C / C++ / MFC

24-Jun-09 1:02

Hey good people,

I am in need of an idea for a problem that has to have been solved a throusand times over. But after implementing some code that should take care of the troublemaker (rand()) - but didn´t - and a lot of research I am at a loss here.

I built a server which has to generate some random numbers for each client that connects. So I created a nice singleton wrapper class for the random generator and now it´s seeded (srand(time(NULL))) once at startup and thereafter every call should present me an actual (pseudo-)random number.
As you may have guessed, theory didn´t work out. All numbers are very random for every single call from ONE client. As soon as another client connects it gets THE SAME 'random' sequence of numbers. Even though the seed was plantet only once AND they don´t even ask at the same time.

Here´s a little code on the number generation, maybe someone has an idea:

ToolBox* ToolBox::m_pToolbox = NULL;

ToolBox::ToolBox(void)
{
	m_pLogger = Logger::GetInstance();
	srand ( time(NULL) );
}

ToolBox::~ToolBox(void)
{
}

ToolBox* ToolBox::GetInstance()
{
	if( m_pToolbox == NULL )
	{
		m_pToolbox = new ToolBox();
	}
	return m_pToolbox;
}

///////////////////////////////////////////////////////////////////////////////////
//		Random number generation
///////////////////////////////////////////////////////////////////////////////////

//
BYTE ToolBox::GenerateRandomByte()
{
	BYTE ret = LOBYTE((WORD)rand());

        // test random numbers
	int r1 = rand();
	int r2 = rand();
	int r3 = rand();
	int r4 = rand();
	m_pLogger->Out( Logger::DEBUG, "TestRand 1: %d\nTestRand 2: %d\nTestRand 3: %d\nTestRand 4: %d\n", r1, r2, r3, r4 );

	return ret;	
}

int ToolBox::GenerateRandomInt()
{
	return rand();
}

Any help is appreciated. Thanks.

Souldrift

Michael Schubert24-Jun-09 1:31

Michael Schubert

24-Jun-09 1:31

Have you tried a third party generator? Try this one:

http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html[^]

Souldrift24-Jun-09 2:29

Re: random numbers - the old bugger ... [modified]

24-Jun-09 2:29

I´ll look into it, thanks Smile | :)

CPallini24-Jun-09 1:40

CPallini

24-Jun-09 1:40

You should move the srand call:


ToolBox::ToolBox(void)
{
	m_pLogger = Logger::GetInstance();
	srand ( time(NULL) );
}

and


ToolBox* ToolBox::GetInstance()
{
	if( m_pToolbox == NULL )
	{
		m_pToolbox = new ToolBox();
               srand ( time(NULL) );
	}
	return m_pToolbox;
}

[added]
Nevermind I made a blunder.
[/added]
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

modified on Wednesday, June 24, 2009 8:49 AM

Souldrift24-Jun-09 2:29

24-Jun-09 2:29

umm, where´s the difference. It gets called once either way.

Cheers

CPallini24-Jun-09 2:49

CPallini

24-Jun-09 2:49

Yes, you're right. I made a blunder, forget it.
Could you please show us how a client uses the ToolBox?
Smile | :)

Souldrift24-Jun-09 3:06

24-Jun-09 3:06

Of course. Only the client doesn´t use the ToolBox. The server does. For each client it has to create an RTP Header for an RTP data transfer. Which is done in my class RTPHeader.

RTPHeader::RTPHeader( int payloadType )
{
	m_pLogger = Logger::GetInstance();
	m_pToolbox = ToolBox::GetInstance();
	// setup header
	m_pLogger->Out(Logger::DEBUG, "RTPHeader: Constructing Header.\n");
	for( int i = 0; i < 12; i++ )
	{
		m_aHeader[i] = 0;
	}

	SetPayloadType( payloadType );
	SetVersion( (BYTE) 2 );
	GenerateNewSsrc();

	m_bFirstGetInc = true;
	
	PrintToConsole();
}

RTPHeader::~RTPHeader(void)
{
}

void RTPHeader::GenerateNewSsrc()
{
	// does this work properly ??
	m_aHeader[9] = m_pToolbox->GenerateRandomByte();
	m_aHeader[10] = m_pToolbox->GenerateRandomByte();
	m_aHeader[11] = m_pToolbox->GenerateRandomByte();

}

.
.
.

In GenerateNewSsrc() the ToolBox´s Random Generator is used. It works nicely for this small piece of code. Only that for the next client that connects to the server it will generate the same sequence all over.
And my test output in the ToolBox class actually shows that it is indeed the rand() method that produces the same results. It´s not a variable that wasn´t cleared or such something. A new RTPHeader class object is created for every client.

Cheers

Stuart Dootson24-Jun-09 3:00

Stuart Dootson

24-Jun-09 3:00

Is your application multi-threaded? Because the state of the random number generator is held in per-thread storage (i.e. there's a different random number state for each thread). And if each of those states is initialised the same way...

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Souldrift24-Jun-09 3:12

24-Jun-09 3:12

Hmm .. good idea. That might be it. Though I don´t thoroughly understand it.

I indeed use multi-threading. Though there is only one object of the number generator and only one call of srand(). So each thread uses the same instance of the generator, which is actually what I intended because if srand() would be called for each worker thread (one per client), it could happen that two clients connect at the same time, get the same srand()-initialization and therewith produce the same sequence of numbers again. Right?

Souldrift

Stuart Dootson24-Jun-09 3:23

Stuart Dootson

24-Jun-09 3:23

Souldrift wrote:
Though there is only one object of the number generator and only one call of srand(). So each thread uses the same instance of the generator, which is actually what I intended because if srand()

No, no, no - each thread will have its own random number generator state - it's held inside the C run-time library (look at rand.c in the C run-time source). Even though you have one toolbox object, that's immaterial, because your object doesn't hold the random number state.

The call to srand() will only effect the thread on which the toolbox object is constructed. The other threads will get some default random number generator state initialisation.

Your best bet would be to use a different PRNG - for example, one of the implementations included in Boost[^], where (as you have full control over the PRNG including the data it uses) you could ensure that you have a single state for ALL threads. Of course, you'd then need to put a lock on the random number acquisition function (to ensure only one thread calls it at once)...

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Souldrift24-Jun-09 3:29

Need a help regarding crystal report

24-Jun-09 3:29

Okay. That´s good to know Smile | :)

.

I´ll look into Boost. And sure thing about the lock ... I would have taken care of that later on, anyway.

Thanks for now

Souldrift

tasumisra23-Jun-09 23:42

tasumisra

23-Jun-09 23:42

Hi Guys i am using crstal report 11.5 to print the sevral reports its working fine but suddenly it starts giving "Invalid TLV record" and then if i uninstall the crstal report and install it back it again working fine ..
any clue whats going wrong...i searched on google and find some good info but
http://forums.techarena.in/software-development/1052995.htm[^]

not able to find the root cause ..

any help will be helpful

Thanks

vikas da

Re: Need a help regarding crystal report

Rajesh R Subramanian24-Jun-09 1:18

Rajesh R Subramanian

24-Jun-09 1:18

This forum is for discussions related to C/C++/MFC.

It is a crappy thing, but it's life -^ Carlo Pallini

Re: Need a help regarding crystal report

tasumisra24-Jun-09 2:30

tasumisra

24-Jun-09 2:30

right i am using MFC to print the report.. Smile | :)

do we have any place in CP where we can discussing about ...

vikas da

calling java dll from MFC

sunnyram23-Jun-09 22:24

sunnyram

23-Jun-09 22:24

I want to call the java dll from MFC application.
can we do this?
if yes how to do it?
Actually i have ssh dll in java,
and i want to call it from MFC.

sunny

Stuart Dootson23-Jun-09 23:07

Stuart Dootson

23-Jun-09 23:07

Use the resources available to you[^]

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

CPallini23-Jun-09 23:11

CPallini

23-Jun-09 23:11

sunnyram wrote:
java dll

What is a 'java dll'? Confused | :confused:

If you have a DLL, you may call the exported functions.
Smile | :)

KarstenK24-Jun-09 2:37

KarstenK

24-Jun-09 2:37

There is a JNI aka "Java Native Interface" functionality in Java. I saw some article here.

this one looks fine: How to Call Java functions from C Using JNI[^]

Press F1 for help or google it.
Greetings from Germany