Subj : Re: Per thread cpu-usage on Linux
To   : comp.programming.threads
From : Christoph Bartoschek
Date : Thu Feb 17 2005 10:58 am

David Schwartz wrote:

> 
> "John G. Shaw" <jshaw@localnet.com> wrote in message
> news:1117lllc05lhi4d@corp.supernews.com...
> 
>> The intent was to use the  pthread_getcpuclockid() function within a
>> running thread (i.e., a function invoked via pthread_create()). I'm a bit
>> surprised it even runs under the main program (I thought pthread_self()
>> would not be valid or even crash). I have used this approach successfully
>> on a parallel computer (SGI Altix series), and it seems to return the
>> thread's CPU time as opposed to "real time" in the thread. It's possible
>> that pthread_self() does not return a thread-dependent clock_id if it is
>> not invoked under a running pthread. It's also possible this may be a
>> system-dependent behaviour. SGI's linux has been significantly modified
>> from most others. (???)
> 
>     Does clock_gettime(CLOCK_THREAD_CPUTIME_ID, ...); work?
> 
>     DS

I've put the measurment in a separate thread and tried
CLOCK_THREAD_CPUTIME_ID. Both lead to the same results. 

extern "C" {
   #include <time.h>
   #include <sys/time.h>
   #include <sys/times.h>
   #include <sys/resource.h>
   #include <errno.h>
   #include <unistd.h>
   #include <pthread.h>
}

#include <iostream>

static double timespec_to_double(struct timespec &ts)
{
   const double ns_to_sec= 1.0e-9;
   double t= double(ts.tv_sec) + double(ts.tv_nsec)*ns_to_sec;
   return t;
}

extern "C" void * execute(void *)
{
   clockid_t clock_id;
   pthread_getcpuclockid(pthread_self(),&clock_id);
   struct timespec ts;
   //clock_gettime(clock_id,&ts);
   clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts);
   double cpuTime0= timespec_to_double(ts);

   for (int i = 0;i != 5; ++i)
   {
      sleep(1);
      //clock_gettime(clock_id,&ts);
      clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts);
      double cpuTime1= timespec_to_double(ts);
      std::cout << "Time: " << cpuTime1-cpuTime0 << std::endl;
   }
   return 0;
}

int main()
{
   pthread_t tid;
   pthread_create(&tid, 0, execute, 0);
   pthread_join(tid, 0);
}


[ponto@burns ponto]$ g++ thread.C -pedantic -Wall -W -g -pthread -lrt
[ponto@burns ponto]$ ./a.out
Time: 1.00561
Time: 2.05453
Time: 3.15841
Time: 4.16581
Time: 5.17434

.