@ -428,7 +428,11 @@ public boolean equals(Object obj) {
*/
@Override
public int hashCode() {
return m_method.hashCode();
int hash = m_method.hashCode();
if (m_instance != null) {
hash = hash * 31 + m_instance.hashCode();
}
Comment on lines +432 to +434
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BaseTestMethod#equals uses identity comparison like getInstance() == other.getInstance(), so the hashCode implementation should use identity hashCode rather than user-provided implementation.

In other words, this should be System.identityHashCode(m_instance)

Other than that, the change is a clear improvement with little-to-no risk, so it is safe to merge if m_instance.hashCode() is replaced with identityHashCode

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I'm confused. How is this a performance improvement? It does more work than the previous implementation.

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Extra work is negligible, and the new implementation produces better hash codes, so there are less chances for collision in

   at java.util.HashSet.add
   at org.testng.internal.DynamicGraph.setStatus 
   at org.testng.internal.thread.graph.GraphThreadPoolExecutor.setStatus

return hash;
}

protected void initGroups(Class<? extends ITestOrConfiguration> annotationClass) {
Expand Down