tryCommit inroduced, some class finals removed, based on code review

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

@@ -13,7 +13,7 @@ import java.util.Iterator;
  * @param <K> the key type
  * @param <V> the value type
  */
-public final class Cursor<K, V> implements Iterator<K> {
+public class Cursor<K, V> implements Iterator<K> {
     private final K to;
     private CursorPos cursorPos;
     private CursorPos keeper;

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

@@ -8,7 +8,7 @@ package org.h2.mvstore;
 /**
  * A position in a cursor
  */
-public final class CursorPos {
+public class CursorPos {
 
     /**
      * The current page.

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

@@ -127,7 +127,7 @@ MVStore:
 /**
  * A persistent storage for maps.
  */
-public final class MVStore {
+public class MVStore {
 
     /**
      * Whether assertions are enabled.
@@ -1037,6 +1037,25 @@ public final class MVStore {
         onVersionChange(version);
     }
 
+    /**
+     * Unlike regular commit this method returns immediately if there is commit
+     * in progress on another thread, otherwise it acts as regular commit.
+     *
+     * This method may return BEFORE this thread changes are actually persisted!
+     *
+     * @return the new version (incremented if there were changes)
+     */
+    public long tryCommit() {
+        // unlike synchronization, this will also prevent re-entrance,
+        // which may be possible, if the meta map have changed
+        if (currentStoreThread.compareAndSet(null, Thread.currentThread())) {
+            synchronized (this) {
+                store();
+            }
+        }
+        return currentVersion;
+    }
+
     /**
      * Commit the changes.
      * <p>
@@ -1053,16 +1072,19 @@ public final class MVStore {
      *
      * @return the new version (incremented if there were changes)
      */
-    public long commit() {
-        // unlike synchronization, this will also prevent re-entrance,
-        // which may be possible, if the meta map have changed
-        if (currentStoreThread.compareAndSet(null, Thread.currentThread())) {
-            synchronized (this) {
+    public synchronized long commit() {
+        currentStoreThread.set(Thread.currentThread());
+        store();
+        return currentVersion;
+    }
+
+    private void store() {
         try {
-                    currentStoreVersion = currentVersion;
             if (!closed && hasUnsavedChangesInternal()) {
+                currentStoreVersion = currentVersion;
                 if (fileStore == null) {
                     lastStoredVersion = currentVersion;
+                    //noinspection NonAtomicOperationOnVolatileField
                     ++currentVersion;
                     setWriteVersion(currentVersion);
                     metaChanged = false;
@@ -1087,9 +1109,6 @@ public final class MVStore {
              currentStoreThread.set(null);
          }
     }
-        }
-        return currentVersion;
-    }
 
     private void storeNow() {
         assert Thread.holdsLock(this);
@@ -2283,7 +2302,7 @@ public final class MVStore {
             saveNeeded = false;
             // check again, because it could have been written by now
             if (unsavedMemory > autoCommitMemory && autoCommitMemory > 0) {
-                commit();
+                tryCommit();
             }
         }
     }
@@ -2578,7 +2597,7 @@ public final class MVStore {
             if (time <= lastCommitTime + autoCommitDelay) {
                 return;
             }
-            commit();
+            tryCommit();
             if (autoCompactFillRate > 0) {
                 // whether there were file read or write operations since
                 // the last time

h2/src/main/org/h2/mvstore/db/TransactionStore.java

@@ -475,7 +475,7 @@ public class TransactionStore {
         t.setStatus(Transaction.STATUS_CLOSED);
         openTransactions.clear(t.transactionId);
         if (oldStatus == Transaction.STATUS_PREPARED || store.getAutoCommitDelay() == 0) {
-            store.commit();
+            store.tryCommit();
             return;
         }
         // to avoid having to store the transaction log,
@@ -486,7 +486,7 @@ public class TransactionStore {
             int max = store.getAutoCommitMemory();
             // save at 3/4 capacity
             if (unsaved * 4 > max * 3) {
-                store.commit();
+                store.tryCommit();
             }
         }
     }