Hi,
I made this simple program. -
UINT Func(void * x)
-
{
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cout << rand() << endl;
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return 0;
-
}
-
-
int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
-
{
-
int nRetCode = 0;
-
-
srand(time(0));
-
-
while(1)
-
{
-
Sleep(10);
-
AfxBeginThread(Func, NULL);
-
//Func(NULL);
-
}
-
-
return nRetCode;
-
}
-
-
Now, All that is printed on the console is a steady stream of 41s. I guess this is because the rand() function is somehow "reset" for different threads. But waht I want to get is actual random numbers for each thread. How can I achieve this? Thanks.
8  3793  Banfa 9,065
Recognized Expert Moderator Expert
Write you own thread re-entrant rand function.
You should be able to find a workable algorithm using Google or Wikipedia.
You can make the function thread re-entrant by using a CriticalSection .
I did modify it by using critical sections, but still the same problem. I don't feel like writing my own rand function. Isn't there anyway to get this done?
here's the modified version: -
CRITICAL_SECTION crtsec;
-
-
static int Rand()
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{
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return rand();
-
}
-
-
UINT Func(void * x)
-
{
-
EnterCriticalSection(&crtsec);
-
srand(timeGetTime());
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cout << rand() << endl;
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LeaveCriticalSection(&crtsec);
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return 0;
-
}
-
-
int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
-
{
-
InitializeCriticalSection(&crtsec);
-
int nRetCode = 0;
-
-
srand(time(0));
-
-
while(1)
-
{
-
Sleep(10);
-
AfxBeginThread(Func, NULL);
-
//Func(NULL);
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}
-
-
DeleteCriticalSection(&crtsec);
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return nRetCode;
-
}
-
Banfa 9,065
Recognized Expert Moderator Expert
I did modify it by using critical sections, but still the same problem. I don't feel like writing my own rand function. Isn't there anyway to get this done?
Not really unless you have a separate thread which serves random numbers to the other threads so that only 1 thread is calling rand. This would be more complecated than writing your own rand function.
The critical sections are not working in this instance because they have no effect on the code they contain all they do is prevent 2 threads running the same bit of code at the same time which would be required if that bit of code was using some static data to prevent data corruptions by multiple accesses to that data.
Honestly writing your own rand function just isn't that hard and I suspect if you check the references I gave you will find the code or pseudo code for one without having to do much writing at all.
So, I'll try my hand at a rand function of my own then. Thanks.
Why not take the random number from the last call and use it as an argument to your thread?
That way your thread could call srand() using the argument followed by
rand() to to get the next random number.
Banfa 9,065
Recognized Expert Moderator Expert
Why not take the random number from the last call and use it as an argument to your thread?
That way your thread could call srand() using the argument followed by
rand() to to get the next random number.
I don't think that would work in this case were a lot of threads are being started asynchonously.
EDIT: Actually I take this back it would with use of critical section.
I don't think that would work in this case were a lot of threads are being started asynchonously.
In that case you could use a server thread to generate the random numbers. This thread would just idle out there looking in a mailbox for a random number request. It could out the random number inthe mailbox. All of the other threads just use the mailbox in a critical section.
Banfa 9,065
Recognized Expert Moderator Expert
In that case you could use a server thread to generate the random numbers. This thread would just idle out there looking in a mailbox for a random number request. It could out the random number inthe mailbox. All of the other threads just use the mailbox in a critical section.
You could do this, in fact I said so. But I think it is easier to write your own PRNG and put it in a critical section.
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