コード

stackswap.h

# ifndef STACKSWAP_H
# define STACKSWAP_H
# include "ruby/ruby.h"

# ifdef DEVELOP
# define DEBUG(...)						\
  do {								\
    printf("%-22s %-32s%4u: ", __FILE__, __func__, __LINE__);	\
    printf(__VA_ARGS__);					\
    printf("\n");						\
  } while(0)
# define RDEBUG(...)							\
  do {									\
    printf("\x1B[31m%-22s %-32s%4u: ", __FILE__, __func__, __LINE__);	\
    printf(__VA_ARGS__);						\
    printf("\x1B[0m\n");						\
  } while(0)
# else
# define DEBUG(...) do{}while(0)
# define RDEBUG(...) do{}while(0)
# endif


# if __GNUC__ >= 3
# define likely(x)	__builtin_expect(!!(x), 1)
# define unlikely(x)	__builtin_expect(!!(x), 0)
# else
# define likely(x) (x)
# define unlikely(x) (x)
# endif

typedef struct rb_thread_struct {
  VALUE self;
  VALUE vm;

  /* execution information */
  VALUE *stack;		/* must free, must mark */
  size_t stack_size;          /* size in word (byte size / sizeof(VALUE)) */
  VALUE cfp;
  int safe_level;
  int raised_flag;
  VALUE last_status; /* $? */

  /* passing state */
  int state;

  int waiting_fd;

  /* for rb_iterate */
  VALUE passed_block;

  /* for bmethod */
  VALUE passed_me;

  /* for cfunc */
  VALUE passed_ci;

  /* for load(true) */
  VALUE top_self;
  VALUE top_wrapper;

  /* eval env */
  VALUE base_block;

  VALUE *root_lep;
  VALUE root_svar;

  /* thread control */
  VALUE thread_id;
  VALUE status;
  int to_kill;
  int priority;

  VALUE native_thread_data;
  void *blocking_region_buffer;

  VALUE thgroup;
  VALUE value;

  /* temporary place of errinfo */
  VALUE errinfo;

  /* temporary place of retval on OPT_CALL_THREADED_CODE */
# if OPT_CALL_THREADED_CODE
  VALUE retval;
# endif

  /* async errinfo queue */
  VALUE pending_interrupt_queue;
  int pending_interrupt_queue_checked;
  VALUE pending_interrupt_mask_stack;

  VALUE interrupt_flag;
  unsigned long interrupt_mask;
  VALUE interrupt_lock;
  VALUE interrupt_cond;
  VALUE unblock;
  VALUE locking_mutex;
  VALUE  keeping_mutexes;

  VALUE tag;
  VALUE protect_tag;

  /*! Thread-local state of evaluation context.
   *
   *  If negative, this thread is evaluating the main program.
   *  If positive, this thread is evaluating a program under Kernel::eval
   *  family.
   */
  int parse_in_eval;

  /*! Thread-local state of compiling context.
   *
   * If non-zero, the parser does not automatically print error messages to
   * stderr. */
  int mild_compile_error;

  /* storage */
  VALUE local_storage;

  VALUE join_list;

  VALUE first_proc;
  VALUE first_args;
  VALUE (*first_func)(ANYARGS);

  /* for GC */
  VALUE *machine_stack_start;
  VALUE *machine_stack_end;
  size_t machine_stack_maxsize;
# ifdef __ia64
  VALUE *machine_register_stack_start;
  VALUE *machine_register_stack_end;
  size_t machine_register_stack_maxsize;
# endif
  VALUE machine_regs;
  int mark_stack_len;

  /* statistics data for profiler */
  VALUE stat_insn_usage;

  /* tracer */
  VALUE event_hooks;
  VALUE trace_arg; /* trace information */

  /* fiber */
  VALUE fiber;
  VALUE root_fiber;
  VALUE root_jmpbuf;

  /* misc */
  int method_missing_reason;
  int abort_on_exception;
# ifdef USE_SIGALTSTACK
  void *altstack;
# endif
  unsigned long running_time_us;
} rb_thread_t;

# endif

stackswap.c

# inlude "stackswap.h"

static VALUE
stackswap(VALUE self)
{
  rb_thread_t *_th;
  _th = (rb_thread_t*)rb_thread_current();
  // _th->stack とかでstackを参照
  return Qnil;
}

void
Init_stackswap(void)
{
  Stackswap = rb_define_module("Stackswap");
  rb_define_module_function(Stackswap, "stackswap", stackswap, 0);
}

Rakefileとかextconf.rbは省略します。

キモはrb_thread_tとrb_thread_current()で、前者はRubyのthreadを扱うための構造体、後者は現在のthreadをVALUEで取得する、RubyレベルでいうとThread.currentと等価なものです。

rb_thread_tはC APIとして提供してないので自前で用意してやる必要があります、また実際はrb_thread_t構造体の中でまた色々Ruby本体でごにょごにょあるんですが、はしょって全部VALUEで置き換えてます。まあ必要になったら都度用意する感じで。

まああとはstackを切り替えてオレオレ継続作ったりして遊んだりできっかな～、って感じですね。