Simplify synchronization (should also be a bit faster).

h2/src/main/org/h2/engine/Database.java

@@ -1159,14 +1159,12 @@ public class Database implements DataHandler {
         }
     }
 
-    private void closeFiles() {
+    private synchronized void closeFiles() {
         try {
-            synchronized (this) {
             if (pageStore != null) {
                 pageStore.close();
                 pageStore = null;
             }
-            }
         } catch (DbException e) {
             trace.error(e, "close");
         }
@@ -1654,43 +1652,37 @@ public class Database implements DataHandler {
      * @param session the session
      * @param transaction the name of the transaction
      */
-    void prepareCommit(Session session, String transaction) {
+    synchronized void prepareCommit(Session session, String transaction) {
         if (readOnly) {
             return;
         }
-        synchronized (this) {
         pageStore.prepareCommit(session, transaction);
     }
-    }
 
     /**
      * Commit the current transaction of the given session.
      *
      * @param session the session
      */
-    void commit(Session session) {
+    synchronized void commit(Session session) {
         if (readOnly) {
             return;
         }
-        synchronized (this) {
         if (pageStore != null) {
             pageStore.commit(session);
         }
         session.setAllCommitted();
     }
-    }
 
     /**
      * Flush all pending changes to the transaction log.
      */
-    public void flush() {
-        synchronized (this) {
+    public synchronized void flush() {
         if (readOnly || pageStore == null) {
             return;
         }
         pageStore.flushLog();
     }
-    }
 
     public void setEventListener(DatabaseEventListener eventListener) {
         this.eventListener = eventListener;
@@ -1760,14 +1752,12 @@ public class Database implements DataHandler {
      * Synchronize the files with the file system. This method is called when
      * executing the SQL statement CHECKPOINT SYNC.
      */
-    public void sync() {
-        synchronized (this) {
+    public synchronized void sync() {
         if (readOnly || pageStore == null) {
             return;
         }
         pageStore.sync();
     }
-    }
 
     public int getMaxMemoryRows() {
         return maxMemoryRows;

h2/src/main/org/h2/engine/SessionRemote.java

@@ -412,12 +412,10 @@ public class SessionRemote extends SessionWithState implements DataHandler {
         switchOffCluster();
     }
 
-    public CommandInterface prepareCommand(String sql, int fetchSize) {
-        synchronized (this) {
+    public synchronized CommandInterface prepareCommand(String sql, int fetchSize) {
         checkClosed();
         return new CommandRemote(this, transferList, sql, fetchSize);
     }
-    }
 
     /**
      * Automatically re-connect if necessary and if configured to do so.

h2/src/main/org/h2/table/Column.java

@@ -168,13 +168,11 @@ public class Column {
      * @param row the row
      * @return the value
      */
-    Value computeValue(Session session, Row row) {
-        synchronized (this) {
+    synchronized Value computeValue(Session session, Row row) {
         computeTableFilter.setSession(session);
         computeTableFilter.set(row);
         return defaultExpression.getValue(session);
     }
-    }
 
     /**
      * Set the default value in the form of a computed expression of other