Another thread can not read main thread class and modules at mruby 3.0

[jakitliang]

When in child thread do some code with:

class AAA; end

Thread.new do
   a = AAA.new
end

Will tiggers:

undefined class/module 'AAA'

Maybe symbols are not beeing migrate?

[mattn]

This is limitation of mruby-thread. Thread is executed as separated VM instance. So you need to pass values to argument of constructor of the Thread.

mruby-thread/example/synchronize.rb

Line 5 in ff77afa

th = Thread.new(v, m) do |v, m|

[jakitliang]

This is limitation of mruby-thread. Thread is executed as separated VM instance. So you need to pass values to argument of constructor of the Thread.

I pass it to the argument but not works

[jakitliang]

I write this example:

class AAA; end

a = AAA.new

t = Thread.new(a) do |a|
  p a
end

Will triggers:

undefined class/module AAA (ArgumentError)
Abort trap: 6

[lemmuh]

What's missing is a migration of the newly generated module/class objects of the main thread (VM)

class A
end

Thread.new(Object.constants) do |constants|
  p constants - Object.constants
end

sleep 1

which will print

[:A, :ARGV]

Does anybody know how to migrate the module/class objects to the new thread (VM) ?

[dearblue]

(I've been probing at mruby/mruby#6077)

undefined class/module AAA (ArgumentError)
Abort trap: 6

This is because mrb_open() is called inside Thread.new, but class AAA is not defined at this time.
Classes, modules, and methods defined after mrb_open() are not defined on the new mruby state side, meaning they are not available.

The workaround I can think of is,

• Create own mrbgem so that class AAA is defined when performing mrb_open().
• Use a serializer such as mruby-marshal and pass it to Thread.new to deserialize the data after defining the class in the thread's block.
• Otherwise, mruby-thread needs to be extended.

---

Also, the reason for the SIGABRT is that the mruby state created by Thread.new does not catch the exception.
This is the same situation as calling mrb_raise() directly in the main() function.
It would be better to pass not only mrb2 variables but also mrb variables when calling path2class(), and mrb_raise() should be addressed to mrb.

mruby-thread/src/mrb_thread.c

Line 417 in ff77afa

c = path2class(mrb2, RSTRING_PTR(cls_path), RSTRING_LEN(cls_path));

mruby-thread/src/mrb_thread.c

Line 364 in ff77afa

mrb_raisef(M, mrb_class_get(M, "ArgumentError"), "undefined class/module %S",