[openmp] [runtime] Use getloadavg() on NetBSD as well

[mgorny]

Summary

Switch NetBSD from reading /proc (which is broken) to getloadavg()
(which is already used by Darwin). NetBSD discourages using procfs
in favor of system API calls.

[mgorny]

runtime/src/z_Linux_util.cpp

2088

BTW this one doesn't seem to be used either. If you agree, I can send a separate change removing it as well.

[krytarowski]

The official core statement in NetBSD is to deprecate /proc. Can we switch to share code with KMP_OS_DARWIN? Are there any issues with it?

If there is need to count running threads, we shall use sysctl(3) to get the list of threads.

[krytarowski]

If there are any issues with getloadavg(3), I will prepare a sysctl(3)-based function.

[krytarowski]

I would leave intact the Linux code as it's used for sanity check.

[mgorny]

@krytarowski, updated as requested. FTR, this branch is using different rules for load-balancing apparently.

runtime/src/z_Linux_util.cpp

int __kmp_get_load_balance(int max) {
   DIR *task_dir = NULL; // Handle of "/proc/<pid>/task/<tid>/" directory.
   struct dirent *task_entry = NULL;
   int task_path_fixed_len;
 
   kmp_str_buf_t stat_path; // "/proc/<pid>/task/<tid>/stat" path.
   int stat_file = -1;
   int stat_path_fixed_len;
 
-  int total_processes = 0; // Total number of processes in system.
   int total_threads = 0; // Total number of threads in system.
 
   double call_time = 0.0;
 
   __kmp_str_buf_init(&task_path);
   __kmp_str_buf_init(&stat_path);
 
   __kmp_elapsed(&call_time);
 
int __kmp_get_load_balance(int max) {
   task_path_fixed_len = task_path.used; // Remember number of used characters.
 
   proc_entry = readdir(proc_dir);
   while (proc_entry != NULL) {
     // Proc entry is a directory and name starts with a digit. Assume it is a
     // process' directory.
     if (proc_entry->d_type == DT_DIR && isdigit(proc_entry->d_name[0])) {
 
-      ++total_processes;
-      // Make sure init process is the very first in "/proc", so we can replace
-      // strcmp( proc_entry->d_name, "1" ) == 0 with simpler total_processes ==
-      // 1. We are going to check that total_processes == 1 => d_name == "1" is
-      // true (where "=>" is implication). Since C++ does not have => operator,
-      // let us replace it with its equivalent: a => b == ! a || b.
-      KMP_DEBUG_ASSERT(total_processes != 1 ||
-                       strcmp(proc_entry->d_name, "1") == 0);
-
       // Construct task_path.
       task_path.used = task_path_fixed_len; // Reset task_path to "/proc/".
       __kmp_str_buf_cat(&task_path, proc_entry->d_name,
                         KMP_STRLEN(proc_entry->d_name));
       __kmp_str_buf_cat(&task_path, "/task", 5);
 
       task_dir = opendir(task_path.str);
       if (task_dir == NULL) {