Two stuck threads in synchronized method - at least it seems like from a stack trace

From:

Greg Stasica <GStasica@googlemail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Mon, 21 Jul 2008 16:08:21 -0700 (PDT)

Message-ID:

<5bc8c9c0-fba6-448c-bde3-aa07923ce53a@k13g2000hse.googlegroups.com>

hi,

from the stack trace it seems like there are two different threads in
synchronized method but how could it be possible ?

public class DBQuery{

    private static DBQuery dbQuery = null;

    public static DBQuery getInstance()
    {
        if (dbQuery == null) {
            dbQuery = new DBQuery();
        }
        return dbQuery;
    }

public synchronized void saveAuditVersion(boolean fIncrementVersion)
{
try{
    doSQLStatement(sql); //line 332
}
catch(SQLException sqle){... }
finally { ...}

if(fIncrementVersion){
    refData.setAuditVersion(refData.getAuditVersion()+1); //line 348
......
}

public static doSQLStatement(String sql){....}

}

Thread-159 "[STUCK] ExecuteThread: '12' for queue:
'weblogic.kernel.Default (self-tuning)'" <alive, in native,
priority=1, DAEMON> {
   jrockit.net.SocketNativeIO.readBytesPinned(Native Method)
   jrockit.net.SocketNativeIO.socketRead(Unknown Source)
   java.net.SocketInputStream.socketRead0(SocketInputStream.java:???)
   java.net.SocketInputStream.read(SocketInputStream.java:129)
   oracle.net.ns.Packet.receive(Unknown Source)
   oracle.net.ns.NSProtocol.connect(Unknown Source)
   oracle.jdbc.ttc7.TTC7Protocol.connect(TTC7Protocol.java:1689)
   oracle.jdbc.ttc7.TTC7Protocol.logon(TTC7Protocol.java:215)
   ^-- Holding lock: oracle.jdbc.ttc7.TTC7Protocol@295b96a[thin lock]
   oracle.jdbc.driver.OracleConnection.<init>(OracleConnection.java:
360)

oracle.jdbc.driver.OracleDriver.getConnectionInstance(OracleDriver.java:
521)
   oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:325)
   java.sql.DriverManager.getConnection(Unknown Source)
   ^-- Holding lock: java.lang.Class@10266d9[recursive lock]
   java.sql.DriverManager.getConnection(Unknown Source)
   ^-- Holding lock: java.lang.Class@10266d9[fat lock]

org.apache.commons.sql.util.DataSourceWrapper.getConnection(DataSourceWrapper.java:
117)
   com.xx.util.DBConnection.connect(DBConnection.java:80)
   com.xx.server.DBQuery.doSqlGetmultColumns(DBQuery.java:7242)
   com.xx.server.DBQuery.doSqlGetmultColumns(DBQuery.java:7219)
   com.xx.server.DBQuery.loadAuditVersion(DBQuery.java:275)
   com.xx.RefData.getAuditVersion(RefData.java:394)
   com.xx.server.DBQuery.saveAuditVersion(DBQuery.java:348)
   ^-- Holding lock: com.xx.DBQuery@d903876[fat lock]
   com.xx.checkSchedule(TestAction.java:904)

Thread-160 "[STUCK] ExecuteThread: '13' for queue:
'weblogic.kernel.Default (self-tuning)'" <alive, in native,
priority=1, DAEMON> {
   jrockit.net.SocketNativeIO.readBytesPinned(Native Method)
   jrockit.net.SocketNativeIO.socketRead(Unknown Source)
   java.net.SocketInputStream.socketRead0(SocketInputStream.java:???)
   java.net.SocketInputStream.read(SocketInputStream.java:129)
   oracle.net.ns.Packet.receive(Unknown Source)
   oracle.net.ns.NSProtocol.connect(Unknown Source)
   oracle.jdbc.ttc7.TTC7Protocol.connect(TTC7Protocol.java:1689)
   oracle.jdbc.ttc7.TTC7Protocol.logon(TTC7Protocol.java:215)
   ^-- Holding lock: oracle.jdbc.ttc7.TTC7Protocol@10ea675f[thin lock]
   oracle.jdbc.driver.OracleConnection.<init>(OracleConnection.java:
360)

oracle.jdbc.driver.OracleDriver.getConnectionInstance(OracleDriver.java:
521)
   oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:325)
   java.sql.DriverManager.getConnection(Unknown Source)
   ^-- Holding lock: java.lang.Class@10266d9[recursive lock]
   java.sql.DriverManager.getConnection(Unknown Source)
   ^-- Holding lock: java.lang.Class@10266d9[fat lock]

org.apache.commons.sql.util.DataSourceWrapper.getConnection(DataSourceWrapper.java:
117)
   com.xx.util.DBConnection.connect(DBConnection.java:80)
   com.xx.server.DBQuery.doSQLStatement(DBQuery.java:7160)
   com.xx.server.DBQuery.saveAuditVersion(DBQuery.java:332)
   ^-- Holding lock: com.xx.server.DBQuery@d903876[fat lock]
     com.xx.checkSchedule(TestAction.java:904)

just to clarify:
DBQuery is although not thread-safe initialized singleton class.
DBConnection is an utility class with no synchronized methods.

As i understand from the stacktrace both threads reference the same
memory address and hold the lock
^-- Holding lock: com.xx.server.DBQuery@d903876[fat lock]
in such a case and excluding any calls to wait() (there is not any)
how is it possible that stack trace shows something as above?