Thread experiment problem

**jeata** · 05-18-2011, 02:22 PM

I've been playing around with threads, but I don't quite get the results I'm looking for.

I have 3 classes

VariablesClass
Has a variable ”number” = the number indicated by the wheel of fortune.
There are four numbers on the wheel of fortune : 1, 2, 3 and 4.

ThreadsClass
A thread spinning the wheel of fortune.
Each pass will move the wheel of fortune one place forward.

TestClass
Creates a wheeloffortune and 3 threads.
Starts the threads, but do not stop them.

Sometimes I get only 2 threads to run, sometimes I get a result saying I get 7,6 for all the threads, sometimes I get an exception.

Here are the classes, it shouldn't be able to get a result bigger than 4.

Java Code:

public class VariablesClass
{
    // instance variables 
    public int ONE=1;
    public int TWO=2;
    public int THREE=3;
    public int FOUR=4;
    private int number;

    // constructor
    public VariablesClass()
    {
        number=ONE;
    }

    // get number
    public int getNumber()
    {
        return number;
    }
    
    // set number
    public void setNumber(int n)
    {
        number=n;
    }
    
}

Java Code:

public class ThreadsClass extends Thread
{
    // instance variables 
    boolean running;
    VariablesClass fortune;
    int id;
    long starttime;
    long endtime;
    DecimalFormat fmt=new DecimalFormat("###0.00");

    // constructor
    public ThreadsClass (VariablesClass fortune, int id)
    {
        this.fortune=fortune;
        this.id=id;
        starttime=System.currentTimeMillis();
        running=true;
    }

    // run
    public void run()
    {
        while(running)
        {
            if(fortune.getNumber()==fortune.FOUR)
            {
                fortune.setNumber(fortune.ONE);
            }
            else
            {
                fortune.setNumber(fortune.getNumber()+1);
                if(fortune.getNumber()>fortune.FOUR)
                {
                    endtime=System.currentTimeMillis();
                    System.out.println("Thread "+id+" stopped after "+fmt.format(0.001*(endtime-starttime))+" sec");
                    System.out.println("number is now = "+fortune.getNumber());
                    stopThread();
                }
            }
        }
    }
    
    // stop
    public void stopThread()
    {
        running=false;
    }
    
}

Java Code:

public class TestClass
    // main
    public static void main(String[] args)
    {
        VariablesClass wof=new VariablesClass();
        ThreadsClass a=new ThreadsClass(wof,1);
        ThreadsClass b=new ThreadsClass(wof,2);
        ThreadsClass c=new ThreadsClass(wof,3);
        a.start();
        b.start();
        c.start();
     }
    
}

**Norm** · 05-18-2011, 02:33 PM

The code you posted does not compile: ThreadsClass vs ThreadClass

Please copy and paste here the output from the program and add some comments showing what the problem is.

I get this:

Thread 2 stopped after 1.77 sec
number is now = 5
Thread 3 stopped after 1.77 sec
number is now = 6
Thread 1 stopped after 1.77 sec
number is now = 7

0 error(s)

Try debugging your code by adding println() statements in various methods to show variable values and program flow.
You will quickly see what the problem is.

**jeata** · 05-18-2011, 02:43 PM

Hi

Here's a couple of compile results

Java Code:

Thread 2 stopped after 0.00 sec
number is now = 2
Thread 3 stopped after 0.00 sec
number is now = 1

Java Code:

Thread 1 stopped after 0.02 sec
number is now = 5
Thread 3 stopped after 0.01 sec
number is now = 5
Thread 2 stopped after 0.01 sec
number is now = 5
Unhandled exception
Type=Segmentation error vmState=0x00000000
J9Generic_Signal_Number=00000004 ExceptionCode=c0000005 ExceptionAddress=02ACD15F ContextFlags=0001003f
Handler1=002EA090 Handler2=001EBE40 InaccessibleAddress=0064EEE4
EDI=005C7FF8 ESI=00601CDC EAX=0064EEE4 EBX=005C8F04
ECX=00000002 EDX=001D313C
EIP=02ACD15F ESP=0056FB3C EBP=001B6A10 EFLAGS=00210206
GS=002B FS=0053 ES=002B DS=002B
Module=D:\Rational Architect\RAT\jdk\jre\bin\j9jvmti24.dll
Module_base_address=02AC0000 Offset_in_DLL=0000d15f
Target=2_40_20091125_047905 (Windows 7 6.1 build 7600)
CPU=x86 (4 logical CPUs) (0xb7486000 RAM)
----------- Stack Backtrace -----------
disposeEnvironment+0xbf (jvmtihelpers.c:216, 0x02ACD15F [j9jvmti24+0xd15f])
shutDownJVMTI+0x58 (jvmtistartup.c:493, 0x02AD6D88 [j9jvmti24+0x16d88])
J9VMDllMain+0x369 (jvmtistartup.c:201, 0x02AD73A9 [j9jvmti24+0x173a9])
runJ9VMDllMain+0xcd (jvminit.c:2483, 0x003069AD [j9vm24+0x269ad])
pool_do+0x54 (pool.c:432, 0x003281C4 [j9vm24+0x481c4])
runShutdownStage+0x53 (jvminit.c:2865, 0x0030AEF3 [j9vm24+0x2aef3])
freeJavaVM+0x178 (jvminit.c:862, 0x0030C058 [j9vm24+0x2c058])
protectedDestroyJavaVM+0x3cc (jniinv.c:421, 0x002FA95C [j9vm24+0x1a95c])
j9sig_protect+0x41 (j9signal.c:144, 0x001EBFA1 [J9PRT24+0xbfa1])
DestroyJavaVM+0x189 (jniinv.c:494, 0x002FABA9 [j9vm24+0x1aba9])
DestroyJavaVM+0xc (jvm.c:402, 0x001A130C [jvm+0x130c])
(0x00403748 [javaw+0x3748])
(0x00409605 [javaw+0x9605])
BaseThreadInitThunk+0x12 (0x75413677 [kernel32+0x13677])
RtlInitializeExceptionChain+0x63 (0x77489D72 [ntdll+0x39d72])
RtlInitializeExceptionChain+0x36 (0x77489D45 [ntdll+0x39d45])
---------------------------------------
JVMDUMP006I Processing dump event "gpf", detail "" - please wait.
JVMDUMP013I Processed dump event "gpf", detail "".

Java Code:

Thread 3 stopped after 0.01 sec
number is now = 2
Thread 2 stopped after 1.57 sec
number is now = 5
Thread 1 stopped after 1.58 sec
number is now = 5
Unhandled exception
Type=Segmentation error vmState=0x00000000
J9Generic_Signal_Number=00000004 ExceptionCode=c0000005 ExceptionAddress=026CD15F ContextFlags=0001003f
Handler1=001CA090 Handler2=0023BE40 InaccessibleAddress=0067EEE4
EDI=005F7FF8 ESI=00631CDC EAX=0067EEE4 EBX=005F8F04
ECX=00000002 EDX=0022313C
EIP=026CD15F ESP=003BFB3C EBP=001B6A10 EFLAGS=00210206
GS=002B FS=0053 ES=002B DS=002B
Module=D:\Rational Architect\RAT\jdk\jre\bin\j9jvmti24.dll
Module_base_address=026C0000 Offset_in_DLL=0000d15f
Target=2_40_20091125_047905 (Windows 7 6.1 build 7600)
CPU=x86 (4 logical CPUs) (0xb7486000 RAM)
----------- Stack Backtrace -----------
disposeEnvironment+0xbf (jvmtihelpers.c:216, 0x026CD15F [j9jvmti24+0xd15f])
shutDownJVMTI+0x58 (jvmtistartup.c:493, 0x026D6D88 [j9jvmti24+0x16d88])
J9VMDllMain+0x369 (jvmtistartup.c:201, 0x026D73A9 [j9jvmti24+0x173a9])
runJ9VMDllMain+0xcd (jvminit.c:2483, 0x001E69AD [j9vm24+0x269ad])
pool_do+0x54 (pool.c:432, 0x002081C4 [j9vm24+0x481c4])
runShutdownStage+0x53 (jvminit.c:2865, 0x001EAEF3 [j9vm24+0x2aef3])
freeJavaVM+0x178 (jvminit.c:862, 0x001EC058 [j9vm24+0x2c058])
protectedDestroyJavaVM+0x3cc (jniinv.c:421, 0x001DA95C [j9vm24+0x1a95c])
j9sig_protect+0x41 (j9signal.c:144, 0x0023BFA1 [J9PRT24+0xbfa1])
DestroyJavaVM+0x189 (jniinv.c:494, 0x001DABA9 [j9vm24+0x1aba9])
DestroyJavaVM+0xc (jvm.c:402, 0x001A130C [jvm+0x130c])
(0x00403748 [javaw+0x3748])
(0x00409605 [javaw+0x9605])
BaseThreadInitThunk+0x12 (0x75413677 [kernel32+0x13677])
RtlInitializeExceptionChain+0x63 (0x77489D72 [ntdll+0x39d72])
RtlInitializeExceptionChain+0x36 (0x77489D45 [ntdll+0x39d45])
---------------------------------------
JVMDUMP006I Processing dump event "gpf", detail "" - please wait.
JVMDUMP013I Processed dump event "gpf", detail "".

Java Code:

Thread 2 stopped after 0.00 sec
number is now = 1
Process model delta has encountered a problem

**Norm** · 05-18-2011, 02:43 PM

Try debugging your code by adding println() statements in various methods to show variable values and program flow.
You will quickly see what the problem is.

**jeata** · 05-18-2011, 02:54 PM

Originally Posted by Norm

Try debugging your code by adding println() statements in various methods to show variable values and program flow.
You will quickly see what the problem is.

Hmm, where exactly, I really have no idea about threads.

**Tolls** · 05-18-2011, 02:56 PM

Is that a Rational-specific JRE, or is that simply an Oracle one supplied with the RAT?
If the former, have you tried running this with an Oracle JRE?

Because that's not an exception...that's your JVM throwing a wobbly.

**Norm** · 05-18-2011, 02:59 PM

Put a println in any of the methods that are called and that change values and that test values.
You want to see where the execution flow goes and how the controlling variables values change.

**jeata** · 05-18-2011, 03:00 PM

Originally Posted by Tolls

Is that a Rational-specific JRE, or is that simply an Oracle one supplied with the RAT?
If the former, have you tried running this with an Oracle JRE?

Because that's not an exception...that's your JVM throwing a wobbly.

Good idea, I'm switching to ubuntu now, to try to compile it in eclipse.

**Tolls** · 05-18-2011, 03:44 PM

Make sure it's run against an Oracle JVM.
I wouldn't necessarily trust the one that came with Eclipse...

**applegigs** · 05-19-2011, 09:12 AM

Isn't this the CA from Knord 2011 Threads ?
the code look identical .

Originally Posted by jeata

I've been playing around with threads, but I don't quite get the results I'm looking for.

I have 3 classes

VariablesClass
Has a variable ”number” = the number indicated by the wheel of fortune.
There are four numbers on the wheel of fortune : 1, 2, 3 and 4.

ThreadsClass
A thread spinning the wheel of fortune.
Each pass will move the wheel of fortune one place forward.

TestClass
Creates a wheeloffortune and 3 threads.
Starts the threads, but do not stop them.

Sometimes I get only 2 threads to run, sometimes I get a result saying I get 7,6 for all the threads, sometimes I get an exception.

Here are the classes, it shouldn't be able to get a result bigger than 4.

Java Code:

public class VariablesClass
{
    // instance variables 
    public int ONE=1;
    public int TWO=2;
    public int THREE=3;
    public int FOUR=4;
    private int number;

    // constructor
    public VariablesClass()
    {
        number=ONE;
    }

    // get number
    public int getNumber()
    {
        return number;
    }
    
    // set number
    public void setNumber(int n)
    {
        number=n;
    }
    
}

Java Code:

public class ThreadsClass extends Thread
{
    // instance variables 
    boolean running;
    VariablesClass fortune;
    int id;
    long starttime;
    long endtime;
    DecimalFormat fmt=new DecimalFormat("###0.00");

    // constructor
    public ThreadsClass (VariablesClass fortune, int id)
    {
        this.fortune=fortune;
        this.id=id;
        starttime=System.currentTimeMillis();
        running=true;
    }

    // run
    public void run()
    {
        while(running)
        {
            if(fortune.getNumber()==fortune.FOUR)
            {
                fortune.setNumber(fortune.ONE);
            }
            else
            {
                fortune.setNumber(fortune.getNumber()+1);
                if(fortune.getNumber()>fortune.FOUR)
                {
                    endtime=System.currentTimeMillis();
                    System.out.println("Thread "+id+" stopped after "+fmt.format(0.001*(endtime-starttime))+" sec");
                    System.out.println("number is now = "+fortune.getNumber());
                    stopThread();
                }
            }
        }
    }
    
    // stop
    public void stopThread()
    {
        running=false;
    }
    
}

Java Code:

public class TestClass
    // main
    public static void main(String[] args)
    {
        VariablesClass wof=new VariablesClass();
        ThreadsClass a=new ThreadsClass(wof,1);
        ThreadsClass b=new ThreadsClass(wof,2);
        ThreadsClass c=new ThreadsClass(wof,3);
        a.start();
        b.start();
        c.start();
     }
    
}

**JosAH** · 05-19-2011, 12:18 PM

The dump definitely is caused by a bug somewhere; incorrect Thread management should never cause it. Your 'number' variable is a shared resource so all reads and writes should occur in a synchronized method in your VariablesClass. Consequently, increment and wrap the number in a synchronized method in that class.

kind regards,

Jos

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