support require in non-main Ractors

Many libraries should be loaded on the main ractor because of
setting constants with unshareable objects and so on.

This patch allows to call `requore` on non-main Ractors by
asking the main ractor to call `require` on it. The calling ractor
waits for the result of `require` from the main ractor.

If the `require` call failed with some reasons, an exception
objects will be deliverred from the main ractor to the calling ractor
if it is copy-able.

Same on `require_relative` and `require` by `autoload`.

Now `Ractor.new{pp obj}` works well (the first call of `pp` requires
`pp` library implicitly).

[Feature #20627]

Author: ko1

bootstraptest/test_ractor.rb

@@ -211,17 +211,6 @@
   Ractor.make_shareable(closure).call
 }
 
-# Now autoload in non-main Ractor is not supported
-assert_equal 'ok', %q{
-  autoload :Foo, 'foo.rb'
-  r = Ractor.new do
-    p Foo
-  rescue Ractor::UnsafeError
-    :ok
-  end
-  r.take
-}
-
 ###
 ###
 # Ractor still has several memory corruption so skip huge number of tests
@@ -1836,3 +1825,80 @@ class C8; def self.foo = 17; end
   shareable = Ractor.make_shareable("chilled")
   shareable == "chilled" && Ractor.shareable?(shareable)
 }
+
+# require in Ractor
+assert_equal 'true', %q{
+  Module.new do
+    def require feature
+      return Ractor._require(feature) unless Ractor.main?
+      super
+    end
+    Object.prepend self
+    set_temporary_name 'Ractor#require'
+  end
+
+  Ractor.new{
+    require 'benchmark'
+    Benchmark.measure{}
+  }.take.real > 0
+}
+
+# require_relative in Ractor
+assert_equal 'true', %q{
+  dummyfile = File.join(__dir__, "dummy#{rand}.rb")
+  return true if File.exist?(dummyfile)
+
+  begin
+    File.write dummyfile, ''
+  rescue Exception
+    # skip on any errors
+    return true
+  end
+
+  begin
+    Ractor.new dummyfile do |f|
+      require_relative File.basename(f)
+    end.take
+  ensure
+    File.unlink dummyfile
+  end
+}
+
+# require_relative in Ractor
+assert_equal 'LoadError', %q{
+  dummyfile = File.join(__dir__, "not_existed_dummy#{rand}.rb")
+  return true if File.exist?(dummyfile)
+
+  Ractor.new dummyfile do |f|
+    begin
+      require_relative File.basename(f)
+    rescue LoadError => e
+      e.class
+    end
+  end.take
+}
+
+# autolaod in Ractor
+assert_equal 'true', %q{
+  autoload :Benchmark, 'benchmark'
+
+  r = Ractor.new do
+    Benchmark.measure{}
+  end
+  r.take.real > 0
+}
+
+# failed in autolaod in Ractor
+assert_equal 'LoadError', %q{
+  dummyfile = File.join(__dir__, "not_existed_dummy#{rand}.rb")
+  autoload :Benchmark, dummyfile
+
+  r = Ractor.new do
+    begin
+      Benchmark.measure{}
+    rescue LoadError => e
+      e.class
+    end
+  end
+  r.take
+}

load.c

@@ -18,6 +18,7 @@
 #include "darray.h"
 #include "ruby/encoding.h"
 #include "ruby/util.h"
+#include "ractor_core.h"
 
 static VALUE ruby_dln_libmap;
 
@@ -1383,17 +1384,25 @@ static VALUE
 rb_require_string_internal(VALUE fname, bool resurrect)
 {
     rb_execution_context_t *ec = GET_EC();
-    int result = require_internal(ec, fname, 1, RTEST(ruby_verbose));
 
-    if (result > TAG_RETURN) {
-        EC_JUMP_TAG(ec, result);
-    }
-    if (result < 0) {
+    // main ractor check
+    if (!rb_ractor_main_p()) {
         if (resurrect) fname = rb_str_resurrect(fname);
-        load_failed(fname);
+        return rb_ractor_require(fname);
     }
+    else {
+        int result = require_internal(ec, fname, 1, RTEST(ruby_verbose));
+
+        if (result > TAG_RETURN) {
+            EC_JUMP_TAG(ec, result);
+        }
+        if (result < 0) {
+            if (resurrect) fname = rb_str_resurrect(fname);
+            load_failed(fname);
+        }
 
-    return RBOOL(result);
+        return RBOOL(result);
+    }
 }
 
 VALUE