When using the MULTI_THREADED option, concurrently reading from a database could…

When using the MULTI_THREADED option, concurrently reading from a database could throw an exception.

h2/src/main/org/h2/index/PageBtreeIndex.java

@@ -323,23 +323,25 @@ public class PageBtreeIndex extends PageIndex {
      * @return the row
      */
     SearchRow readRow(Data data, int offset, boolean onlyPosition, boolean needData) {
-        data.setPos(offset);
-        long key = data.readVarLong();
-        if (onlyPosition) {
-            if (needData) {
-                return tableData.getRow(null, key);
+        synchronized (data) {
+            data.setPos(offset);
+            long key = data.readVarLong();
+            if (onlyPosition) {
+                if (needData) {
+                    return tableData.getRow(null, key);
+                }
+                SearchRow row = table.getTemplateSimpleRow(true);
+                row.setKey(key);
+                return row;
             }
-            SearchRow row = table.getTemplateSimpleRow(true);
+            SearchRow row = table.getTemplateSimpleRow(columns.length == 1);
             row.setKey(key);
+            for (Column col : columns) {
+                int idx = col.getColumnId();
+                row.setValue(idx, data.readValue());
+            }
             return row;
         }
-        SearchRow row = table.getTemplateSimpleRow(columns.length == 1);
-        row.setKey(key);
-        for (Column col : columns) {
-            int idx = col.getColumnId();
-            row.setValue(idx, data.readValue());
-        }
-        return row;
     }
 
     /**

h2/src/main/org/h2/index/PageData.java

@@ -122,12 +122,12 @@ abstract class PageData extends Page {
      * Get a cursor.
      *
      * @param session the session
-     * @param min the smallest key
-     * @param max the largest key
+     * @param minKey the smallest key
+     * @param maxKey the largest key
      * @param multiVersion if the delta should be used
      * @return the cursor
      */
-    abstract Cursor find(Session session, long min, long max, boolean multiVersion);
+    abstract Cursor find(Session session, long minKey, long maxKey, boolean multiVersion);
 
     /**
      * Get the key at this position.

h2/src/main/org/h2/index/PageDataCursor.java

@@ -19,16 +19,16 @@ class PageDataCursor implements Cursor {
 
     private PageDataLeaf current;
     private int idx;
-    private final long max;
+    private final long maxKey;
     private Row row;
     private final boolean multiVersion;
     private final Session session;
     private Iterator<Row> delta;
 
-    PageDataCursor(Session session, PageDataLeaf current, int idx, long max, boolean multiVersion) {
+    PageDataCursor(Session session, PageDataLeaf current, int idx, long maxKey, boolean multiVersion) {
         this.current = current;
         this.idx = idx;
-        this.max = max;
+        this.maxKey = maxKey;
         this.multiVersion = multiVersion;
         this.session = session;
         if (multiVersion) {
@@ -73,9 +73,9 @@ class PageDataCursor implements Cursor {
 
     private boolean checkMax() {
         if (row != null) {
-            if (max != Long.MAX_VALUE) {
-                long x = current.index.getLong(row, Long.MAX_VALUE);
-                if (x > max) {
+            if (maxKey != Long.MAX_VALUE) {
+                long x = current.index.getKey(row, Long.MAX_VALUE);
+                if (x > maxKey) {
                     row = null;
                     return false;
                 }

h2/src/main/org/h2/index/PageDataIndex.java

@@ -239,13 +239,13 @@ public class PageDataIndex extends PageIndex {
     }
 
     /**
-     * Get the key from the row
+     * Get the key from the row.
      *
      * @param row the row
      * @param ifEmpty the value to use if the row is empty
      * @return the key
      */
-    long getLong(SearchRow row, long ifEmpty) {
+    long getKey(SearchRow row, long ifEmpty) {
         if (row == null) {
             return ifEmpty;
         }
@@ -402,13 +402,17 @@ public class PageDataIndex extends PageIndex {
      * Read a row from the data page at the given position.
      *
      * @param data the data page
+     * @param pos the position to read from
      * @param columnCount the number of columns
      * @return the row
      */
-    Row readRow(Data data, int columnCount) {
+    Row readRow(Data data, int pos, int columnCount) {
         Value[] values = new Value[columnCount];
-        for (int i = 0; i < columnCount; i++) {
-            values[i] = data.readValue();
+        synchronized (data) {
+            data.setPos(pos);
+            for (int i = 0; i < columnCount; i++) {
+                values[i] = data.readValue();
+            }
         }
         return tableData.createRow(values);
     }

h2/src/main/org/h2/index/PageDataLeaf.java

@@ -306,9 +306,9 @@ public class PageDataLeaf extends PageData {
         rows = remove(rows, entryCount + 1, i);
     }
 
-    Cursor find(Session session, long min, long max, boolean multiVersion) {
-        int x = find(min);
-        return new PageDataCursor(session, this, x, max, multiVersion);
+    Cursor find(Session session, long minKey, long maxKey, boolean multiVersion) {
+        int x = find(minKey);
+        return new PageDataCursor(session, this, x, maxKey, multiVersion);
     }
 
     /**
@@ -321,8 +321,7 @@ public class PageDataLeaf extends PageData {
         Row r = rows[at];
         if (r == null) {
             if (firstOverflowPageId == 0) {
-                data.setPos(offsets[at]);
-                r = index.readRow(data, columnCount);
+                r = index.readRow(data, offsets[at], columnCount);
             } else {
                 if (rowRef != null) {
                     r = rowRef.get();
@@ -341,8 +340,7 @@ public class PageDataLeaf extends PageData {
                     next = page.readInto(buff);
                 } while (next != 0);
                 overflowRowSize = pageSize + buff.length();
-                buff.setPos(0);
-                r = index.readRow(buff, columnCount);
+                r = index.readRow(buff, 0, columnCount);
             }
             r.setKey(keys[at]);
             if (firstOverflowPageId != 0) {

h2/src/main/org/h2/index/PageDataNode.java

@@ -158,10 +158,10 @@ public class PageDataNode extends PageData {
         }
     }
 
-    Cursor find(Session session, long min, long max, boolean multiVersion) {
-        int x = find(min);
+    Cursor find(Session session, long minKey, long maxKey, boolean multiVersion) {
+        int x = find(minKey);
         int child = childPageIds[x];
-        return index.getPage(child, getPos()).find(session, min, max, multiVersion);
+        return index.getPage(child, getPos()).find(session, minKey, maxKey, multiVersion);
     }
 
     PageData split(int splitPoint) {

h2/src/main/org/h2/index/PageDelegateIndex.java

@@ -53,8 +53,8 @@ public class PageDelegateIndex extends PageIndex {
     }
 
     public Cursor find(Session session, SearchRow first, SearchRow last) {
-        long min = mainIndex.getLong(first, Long.MIN_VALUE);
-        long max = mainIndex.getLong(last, Long.MAX_VALUE);
+        long min = mainIndex.getKey(first, Long.MIN_VALUE);
+        long max = mainIndex.getKey(last, Long.MAX_VALUE);
         return mainIndex.find(session, min, max, false);
     }
 

h2/src/test/org/h2/test/db/TestMultiThreadedKernel.java

@@ -45,6 +45,7 @@ public class TestMultiThreadedKernel extends TestBase {
             return;
         }
         deleteDb("multiThreadedKernel");
+        testConcurrentRead();
         testCache();
         deleteDb("multiThreadedKernel");
         final String url = getURL("multiThreadedKernel;DB_CLOSE_DELAY=-1;MULTI_THREADED=1", true);
@@ -88,6 +89,45 @@ public class TestMultiThreadedKernel extends TestBase {
         deleteDb("multiThreadedKernel");
     }
 
+    private void testConcurrentRead() throws Exception {
+        ArrayList<Thread> list = New.arrayList();
+        int size = 2;
+        final int count = 1000;
+        final boolean[] stopped = { false };
+        String url = getURL("multiThreadedKernel;MULTI_THREADED=TRUE;CACHE_SIZE=16", true);
+        for (int i = 0; i < size; i++) {
+            final Connection conn = DriverManager.getConnection(url, getUser(), getPassword());
+            if (i == 0) {
+                Statement stat = conn.createStatement();
+                stat.execute("drop table test if exists");
+                stat.execute("create table test(id int primary key, name varchar) "
+                        + "as select x, x || space(10) from system_range(1, " + count + ")");
+            }
+            final Random random = new Random(i);
+            Thread t = new Thread() {
+                public void run() {
+                    try {
+                        PreparedStatement prep = conn.prepareStatement(
+                                "select * from test where id = ?");
+                        while (!stopped[0]) {
+                            prep.setInt(1, random.nextInt(count));
+                            prep.execute();
+                        }
+                    } catch (Exception e) {
+                        e.printStackTrace();
+                    }
+                }
+            };
+            t.start();
+            list.add(t);
+        }
+        Thread.sleep(1000);
+        stopped[0] = true;
+        for (Thread t : list) {
+            t.join();
+        }
+    }
+
     private void testCache() throws Exception {
         ArrayList<Thread> list = New.arrayList();
         int size = 3;
@@ -98,6 +138,7 @@ public class TestMultiThreadedKernel extends TestBase {
             final Connection conn = DriverManager.getConnection(url, getUser(), getPassword());
             if (i == 0) {
                 Statement stat = conn.createStatement();
+                stat.execute("drop table test if exists");
                 stat.execute("create table test(id int primary key, name varchar) "
                         + "as select x, space(3000) from system_range(1, " + count + ")");
             }