1 files changed, 54 insertions, 2 deletions

diff --git a/cpp/039wait.cc b/cpp/039wait.cc
index b9208590..940cba89 100644
--- a/cpp/039wait.cc
+++ b/cpp/039wait.cc
@@ -40,7 +40,7 @@ case WAIT_FOR_LOCATION: {
   Current_routine->state = WAITING;
   Current_routine->waiting_on_location = loc.value;
   Current_routine->old_value_of_wating_location = Memory[loc.value];
-  trace("run") << "waiting for " << loc.value << " to change from " << Memory[loc.value];
+  trace("run") << "waiting for location " << loc.value << " to change from " << Memory[loc.value];
   break;
 }
 
@@ -49,9 +49,61 @@ case WAIT_FOR_LOCATION: {
 :(before "End Scheduler State Transitions")
 for (index_t i = 0; i < Routines.size(); ++i) {
   if (Routines[i]->state != WAITING) continue;
-  if (Memory[Routines[i]->waiting_on_location] != Routines[i]->old_value_of_wating_location) {
+  if (Memory[Routines[i]->waiting_on_location] &&
+      Memory[Routines[i]->waiting_on_location] != Routines[i]->old_value_of_wating_location) {
     trace("schedule") << "waking up routine\n";
     Routines[i]->state = RUNNING;
     Routines[i]->waiting_on_location = Routines[i]->old_value_of_wating_location = 0;
   }
 }
+
+//: also allow waiting on a routine
+
+:(scenario wait_for_routine)
+recipe f1 [
+  1:integer <- copy 0:literal
+  2:integer/routine <- start-running f2:recipe
+  wait-for-routine 2:integer/routine
+  # now wait for f2 to run and modify location 1 before using its value
+  3:integer <- copy 1:integer
+]
+recipe f2 [
+  1:integer <- copy 34:literal
+]
+# if we got the synchronization wrong we'd be storing 0 in location 3
++mem: storing 34 in location 3
+
+:(before "End routine Fields")
+// only if state == WAITING
+index_t waiting_on_routine;
+:(before "End routine Constructor")
+waiting_on_routine = 0;
+
+:(before "End Primitive Recipe Declarations")
+WAIT_FOR_ROUTINE,
+:(before "End Primitive Recipe Numbers")
+Recipe_number["wait-for-routine"] = WAIT_FOR_ROUTINE;
+:(before "End Primitive Recipe Implementations")
+case WAIT_FOR_ROUTINE: {
+  reagent loc = canonize(current_instruction().ingredients[0]);
+  Current_routine->state = WAITING;
+  Current_routine->waiting_on_routine = loc.value;
+  trace("run") << "waiting for routine " << loc.value;
+  break;
+}
+
+:(before "End Scheduler State Transitions")
+for (index_t i = 0; i < Routines.size(); ++i) {
+  if (Routines[i]->state != WAITING) continue;
+  if (!Routines[i]->waiting_on_routine) continue;
+  index_t id = Routines[i]->waiting_on_routine;
+  assert(id != i);
+  for (index_t j = 0; j < Routines.size(); ++j) {
+    if (Routines[j]->id == id && Routines[j]->state != WAITING) {
+      trace("schedule") << "waking up routine\n";
+      Routines[i]->state = RUNNING;
+      Routines[i]->waiting_on_routine = 0;
+    }
+  }
+}
+