076continuation.cc « 1.vm « archive - mu - Soul of a tiny new machine. More thorough tests → More comprehensible and rewrite-friendly software → More resilient society.

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<a href='https://github.com/akkartik/mu/blob/master/053new-segment.subx'>https://github.com/akkartik/mu/blob/master/053new-segment.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Create a new segment (pool of memory for allocating chunks from) in the form</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment"># of an *allocation descriptor* that can be passed to the memory allocator</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment"># (defined in a later layer).</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment">#</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># Currently an allocation descriptor consists of just the bounds of the pool of</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># available memory:</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment">#</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment">#   curr : address</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxComment">#   end : address</span>
<span id="L10" class="LineNr">10 </span><span class="subxComment">#</span>
<span id="L11" class="LineNr">11 </span><span class="subxComment"># This isn't enough information to reclaim individual allocations. We can't</span>
<span id="L12" class="LineNr">12 </span><span class="subxComment"># support arbitrary reclamation yet.</span>
<span id="L13" class="LineNr">13 </span>
<span id="L14" class="LineNr">14 </span>== code
<span id="L15" class="LineNr">15 </span><span class="subxComment">#   instruction                     effective address                                                   register    displacement    immediate</span>
<span id="L16" class="LineNr">16 </span><span class="subxS1Comment"># . op          subop               mod             rm32          base        index         scale       r32</span>
<span id="L17" class="LineNr">17 </span><span class="subxS1Comment"># . 1-3 bytes   3 bits              2 bits          3 bits        3 bits      3 bits        2 bits      2 bits      0/1/2/4 bytes   0/1/2/4 bytes</span>
<span id="L18" class="LineNr">18 </span>
<span id="L19" class="LineNr">19 </span><span class="SpecialChar">Entry</span>:   <span class="subxComment"># manual test</span>
<span id="L20" class="LineNr">20 </span>    <span class="subxComment"># var ad/ECX : (address allocation-descriptor) = {0, 0}</span>
<span id="L21" class="LineNr">21 </span>    68/push  0/imm32/limit
<span id="L22" class="LineNr">22 </span>    68/push  0/imm32/curr
<span id="L23" class="LineNr">23 </span>    89/copy                         3/mod/direct    1/rm32/ECX   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          4/r32/ESP  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy ESP to ECX</span>
<span id="L24" class="LineNr">24 </span>    <span class="subxComment"># new-segment(0x1000, ad)</span>
<span id="L25" class="LineNr">25 </span>    <span class="subxS2Comment"># . . push args</span>
<span id="L26" class="LineNr">26 </span>    51/push-ECX
<span id="L27" class="LineNr">27 </span>    68/push  0x1000/imm32
<span id="L28" class="LineNr">28 </span>    <span class="subxS2Comment"># . . call</span>
<span id="L29" class="LineNr">29 </span>    e8/call  <a href='053new-segment.subx.html#L41'>new-segment</a>/disp32
<span id="L30" class="LineNr">30 </span>    <span class="subxS2Comment"># . . discard args</span>
<span id="L31" class="LineNr">31 </span>    81          0/subop/add         3/mod/direct    4/rm32/ESP   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>         <span class="Normal"> . </span>         <span class="Normal"> . </span>              8/imm32           <span class="subxComment"># add to ESP</span>
<span id="L32" class="LineNr">32 </span>    <span class="subxComment"># EAX = ad-&gt;curr</span>
<span id="L33" class="LineNr">33 </span>    8b/copy                         0/mod/indirect  1/rm32/ECX   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          0/r32/EAX  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy *ECX to EAX</span>
<span id="L34" class="LineNr">34 </span>    <span class="subxComment"># write to *EAX to check that we have access to the newly-allocated segment</span>
<span id="L35" class="LineNr">35 </span>    c7          0/subop/copy        0/mod/direct    0/rm32/EAX   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>         <span class="Normal"> . </span>         <span class="Normal"> . </span>              0x34/imm32        <span class="subxComment"># copy to *EAX</span>
<span id="L36" class="LineNr">36 </span>    <span class="subxComment"># syscall(exit, EAX)</span>
<span id="L37" class="LineNr">37 </span>    89/copy                         3/mod/direct    3/rm32/EBX   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          0/r32/EAX  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy EAX to EBX</span>
<span id="L38" class="LineNr">38 </span>    b8/copy-to-EAX  1/imm32/exit
<span id="L39" class="LineNr">39 </span>    cd/syscall  0x80/imm8
<span id="L40" class="LineNr">40 </span>
<span id="L41" class="LineNr">41 </span><span class="subxFunction">new-segment</span>:  <span class="subxComment"># len : int, ad : (address allocation-descriptor)</span>
<span id="L42" class="LineNr">42 </span>    <span class="subxS1Comment"># . prolog</span>
<span id="L43" class="LineNr">43 </span>    55/push-EBP
<span id="L44" class="LineNr">44 </span>    89/copy                         3/mod/direct    5/rm32/EBP   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          4/r32/ESP  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy ESP to EBP</span>
<span id="L45" class="LineNr">45 </span>    <span class="subxS1Comment"># . save registers</span>
<span id="L46" class="LineNr">46 </span>    50/push-EAX
<span id="L47" class="LineNr">47 </span>    53/push-EBX
<span id="L48" class="LineNr">48 </span>    <span class="subxComment"># copy len to _mmap-new-segment-&gt;len</span>
<span id="L49" class="LineNr">49 </span>    8b/copy                         1/mod/*+disp8   5/rm32/EBP   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          0/r32/EAX   8/disp8        <span class="Normal"> . </span>                <span class="subxComment"># copy *(EBP+8) to EAX</span>
<span id="L50" class="LineNr">50 </span>    89/copy                         0/mod/indirect  5/rm32/.disp32           <span class="Normal"> . </span>           <span class="Normal"> . </span>          0/r32/EAX   <a href='053new-segment.subx.html#L75'>_mmap-new-segment</a>:len/disp32      <span class="subxComment"># copy EAX to *_mmap-new-segment:len</span>
<span id="L51" class="LineNr">51 </span>    <span class="subxComment"># mmap(_mmap-new-segment)</span>
<span id="L52" class="LineNr">52 </span>    bb/copy-to-EBX  <a href='053new-segment.subx.html#L75'>_mmap-new-segment</a>/imm32
<span id="L53" class="LineNr">53 </span>    b8/copy-to-EAX  0x5a/imm32/mmap
<span id="L54" class="LineNr">54 </span>    cd/syscall  0x80/imm8
<span id="L55" class="LineNr">55 </span>    <span class="subxComment"># copy {EAX, EAX+len} to *ad</span>
<span id="L56" class="LineNr">56 </span>    <span class="subxS1Comment"># . EBX = ad</span>
<span id="L57" class="LineNr">57 </span>    8b/copy                         1/mod/*+disp8   5/rm32/EBP   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          3/r32/EBX   0xc/disp8      <span class="Normal"> . </span>                <span class="subxComment"># copy *(EBP+12) to EBX</span>
<span id="L58" class="LineNr">58 </span>    <span class="subxS1Comment"># . *EBX = EAX</span>
<span id="L59" class="LineNr">59 </span>    89/copy                         0/mod/indirect  3/rm32/EBX   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          0/r32/EAX  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy EAX to *EBX</span>
<span id="L60" class="LineNr">60 </span>    <span class="subxS1Comment"># . *(EBX+4) = EAX+len</span>
<span id="L61" class="LineNr">61 </span>    03/add                          1/mod/*+disp8   5/rm32/EBP   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          0/r32/EAX   8/disp8        <span class="Normal"> . </span>                <span class="subxComment"># add *(EBP+8) to EAX</span>
<span id="L62" class="LineNr">62 </span>    89/copy                         1/mod/*+disp8   3/rm32/EBX   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          0/r32/EAX   4/disp8        <span class="Normal"> . </span>                <span class="subxComment"># copy EAX to *(EBX+4)</span>
<span id="L63" class="LineNr">63 </span><span class="Constant">$new-segment:end</span>:
<span id="L64" class="LineNr">64 </span>    <span class="subxS1Comment"># . restore registers</span>
<span id="L65" class="LineNr">65 </span>    5b/pop-to-EBX
<span id="L66" class="LineNr">66 </span>    58/pop-to-EAX
<span id="L67" class="LineNr">67 </span>    <span class="subxS1Comment"># . epilog</span>
<span id="L68" class="LineNr">68 </span>    89/copy                         3/mod/direct    4/rm32/ESP   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          5/r32/EBP  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy EBP to ESP</span>
<span id="L69" class="LineNr">69 </span>    5d/pop-to-EBP
<span id="L70" class="LineNr">70 </span>    c3/return
<span id="L71" class="LineNr">71 </span>
<span id="L72" class="LineNr">72 </span>== data
<span id="L73" class="LineNr">73 </span>
<span id="L74" class="LineNr">74 </span><span class="subxComment"># various constants used here were found in the Linux sources (search for file mman-common.h)</span>
<span id="L75" class="LineNr">75 </span><span class="subxMinorFunction">_mmap-new-segment</span>:  <span class="subxComment"># type mmap_arg_struct</span>
<span id="L76" class="LineNr">76 </span>    <span class="subxComment"># addr</span>
<span id="L77" class="LineNr">77 </span>    0/imm32
<span id="L78" class="LineNr">78 </span><span class="subxMinorFunction">_mmap-new-segment:len</span>:
<span id="L79" class="LineNr">79 </span>    <span class="subxComment"># len</span>
<span id="L80" class="LineNr">80 </span>    0/imm32
<span id="L81" class="LineNr">81 </span>    <span class="subxComment"># protection flags</span>
<span id="L82" class="LineNr">82 </span>    3/imm32  <span class="subxComment"># PROT_READ | PROT_WRITE</span>
<span id="L83" class="LineNr">83 </span>    <span class="subxComment"># sharing flags</span>
<span id="L84" class="LineNr">84 </span>    0x22/imm32  <span class="subxComment"># MAP_PRIVATE | MAP_ANONYMOUS</span>
<span id="L85" class="LineNr">85 </span>    <span class="subxComment"># fd</span>
<span id="L86" class="LineNr">86 </span>    -1/imm32  <span class="subxComment"># since MAP_ANONYMOUS is specified</span>
<span id="L87" class="LineNr">87 </span>    <span class="subxComment"># offset</span>
<span id="L88" class="LineNr">88 </span>    0/imm32  <span class="subxComment"># since MAP_ANONYMOUS is specified</span>
<span id="L89" class="LineNr">89 </span>
<span id="L90" class="LineNr">90 </span><span class="subxS2Comment"># . . vim&#0058;nowrap:textwidth=0</span>
</pre>
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<!-- vim: set foldmethod=manual : -->

ss="o">->calls.front().continuation_mark_tag = current_instruction().ingredients.at(0).value;
  Current_routine->calls.push_front(call(ingredients.at(1).at(0)));
  // drop the mark
  caller_instruction.ingredients.erase(caller_instruction.ingredients.begin());
  ingredients.erase(ingredients.begin());
  // drop the callee
  caller_instruction.ingredients.erase(caller_instruction.ingredients.begin());
  ingredients.erase(ingredients.begin());
  finish_call_housekeeping(caller_instruction, ingredients);
  continue;
}

:(code)
void test_next_ingredient_inside_continuation() {
  run(
      "recipe main [\n"
      "  call-with-continuation-mark 233/mark, f, true\n"
      "]\n"
      "recipe f [\n"
      "  10:bool <- next-input\n"
      "]\n"
  );
  CHECK_TRACE_CONTENTS(
      "mem: storing 1 in location 10\n"
  );
}

void test_delimited_continuation_out_of_recipe_variable() {
  run(
      "recipe main [\n"
      "  x:recipe <- copy f\n"
      "  call-with-continuation-mark 233/mark, x, true\n"
      "]\n"
      "recipe f [\n"
      "  10:bool <- next-input\n"
      "]\n"
  );
  CHECK_TRACE_CONTENTS(
      "mem: storing 1 in location 10\n"
  );
}

//: save the slice of current call stack until the 'call-with-continuation-mark'
//: call, and return it as the result.
//: todo: implement delimited continuations in Mu's memory
:(before "End Types")
struct delimited_continuation {
  call_stack frames;
  int nrefs;
  delimited_continuation(call_stack::iterator begin, call_stack::iterator end) :frames(call_stack(begin, end)), nrefs(0) {}
};
:(before "End Globals")
map<long long int, delimited_continuation> Delimited_continuation;
long long int Next_delimited_continuation_id = 1;  // 0 is null just like an address
:(before "End Reset")
Delimited_continuation.clear();
Next_delimited_continuation_id = 1;

:(before "End Primitive Recipe Declarations")
RETURN_CONTINUATION_UNTIL_MARK,
:(before "End Primitive Recipe Numbers")
Recipe_ordinal["return-continuation-until-mark"] = RETURN_CONTINUATION_UNTIL_MARK;
:(before "End Primitive Recipe Checks")
case RETURN_CONTINUATION_UNTIL_MARK: {
  if (inst.ingredients.empty()) {
    raise << maybe(get(Recipe, r).name) << "'" << to_original_string(inst) << "' requires at least one ingredient: a mark tag (number)\n" << end();
  }
  break;
}
:(before "End Primitive Recipe Implementations")
case RETURN_CONTINUATION_UNTIL_MARK: {
  // I don't know how to think about next-ingredient in combination with
  // continuations, so seems cleaner to just kill it. Functions have to read
  // their inputs before ever returning a continuation.
  Current_routine->calls.front().ingredient_atoms.clear();
  Current_routine->calls.front().next_ingredient_to_process = 0;
  // copy the current call stack until the most recent marked call
  call_stack::iterator find_base_of_continuation(call_stack&, int);  // manual prototype containing '::'
  call_stack::iterator base = find_base_of_continuation(Current_routine->calls, /*mark tag*/current_instruction().ingredients.at(0).value);
  if (base == Current_routine->calls.end()) {
    raise << maybe(current_recipe_name()) << "couldn't find a 'call-with-continuation-mark' to return to with tag " << current_instruction().ingredients.at(0).original_string << '\n' << end();
    raise << maybe(current_recipe_name()) << "call stack:\n" << end();
    for (call_stack::iterator p = Current_routine->calls.begin();  p != Current_routine->calls.end();  ++p)
      raise << maybe(current_recipe_name()) << "  " << get(Recipe, p->running_recipe).name << '\n' << end();
    break;
  }
  trace(Callstack_depth+1, "run") << "creating continuation " << Next_delimited_continuation_id << end();
  put(Delimited_continuation, Next_delimited_continuation_id, delimited_continuation(Current_routine->calls.begin(), base));
  while (Current_routine->calls.begin() != base) {
    --Callstack_depth;
    assert(Callstack_depth >= 0);
    Current_routine->calls.pop_front();
  }
  // return it as the result of the marked call
  products.resize(1);
  products.at(0).push_back(Next_delimited_continuation_id);
  // return any other ingredients passed in
  copy(/*skip mark tag*/++ingredients.begin(), ingredients.end(), inserter(products, products.end()));
  ++Next_delimited_continuation_id;
  break;  // continue to process rest of marked call
}

:(code)
call_stack::iterator find_base_of_continuation(call_stack& c, int mark_tag) {
  for (call_stack::iterator p = c.begin(); p != c.end(); ++p)
    if (p->continuation_mark_tag == mark_tag) return p;
  return c.end();
}

//: overload 'call' for continuations
:(after "Begin Call")
if (is_mu_continuation(current_instruction().ingredients.at(0))) {
  // copy multiple calls on to current call stack
  assert(scalar(ingredients.at(0)));
  trace(Callstack_depth+1, "run") << "calling continuation " << ingredients.at(0).at(0) << end();
  if (!contains_key(Delimited_continuation, ingredients.at(0).at(0)))
    raise << maybe(current_recipe_name()) << "no such delimited continuation " << current_instruction().ingredients.at(0).original_string << '\n' << end();
  const call_stack& new_frames = get(Delimited_continuation, ingredients.at(0).at(0)).frames;
  for (call_stack::const_reverse_iterator p = new_frames.rbegin(); p != new_frames.rend(); ++p)
    Current_routine->calls.push_front(*p);
  trace(Callstack_depth+1, "trace") << "calling delimited continuation; growing callstack depth to " << Callstack_depth+SIZE(new_frames) << end();
  Callstack_depth += SIZE(new_frames);
  assert(Callstack_depth < Max_depth);
  // no call housekeeping; continuations don't support next-ingredient
  copy(/*drop continuation*/++ingredients.begin(), ingredients.end(), inserter(products, products.begin()));
  break;  // record results of resuming 'return-continuation-until-mark' instruction
}

:(code)
void test_continuations_can_return_values() {
  run(
      "def main [\n"
      "  local-scope\n"
      "  k:continuation, 1:num/raw <- call-with-continuation-mark 233/mark, f\n"
      "]\n"
      "def f [\n"
      "  local-scope\n"
      "  g\n"
      "]\n"
      "def g [\n"
      "  local-scope\n"
      "  return-continuation-until-mark 233/mark, 34\n"
      "  stash [continuation called]\n"
      "]\n"
  );
  CHECK_TRACE_CONTENTS(
      "mem: storing 34 in location 1\n"
  );
}

void test_continuations_continue_to_matching_mark() {
  run(
      "def main [\n"
      "  local-scope\n"
      "  k:continuation, 1:num/raw <- call-with-continuation-mark 233/mark, f\n"
      "  add 1, 1\n"
      "]\n"
      "def f [\n"
      "  local-scope\n"
      "  k2:continuation <- call-with-continuation-mark 234/mark, g\n"
      "  add 2, 2\n"
      "]\n"
      "def g [\n"
      "  local-scope\n"
      "  return-continuation-until-mark 233/mark, 34\n"
      "  stash [continuation called]\n"
      "]\n"
  );
  CHECK_TRACE_CONTENTS(
      "run: add {1: \"literal\"}, {1: \"literal\"}\n"
  );
  CHECK_TRACE_DOESNT_CONTAIN("run: add {2: \"literal\"}, {2: \"literal\"}");
}

//: Allow shape-shifting recipes to return continuations.

void test_call_shape_shifting_recipe_with_continuation_mark() {
  run(
      "def main [\n"
      "  1:num <- call-with-continuation-mark 233/mark, f, 34\n"
      "]\n"
      "def f x:_elem -> y:_elem [\n"
      "  local-scope\n"
      "  load-ingredients\n"
      "  y <- copy x\n"
      "]\n"
  );
  CHECK_TRACE_CONTENTS(
      "mem: storing 34 in location 1\n"
  );
}

:(before "End resolve_ambiguous_call(r, index, inst, caller_recipe) Special-cases")
if (inst.name == "call-with-continuation-mark") {
  if (SIZE(inst.ingredients) > 1 && is_recipe_literal(inst.ingredients.at(/*skip mark*/1))) {
  resolve_indirect_continuation_call(r, index, inst, caller_recipe);
  return;
  }
}
:(code)
void resolve_indirect_continuation_call(const recipe_ordinal r, int index, instruction& inst, const recipe& caller_recipe) {
  instruction inst2;
  inst2.name = inst.ingredients.at(/*skip mark*/1).name;
  for (int i = /*skip mark and recipe*/2;  i < SIZE(inst.ingredients);  ++i)
    inst2.ingredients.push_back(inst.ingredients.at(i));
  for (int i = /*skip continuation*/1;  i < SIZE(inst.products);  ++i)
    inst2.products.push_back(inst.products.at(i));
  resolve_ambiguous_call(r, index, inst2, caller_recipe);
  inst.ingredients.at(/*skip mark*/1).name = inst2.name;
  inst.ingredients.at(/*skip mark*/1).set_value(get(Recipe_ordinal, inst2.name));
}

void test_call_shape_shifting_recipe_with_continuation_mark_and_no_outputs() {
  run(
      "def main [\n"
      "  1:continuation <- call-with-continuation-mark 233/mark, f, 34\n"
      "]\n"
      "def f x:_elem [\n"
      "  local-scope\n"
      "  load-ingredients\n"
      "  return-continuation-until-mark 233/mark\n"
      "]\n"
  );
  CHECK_TRACE_COUNT("error", 0);
}

void test_continuation1() {
  run(
      "def main [\n"
      "  local-scope\n"
      "  k:continuation <- call-with-continuation-mark 233/mark, create-yielder\n"
      "  10:num/raw <- call k\n"
      "]\n"
      "def create-yielder -> n:num [\n"
      "  local-scope\n"
      "  load-inputs\n"
      "  return-continuation-until-mark 233/mark\n"
      "  return 1\n"
      "]\n"
  );
  CHECK_TRACE_CONTENTS(
      "mem: storing 1 in location 10\n"
  );
  CHECK_TRACE_COUNT("error", 0);
}

:(code)
bool is_mu_continuation(reagent/*copy*/ x) {
  canonize_type(x);
  return x.type && x.type->atom && x.type->value == get(Type_ordinal, "continuation");
}

// helper for debugging
void dump(const int continuation_id) {
  if (!contains_key(Delimited_continuation, continuation_id)) {
    raise << "missing delimited continuation: " << continuation_id << '\n' << end();
    return;
  }
  delimited_continuation& curr = get(Delimited_continuation, continuation_id);
  dump(curr.frames);
}