HCOLL-392 Add entry checksums

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

@@ -0,0 +1,43 @@
+/*
+ *      Copyright (C) 2015  higherfrequencytrading.com
+ *
+ *      This program is free software: you can redistribute it and/or modify
+ *      it under the terms of the GNU Lesser General Public License as published by
+ *      the Free Software Foundation, either version 3 of the License.
+ *
+ *      This program is distributed in the hope that it will be useful,
+ *      but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *      GNU Lesser General Public License for more details.
+ *
+ *      You should have received a copy of the GNU Lesser General Public License
+ *      along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package net.openhft.chronicle.hash;
+
+import net.openhft.chronicle.map.MapAbsentEntry;
+import net.openhft.chronicle.map.MapEntry;
+
+/**
+ * Abstracts entries of hash containers, created by {@link ChronicleHashBuilder}s
+ * with {@link ChronicleHashBuilder#checksumEntries(boolean)} configured to {@code true}.
+ */
+public interface ChecksumEntry {
+
+    /**
+     * Re-computes and stores checksum for the entry. This method <i>shouldn't</i> be called before
+     * or after ordinary operations like {@link MapAbsentEntry#doInsert(Data)}, {@link
+     * MapEntry#doReplaceValue(Data)}: it is performed automatically underneath. Call this method,
+     * only when value bytes was updated directly, for example though Chronicle-Value-generated
+     * interface.
+     */
+    void updateChecksum();
+
+    /**
+     * 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
+     */
+    boolean checkSum();
+}