What am I doing wrong below? The code pegs CPU at 100% and does not end. Seems to be an infinite loop. Help appreciated.

#include <stdio.h>

int main(void)
{
  
  unsigned long number2;
  unsigned long number = 1;
   
  #pragma omp parallel for  
  for (number = 1; number <= 10000; number  )
  {
    unsigned long max = 0, count = 0;    
    number2 = number;

    while (number2 != 1)
    {
      if (number2 > max)
        max = number2;
      if (number2 % 2 == 0)
        number2 /= 2;
      else
        number2 = 3 * number2   1;
      count  ;
    }    
  }

}

Update: The following works.

Not sure what the root cause was. It could've been

1. data type was overflowing its boundaries, i.e. int -> unsigned int
2. number2 had to be made private, etc.

#include <omp.h>

int main(int argc, char **argv)
{
  unsigned int i;
  #pragma omp parallel for
  for (i = 1; i < 10000000; i  )
  {
    unsigned int number2 = i; unsigned int max; unsigned int count = 0;
    while (number2 != 1)
    {
      if (number2 > max)
        max = number2;
      if (number2 % 2 == 0)
        number2 /= 2;
      else
        number2 = 3 * number2   1;
      count  ;
    }
  }
}```

CodePudding user response：

In the first version of your code number2 is shared, all threads access/modify it simultaneously. It is a data race ---> undefined behavior.

CodePudding user response：

Resolved.

Not sure what the root cause was. It could've been

data type was overflowing its boundaries, i.e. int -> unsigned int

or number2 had to be made private, etc.