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, 18 insertions, 0 deletions

diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index eb9a7e4d0f..0c1e1c2a6e 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -270,6 +270,24 @@ RBIMPL_ATTR_FORMAT(RBIMPL_PRINTF_FORMAT, 3, 0)
  */
 int ruby_vsnprintf(char *str, size_t n, char const *fmt, va_list ap);
 
+// TODO: doc
+
+#include <errno.h>
+
+int rb_errno(void);
+void rb_errno_set(int);
+int *rb_errno_ptr(void);
+
+static inline int *
+rb_orig_errno_ptr(void)
+{
+    return &errno;
+}
+
+#define rb_orig_errno errno
+#undef errno
+#define errno (*rb_errno_ptr())
+
 /** @cond INTERNAL_MACRO */
 #if RBIMPL_HAS_WARNING("-Wgnu-zero-variadic-macro-arguments")
 # /* Skip it; clang -pedantic doesn't like the following */