CABI: move the call state out of the event-code enum and into the payload

Resolves #492

Author: lukewagner

design/mvp/CanonicalABI.md

@@ -813,20 +813,13 @@ to be interpreted based on the `EventCode`. The meaning of the different
 code that produces the events (specifically, in `subtask_event` and
 `copy_event`).
 ```python
-class CallState(IntEnum):
-  STARTING = 1
-  STARTED = 2
-  RETURNED = 3
-
 class EventCode(IntEnum):
   NONE = 0
-  CALL_STARTING = CallState.STARTING
-  CALL_STARTED = CallState.STARTED
-  CALL_RETURNED = CallState.RETURNED
-  STREAM_READ = 5
-  STREAM_WRITE = 6
-  FUTURE_READ = 7
-  FUTURE_WRITE = 8
+  SUBTASK = 1
+  STREAM_READ = 2
+  STREAM_WRITE = 3
+  FUTURE_READ = 4
+  FUTURE_WRITE = 5
 
 EventTuple = tuple[EventCode, int, int]
 ```
@@ -966,6 +959,11 @@ only manages a few fields of state that are relevant to the caller. As with
 `Task`, this section will introduce `Subtask` incrementally, starting with its
 fields and initialization:
 ```python
+class CallState(IntEnum):
+  STARTING = 0
+  STARTED = 1
+  RETURNED = 2
+
 class Subtask(Waitable):
   state: CallState
   lenders: list[ResourceHandle]
@@ -978,10 +976,10 @@ class Subtask(Waitable):
     self.finished = False
     self.supertask = None
 ```
-The `state` field of `Subtask` holds a `CallState` enum value (defined above as
-part of the definition of `EventCode`) that describes the callee's current
-state along the linear progression from [`STARTING`](Async.md#backpressure) to
-`STARTED` to [`RETURNED`](Async.md#returning).
+The `state` field of `Subtask` holds a `CallState` enum value that describes
+the callee's current state along the linear progression from
+[`STARTING`](Async.md#backpressure) to `STARTED` to
+[`RETURNED`](Async.md#returning).
 
 Although `Subtask` derives `Waitable`, `__init__` does not initialize the
 `Waitable` base object. Instead, the `Waitable` base is only initialized when
@@ -2993,7 +2991,7 @@ immediately return control flow back to the `async` caller if `callee` blocks:
           def subtask_event():
             if subtask.state == CallState.RETURNED:
               subtask.finish()
-            return (EventCode(subtask.state), subtaski, 0)
+            return (EventCode.SUBTASK, subtaski, subtask.state)
           subtask.set_event(subtask_event)
         assert(0 < subtaski <= Table.MAX_LENGTH < 2**28)
         assert(0 <= int(subtask.state) < 2**4)

design/mvp/canonical-abi/definitions.py

@@ -506,20 +506,13 @@ def exit(self):
 
 #### Waitable State
 
-class CallState(IntEnum):
-  STARTING = 1
-  STARTED = 2
-  RETURNED = 3
-
 class EventCode(IntEnum):
   NONE = 0
-  CALL_STARTING = CallState.STARTING
-  CALL_STARTED = CallState.STARTED
-  CALL_RETURNED = CallState.RETURNED
-  STREAM_READ = 5
-  STREAM_WRITE = 6
-  FUTURE_READ = 7
-  FUTURE_WRITE = 8
+  SUBTASK = 1
+  STREAM_READ = 2
+  STREAM_WRITE = 3
+  FUTURE_READ = 4
+  FUTURE_WRITE = 5
 
 EventTuple = tuple[EventCode, int, int]
 
@@ -600,6 +593,11 @@ def drop(self):
 
 #### Subtask State
 
+class CallState(IntEnum):
+  STARTING = 0
+  STARTED = 1
+  RETURNED = 2
+
 class Subtask(Waitable):
   state: CallState
   lenders: list[ResourceHandle]
@@ -1841,7 +1839,7 @@ def on_progress():
           def subtask_event():
             if subtask.state == CallState.RETURNED:
               subtask.finish()
-            return (EventCode(subtask.state), subtaski, 0)
+            return (EventCode.SUBTASK, subtaski, subtask.state)
           subtask.set_event(subtask_event)
         assert(0 < subtaski <= Table.MAX_LENGTH < 2**28)
         assert(0 <= int(subtask.state) < 2**4)

design/mvp/canonical-abi/run_tests.py

@@ -583,19 +583,22 @@ async def consumer(task, args):
 
     waitretp = consumer_heap.realloc(0, 0, 8, 4)
     [event] = await canon_waitable_set_wait(False, consumer_heap.memory, task, seti, waitretp)
-    assert(event == EventCode.CALL_RETURNED)
+    assert(event == EventCode.SUBTASK)
     assert(consumer_heap.memory[waitretp] == subi1)
+    assert(consumer_heap.memory[waitretp+4] == CallState.RETURNED)
     [] = await canon_subtask_drop(task, subi1)
 
     [event] = await canon_waitable_set_wait(True, consumer_heap.memory, task, seti, waitretp)
-    assert(event == EventCode.CALL_STARTED)
+    assert(event == EventCode.SUBTASK)
     assert(consumer_heap.memory[waitretp] == subi2)
+    assert(consumer_heap.memory[waitretp+4] == CallState.STARTED)
     assert(consumer_heap.memory[retp] == 13)
     fut2.set_result(None)
 
     [event] = await canon_waitable_set_wait(False, consumer_heap.memory, task, seti, waitretp)
-    assert(event == EventCode.CALL_RETURNED)
+    assert(event == EventCode.SUBTASK)
     assert(consumer_heap.memory[waitretp] == subi2)
+    assert(consumer_heap.memory[waitretp+4] == CallState.RETURNED)
     assert(consumer_heap.memory[retp] == 44)
     [] = await canon_subtask_drop(task, subi2)
     fut3.set_result(None)
@@ -623,8 +626,9 @@ async def dtor(task, args):
 
     [] = await canon_waitable_join(task, dtorsubi, seti)
     [event] = await canon_waitable_set_wait(False, consumer_heap.memory, task, seti, waitretp)
-    assert(event == CallState.RETURNED)
+    assert(event == EventCode.SUBTASK)
     assert(consumer_heap.memory[waitretp] == dtorsubi)
+    assert(consumer_heap.memory[waitretp+4] == CallState.RETURNED)
     assert(dtor_value == 50)
     [] = await canon_subtask_drop(task, dtorsubi)
     [] = await canon_waitable_set_drop(task, seti)
@@ -695,9 +699,9 @@ async def callback(task, args):
     [ctx] = await canon_context_get('i32', 0, task)
     match ctx:
       case 42:
-        assert(args[0] == EventCode.CALL_RETURNED)
+        assert(args[0] == EventCode.SUBTASK)
         assert(args[1] == 1)
-        assert(args[2] == 0)
+        assert(args[2] == CallState.RETURNED)
         await canon_subtask_drop(task, 1)
         [] = await canon_context_set('i32', 0, task, 52)
         return [definitions.CallbackCode.YIELD]
@@ -709,9 +713,9 @@ async def callback(task, args):
         [] = await canon_context_set('i32', 0, task, 62)
         return [definitions.CallbackCode.WAIT]
       case 62:
-        assert(args[0] == EventCode.CALL_RETURNED)
+        assert(args[0] == EventCode.SUBTASK)
         assert(args[1] == 2)
-        assert(args[2] == 0)
+        assert(args[2] == CallState.RETURNED)
         await canon_subtask_drop(task, 2)
         [] = await canon_task_return(task, [U32Type()], opts, [83])
         return [definitions.CallbackCode.EXIT]
@@ -786,8 +790,9 @@ async def consumer(task, args):
 
     retp = consumer_heap.realloc(0,0,8,4)
     [event] = await canon_waitable_set_wait(False, consumer_heap.memory, task, seti, retp)
-    assert(event == EventCode.CALL_RETURNED)
+    assert(event == EventCode.SUBTASK)
     assert(consumer_heap.memory[retp] == subi1)
+    assert(consumer_heap.memory[retp+4] == CallState.RETURNED)
     await canon_subtask_drop(task, subi1)
     assert(producer1_done == True)
 
@@ -796,8 +801,9 @@ async def consumer(task, args):
     assert(producer2_done == True)
 
     [event] = await canon_waitable_set_poll(False, consumer_heap.memory, task, seti, retp)
-    assert(event == EventCode.CALL_RETURNED)
+    assert(event == EventCode.SUBTASK)
     assert(consumer_heap.memory[retp] == subi2)
+    assert(consumer_heap.memory[retp+4] == CallState.RETURNED)
     await canon_subtask_drop(task, subi2)
     assert(producer2_done == True)
 
@@ -873,13 +879,15 @@ async def consumer(task, args):
 
     retp = consumer_heap.realloc(0,0,8,4)
     [event] = await canon_waitable_set_wait(False, consumer_heap.memory, task, seti, retp)
-    assert(event == EventCode.CALL_RETURNED)
+    assert(event == EventCode.SUBTASK)
     assert(consumer_heap.memory[retp] == subi1)
+    assert(consumer_heap.memory[retp+4] == CallState.RETURNED)
     assert(producer1_done == True)
 
     [event] = await canon_waitable_set_poll(False, consumer_heap.memory, task, seti, retp)
-    assert(event == EventCode.CALL_RETURNED)
+    assert(event == EventCode.SUBTASK)
     assert(consumer_heap.memory[retp] == subi2)
+    assert(consumer_heap.memory[retp+4] == CallState.RETURNED)
     assert(producer2_done == True)
 
     await canon_subtask_drop(task, subi1)
@@ -941,14 +949,16 @@ async def core_func(task, args):
 
     retp = lower_heap.realloc(0,0,8,4)
     [event] = await canon_waitable_set_wait(False, lower_heap.memory, task, seti, retp)
-    assert(event == EventCode.CALL_RETURNED)
+    assert(event == EventCode.SUBTASK)
     assert(lower_heap.memory[retp] == subi1)
+    assert(lower_heap.memory[retp+4] == CallState.RETURNED)
 
     fut2.set_result(None)
 
     [event] = await canon_waitable_set_wait(False, lower_heap.memory, task, seti, retp)
-    assert(event == EventCode.CALL_RETURNED)
+    assert(event == EventCode.SUBTASK)
     assert(lower_heap.memory[retp] == subi2)
+    assert(lower_heap.memory[retp+4] == CallState.RETURNED)
 
     await canon_subtask_drop(task, subi1)
     await canon_subtask_drop(task, subi2)