fix deadlock

need to take the TransactionStore RWLock before we synchronize on the
MVMap

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

@@ -946,6 +946,8 @@ public class TransactionStore {
          * @return the size
          */
         public long sizeAsLong() {
+            transaction.store.rwLock.readLock().lock();
+            try {
                 long sizeRaw = map.sizeAsLong();
                 MVMap<Long, Object[]> undo = transaction.store.undoLog;
                 long undoLogSize;
@@ -962,13 +964,8 @@ public class TransactionStore {
                     Cursor<K, VersionedValue> cursor = map.cursor(null);
                     while (cursor.hasNext()) {
                         VersionedValue data;
-                    transaction.store.rwLock.readLock().lock();
-                    try {
                         K key = cursor.next();
                         data = getValue(key, readLogId, cursor.getValue());
-                    } finally {
-                        transaction.store.rwLock.readLock().unlock();
-                    }
                         if (data != null && data.value != null) {
                             size++;
                         }
@@ -980,7 +977,8 @@ public class TransactionStore {
                 synchronized (undo) {
                     // re-fetch in case any transaction was committed now
                     long size = map.sizeAsLong();
-                MVMap<Object, Integer> temp = transaction.store.createTempMap();
+                    MVMap<Object, Integer> temp = transaction.store
+                            .createTempMap();
                     try {
                         for (Entry<Long, Object[]> e : undo.entrySet()) {
                             Object[] op = e.getValue();
@@ -993,7 +991,8 @@ public class TransactionStore {
                             K key = (K) op[1];
                             if (get(key) == null) {
                                 Integer old = temp.put(key, 1);
-                            // count each key only once (there might be multiple
+                                // count each key only once (there might be
+                                // multiple
                                 // changes for the same key)
                                 if (old == null) {
                                     size--;
@@ -1005,6 +1004,9 @@ public class TransactionStore {
                     }
                     return size;
                 }
+            } finally {
+                transaction.store.rwLock.readLock().unlock();
+            }
         }
 
         /**