MVStore: atomic operations

h2/src/main/org/h2/mvstore/MVMap.java

@@ -582,13 +582,22 @@ public class MVMap<K, V> extends AbstractMap<K, V>
      */
     public synchronized boolean remove(Object key, Object value) {
         V old = get(key);
-        if (old.equals(value)) {
+        if (equalsValue(old, value)) {
             remove(key);
             return true;
         }
         return false;
     }
     
+    private boolean equalsValue(Object a, Object b) {
+        if (a == b) {
+            return true;
+        } else if (a == null || b == null) {
+            return false;
+        }
+        return valueType.compare(a, b) == 0;
+    }
+
     /**
      * Replace a value for an existing key, if the value matches.
      *
@@ -599,7 +608,7 @@ public class MVMap<K, V> extends AbstractMap<K, V>
      */
     public synchronized boolean replace(K key, V oldValue, V newValue) {
         V old = get(key);
-        if (old.equals(oldValue)) {
+        if (equalsValue(old, oldValue)) {
             put(key, newValue);
             return true;
         }
@@ -611,7 +620,7 @@ public class MVMap<K, V> extends AbstractMap<K, V>
      *
      * @param key the key (may not be null)
      * @param value the new value
-     * @return true if the value was replaced
+     * @return the old value, if the value was replaced, or null
      */
     public synchronized V replace(K key, V value) {
         V old = get(key);

h2/src/main/org/h2/mvstore/MVStore.java

@@ -49,7 +49,7 @@ TODO:
 - additional test async write / read algorithm for speed and errors
 - move setters to the builder, except for setRetainVersion, setReuseSpace,
     and settings that are persistent (setStoreVersion)
-- test & document meta table rollback: it is changed after save; could rollback break it?
+- test meta rollback: it is changed after save; could rollback break it?
 - automated 'kill process' and 'power failure' test
 - update checkstyle
 - maybe split database into multiple files, to speed up compact
@@ -94,6 +94,7 @@ TODO:
     to store committed changes
 - to save space when persisting very small transactions,
 -- use a transaction log where only the deltas are stored
+- serialization for lists, sets, sets, sorted sets, maps, sorted maps
 
 */
 
@@ -1680,7 +1681,7 @@ public class MVStore {
         if (closed || unsavedPageCount == 0) {
             return;
         }
-        // could also store when there are many unstored pages,
+        // could also store when there are many unsaved pages,
         // but according to a test it doesn't really help
         if (lastCommittedVersion >= currentVersion) {
             return;

h2/src/main/org/h2/mvstore/type/StringDataType.java

@@ -16,19 +16,23 @@ public class StringDataType implements DataType {
 
     public static final StringDataType INSTANCE = new StringDataType();
 
+    @Override
     public int compare(Object a, Object b) {
         return a.toString().compareTo(b.toString());
     }
 
+    @Override
     public int getMemory(Object obj) {
         return 24 + 2 * obj.toString().length();
     }
 
+    @Override
     public String read(ByteBuffer buff) {
         int len = DataUtils.readVarInt(buff);
         return DataUtils.readString(buff, len);
     }
 
+    @Override
     public ByteBuffer write(ByteBuffer buff, Object obj) {
         String s = obj.toString();
         int len = s.length();

h2/src/test/org/h2/test/store/TestConcurrent.java

@@ -221,7 +221,8 @@ public class TestConcurrent extends TestMVStore {
         assertTrue(notDetected.get() * 10 <= detected.get());
     }
 
-    private void testConcurrentWrite(final AtomicInteger detected, final AtomicInteger notDetected) throws InterruptedException {
+    private void testConcurrentWrite(final AtomicInteger detected,
+            final AtomicInteger notDetected) throws InterruptedException {
         final MVStore s = openStore(null);
         final MVMap<Integer, Integer> m = s.openMap("data");
         final int size = 20;

h2/src/test/org/h2/test/store/TestMVStore.java

@@ -42,6 +42,7 @@ public class TestMVStore extends TestBase {
         FileUtils.deleteRecursive(getBaseDir(), true);
         FileUtils.createDirectories(getBaseDir());
 
+        testAtomicOperations();
         testWriteBuffer();
         testWriteDelay();
         testEncryptedFile();
@@ -79,6 +80,41 @@ public class TestMVStore extends TestBase {
         testSimple();
     }
     
+    private void testAtomicOperations() {
+        String fileName = getBaseDir() + "/testAtomicOperations.h3";
+        FileUtils.delete(fileName);
+        MVStore s;
+        MVMap<Integer, byte[]> m;
+        s = new MVStore.Builder().
+                fileName(fileName).
+                open();
+        m = s.openMap("data");
+        
+        // putIfAbsent
+        assertNull(m.putIfAbsent(1, new byte[1]));
+        assertEquals(1, m.putIfAbsent(1, new byte[2]).length);
+        assertEquals(1, m.get(1).length);
+        
+        // replace
+        assertNull(m.replace(2, new byte[2]));
+        assertNull(m.get(2));
+        assertEquals(1, m.replace(1, new byte[2]).length);
+        assertEquals(2, m.replace(1, new byte[3]).length);
+        assertEquals(3, m.replace(1, new byte[1]).length);
+        
+        // replace with oldValue
+        assertFalse(m.replace(1, new byte[2], new byte[10]));
+        assertTrue(m.replace(1, new byte[1], new byte[2]));
+        assertTrue(m.replace(1, new byte[2], new byte[1]));
+        
+        // remove
+        assertFalse(m.remove(1, new byte[2]));
+        assertTrue(m.remove(1, new byte[1]));
+                
+        s.close();
+        FileUtils.delete(fileName);        
+    }
+
     private void testWriteBuffer() throws IOException {
         String fileName = getBaseDir() + "/testAutoStoreBuffer.h3";
         FileUtils.delete(fileName);