From: "Marc-André Cournoyer" <macournoyer@...>
Date: 2008-04-16T23:46:39+09:00
Subject: How to get number of active threads in C ?

Hi all,

I'm writing a Ruby C extension and I need a fast way to get the number  
of active threads. I got something working for 1.8.6 but it's not  
portable to other Ruby version like 1.9 (because I can't include the  
header for rb_thread_t struct and the like) and it doesn't look very  
sane.

Here's my code for Ruby 1.8.6:

   #include "node.h"
   ...

   rb_thread_t mainth = (rb_thread_t) RDATA(rb_thread_main())->data;
   rb_thread_t th     = mainth;
   size_t      num_threads    = 0;

   do {
     th = th->next;
     if (th->status != THREAD_KILLED)
       num_threads ++;
   } while (th != mainth);

   printf("%d active threads\n", num_threads);

I'm wondering if there's a better way to do this. I know there's the  
rb_thread_list, but I would like to avoid creating a new Ruby Array on  
each call.

Any suggestion?
thx,
Marc