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, 2 insertions, 2 deletions

diff --git a/dir.c b/dir.c
index 9c9f594a78..21b1acada3 100644
--- a/dir.c
+++ b/dir.c
@@ -805,7 +805,7 @@ dir_read(VALUE dir)
     struct dirent *dp;
 
     GetDIR(dir, dirp);
-    errno = 0;
+    rb_errno_set(0);
     if ((dp = READDIR(dirp->dir, dirp->enc)) != NULL) {
         return rb_external_str_new_with_enc(dp->d_name, NAMLEN(dp), dirp->enc);
     }
@@ -1723,7 +1723,7 @@ nogvl_opendir_at(void *ptr)
             /* fallthrough*/
           case 0:
             if (fd >= 0) close(fd);
-            errno = e;
+            rb_errno_set(e);
         }
     }
 #else  /* !USE_OPENDIR_AT */