How Does Java 8\'s JIT Optimization Impact Maximum Recursion Depth?

Determining the Depth of Recursion

To gauge the maximum depth of recursion, it's often desirable to count the current stack depth and levels of recursion that can be executed before triggering a StackOverflowError.

Counting Stack Depth

The method levelsDeep() aims to determine the current stack depth by generating and catching an exception and examining the resulting stack trace. However, its limitation of a maximum depth of 1024 poses a hurdle.

Counting Levels of Recursion

The stackLeft() method attempts to count the remaining stack depth by recursively calling itself until a StackOverflowError occurs. This appears to be a reliable approach.

Non-Deterministic Stack Depth in Java 8

Unexpectedly, using stackLeft() with certain versions of Java (e.g., Oracle Java 8) yields non-deterministic results. The maximum recursion depth varies between approximately 18,500 and 20,700. This behavior is not observed in OpenJDK 7, where the depth remains consistent.

Cause of Non-Determinism

This non-deterministic behavior stems from the interactions between Java's Hotspot optimizer and various factors, such as:

• JIT Optimization: The HotSpot optimizer plays a significant role in reducing stack space requirements for method invocations, which can affect the maximum recursion depth.
• Tiered Compilation: JIT optimization is performed in tiers, and the behavior may vary depending on the tier of compilation.
• Stack Alignment and ASLR: The JVM requires specific alignment of the stack end address and memory allocation addresses. This alignment, combined with ASLR (Address Space Layout Randomization), could introduce variability in the recursion depth.

Therefore, the maximum recursion depth on Java 8 can vary depending on a combination of these factors, making it non-deterministic.

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