How to Get Stack Traces for NullPointerExceptions When Optimization Hinders Them?

How to Retrieve Stack Traces for NullPointerExceptions Without an Exception

When dealing with NullPointerExceptions in Java, developers may encounter situations where the stack trace is absent altogether, rendering it difficult to trace the source of the exception.

Understanding the Issue

Typically, when a NullPointerException is thrown, its stack trace provides valuable information about the offending code path. However, certain optimizations performed by the HotSpot JVM can suppress these stack traces.

Solution: Disabling Optimization

To retrieve the stack traces, the following option must be passed to the JVM:

-XX:-OmitStackTraceInFastThrow

This option instructs the JVM to refrain from optimizing the handling of NullPointerExceptions, ensuring that stack traces are printed for each occurrence of the exception.

How the Optimization Works

The HotSpot JVM employs an optimization technique that caches stack traces for frequently occurring exceptions, particularly NullPointerExceptions. This optimization aims to enhance performance and prevent excessive logging of identical stack traces.

Implementation Details

In the HotSpot JVM, this optimization is implemented in the file graphKit.cpp. It involves a global variable named OmitStackTraceInFastThrow, which controls the suppression of stack traces.

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