Hello!

I'm using more than one thread in my application. In one thread I listen to notifications from the database and another one checks if the connection is alive by doing a "select 1".
Sometimes I get a deadlock!!!
I'm using postgresql-8.2-508.jdbc4.jar.

The thread dump gives me this:

Java stack information for the threads listed above:
================================================== =
"DB connection select 1":
at org.postgresql.core.v3.ProtocolConnectionImpl.setT ransactionState(ProtocolConnectionImpl.java:191)
- waiting to lock <0xb1a00f88> (a org.postgresql.core.v3.ProtocolConnectionImpl)
at org.postgresql.core.v3.QueryExecutorImpl.receiveRF Q(QueryExecutorImpl.java:1654)
at org.postgresql.core.v3.QueryExecutorImpl.processRe sults(QueryExecutorImpl.java:1410)
at org.postgresql.core.v3.QueryExecutorImpl.execute(Q ueryExecutorImpl.java:193)
- locked <0xb1a033e0> (a org.postgresql.core.v3.QueryExecutorImpl)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execut e(AbstractJdbc2Statement.java:452)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execut eWithFlags(AbstractJdbc2Statement.java:337)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execut eQuery(AbstractJdbc2Statement.java:236)
at database.DatabaseManager$SelectRunnable.run(Databa seManager.java:483)
at java.lang.Thread.run(Thread.java:619)
"Database tables listener":
at org.postgresql.core.v3.QueryExecutorImpl.processNo tifies(QueryExecutorImpl.java:547)
- waiting to lock <0xb1a033e0> (a org.postgresql.core.v3.QueryExecutorImpl)
at org.postgresql.core.v3.ProtocolConnectionImpl.getN otifications(ProtocolConnectionImpl.java:68)
- locked <0xb1a00f88> (a org.postgresql.core.v3.ProtocolConnectionImpl)
at org.postgresql.jdbc2.AbstractJdbc2Connection.getNo tifications(AbstractJdbc2Connection.java:1013)
at database.DbListenerHandler$DbListener.run(DbListen erHandler.java:134)
at java.lang.Thread.run(Thread.java:619)

Found 1 deadlock.

I've marked the places where the deadlock occurs with "\\<<<<<<<<<<<".

In the "DB connection select 1" thread I have:
====================================
success = false;
Statement stmt = null;
try {
int i = 0;
stmt = getCon().createStatement();
ResultSet rs = stmt.executeQuery("SELECT 1");\\<<<<<<<<<<<

if (rs.next()) {
i = rs.getInt(1);
}
if (i == 1) {
success = true;
}
} catch (SQLException ex) {
} finally {
if (stmt != null) {
try {
stmt.close();
} catch (SQLException ex) {
}
}
}

====================================

And in the "Database tables listener" thread I have:
====================================
while (...) {
try {
PGNotification notifications[] =pgconn.getNotifications();\\<<<<<<<<<<<
if (notifications != null) {
....
}
Thread.sleep(300);
} catch (SQLException sqle) {
....
} catch (InterruptedException ie) {
....
}
}
====================================

Is this a bug in jdbc-postgres?

Joao Leal

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