get cpu time of an external process and it children while it still running on OS X

Question

On linux I can use /proc as stated in How to calculate the CPU usage of a process by PID in Linux from C? to get the cpu time of a process and it children.

How would I do this on OS X?

Answer 1

You can get process information using sysctl. So, let's assume that you have the pid for a process: -

#include <sys/sysctl.h>

struct kinfo_proc *getProcessInfo(pid_t pid)
{
    struct kinfo_proc* list = NULL;

    int mib[] = {CTL_KERN, KERN_PROC, KERN_PROC_PID, pid};
    size_t size = 0;

    sysctl(mib, sizeof(mib) / sizeof(*mib), NULL, &size, NULL, 0);

    list = (kinfo_proc*)malloc(size);
    sysctl(mib, sizeof(mib) / sizeof(*mib), list, &size, NULL, 0);

    return list;
}

Remember to check for errors returned from sysctl. I've left them out for brevity and don't forget to free the returned structure when you're finished with it.

The returned kinfo_proc structure contains a structure extern_proc, which you will see has the following attributes: -

struct extern_proc {
    union {
        struct {
            struct  proc *__p_forw; /* Doubly-linked run/sleep queue. */
            struct  proc *__p_back;
        } p_st1;
        struct timeval __p_starttime;   /* process start time */
    } p_un;

    ....
}

__p_starttime, is what you're looking for.