Re: gettimeofday problem

[Salvatore D'Angelo]

In this piece of code I convert seconds and microseconds in 
milliseconds. I think the problem is not in my code, in fact I wrote the 
following piece of code in Java, and it does not work too. In the for 
loop the 90% of times b > a while for 10% of times not.

    class Prova {
          public static void main(....) {
               for (;;) {
                    long a = System.currentTimeMillis();
                    long b = System.currentTimeMillis();

                    if (a > b) {
                         System.out.println("Wrong!!!!!!!!!!!!!");
                    }
               }
          }
    }

Chris McDonald wrote:

>In linux.kernel you write:
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>>Hi,
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>>I am writing a small piece of code that use the gettimeofday routine and 
>>I have noticed a very strange behaviour. If I call the routine two times 
>>in sequence I expect that the second value is greater than or equal to 
>>the first one, but it is not true.
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>Perhaps because tv_usecs are MICROsecs, not MILLIsecs ?
>
>_______________________________________________________________________________
>                  Dr Chris McDonald   EMAIL:  [e-mail]
>     Department of Computer Science & Software Engineering
>The University of Western Australia   WWW: http://www.csse.uwa.edu.au/~chris
>   Crawley, Western Australia, 6009   PH: [phone], FAX: [phone]
>
>
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>>please check the following code.
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>>Sometimes happen that the string "Strange Behaviour" is printed with 
>>kernel 2.4.18.
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>>I tried to find in the Linux Archive patches to solve this problem,  but 
>>I didn't find anything (there are emails that talk about gettimeofday, 
>>but probably they do not answer to my questions).
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>>The same thing happen in Java using the System.currentTimeMillis() routine.
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>>#include <fstream.h>
>>#include <sys/time.h>
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>>// this routine calculate the current time returning its value in long 
>>long format.
>>long long currentTimeMillis() {
>>  long long t;
>>  struct timeval tv;
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>>  gettimeofday(&tv, 0);
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>>  t = tv.tv_sec;
>>  t = (t *1000) + (tv.tv_usec/1000);
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>>  return t;
>>}
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>>void main() {
>>  for (;;) {
>>      long long a = currentTimeMillis();
>>      long long b = currentTimeMillis();
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>>      if (a>b) {
>>          cout << "Strange Behaviour" << endl;
>>      }
>>  }
>>}
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