M:N thread scheduler for Ractors

This patch introduce M:N thread scheduler for Ractor system.

In general, M:N thread scheduler employs N native threads (OS threads)
to manage M user-level threads (Ruby threads in this case).
On the Ruby interpreter, 1 native thread is provided for 1 Ractor
and all Ruby threads are managed by the native thread.

From Ruby 1.9, the interpreter uses 1:1 thread scheduler which means
1 Ruby thread has 1 native thread. M:N scheduler change this strategy.

Because of compatibility issue (and stableness issue of the implementation)
main Ractor doesn't use M:N scheduler on default. On the other words,
threads on the main Ractor will be managed with 1:1 thread scheduler.

There are additional settings by environment variables:

`RUBY_MN_THREADS=1` enables M:N thread scheduler on the main ractor.
Note that non-main ractors use the M:N scheduler without this
configuration. With this configuration, single ractor applications
run threads on M:1 thread scheduler (green threads, user-level threads).

`RUBY_MAX_CPU=n` specifies maximum number of native threads for
M:N scheduler (default: 8).

This patch will be reverted soon if non-easy issues are found.

[Bug #19842]

1 files changed, 7 insertions, 2 deletions

diff --git a/debug.c b/debug.c
index b65f368fbf..e84e3d602a 100644
--- a/debug.c
+++ b/debug.c
@@ -443,6 +443,10 @@ setup_debug_log(void)
                 (ruby_debug_log_mode & ruby_debug_log_memory) ? "[mem]" : "",
                 (ruby_debug_log_mode & ruby_debug_log_stderr) ? "[stderr]" : "",
                 (ruby_debug_log_mode & ruby_debug_log_file)   ? "[file]" : "");
+        if (debug_log.output_file[0]) {
+            fprintf(stderr, "RUBY_DEBUG_LOG filename=%s\n", debug_log.output_file);
+        }
+
         rb_nativethread_lock_initialize(&debug_log.lock);
 
         setup_debug_log_filter();
@@ -609,10 +613,11 @@ ruby_debug_log(const char *file, int line, const char *func_name, const char *fm
         // ractor information
         if (ruby_single_main_ractor == NULL) {
             rb_ractor_t *cr = th ? th->ractor : NULL;
+            rb_vm_t *vm = GET_VM();
 
             if (r && len < MAX_DEBUG_LOG_MESSAGE_LEN) {
-                r = snprintf(buff + len, MAX_DEBUG_LOG_MESSAGE_LEN - len, "\tr:#%d/%u",
-                             cr ? (int)rb_ractor_id(cr) : -1, GET_VM()->ractor.cnt);
+                r = snprintf(buff + len, MAX_DEBUG_LOG_MESSAGE_LEN - len, "\tr:#%d/%u (%u)",
+                             cr ? (int)rb_ractor_id(cr) : -1, vm->ractor.cnt, vm->ractor.sched.running_cnt);
 
                 if (r < 0) rb_bug("ruby_debug_log returns %d", r);
                 len += r;