webassembly/asyncio: Support top-level await of asyncio Task and Event.

This change allows doing a top-level await on an asyncio primitive like
Task and Event.

This feature enables a better interaction and synchronisation between
JavaScript and Python, because `api.runPythonAsync` can now be used (called
from JavaScript) to await on the completion of asyncio primitives.

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 18 insertions, 6 deletions

diff --git a/ports/webassembly/asyncio/core.py b/ports/webassembly/asyncio/core.py
index f6f9d19e5c..cc26e7b8d5 100644
--- a/ports/webassembly/asyncio/core.py
+++ b/ports/webassembly/asyncio/core.py
@@ -50,9 +50,6 @@ class SingletonGenerator:
 # Pause task execution for the given time (integer in milliseconds, uPy extension)
 # Use a SingletonGenerator to do it without allocating on the heap
 def sleep_ms(t, sgen=SingletonGenerator()):
-    if cur_task is None:
-        # Support top-level asyncio.sleep, via a JavaScript Promise.
-        return jsffi.async_timeout_ms(t)
     assert sgen.state is None
     sgen.state = ticks_add(ticks(), max(0, t))
     return sgen
@@ -69,6 +66,18 @@ def sleep(t):
 asyncio_timer = None
 
 
+class TopLevelCoro:
+    @staticmethod
+    def set(resolve, reject):
+        TopLevelCoro.resolve = resolve
+        TopLevelCoro.reject = reject
+        _schedule_run_iter(0)
+
+    @staticmethod
+    def send(value):
+        TopLevelCoro.resolve()
+
+
 class ThenableEvent:
     def __init__(self, thenable):
         self.result = None  # Result of the thenable
@@ -122,12 +131,12 @@ def _run_iter():
             dt = max(0, ticks_diff(t.ph_key, ticks()))
         else:
             # No tasks can be woken so finished running
-            cur_task = None
+            cur_task = _top_level_task
             return
 
         if dt > 0:
             # schedule to call again later
-            cur_task = None
+            cur_task = _top_level_task
             _schedule_run_iter(dt)
             return
 
@@ -198,11 +207,14 @@ def create_task(coro):
     return t
 
 
+# Task used to suspend and resume top-level await.
+_top_level_task = Task(TopLevelCoro, globals())
+
 ################################################################################
 # Event loop wrapper
 
 
-cur_task = None
+cur_task = _top_level_task
 
 
 class Loop: