Require update lock level for checking entry checksum

src/main/java/net/openhft/chronicle/hash/ChecksumEntry.java

@@ -32,6 +32,13 @@ public interface ChecksumEntry {
      * only when value bytes was updated directly, for example though flyweight implementation of
      * a <a href="https://github.com/OpenHFT/Chronicle-Values#value-interface-specification">value
      * interface</a>.
+     *
+     * @throws UnsupportedOperationException if checksums are not stored in the containing Chronicle
+     * Hash
+     * @throws RuntimeException if the context of this entry is locked improperly, e. g. on the
+     * {@linkplain HashQueryContext#readLock() read} level, that is not upgradable to the
+     * {@linkplain HashQueryContext#updateLock() update} level. Calling {@code updateChecksum()}
+     * method is enabled when at least update lock is held.
      */
     void updateChecksum();
 
@@ -39,6 +46,12 @@ public interface ChecksumEntry {
      * Computes checksum from the entry bytes and checks whether it is equal to the stored checksum.
      *
      * @return {@code true} if stored checksum equals to checksum computed from the entry bytes
+     * @throws UnsupportedOperationException if checksums are not stored in the containing Chronicle
+     * Hash
+     * @throws RuntimeException if the context of this entry is locked improperly, e. g. on the
+     * {@linkplain HashQueryContext#readLock() read} level, that is not upgradable to the
+     * {@linkplain HashQueryContext#updateLock() update} level. Calling {@code checkSum()} method is
+     * enabled when at least update lock is held.
      */
     boolean checkSum();
 }

src/main/java/net/openhft/chronicle/hash/impl/stage/entry/HashEntryStages.java

@@ -164,6 +164,7 @@ public abstract class HashEntryStages<K> implements HashEntry<K>, ChecksumEntry
             throw new UnsupportedOperationException(
                     "Checksum is not stored in this Chronicle Hash");
         }
+        s.innerUpdateLock.lock();
         initDelayedUpdateChecksum(true);
     }
 
@@ -174,6 +175,10 @@ public abstract class HashEntryStages<K> implements HashEntry<K>, ChecksumEntry
             throw new UnsupportedOperationException(
                     "Checksum is not stored in this Chronicle Hash");
         }
+        // This is needed, because a concurrent update lock holder might perform an entry update,
+        // but not yet written a checksum (because checksum write is delayed to the update unlock).
+        // So checkSum() on read lock level might result to false negative results.
+        s.innerUpdateLock.lock();
         return delayedUpdateChecksumInit() || checksumStrategy.innerCheckSum();
     }