mrb_gc_register() may cause GC and collect the object being protected

[catsidhe]

mrb_gc_register() calls mrb_ary_new() or mrb_ary_push() - both of which may trigger garbage collection (always triggers in case of MRB_GC_STRESS), which in turn could reclaim the object we're trying to push to GC_ROOT_SYM.

[dearblue]

A simple workaround is to reserve it before the critical section (not only for mruby).
An example using mrb_top_self(mrb) is shown below.

mrb_gc_register(mrb, mrb_top_self(mrb));    // RESERVED!

mrb_value need_protect = ...;
mrb_gc_unregister(mrb, mrb_top_self(mrb));  // RESTORE!
mrb_gc_register(mrb, need_protect);

However, this will keep squeezing memory if an exception occurs at the need_protect = ....
You may need to use mrb_protect_error() as well.

[matz]

I tried to address this issue. If it still causes problems, reopen this issue.