mrubyのProcess.forkがC言語からだとうまく動かない問題

forktest.c

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include "mruby.h"
#include "mruby/proc.h"
#include <mruby/compile.h>
#include <mruby/string.h>

mrb_value mrb_get_backtrace(mrb_state *mrb, mrb_value self);

int gCnt=0;
static mrb_value myfunc(mrb_state *mrb, mrb_value obj) {
        printf("myfunc: start\n");
        gCnt++;
        printf("myfunc: end\n");
        fflush(stdout);
        return mrb_nil_value();
}

int main() {
        FILE *f;
        struct RProc *blk;
        mrb_state *mrb;
        mrb_value val,proc;

        mrb = mrb_open();
        f = fopen("fork.rb", "r");
        mrb_load_file(mrb, f);
        fclose(f);
        fflush(stdout);
        blk = mrb_proc_new_cfunc(mrb, myfunc);
        proc = mrb_obj_value(blk);
        val = mrb_funcall_with_block(mrb, mrb_top_self(mrb), mrb_intern_cstr(mrb, "mymethod"), 0, NULL, proc);
        mrb_funcall(mrb,mrb_top_self(mrb),"p",1,proc);
        fflush(stdout);
        printf("gCnt = [%d]\n",gCnt);
        printf("next is forking..\n");
        val = mrb_funcall_with_block(mrb, mrb_obj_value(mrb_module_get(mrb, "Process")), mrb_intern_cstr(mrb, "fork"), 0, NULL, proc);
        if(mrb->exc) {
                mrb_value exc = mrb_obj_value(mrb->exc);
                // エラー内容を取得
                mrb_value backtrace = mrb_get_backtrace(mrb, exc);
                printf("%s",mrb_str_to_cstr(mrb, mrb_inspect(mrb, backtrace)));
                //
        }
        perror("check fork");
        fflush(stdout);
        mrb_funcall(mrb,mrb_top_self(mrb),"p",1,val);
        mrb_funcall(mrb,mrb_obj_value(mrb_module_get(mrb, "Process")),"waitpid",1,val);
        if(mrb->exc) {
                mrb_value exc = mrb_obj_value(mrb->exc);
                // [34m~B�[34m~C�[34m~C�[34m~F~E容[34m~B~R[34m~O~V[34m~W
                mrb_value backtrace = mrb_get_backtrace(mrb, exc);
                printf("%s",mrb_str_to_cstr(mrb, mrb_inspect(mrb, backtrace)));
        }
        printf("gCnt = [%d]\n",gCnt);
        return 0;
}

gistfile1.txt

def mymethod(&blk)
    p "Hello, this is mymethod."
      yield
      pid = Process.fork(&blk)
      Process.waitpid pid
end
mymethod {p "test"}

gistfile2.txt

./a.out        
"Hello, this is mymethod."
"test"
f_fork: I'm child
b is not nil
"test"
now child process is  exitting!
"Hello, this is mymethod."
myfunc: start
myfunc: end
f_fork: I'm child
b is not nil
#<Proc:0x7f891c025ae0>
gCnt = [1]
next is forking..
check fork: Undefined error: 0
56386
f_fork: I'm child
b is not nil
gCnt = [1]

process.c

static mrb_value
mrb_f_fork(mrb_state *mrb, mrb_value klass)
{
  mrb_value b, result;
  int pid;

  mrb_get_args(mrb, "&", &b);

  switch (pid = fork()) {
  case 0:
          printf("f_fork: I'm child\n");
    if (!mrb_nil_p(b)) {
            printf("b is not nil\n");
      mrb_yield(mrb, b, result);
      printf("now child process is  exitting!\n");
      fflush(stdout);
      _exit(0);
    }
    printf("oops b is nil!\n");
    return mrb_nil_value();

  case -1:
    mrb_sys_fail(mrb, "fork failed");
    return mrb_nil_value();

  default:
    return mrb_fixnum_value(pid);
  }
}