webassembly/asyncio: Implement asyncio.Event class.

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

ports/webassembly/asyncio.py

@@ -1,7 +1,32 @@
 # Minimal asyncio interface that uses JavaScript for scheduling.
 # Only implements a very small subset of the asyncio API.
 
-import jsffi
+import js, jsffi
+
+
+class Event:
+    def __init__(self):
+        self.clear()
+
+    def _set_callbacks(self, resolve, reject):
+        self._resolve = resolve
+        self._reject = reject
+
+    def is_set(self):
+        return self._promise is None
+
+    def set(self):
+        if self._promise is not None:
+            self._resolve()
+            self._promise = None
+
+    def clear(self):
+        self._promise = js.Promise.new(self._set_callbacks)
+
+    async def wait(self):
+        if self._promise is not None:
+            await self._promise
+        return True
 
 
 class Task:

tests/ports/webassembly/asyncio_event.mjs

@@ -0,0 +1,57 @@
+// Test asyncio.Event.
+//
+// This test is taken from tests/extmod/asyncio_event.py and adapted:
+// - changed asyncio.run(main()) to await main()
+// - removed cancel and wait_for parts of the test
+
+const mp = await (await import(process.argv[2])).loadMicroPython();
+
+await mp.runPythonAsync(`
+import asyncio
+
+async def task(id, ev):
+    print("start", id)
+    print(await ev.wait())
+    print("end", id)
+
+
+async def main():
+    ev = asyncio.Event()
+
+    # Set and clear without anything waiting, and test is_set()
+    print(ev.is_set())
+    ev.set()
+    print(ev.is_set())
+    ev.clear()
+    print(ev.is_set())
+
+    # Create 2 tasks waiting on the event
+    print("----")
+    asyncio.create_task(task(1, ev))
+    asyncio.create_task(task(2, ev))
+    print("yield")
+    await asyncio.sleep(0)
+    print("set event")
+    ev.set()
+    print("yield")
+    await asyncio.sleep(0)
+
+    # Create a task waiting on the already-set event
+    print("----")
+    asyncio.create_task(task(3, ev))
+    print("yield")
+    await asyncio.sleep(0)
+
+    # Clear event, start a task, then set event again
+    print("----")
+    print("clear event")
+    ev.clear()
+    asyncio.create_task(task(4, ev))
+    await asyncio.sleep(0)
+    print("set event")
+    ev.set()
+    await asyncio.sleep(0)
+
+
+await main()
+`);

tests/ports/webassembly/asyncio_event.mjs.exp

@@ -0,0 +1,24 @@
+False
+True
+False
+----
+yield
+start 1
+start 2
+set event
+yield
+True
+end 1
+True
+end 2
+----
+yield
+start 3
+True
+end 3
+----
+clear event
+start 4
+set event
+True
+end 4