micro-optimization in (web server)

[bpt/guile.git] / libguile / control.c

/* Copyright (C) 2010, 2011, 2012  Free Software Foundation, Inc.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 3 of
 * the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301 USA
 */

#if HAVE_CONFIG_H
#  include <config.h>
#endif

#include <alloca.h>

#include "libguile/_scm.h"
#include "libguile/control.h"
#include "libguile/objcodes.h"
#include "libguile/instructions.h"
#include "libguile/vm.h"

\f

#define PROMPT_ESCAPE_P(p)                              \
  (SCM_DYNSTACK_TAG_FLAGS (SCM_DYNSTACK_TAG (p))        \
   & SCM_F_DYNSTACK_PROMPT_ESCAPE_ONLY)

\f


scm_t_prompt_registers*
scm_c_make_prompt_registers (SCM *fp, SCM *sp, scm_t_uint8 *abort_ip,
                             scm_t_int64 vm_cookie)
{
  scm_t_prompt_registers *regs;

  regs = scm_gc_malloc_pointerless (sizeof (*regs), "prompt registers");
  regs->fp = fp;
  regs->sp = sp;
  regs->ip = abort_ip;
  regs->cookie = vm_cookie;

  return regs;
}

/* Only to be called if the SCM_I_SETJMP returns 1 */
SCM
scm_i_prompt_pop_abort_args_x (SCM vm)
{
  size_t i, n;
  SCM vals = SCM_EOL;

  n = scm_to_size_t (SCM_VM_DATA (vm)->sp[0]);
  for (i = 0; i < n; i++)
    vals = scm_cons (SCM_VM_DATA (vm)->sp[-(i + 1)], vals);

  /* The abort did reset the VM's registers, but then these values
     were pushed on; so we need to pop them ourselves. */
  SCM_VM_DATA (vm)->sp -= n + 1;
  /* FIXME NULLSTACK */

  return vals;
}


#ifdef WORDS_BIGENDIAN
#define OBJCODE_HEADER(main,meta) 0, 0, 0, main, 0, 0, 0, meta+8
#define META_HEADER(meta)         0, 0, 0, meta, 0, 0, 0, 0
#else
#define OBJCODE_HEADER(main,meta) main, 0, 0, 0, meta+8, 0, 0, 0
#define META_HEADER(meta)         meta, 0, 0, 0, 0,      0, 0, 0
#endif

#define OBJCODE_TAG SCM_MAKE_OBJCODE_TAG (SCM_OBJCODE_TYPE_STATIC, 0)

#if defined (SCM_ALIGNED)
#define SCM_DECLARE_STATIC_ALIGNED_ARRAY(type, sym)     \
static const type sym[]
#define SCM_STATIC_ALIGNED_ARRAY(alignment, type, sym)  \
static SCM_ALIGNED (alignment) const type sym[]
#define SCM_STATIC_OBJCODE(sym)                                         \
  SCM_DECLARE_STATIC_ALIGNED_ARRAY (scm_t_uint8, sym##__bytecode);      \
  SCM_STATIC_ALIGNED_ARRAY (8, scm_t_cell, sym##__cells) = {            \
    { SCM_PACK (OBJCODE_TAG), SCM_PACK (sym##__bytecode) },             \
    { SCM_BOOL_F, SCM_PACK (0) }                                        \
  };                                                                    \
  static const SCM sym = SCM_PACK (sym##__cells);                       \
  SCM_STATIC_ALIGNED_ARRAY (8, scm_t_uint8, sym##__bytecode)
#else
#define SCM_STATIC_OBJCODE(sym)                                         \
static SCM sym;                                                         \
static scm_t_uint8 *sym##_bytecode;                                     \
SCM_SNARF_INIT(sym##_bytecode = scm_gc_malloc_pointerless (sizeof(sym##_bytecode__unaligned), "partial continuation stub"); \
               memcpy (sym##_bytecode, sym##_bytecode__unaligned, sizeof(sym##_bytecode__unaligned));) \
SCM_SNARF_INIT(sym = scm_double_cell (OBJCODE_TAG,                      \
                                      (scm_t_bits)sym##_bytecode,       \
                                      SCM_UNPACK (SCM_BOOL_F),          \
                                      0);)                              \
static const scm_t_uint8 sym##_bytecode__unaligned[]
#endif


SCM_STATIC_OBJCODE (cont_objcode) = {
  /* Like in continuations.c, but with partial-cont-call. */
  OBJCODE_HEADER (8, 19),
  /* leave args on the stack */
  /* 0 */ scm_op_object_ref, 0, /* push scm_vm_cont object */
  /* 2 */ scm_op_partial_cont_call, /* and go! */
  /* 3 */ scm_op_nop,
  /* 4 */ scm_op_nop, scm_op_nop, scm_op_nop, scm_op_nop, /* pad to 8 bytes */
  /* 8 */

  /* We could put some meta-info to say that this proc is a continuation. Not sure
     how to do that, though. */
  META_HEADER (19),
  /* 0 */ scm_op_make_eol, /* bindings */
  /* 1 */ scm_op_make_eol, /* sources */
  /* 2 */ scm_op_make_int8, 0, scm_op_make_int8, 3, /* arity: from ip 0 to ip 3 */
  /* 6 */ scm_op_make_int8_0, /* the arity is 0 required args */
  /* 7 */ scm_op_make_int8_0, /* 0 optionals */
  /* 8 */ scm_op_make_true, /* and a rest arg */
  /* 9 */ scm_op_list, 0, 5, /* make a list of those 5 vals */
  /* 12 */ scm_op_list, 0, 1, /* and the arities will be a list of that one list */
  /* 15 */ scm_op_list, 0, 3, /* pack bindings, sources, and arities into list */
  /* 18 */ scm_op_return /* and return */
  /* 19 */
};


static SCM
reify_partial_continuation (SCM vm, scm_t_prompt_registers *regs,
                            scm_t_dynstack *dynstack,
                            scm_t_int64 cookie)
{
  SCM vm_cont, ret;
  scm_t_uint32 flags;

  flags = SCM_F_VM_CONT_PARTIAL;
  if (cookie >= 0 && regs->cookie == cookie)
    flags |= SCM_F_VM_CONT_REWINDABLE;

  /* Since non-escape continuations should begin with a thunk application, the
     first bit of the stack should be a frame, with the saved fp equal to the fp
     that was current when the prompt was made. */
  if ((SCM*)SCM_UNPACK (regs->sp[1]) != regs->fp)
    abort ();

  /* Capture from the top of the thunk application frame up to the end. Set an
     MVRA only, as the post-abort code is in an MV context. */
  vm_cont = scm_i_vm_capture_stack (regs->sp + 4,
                                    SCM_VM_DATA (vm)->fp,
                                    SCM_VM_DATA (vm)->sp,
                                    NULL,
                                    SCM_VM_DATA (vm)->ip,
                                    dynstack,
                                    flags);

  ret = scm_make_program (cont_objcode,
                          scm_c_make_vector (1, vm_cont),
                          SCM_BOOL_F);
  SCM_SET_CELL_WORD_0 (ret,
                       SCM_CELL_WORD_0 (ret) | SCM_F_PROGRAM_IS_PARTIAL_CONTINUATION);
  return ret;
}

void
scm_c_abort (SCM vm, SCM tag, size_t n, SCM *argv, scm_t_int64 cookie)
{
  SCM cont;
  scm_t_dynstack *dynstack = &SCM_I_CURRENT_THREAD->dynstack;
  scm_t_bits *prompt;
  scm_t_prompt_registers *regs;
  scm_t_dynstack_prompt_flags flags;
  size_t i;

  prompt = scm_dynstack_find_prompt (dynstack, tag, &regs, &flags);

  if (!prompt)
    scm_misc_error ("abort", "Abort to unknown prompt", scm_list_1 (tag));

  /* Only reify if the continuation referenced in the handler. */
  if (flags & SCM_F_DYNSTACK_PROMPT_ESCAPE_ONLY)
    cont = SCM_BOOL_F;
  else
    {
      scm_t_dynstack *captured;

      captured = scm_dynstack_capture (dynstack, SCM_DYNSTACK_NEXT (prompt));
      cont = reify_partial_continuation (vm, regs, captured, cookie);
    }

  /* Unwind.  */
  scm_dynstack_unwind (dynstack, prompt);

  /* Unwinding may have changed the current thread's VM, so use the
     new one.  */
  vm = scm_the_vm ();

  /* Restore VM regs */
  SCM_VM_DATA (vm)->fp = regs->fp;
  SCM_VM_DATA (vm)->sp = regs->sp;
  SCM_VM_DATA (vm)->ip = regs->ip;

  /* Since we're jumping down, we should always have enough space.  */
  if (SCM_VM_DATA (vm)->sp + n + 1 >= SCM_VM_DATA (vm)->stack_limit)
    abort ();

  /* Push vals */
  *(++(SCM_VM_DATA (vm)->sp)) = cont;
  for (i = 0; i < n; i++)
    *(++(SCM_VM_DATA (vm)->sp)) = argv[i];
  *(++(SCM_VM_DATA (vm)->sp)) = scm_from_size_t (n+1); /* +1 for continuation */

  /* Jump! */
  SCM_I_LONGJMP (regs->regs, 1);

  /* Shouldn't get here */
  abort ();
}

SCM_DEFINE (scm_at_abort, "@abort", 2, 0, 0, (SCM tag, SCM args),
            "Abort to the nearest prompt with tag @var{tag}.")
#define FUNC_NAME s_scm_at_abort
{
  SCM *argv;
  size_t i;
  long n;

  SCM_VALIDATE_LIST_COPYLEN (SCM_ARG2, args, n);
  argv = alloca (sizeof (SCM)*n);
  for (i = 0; i < n; i++, args = scm_cdr (args))
    argv[i] = scm_car (args);

  scm_c_abort (scm_the_vm (), tag, n, argv, -1);

  /* Oh, what, you're still here? The abort must have been reinstated. Actually,
     that's quite impossible, given that we're already in C-land here, so...
     abort! */

  abort ();
}
#undef FUNC_NAME

void
scm_init_control (void)
{
#include "libguile/control.x"
}

/*
  Local Variables:
  c-file-style: "gnu"
  End:
*/