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();
 }