Synchronize on undoLog when following MVMap get with TransactionMap getValue

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

@@ -933,9 +933,11 @@ public class TransactionStore {
                 long size = 0;
                 Cursor<K, VersionedValue> cursor = map.cursor(null);
                 while (cursor.hasNext()) {
+                    VersionedValue data;
+                    synchronized (transaction.store.undoLog) {
                         K key = cursor.next();
-                    VersionedValue data = cursor.getValue();
-                    data = getValue(key, readLogId, data);
+                        data = getValue(key, readLogId, cursor.getValue());
+                    }
                     if (data != null && data.value != null) {
                         size++;
                     }
@@ -1197,9 +1199,11 @@ public class TransactionStore {
         }
 
         private VersionedValue getValue(K key, long maxLog) {
+            synchronized (transaction.store.undoLog) {
                 VersionedValue data = map.get(key);
                 return getValue(key, maxLog, data);
             }
+        }
 
         /**
          * Get the versioned value for the given key.
@@ -1210,6 +1214,13 @@ public class TransactionStore {
          * @return the value
          */
         VersionedValue getValue(K key, long maxLog, VersionedValue data) {
+            if (MVStore.ASSERT) {
+                if (!Thread.holdsLock(transaction.store.undoLog)) {
+                    throw DataUtils.newIllegalStateException(
+                            DataUtils.ERROR_INTERNAL,
+                            "getValue not invoked while synchronized on undoLog");
+                }
+            }
             while (true) {
                 if (data == null) {
                     // doesn't exist or deleted by a committed transaction
@@ -1229,9 +1240,7 @@ public class TransactionStore {
                 }
                 // get the value before the uncommitted transaction
                 Object[] d;
-                synchronized (transaction.store.undoLog) {
                 d = transaction.store.undoLog.get(id);
-                }
                 if (d == null) {
                     // this entry should be committed or rolled back
                     // in the meantime (the transaction might still be open)
@@ -1441,6 +1450,7 @@ public class TransactionStore {
                 private void fetchNext() {
                     while (cursor.hasNext()) {
                         K k;
+                        synchronized (transaction.store.undoLog) {
                             try {
                                 k = cursor.next();
                             } catch (IllegalStateException e) {
@@ -1473,6 +1483,7 @@ public class TransactionStore {
                                 return;
                             }
                         }
+                    }
                     current = null;
                     currentKey = null;
                 }