Issue 315: Access to LOBs could cause a Java level deadlock.

h2/src/docsrc/html/changelog.html

@@ -17,7 +17,8 @@ Change Log
 
 <h1>Change Log</h1>
 <h2>Next Version (unreleased)</h2>
-<ul><li>Support for the ICU4J collator.
+<ul><li>Issue 315: Access to LOBs could cause a Java level deadlock.
+</li><li>Support for the ICU4J collator.
 </li><li>Improved Oracle compatibility: support for NVL2. Thanks to litailang for the patch!
 </li><li>Improved PostgreSQL compatibility: support for RANDOM() in addition to RAND().
 </li><li>There was a classloader memory leak problem because a class contained a static

h2/src/main/org/h2/store/LobStorage.java

@@ -80,10 +80,11 @@ public class LobStorage {
     /**
      * Initialize the lob storage.
      */
-    public synchronized void init() {
+    public void init() {
         if (init) {
             return;
         }
+        synchronized (handler) {
             conn = handler.getLobConnection();
             init = true;
             if (conn == null) {
@@ -107,6 +108,7 @@ public class LobStorage {
                 throw DbException.convert(e);
             }
         }
+    }
 
     private long getNextLobId() throws SQLException {
         String sql = "SELECT MAX(LOB) FROM " + LOB_MAP;
@@ -173,42 +175,43 @@ public class LobStorage {
         return ValueLob.createSmallLob(type, small);
     }
 
+    byte[] readBlock(long lob, int seq) throws SQLException {
+        synchronized (handler) {
+            String sql = "SELECT COMPRESSED, DATA FROM " + LOB_MAP + " M " +
+                    "INNER JOIN " + LOB_DATA + " D ON M.BLOCK = D.BLOCK " +
+                    "WHERE M.LOB = ? AND M.SEQ = ?";
+            PreparedStatement prep = prepare(sql);
+            prep.setLong(1, lob);
+            prep.setInt(2, seq);
+            ResultSet rs = prep.executeQuery();
+            if (!rs.next()) {
+                throw DbException.get(ErrorCode.IO_EXCEPTION_1, "Missing lob entry: "+ lob + "/" + seq).getSQLException();
+            }
+            int compressed = rs.getInt(1);
+            byte[] buffer = rs.getBytes(2);
+            if (compressed != 0) {
+                buffer = compress.expand(buffer);
+            }
+            reuse(sql, prep);
+            return buffer;
+        }
+    }
+
     /**
      * An input stream that reads from a LOB.
      */
-    public static class LobInputStream extends InputStream {
+    public class LobInputStream extends InputStream {
 
-        private final Connection conn;
-        private PreparedStatement prepSelect;
         private byte[] buffer;
         private int pos;
         private long remainingBytes;
         private long lob;
         private int seq;
-        private CompressTool compress;
 
-        public LobInputStream(Connection conn, long lob, long byteCount) throws IOException {
-            this.conn = conn;
-            this.lob = lob;
-            if (byteCount == -1) {
-                try {
+        public LobInputStream(long lob, long byteCount) {
             this.lob = lob;
-                    PreparedStatement prep = conn.prepareStatement(
-                            "SELECT BYTE_COUNT FROM " + LOBS + " WHERE ID = ?");
-                    prep.setLong(1, lob);
-                    ResultSet rs = prep.executeQuery();
-                    if (!rs.next()) {
-                        throw DbException.get(ErrorCode.IO_EXCEPTION_1, "Missing lob: "+ lob).getSQLException();
-                    }
-                    remainingBytes = rs.getLong(1);
-                    rs.close();
-                } catch (SQLException e) {
-                    throw DbException.convertToIOException(e);
-                }
-            } else {
             remainingBytes = byteCount;
         }
-        }
 
         public int read() throws IOException {
             fillBuffer();
@@ -257,27 +260,7 @@ public class LobStorage {
                 return;
             }
             try {
-                if (prepSelect == null) {
-                    prepSelect = conn.prepareStatement(
-                        "SELECT COMPRESSED, DATA FROM " + LOB_MAP + " M " +
-                        "INNER JOIN " + LOB_DATA + " D ON M.BLOCK = D.BLOCK " +
-                        "WHERE M.LOB = ? AND M.SEQ = ?");
-                }
-                prepSelect.setLong(1, lob);
-                prepSelect.setInt(2, seq);
-                ResultSet rs = prepSelect.executeQuery();
-                if (!rs.next()) {
-                    throw DbException.get(ErrorCode.IO_EXCEPTION_1, "Missing lob entry: "+ lob + "/" + seq).getSQLException();
-                }
-                seq++;
-                int compressed = rs.getInt(1);
-                buffer = rs.getBytes(2);
-                if (compressed != 0) {
-                    if (compress == null) {
-                        compress = CompressTool.getInstance();
-                    }
-                    buffer = compress.expand(buffer);
-                }
+                buffer = readBlock(lob, seq++);
                 pos = 0;
             } catch (SQLException e) {
                 throw DbException.convertToIOException(e);
@@ -286,7 +269,12 @@ public class LobStorage {
 
     }
 
-    private synchronized PreparedStatement prepare(String sql) throws SQLException {
+    private PreparedStatement prepare(String sql) throws SQLException {
+        if (SysProperties.CHECK2) {
+            if (!Thread.holdsLock(handler)) {
+                throw DbException.throwInternalError();
+            }
+        }
         PreparedStatement prep = prepared.remove(sql);
         if (prep == null) {
             prep = conn.prepareStatement(sql);
@@ -294,11 +282,17 @@ public class LobStorage {
         return prep;
     }
 
-    private synchronized void reuse(String sql, PreparedStatement prep) {
+    private void reuse(String sql, PreparedStatement prep) {
+        if (SysProperties.CHECK2) {
+            if (!Thread.holdsLock(handler)) {
+                throw DbException.throwInternalError();
+            }
+        }
         prepared.put(sql, prep);
     }
 
-    private synchronized void deleteLob(long lob) throws SQLException {
+    private void deleteLob(long lob) throws SQLException {
+        synchronized (handler) {
             String sql = "SELECT BLOCK, HASH FROM " + LOB_MAP + " D WHERE D.LOB = ? " +
                     "AND NOT EXISTS(SELECT 1 FROM " + LOB_MAP + " O " +
                     "WHERE O.BLOCK = D.BLOCK AND O.LOB <> ?)";
@@ -334,6 +328,7 @@ public class LobStorage {
             prep.execute();
             reuse(sql, prep);
         }
+    }
 
     /**
      * Get the input stream for the given lob.
@@ -344,7 +339,24 @@ public class LobStorage {
      */
     public InputStream getInputStream(long lobId, long byteCount) throws IOException {
         init();
-        return new LobInputStream(conn, lobId, byteCount);
+        if (byteCount == -1) {
+            synchronized (handler) {
+                try {
+                    String sql = "SELECT BYTE_COUNT FROM " + LOBS + " WHERE ID = ?";
+                    PreparedStatement prep = prepare(sql);
+                    prep.setLong(1, lobId);
+                    ResultSet rs = prep.executeQuery();
+                    if (!rs.next()) {
+                        throw DbException.get(ErrorCode.IO_EXCEPTION_1, "Missing lob: "+ lobId).getSQLException();
+                    }
+                    byteCount = rs.getLong(1);
+                    reuse(sql, prep);
+                } catch (SQLException e) {
+                    throw DbException.convertToIOException(e);
+                }
+            }
+        }
+        return new LobInputStream(lobId, byteCount);
     }
 
     private ValueLobDb addLob(InputStream in, long maxLength, int type) {
@@ -378,7 +390,7 @@ public class LobStorage {
                         small = b;
                         break;
                     }
-                    synchronized (this) {
+                    synchronized (handler) {
                         if (seq == 0) {
                             lobId = getNextLobId();
                         }
@@ -407,6 +419,7 @@ public class LobStorage {
     }
 
     private ValueLobDb registerLob(int type, long lobId, int tableId, long byteCount) {
+        synchronized (handler) {
             try {
                 String sql = "INSERT INTO " + LOBS + "(ID, BYTE_COUNT, TABLE) VALUES(?, ?, ?)";
                 PreparedStatement prep = prepare(sql);
@@ -421,6 +434,7 @@ public class LobStorage {
                 throw DbException.convert(e);
             }
         }
+    }
 
     /**
      * Copy a lob.
@@ -431,7 +445,8 @@ public class LobStorage {
      * @param length the length
      * @return the new lob
      */
-    public synchronized ValueLobDb copyLob(int type, long oldLobId, int tableId, long length) {
+    public ValueLobDb copyLob(int type, long oldLobId, int tableId, long length) {
+        synchronized (handler) {
             try {
                 init();
                 long lobId = getNextLobId();
@@ -458,6 +473,7 @@ public class LobStorage {
                 throw DbException.convert(e);
             }
         }
+    }
 
     private long getHashCacheBlock(int hash) {
         if (HASH_CACHE_SIZE > 0) {
@@ -486,13 +502,14 @@ public class LobStorage {
      * @param b the data
      * @param compressAlgorithm the compression algorithm (may be null)
      */
-    synchronized void storeBlock(long lobId, int seq, byte[] b, String compressAlgorithm) throws SQLException {
+    void storeBlock(long lobId, int seq, byte[] b, String compressAlgorithm) throws SQLException {
         long block;
         boolean blockExists = false;
         if (compressAlgorithm != null) {
             b = compress.compress(b, compressAlgorithm);
         }
         int hash = Arrays.hashCode(b);
+        synchronized (handler) {
             block = getHashCacheBlock(hash);
             if (block != -1) {
                 String sql =  "SELECT COMPRESSED, DATA FROM " + LOB_DATA +
@@ -529,6 +546,7 @@ public class LobStorage {
             prep.execute();
             reuse(sql, prep);
         }
+    }
 
     /**
      * An input stream that reads the data from a reader.
@@ -651,6 +669,7 @@ public class LobStorage {
      * @param table the table
      */
     public void setTable(long lobId, int table) {
+        synchronized (handler) {
             try {
                 init();
                 String sql = "UPDATE " + LOBS + " SET TABLE = ? WHERE ID = ?";
@@ -663,5 +682,6 @@ public class LobStorage {
                 throw DbException.convert(e);
             }
         }
+    }
 
 }

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

@@ -54,6 +54,7 @@ public class TestLob extends TestBase {
     }
 
     public void test() throws Exception {
+        testDeadlock();
         testCopyManyLobs();
         testCopyLob();
         testConcurrentCreate();
@@ -95,6 +96,41 @@ public class TestLob extends TestBase {
         IOUtils.deleteRecursive(TEMP_DIR, true);
     }
 
+    /**
+     * Test for issue 315: Java Level Deadlock on Database & Session Objects
+     */
+    private void testDeadlock() throws Exception {
+        deleteDb("lob");
+        Connection conn = getConnection("lob");
+        Statement stat = conn.createStatement();
+        stat.execute("create table test(id int primary key, name clob)");
+        stat.execute("insert into test select x, space(10000) from system_range(1, 3)");
+        final Connection conn2 = getConnection("lob");
+        Task task = new Task() {
+
+            public void call() throws Exception {
+                Statement stat = conn2.createStatement();
+                stat.setFetchSize(1);
+                for (int i = 0; !stop; i++) {
+                    ResultSet rs = stat.executeQuery("select * from test where id > -" + i);
+                    while (rs.next()) {
+                        // ignore
+                    }
+                }
+            }
+
+        };
+        task.execute();
+        stat.execute("create table test2(id int primary key, name clob)");
+        for (int i = 0; i < 1000; i++) {
+            stat.execute("delete from test2");
+            stat.execute("insert into test2 values(1, space(10000 + " + i + "))");
+        }
+        task.get();
+        conn.close();
+        conn2.close();
+    }
+
     private void testCopyManyLobs() throws Exception {
         deleteDb("lob");
         Connection conn = getConnection("lob");