Possible deadlock issues.

[Pavan Kumar]

Friends,

I am looking at an application, which hangs after a while. We have taken a thread dump, and I am trying to analyze the problem.

Unfortunately, I could not figure out very much out of the dump as my skills are a little inferior at the moment. But one thing that looks like causing the problem is the following thread dump. I see this multiple multiple times in the dump.

 "Thread-167" prio=5 tid=0x00a8afc0 nid=0xbe waiting for monitor entry [e07ff000..e07ffc28]
at java.io.PrintWriter.write(PrintWriter.java:229)
- waiting to lock <0xea4df5e0> (a java.io.BufferedWriter)
at java.io.PrintWriter.write(PrintWriter.java:247)
at com.ml.log4jserver.ExecMessageProcessor$Handler.outputMessageToClient(ExecMessageProcessor.java:343)
at com.ml.log4jserver.ExecMessageProcessor$Handler.access$1(ExecMessageProcessor.java:338)
at com.ml.log4jserver.ExecMessageProcessor$Handler$ClientOutputWriter.run(ExecMessageProcessor.java:360)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$RunWhenBlocked.blockedAction(PooledExecutor.java:777)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor.execute(PooledExecutor.java:898)
at com.ml.log4jserver.ExecMessageProcessor$Handler.processMessage(ExecMessageProcessor.java:152)
at com.ml.log4jserver.ExecMessageProcessor$Handler.run(ExecMessageProcessor.java:130)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Worker.run(PooledExecutor.java:743)
at java.lang.Thread.run(Thread.java:534) 

Here's the code fragment, that writes to the clients.

 private Map clients = Collections.synchronizedMap(new HashMap());
 
public  void clientConnected(Object client, String uid) {
try {
synchronized (clients) 
{
Socket clientSocket = (Socket) client;
PrintWriter writer = new PrintWriter(clientSocket.getOutputStream());
logger.debug("----------------Adding Client " + uid);
clients.put(uid, writer);
}
} catch (IOException e) {
logger.warn("Cient disconnected " + e, e);
}
}
Map getClients(){
synchronized (clients) {
return new HashMap(clients);
}
}
private  void outputMessageToClient(String message, String status) {
Collection clientCollection = getClients().values();
for (Iterator iter = clientCollection.iterator(); iter.hasNext(); ) {
PrintWriter writer = (PrintWriter) iter.next();
if (writer != null) {
writer.write(message + ";" + status);
writer.write('\n');
writer.flush();
if (logger.isDebugEnabled()) {
logger.debug("Message Written to Client ---- "+ message + ";" + status);
}
}
}
}
 

Upon looking at the javadoc for PrintWriter, I think using the following is better.

 PrintWriter writer = new PrintWriter(clientSocket.getOutputStream(), true);
writer.println(String);
 

Actual thread dump is pretty long. Could you please suggest what steps should I take to be able to understand the problem better.

Thanks Very much,
Cnu.