multithread problem - start is not calling run() - child thread is not completing before parent

[majety srikanth]

class ChildThread extends Thread
{
public boolean processing = false;
public void run()
{
getResult();
}
public void getResult()
{
connect with webservice and get some data from it. once it is successfully completed,Iam changing the flag value

processing = false;
}
public void post(string params)
{
after getting parameters from calling method, i am starting this thread
and setting flag value

processing = true;
this. start(); // starting the thread to call run method
}
}
########################

class parent
{
method()
{
new ChildThread().post(String params);
while(processing)
{
print("processing is going on...");
}
doSomethingElse();
}
}
doSomthingElse() gets executed before the childThread run() method is run at all. orelse some times, the childThread start() is not at all calling run() method sothat the parent is going to infinte loop.
I set high priority to childThread . but no use.


As i am using J2ME CLDC 1.1, there is no join() concept or java.util.concurrent library support. If any one knows the solution to how to handle this, kindly post here.

[Deepak Chopra]

I would recommend you to use "wait" and "notify" instead of going in an infinite loop.

Lets the parent thread wait on an object and let the child thread notify parent thread once it finish the processing. This would give very good performance CPU wise and will reduce your execution time as well.

[majety srikanth]

Thanks Sunny Jain. I have tried your suggestion.

in the Parent class
{
ChildThread childThread = new ChildThread();
childThread.post(params);

// replaced While loop with the following code

synchronized(childThread)
{
try {
System.out.println("waiting for the thread process.......");
childThread.wait();
System.out.println("waiting is over .......");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}


#####################
in ChildThread
#####################
public void getResult()
{
synchronized (this)
{
connect with webservice and get some data from it. once it is successfully completed,Iam changing the flag value

processing = false;
this.notifyAll();
}
}


But in output .... parent is stopping in waiting for ever. Am I using synchronization - wait and notify correctly ?
Please let me know.

Thanks for your help.

[Vijitha Kumara]

Hi majety,

Please UseCodeTags when posting code in forums. Unformatted code is difficult to read...

[Vijitha Kumara]

How is your getResult() method being called from the code you are calling?

[Ernest Friedman-Hill]

I'm afraid the truth is that no one can really tell if you're doing anything correctly, or what problems you might be having, because you're not posting real code, only summaries. The problem with that is that the summaries reflect what you think the code looks like, whereas often if there's a problem it's because the actual code has some major problem that isn't reproduced in your summary. There's a page on our Wiki called PostRealCode (that's a link) which explains why this is a good idea.

[majety srikanth]

Hi,
Thanks for your reply.

I have already posted my real code here.
https://coderanch.com/t/526710/JME/Mobile/Multithreading-me-webservice-connection

But, I did not get any reply for that. I thought, it is time taking to understand the whole code and posted it in snippets form.

for Vijitha Kumara' query : childThread's run method is calling GetResult() method. If you see the above link or my first post, you can understand this.

I am a new person to the forums and all. So, still if I miss any information please let me know with out getting angry.

[majety srikanth]

Sorry.. here is my code in properly arranged code format.
What I want is, my Parent (Sync) has to wait until the child(TestConnectionThread) completes.
i.e in the output - the red colour lines should be interchanged so that Sync - checkTestConnection() - isConnection value willbecome true;

public class Sync {
private static STCMidlet stcMidlet;
public Sync()
{
}
public Sync(STCMidlet stcMidlet)
{
this.stcMidlet = stcMidlet;
}
public boolean checkTestConnection(String url)
{
System.out.println("Sync - checkTestConnection()");
boolean value = false;
boolean isConnection=false;
Date date = new Date();
StringBuffer sb = new StringBuffer("Connecting To Server..");
System.out.println("current thread name & priority:"+ Thread.currentThread().getName() +"-" + Thread.currentThread().getPriority());
TestConnectionThread childThread = new TestConnectionThread();
childThread.setPriority(Thread.MAX_PRIORITY);
childThread.post(url);
long time = new Date().getTime();
[color=green]/* synchronized(childThread)
{
try {
System.out.println("waiting for the thread process.......");
childThread.wait();
System.out.println("waiting is over .......");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
*/[/color] while (childThread.sending)
{
//TODO : Temporary crack. but value will be always true. Change the logic afterwards
try
{
// System.out.println("St-Time --->" + date.getTime());
sb.append(".").toString();
System.out.println(sb);
Thread.sleep(1000);
value = true;
}
catch (InterruptedException e)
{ e.printStackTrace(); }
/* if((new Date().getTime() - time) > 5000.0)
{
System.out.println("Sync-checkTestConnection()- inside time out");
childThread.killThread();
value = false;
}
*/
}
System.out.println("Sync-checkTestConnection()-while is over");
if (!childThread.sendResult)
{
System.out.println("Connection Failed");
}
else
{
System.out.println("Sync-checkTestConnection()- inside else block>>>>>>>>>>>>>>>>>>>>>>");
if(url != null && value==true)
{
isConnection= true;
}
else
{
isConnection= false;
}
}
System.out.println("Sync - checkTestConnection() - finally value is set to : " + value );
System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>> Sync - checkTestConnection() - isConnection value =" + isConnection);
return isConnection;
}
/******************************************************************************************************/
public class TestConnectionThread extends Thread {
private boolean start = false;
private boolean stop = false;
public boolean sendResult = false;
public boolean sending = false;
public String url = "";
private String culture = "";
private boolean running = false;
public void run()
{
System.out.println("TestConnectionThread - run()");
System.out.println("TestConnectionThread - run() - thread name and priority :"+ Thread.currentThread().getName() +"-" + Thread.currentThread().getPriority());
while (running)
{
System.out.println("TestConnectionThread - run()-inside thread running");
if (start == false && stop == false)
{
try
{
sleep(200);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
else if (stop)
{
return;
}
else if (start)
{
GetResult();
}
}
}
private void GetResult()
{
System.out.println("TestConnection Thread - GetResult()");
[color=green]/*synchronized (this) {
System.out.println("entered synchronization ...........");*/[/color]
try
{
String methodName = "TestConnection";
String soapAction = Constants.serviceNamespace + methodName;
System.out.println("soapAction"+soapAction);
SoapObject rpc = new SoapObject(Constants.serviceNamespace, methodName);
// rpc.addProperty("culture","en-gb");
SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER11);
envelope.bodyOut = rpc;
envelope.dotNet = true;
envelope.encodingStyle = SoapSerializationEnvelope.XSD;
HttpTransport ht = new HttpTransport(url);
System.out.println("In URL " + url);
ht.debug = true;
ht.setXmlVersionTag("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");
sendResult = true;
try
{
System.out.println("TestConnection Thread - GetResult() - before ht.call");
ht.call(soapAction, envelope);
System.out.println("TestConnection Thread - GetResult() - after ht.call");
String result = (envelope.getResponse()).toString();
System.out.println(" >>>>>>>>>>>>>>>>>>>>>>>>> TestConnection Thread - GetResult()- got response from webservice:" + result);
if(result.equalsIgnoreCase("true"))
{
Constants.C_url = url;
Constants.setServiceUrl(url);
Constants.C_culture = culture;
System.out.println("");
sending = false;
}
else
{
Constants.C_url = "";
Constants.setServiceUrl(null);
Constants.C_culture=null;
sendResult = false;
}
System.out.println("TestConnection Thread - GetResult() - set constants url as " + Constants.C_url);
}
catch(org.kxml2.xmlpull.v1.XmlPullParserException ex2)
{
/*Alert error = new Alert("Unable to connect to server", "Unable to connect to server", null, AlertType.ERROR);
error.setTimeout(Alert.FOREVER);*/
System.out.println("Error" +ex2);
Constants.exception = "Unable to connect to server";
sendResult = false;
}
catch(Exception ex)
{
System.out.println("Error" +ex.toString());
Constants.exception = ex.toString();
sendResult = false;
}
start = false;
sending = false;
stop = true;
System.out.println("TestConnection Thread - GetResult() - sending value :" + sending);
}
catch(Exception e)
{
System.out.println("In Error" + e.toString());
}
sending = false;
[color=green]/*this.notifyAll();
System.out.println("notified all threads ...........");
}*/[/color]
}
public void post(String url)
{
System.out.println("TestConnection Thread - posted parameters - url" + url);
this.url = url;
System.out.println("In URL " + url);
sendResult = false;
sending = true;
start = true;
running = true;
this.start();
}
public void killThread()
{
running = false;
sending = false;
System.out.println(" <<<<<<<<<<< thread killed <<<<<<<<<<<<<<<<");
}
public void stop() {
stop = true;
}
}

output :
Sync - checkTestConnection()
current thread name & priority:Thread-4-5
TestConnection Thread - posted parameters - url <url - value>
In URL <properly working url - value>
Connecting To Server...
TestConnectionThread - run()
TestConnectionThread - run() - thread name and priority :Thread-7-10
TestConnectionThread - run()-inside thread running
TestConnection Thread - GetResult()
soapAction <soap-action value >
In URL <properly working url - value>
TestConnection Thread - GetResult() - before ht.call
Connecting To Server....
Connecting To Server.....
Connecting To Server......
Connecting To Server.......
Sync-checkTestConnection()- inside time out
<<<<<<<<<<< thread killed <<<<<<<<<<<<<<<<
Sync-checkTestConnection()-while is over
Sync-checkTestConnection()- inside else block>>>>>>>>>>>>>>>>>>>>>>
Sync - checkTestConnection() - finally value is set to : false
>>>>>>>>>>>>>>>>>>>>>>>>> Sync - checkTestConnection() - isConnection value =falseTestConnection Thread - GetResult() - after ht.call
>>>>>>>>>>>>>>>>>>>>>>>>> TestConnection Thread - GetResult()- got response from webservice:trueTestConnection Thread - GetResult() - set constants url as <properly working url - value>
TestConnection Thread - GetResult() - sending value :false
Execution completed.