3991 - start work on making continuations safe

Plan:
1. Fix a hole where addresses are shared between routines when passed in
as arguments to `start-running`.
2. Switch to a new approach to refcount management: instead of updating
refcounts when writing products of instructions by default, increment
refcounts inside instructions by default and decrement refcounts in
caller. More details in future when I actually implement this.
3. Now we shouldn't need a distinction between `new-default-space` and
`local-scope`, and all functions can simply decrement refcounts of
their default-space, consistently handling any refcounts in the space.

At this point if all goes well, continuations should be safe!

This commit is just preparation for step 1.

1 files changed, 706 insertions, 0 deletions

diff --git a/073scheduler.cc b/073scheduler.cc
new file mode 100644
index 00000000..e3ac18cf
--- /dev/null
+++ b/073scheduler.cc
@@ -0,0 +1,706 @@
+//: Run a second routine concurrently using 'start-running', without any
+//: guarantees on how the operations in each are interleaved with each other.
+
+:(scenario scheduler)
+def f1 [
+  start-running f2
+  # wait for f2 to run
+  {
+    jump-unless 1:num, -1
+  }
+]
+def f2 [
+  1:num <- copy 1
+]
++schedule: f1
++schedule: f2
+
+//: first, add a deadline to run(routine)
+:(before "End Globals")
+int Scheduling_interval = 500;
+:(before "End routine Fields")
+int instructions_run_this_scheduling_slice;
+:(before "End routine Constructor")
+instructions_run_this_scheduling_slice = 0;
+:(after "Running One Instruction")
+ ++Current_routine->instructions_run_this_scheduling_slice;
+:(replace{} "bool should_continue_running(const routine* current_routine)")
+bool should_continue_running(const routine* current_routine) {
+  assert(current_routine == Current_routine);  // argument passed in just to make caller readable above
+  return Current_routine->state == RUNNING
+      && Current_routine->instructions_run_this_scheduling_slice < Scheduling_interval;
+}
+:(after "stop_running_current_routine:")
+// Reset instructions_run_this_scheduling_slice
+Current_routine->instructions_run_this_scheduling_slice = 0;
+
+//: now the rest of the scheduler is clean
+
+:(before "struct routine")
+enum routine_state {
+  RUNNING,
+  COMPLETED,
+  // End routine States
+};
+:(before "End routine Fields")
+enum routine_state state;
+:(before "End routine Constructor")
+state = RUNNING;
+
+:(before "End Globals")
+vector<routine*> Routines;
+int Current_routine_index = 0;
+:(before "End Reset")
+Scheduling_interval = 500;
+for (int i = 0;  i < SIZE(Routines);  ++i)
+  delete Routines.at(i);
+Routines.clear();
+Current_routine = NULL;
+:(replace{} "void run(const recipe_ordinal r)")
+void run(const recipe_ordinal r) {
+  run(new routine(r));
+}
+
+:(code)
+void run(routine* rr) {
+  Routines.push_back(rr);
+  Current_routine_index = 0, Current_routine = Routines.at(0);
+  while (!all_routines_done()) {
+    skip_to_next_routine();
+    assert(Current_routine);
+    assert(Current_routine->state == RUNNING);
+    trace(9990, "schedule") << current_routine_label() << end();
+    run_current_routine();
+    // Scheduler State Transitions
+    if (Current_routine->completed())
+      Current_routine->state = COMPLETED;
+    // End Scheduler State Transitions
+
+    // Scheduler Cleanup
+    // End Scheduler Cleanup
+  }
+  // End Run Routine
+}
+
+bool all_routines_done() {
+  for (int i = 0;  i < SIZE(Routines);  ++i) {
+    if (Routines.at(i)->state == RUNNING)
+      return false;
+  }
+  return true;
+}
+
+// skip Current_routine_index past non-RUNNING routines
+void skip_to_next_routine() {
+  assert(!Routines.empty());
+  assert(Current_routine_index < SIZE(Routines));
+  for (int i = (Current_routine_index+1)%SIZE(Routines);  i != Current_routine_index;  i = (i+1)%SIZE(Routines)) {
+    if (Routines.at(i)->state == RUNNING) {
+      Current_routine_index = i;
+      Current_routine = Routines.at(i);
+      return;
+    }
+  }
+}
+
+string current_routine_label() {
+  return routine_label(Current_routine);
+}
+
+string routine_label(routine* r) {
+  ostringstream result;
+  const call_stack& calls = r->calls;
+  for (call_stack::const_iterator p = calls.begin();  p != calls.end();  ++p) {
+    if (p != calls.begin()) result << '/';
+    result << get(Recipe, p->running_recipe).name;
+  }
+  return result.str();
+}
+
+//: special case for the very first routine
+:(replace{} "void run_main(int argc, char* argv[])")
+void run_main(int argc, char* argv[]) {
+  recipe_ordinal r = get(Recipe_ordinal, "main");
+  assert(r);
+  routine* main_routine = new routine(r);
+  // pass in commandline args as ingredients to main
+  // todo: test this
+  Current_routine = main_routine;
+  for (int i = 1;  i < argc;  ++i) {
+    vector<double> arg;
+    arg.push_back(new_mu_text(argv[i]));
+    assert(get(Memory, arg.back()) == 0);
+    put(Memory, arg.back(), 1);  // update refcount
+    current_call().ingredient_atoms.push_back(arg);
+  }
+  run(main_routine);
+}
+
+//:: To schedule new routines to run, call 'start-running'.
+
+//: 'start-running' will return a unique id for the routine that was created.
+//: routine id is a number, but don't do any arithmetic on it
+:(before "End routine Fields")
+int id;
+:(before "End Globals")
+int Next_routine_id = 1;
+:(before "End Reset")
+Next_routine_id = 1;
+:(before "End routine Constructor")
+id = Next_routine_id;
+++Next_routine_id;
+
+//: routines save the routine that spawned them
+:(before "End routine Fields")
+// todo: really should be routine_id, but that's less efficient.
+int parent_index;  // only < 0 if there's no parent_index
+:(before "End routine Constructor")
+parent_index = -1;
+
+:(before "End Primitive Recipe Declarations")
+START_RUNNING,
+:(before "End Primitive Recipe Numbers")
+put(Recipe_ordinal, "start-running", START_RUNNING);
+:(before "End Primitive Recipe Checks")
+case START_RUNNING: {
+  if (inst.ingredients.empty()) {
+    raise << maybe(get(Recipe, r).name) << "'start-running' requires at least one ingredient: the recipe to start running\n" << end();
+    break;
+  }
+  if (!is_mu_recipe(inst.ingredients.at(0))) {
+    raise << maybe(get(Recipe, r).name) << "first ingredient of 'start-running' should be a recipe, but got '" << to_string(inst.ingredients.at(0)) << "'\n" << end();
+    break;
+  }
+  break;
+}
+:(before "End Primitive Recipe Implementations")
+case START_RUNNING: {
+  routine* new_routine = new routine(ingredients.at(0).at(0));
+  new_routine->parent_index = Current_routine_index;
+  // populate ingredients
+  for (int i = 1;  i < SIZE(current_instruction().ingredients);  ++i) {
+    new_routine->calls.front().ingredient_atoms.push_back(ingredients.at(i));
+    reagent/*copy*/ ingredient = current_instruction().ingredients.at(i);
+    canonize_type(ingredient);
+    new_routine->calls.front().ingredients.push_back(ingredient);
+    // End Populate start-running Ingredient
+  }
+  Routines.push_back(new_routine);
+  products.resize(1);
+  products.at(0).push_back(new_routine->id);
+  break;
+}
+
+:(scenario scheduler_runs_single_routine)
+% Scheduling_interval = 1;
+def f1 [
+  1:num <- copy 0
+  2:num <- copy 0
+]
++schedule: f1
++run: {1: "number"} <- copy {0: "literal"}
++schedule: f1
++run: {2: "number"} <- copy {0: "literal"}
+
+:(scenario scheduler_interleaves_routines)
+% Scheduling_interval = 1;
+def f1 [
+  start-running f2
+  1:num <- copy 0
+  2:num <- copy 0
+]
+def f2 [
+  3:num <- copy 0
+  4:num <- copy 0
+]
++schedule: f1
++run: start-running {f2: "recipe-literal"}
++schedule: f2
++run: {3: "number"} <- copy {0: "literal"}
++schedule: f1
++run: {1: "number"} <- copy {0: "literal"}
++schedule: f2
++run: {4: "number"} <- copy {0: "literal"}
++schedule: f1
++run: {2: "number"} <- copy {0: "literal"}
+
+:(scenario start_running_takes_ingredients)
+def f1 [
+  start-running f2, 3
+  # wait for f2 to run
+  {
+    jump-unless 1:num, -1
+  }
+]
+def f2 [
+  1:num <- next-ingredient
+  2:num <- add 1:num, 1
+]
++mem: storing 4 in location 2
+
+//: type-checking for 'start-running'
+
+:(scenario start_running_checks_types)
+% Hide_errors = true;
+def f1 [
+  start-running f2, 3
+]
+def f2 n:&:num [
+]
++error: f1: ingredient 0 has the wrong type at 'start-running f2, 3'
+
+// 'start-running' only uses the ingredients of the callee, not its products
+:(before "End is_indirect_call_with_ingredients Special-cases")
+if (r == START_RUNNING) return true;
+
+//: more complex: refcounting management when starting up new routines
+
+:(scenario start_running_immediately_updates_refcounts_of_ingredients)
+% Scheduling_interval = 1;
+def main [
+  local-scope
+  create-new-routine
+  # padding to make sure we run new-routine before returning
+  dummy:num <- copy 0
+  dummy:num <- copy 0
+]
+def create-new-routine [
+  local-scope
+  n:&:num <- new number:type
+  *n <- copy 34
+  start-running new-routine, n
+  # refcount of n decremented
+]
+def new-routine n:&:num [
+  local-scope
+  load-ingredients
+  1:num/raw <- copy *n
+]
+# check that n wasn't reclaimed when create-new-routine returned
++mem: storing 34 in location 1
+
+//: to support the previous scenario we'll increment refcounts for all call
+//: ingredients right at call time, and stop incrementing refcounts inside
+//: next-ingredient
+:(before "End Populate Call Ingredient")
+increment_any_refcounts(ingredient, ingredients.at(i));
+:(before "End Populate start-running Ingredient")
+increment_any_refcounts(ingredient, ingredients.at(i));
+:(after "should_update_refcounts() Special-cases When Writing Products Of Primitive Instructions")
+if (inst.operation == NEXT_INGREDIENT || inst.operation == NEXT_INGREDIENT_WITHOUT_TYPECHECKING) {
+  if (space_index(inst.products.at(0)) > 0) return true;
+  if (has_property(inst.products.at(0), "raw")) return true;
+  return false;
+}
+
+// ensure this works with indirect calls using 'call' as well
+:(scenario start_running_immediately_updates_refcounts_of_ingredients_of_indirect_calls)
+% Scheduling_interval = 1;
+def main [
+  local-scope
+  n:&:num <- new number:type
+  *n <- copy 34
+  call f1, n
+  1:num/raw <- copy *n
+]
+def f1 n:&:num [
+  local-scope
+  load-ingredients
+]
+# check that n wasn't reclaimed when f1 returned
++mem: storing 34 in location 1
+
+:(scenario next_ingredient_never_leaks_refcounts)
+def create-space n:&:num -> default-space:space [
+  default-space <- new location:type, 2
+  load-ingredients
+]
+def use-space [
+  local-scope
+  0:space/names:create-space <- next-ingredient
+  n:&:num/space:1 <- next-ingredient  # should decrement refcount
+  *n/space:1 <- copy 34
+  n2:num <- add *n/space:1, 1
+  return n2
+]
+def main [
+  local-scope
+  n:&:num <- copy 12000/unsafe  # pretend allocation with a known address
+  *n <- copy 23
+  space:space <- create-space n
+  n2:&:num <- copy 13000/unsafe
+  n3:num <- use-space space, n2
+]
++run: {n: ("address" "number"), "space": "1"} <- next-ingredient
++mem: decrementing refcount of 12000: 2 -> 1
++run: {n: ("address" "number"), "space": "1", "lookup": ()} <- copy {34: "literal"}
+
+//: back to testing 'start-running'
+
+:(scenario start_running_returns_routine_id)
+def f1 [
+  1:num <- start-running f2
+]
+def f2 [
+  12:num <- copy 44
+]
++mem: storing 2 in location 1
+
+//: this scenario will require some careful setup in escaped C++
+//: (straining our tangle capabilities to near-breaking point)
+:(scenario scheduler_skips_completed_routines)
+% recipe_ordinal f1 = load("recipe f1 [\n1:num <- copy 0\n]\n").front();
+% recipe_ordinal f2 = load("recipe f2 [\n2:num <- copy 0\n]\n").front();
+% Routines.push_back(new routine(f1));  // f1 meant to run
+% Routines.push_back(new routine(f2));
+% Routines.back()->state = COMPLETED;  // f2 not meant to run
+# must have at least one routine without escaping
+def f3 [
+  3:num <- copy 0
+]
+# by interleaving '+' lines with '-' lines, we allow f1 and f3 to run in any order
++schedule: f1
++mem: storing 0 in location 1
+-schedule: f2
+-mem: storing 0 in location 2
++schedule: f3
++mem: storing 0 in location 3
+
+:(scenario scheduler_starts_at_middle_of_routines)
+% Routines.push_back(new routine(COPY));
+% Routines.back()->state = COMPLETED;
+def f1 [
+  1:num <- copy 0
+  2:num <- copy 0
+]
++schedule: f1
+-run: idle
+
+//:: Errors in a routine cause it to terminate.
+
+:(scenario scheduler_terminates_routines_after_errors)
+% Hide_errors = true;
+% Scheduling_interval = 2;
+def f1 [
+  start-running f2
+  1:num <- copy 0
+  2:num <- copy 0
+]
+def f2 [
+  # divide by 0 twice
+  3:num <- divide-with-remainder 4, 0
+  4:num <- divide-with-remainder 4, 0
+]
+# f2 should stop after first divide by 0
++error: f2: divide by zero in '3:num <- divide-with-remainder 4, 0'
+-error: f2: divide by zero in '4:num <- divide-with-remainder 4, 0'
+
+:(after "operator<<(ostream& os, unused end)")
+  if (Trace_stream && Trace_stream->curr_label == "error" && Current_routine) {
+    Current_routine->state = COMPLETED;
+  }
+
+//:: Routines are marked completed when their parent completes.
+
+:(scenario scheduler_kills_orphans)
+def main [
+  start-running f1
+  # f1 never actually runs because its parent completes without waiting for it
+]
+def f1 [
+  1:num <- copy 0
+]
+-schedule: f1
+
+:(before "End Scheduler Cleanup")
+for (int i = 0;  i < SIZE(Routines);  ++i) {
+  if (Routines.at(i)->state == COMPLETED) continue;
+  if (Routines.at(i)->parent_index < 0) continue;  // root thread
+  // structured concurrency: http://250bpm.com/blog:71
+  if (has_completed_parent(i)) {
+    Routines.at(i)->state = COMPLETED;
+  }
+}
+
+:(code)
+bool has_completed_parent(int routine_index) {
+  for (int j = routine_index;  j >= 0;  j = Routines.at(j)->parent_index) {
+    if (Routines.at(j)->state == COMPLETED)
+      return true;
+  }
+  return false;
+}
+
+//:: 'routine-state' can tell if a given routine id is running
+
+:(scenario routine_state_test)
+% Scheduling_interval = 2;
+def f1 [
+  1:num/child-id <- start-running f2
+  12:num <- copy 0  # race condition since we don't care about location 12
+  # thanks to Scheduling_interval, f2's one instruction runs in between here and completes
+  2:num/state <- routine-state 1:num/child-id
+]
+def f2 [
+  12:num <- copy 0
+  # trying to run a second instruction marks routine as completed
+]
+# recipe f2 should be in state COMPLETED
++mem: storing 1 in location 2
+
+:(before "End Primitive Recipe Declarations")
+ROUTINE_STATE,
+:(before "End Primitive Recipe Numbers")
+put(Recipe_ordinal, "routine-state", ROUTINE_STATE);
+:(before "End Primitive Recipe Checks")
+case ROUTINE_STATE: {
+  if (SIZE(inst.ingredients) != 1) {
+    raise << maybe(get(Recipe, r).name) << "'routine-state' requires exactly one ingredient, but got '" << to_original_string(inst) << "'\n" << end();
+    break;
+  }
+  if (!is_mu_number(inst.ingredients.at(0))) {
+    raise << maybe(get(Recipe, r).name) << "first ingredient of 'routine-state' should be a routine id generated by 'start-running', but got '" << inst.ingredients.at(0).original_string << "'\n" << end();
+    break;
+  }
+  break;
+}
+:(before "End Primitive Recipe Implementations")
+case ROUTINE_STATE: {
+  int id = ingredients.at(0).at(0);
+  int result = -1;
+  for (int i = 0;  i < SIZE(Routines);  ++i) {
+    if (Routines.at(i)->id == id) {
+      result = Routines.at(i)->state;
+      break;
+    }
+  }
+  products.resize(1);
+  products.at(0).push_back(result);
+  break;
+}
+
+//:: miscellaneous helpers
+
+:(before "End Primitive Recipe Declarations")
+STOP,
+:(before "End Primitive Recipe Numbers")
+put(Recipe_ordinal, "stop", STOP);
+:(before "End Primitive Recipe Checks")
+case STOP: {
+  if (SIZE(inst.ingredients) != 1) {
+    raise << maybe(get(Recipe, r).name) << "'stop' requires exactly one ingredient, but got '" << to_original_string(inst) << "'\n" << end();
+    break;
+  }
+  if (!is_mu_number(inst.ingredients.at(0))) {
+    raise << maybe(get(Recipe, r).name) << "first ingredient of 'stop' should be a routine id generated by 'start-running', but got '" << inst.ingredients.at(0).original_string << "'\n" << end();
+    break;
+  }
+  break;
+}
+:(before "End Primitive Recipe Implementations")
+case STOP: {
+  int id = ingredients.at(0).at(0);
+  for (int i = 0;  i < SIZE(Routines);  ++i) {
+    if (Routines.at(i)->id == id) {
+      Routines.at(i)->state = COMPLETED;
+      break;
+    }
+  }
+  break;
+}
+
+:(before "End Primitive Recipe Declarations")
+_DUMP_ROUTINES,
+:(before "End Primitive Recipe Numbers")
+put(Recipe_ordinal, "$dump-routines", _DUMP_ROUTINES);
+:(before "End Primitive Recipe Checks")
+case _DUMP_ROUTINES: {
+  break;
+}
+:(before "End Primitive Recipe Implementations")
+case _DUMP_ROUTINES: {
+  for (int i = 0;  i < SIZE(Routines);  ++i) {
+    cerr << i << ": " << Routines.at(i)->id << ' ' << Routines.at(i)->state << ' ' << Routines.at(i)->parent_index << '\n';
+  }
+  break;
+}
+
+//: support for stopping routines after some number of cycles
+
+:(scenario routine_discontinues_past_limit)
+% Scheduling_interval = 2;
+def f1 [
+  1:num/child-id <- start-running f2
+  limit-time 1:num/child-id, 10
+  # padding loop just to make sure f2 has time to completed
+  2:num <- copy 20
+  2:num <- subtract 2:num, 1
+  jump-if 2:num, -2:offset
+]
+def f2 [
+  jump -1:offset  # run forever
+  $print [should never get here], 10/newline
+]
+# f2 terminates
++schedule: discontinuing routine 2
+
+:(before "End routine States")
+DISCONTINUED,
+:(before "End Scheduler State Transitions")
+if (Current_routine->limit >= 0) {
+  if (Current_routine->limit <= Scheduling_interval) {
+    trace(9999, "schedule") << "discontinuing routine " << Current_routine->id << end();
+    Current_routine->state = DISCONTINUED;
+    Current_routine->limit = 0;
+  }
+  else {
+    Current_routine->limit -= Scheduling_interval;
+  }
+}
+
+:(before "End Test Teardown")
+if (Passed && any_routines_with_error())
+  raise << "some routines died with errors\n" << end();
+:(before "End Mu Test Teardown")
+if (Passed && any_routines_with_error())
+  raise << Current_scenario->name << ": some routines died with errors\n" << end();
+
+:(code)
+bool any_routines_with_error() {
+  for (int i = 0;  i < SIZE(Routines);  ++i) {
+    if (Routines.at(i)->state == DISCONTINUED)
+      return true;
+  }
+  return false;
+}
+
+:(before "End routine Fields")
+int limit;
+:(before "End routine Constructor")
+limit = -1;  /* no limit */
+
+:(before "End Primitive Recipe Declarations")
+LIMIT_TIME,
+:(before "End Primitive Recipe Numbers")
+put(Recipe_ordinal, "limit-time", LIMIT_TIME);
+:(before "End Primitive Recipe Checks")
+case LIMIT_TIME: {
+  if (SIZE(inst.ingredients) != 2) {
+    raise << maybe(get(Recipe, r).name) << "'limit-time' requires exactly two ingredient, but got '" << to_original_string(inst) << "'\n" << end();
+    break;
+  }
+  if (!is_mu_number(inst.ingredients.at(0))) {
+    raise << maybe(get(Recipe, r).name) << "first ingredient of 'limit-time' should be a routine id generated by 'start-running', but got '" << inst.ingredients.at(0).original_string << "'\n" << end();
+    break;
+  }
+  if (!is_mu_number(inst.ingredients.at(1))) {
+    raise << maybe(get(Recipe, r).name) << "second ingredient of 'limit-time' should be a number (of instructions to run for), but got '" << inst.ingredients.at(1).original_string << "'\n" << end();
+    break;
+  }
+  break;
+}
+:(before "End Primitive Recipe Implementations")
+case LIMIT_TIME: {
+  int id = ingredients.at(0).at(0);
+  for (int i = 0;  i < SIZE(Routines);  ++i) {
+    if (Routines.at(i)->id == id) {
+      Routines.at(i)->limit = ingredients.at(1).at(0);
+      break;
+    }
+  }
+  break;
+}
+
+:(before "End routine Fields")
+int instructions_run;
+:(before "End routine Constructor")
+instructions_run = 0;
+:(before "Reset instructions_run_this_scheduling_slice")
+Current_routine->instructions_run += Current_routine->instructions_run_this_scheduling_slice;
+:(before "End Primitive Recipe Declarations")
+NUMBER_OF_INSTRUCTIONS,
+:(before "End Primitive Recipe Numbers")
+put(Recipe_ordinal, "number-of-instructions", NUMBER_OF_INSTRUCTIONS);
+:(before "End Primitive Recipe Checks")
+case NUMBER_OF_INSTRUCTIONS: {
+  if (SIZE(inst.ingredients) != 1) {
+    raise << maybe(get(Recipe, r).name) << "'number-of-instructions' requires exactly one ingredient, but got '" << to_original_string(inst) << "'\n" << end();
+    break;
+  }
+  if (!is_mu_number(inst.ingredients.at(0))) {
+    raise << maybe(get(Recipe, r).name) << "first ingredient of 'number-of-instructions' should be a routine id generated by 'start-running', but got '" << inst.ingredients.at(0).original_string << "'\n" << end();
+    break;
+  }
+  break;
+}
+:(before "End Primitive Recipe Implementations")
+case NUMBER_OF_INSTRUCTIONS: {
+  int id = ingredients.at(0).at(0);
+  int result = -1;
+  for (int i = 0;  i < SIZE(Routines);  ++i) {
+    if (Routines.at(i)->id == id) {
+      result = Routines.at(i)->instructions_run;
+      break;
+    }
+  }
+  products.resize(1);
+  products.at(0).push_back(result);
+  break;
+}
+
+:(scenario number_of_instructions)
+def f1 [
+  10:num/child-id <- start-running f2
+  {
+    loop-unless 20:num
+  }
+  11:num <- number-of-instructions 10:num
+]
+def f2 [
+  # 2 instructions worth of work
+  1:num <- copy 34
+  20:num <- copy 1
+]
+# f2 runs an extra instruction for the implicit return added by the
+# fill_in_return_ingredients transform
++mem: storing 3 in location 11
+
+:(scenario number_of_instructions_across_multiple_scheduling_intervals)
+% Scheduling_interval = 1;
+def f1 [
+  10:num/child-id <- start-running f2
+  {
+    loop-unless 20:num
+  }
+  11:num <- number-of-instructions 10:num
+]
+def f2 [
+  # 4 instructions worth of work
+  1:num <- copy 34
+  2:num <- copy 1
+  2:num <- copy 3
+  20:num <- copy 1
+]
+# f2 runs an extra instruction for the implicit return added by the
+# fill_in_return_ingredients transform
++mem: storing 5 in location 11
+
+//:: make sure that each routine gets a different alloc to start
+
+:(scenario new_concurrent)
+def f1 [
+  start-running f2
+  1:&:num/raw <- new number:type
+  # wait for f2 to complete
+  {
+    loop-unless 4:num/raw
+  }
+]
+def f2 [
+  2:&:num/raw <- new number:type
+  # hack: assumes scheduler implementation
+  3:bool/raw <- equal 1:&:num/raw, 2:&:num/raw
+  # signal f2 complete
+  4:num/raw <- copy 1
+]
++mem: storing 0 in location 3