From 6c75905008bffc9f09215cf9eaa6fa0d140b25eb Mon Sep 17 00:00:00 2001
From: Larry Booker <lbooker42@gmail.com>
Date: Thu, 20 Mar 2025 12:22:09 -0700
Subject: [PATCH 1/2] Added error messages instead of recurring while hashing.

---
 src/main/java/io/deephaven/hash/KHash.java       | 16 ++++++++++++++++
 .../java/io/deephaven/hash/KeyedObjectHash.java  | 15 +++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/src/main/java/io/deephaven/hash/KHash.java b/src/main/java/io/deephaven/hash/KHash.java
index 5bc148b..acb02df 100644
--- a/src/main/java/io/deephaven/hash/KHash.java
+++ b/src/main/java/io/deephaven/hash/KHash.java
@@ -210,6 +210,22 @@ protected final void postInsertHook(boolean usedFreeSlot) {
       // if we've exhausted the free spots, rehash to the same capacity,
       // which will free up any stale removed slots for reuse.
       int newCapacity = _size > _maxSize ? PrimeFinder.nextPrime(capacity() << 1) : capacity();
+
+      // Before rehashing, make sure we have not reduced the capacity below the current size.
+      if (newCapacity < capacity()) {
+        throw new IllegalStateException(
+            "Internal error: newCapacity < capacity, newCapacity="
+                + newCapacity
+                + ", capacity="
+                + capacity()
+                + ", _free="
+                + _free
+                + ", _size="
+                + _size
+                + ", _maxSize="
+                + _maxSize);
+      }
+
       rehash(newCapacity);
       computeMaxSize(capacity());
     }
diff --git a/src/main/java/io/deephaven/hash/KeyedObjectHash.java b/src/main/java/io/deephaven/hash/KeyedObjectHash.java
index 7e08add..97acfa9 100644
--- a/src/main/java/io/deephaven/hash/KeyedObjectHash.java
+++ b/src/main/java/io/deephaven/hash/KeyedObjectHash.java
@@ -192,6 +192,21 @@ protected void rehash(int newCapacity) {
     h.storage = (V[]) new Object[newCapacity];
     for (V v : storage) {
       if (v != null && v != DELETED) {
+        // Before adding the next value, make sure we won't recurse by verifying h._free > 2 before
+        // the add
+        if (h._free <= 2) {
+          throw new IllegalStateException(
+              "Internal error: h._free <= 2, newCapacity="
+                  + newCapacity
+                  + ", h.capacity="
+                  + h.capacity()
+                  + ", h._free="
+                  + h._free
+                  + ", h._size="
+                  + h._size
+                  + ", h._maxSize="
+                  + h._maxSize);
+        }
         h.internalPut(v, NORMAL, null);
       }
     }

From 608f3fa5db44bee19700b552408fbbcfc1cca337 Mon Sep 17 00:00:00 2001
From: Larry Booker <lbooker42@gmail.com>
Date: Thu, 20 Mar 2025 15:01:31 -0700
Subject: [PATCH 2/2] Improved error message to include current structure data.

---
 src/main/java/io/deephaven/hash/KeyedObjectHash.java | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/main/java/io/deephaven/hash/KeyedObjectHash.java b/src/main/java/io/deephaven/hash/KeyedObjectHash.java
index 97acfa9..eb68d15 100644
--- a/src/main/java/io/deephaven/hash/KeyedObjectHash.java
+++ b/src/main/java/io/deephaven/hash/KeyedObjectHash.java
@@ -198,6 +198,14 @@ protected void rehash(int newCapacity) {
           throw new IllegalStateException(
               "Internal error: h._free <= 2, newCapacity="
                   + newCapacity
+                  + ", capacity="
+                  + capacity()
+                  + ", _free="
+                  + _free
+                  + ", _size="
+                  + _size
+                  + ", _maxSize="
+                  + _maxSize
                   + ", h.capacity="
                   + h.capacity()
                   + ", h._free="