Android set thread affinity

Question

Following the answer from this StackOverflow question how do I create the proper integer for mask?

I made some googling and the everything I found uses CPU_SET macro from sched.h but it operates on cpu_set_t structures which are undefined when using NDK. When try using CPU_SET linker gives me undefined reference error (even though I link against pthread).

Answer 1

Well, in the end I found some version which was taken directly from sched.h. Im posting this here if anyone has the same problem and doesn't want to spend the time searching for it. This is quite useful.

#define CPU_SETSIZE 1024
#define __NCPUBITS  (8 * sizeof (unsigned long))
typedef struct
{
   unsigned long __bits[CPU_SETSIZE / __NCPUBITS];
} cpu_set_t;

#define CPU_SET(cpu, cpusetp) \
  ((cpusetp)->__bits[(cpu)/__NCPUBITS] |= (1UL << ((cpu) % __NCPUBITS)))
#define CPU_ZERO(cpusetp) \
  memset((cpusetp), 0, sizeof(cpu_set_t))

This works well when the parameter type in the original setCurrentThreadAffinityMask (from the post mentioned in the question) is simply replaced with cpu_set_t.

Answer 2

I would like to pay your attention that function from link in the first post doesn't set the thread cpu affinity. It suits to set the process cpu affinity. Of course, if you have one thread in your application it works well but it is wrong for several threads. Check up sched_setaffinity() description for example on http://linux.die.net/man/2/sched_setaffinity

Answer 3

Try add this before your include <sched.h>

#define _GNU_SOURCE