webassembly: Add JavaScript-based asyncio support.

This commit adds a significant portion of the existing MicroPython asyncio
module to the webassembly port, using parts of the existing asyncio code
and some custom JavaScript parts.

The key difference to the standard asyncio is that this version uses the
JavaScript runtime to do the actual scheduling and waiting on events, eg
Promise fulfillment, timeouts, fetching URLs.

This implementation does not include asyncio.run(). Instead one just uses
asyncio.create_task(..) to start tasks and then returns to the JavaScript.
Then JavaScript will run the tasks.

The implementation here tries to reuse as much existing asyncio code as
possible, and gets all the semantics correct for things like cancellation
and asyncio.wait_for.  An alternative approach would reimplement Task,
Event, etc using JavaScript Promise's.  That approach is very difficult to
get right when trying to implement cancellation (because it's not possible
to cancel a JavaScript Promise).

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

tests/ports/webassembly/asyncio_create_task.mjs

@@ -0,0 +1,44 @@
+// Test asyncio.create_task(), and tasks waiting on a Promise.
+
+const mp = await (await import(process.argv[2])).loadMicroPython();
+
+globalThis.p0 = new Promise((resolve, reject) => {
+    resolve(123);
+});
+
+globalThis.p1 = new Promise((resolve, reject) => {
+    setTimeout(() => {
+        console.log("setTimeout resolved");
+        resolve(456);
+    }, 200);
+});
+
+mp.runPython(`
+import js
+import asyncio
+
+async def task(id, promise):
+    print("task start", id)
+    print("task await", id, await promise)
+    print("task await", id, await promise)
+    print("task end", id)
+
+print("start")
+t1 = asyncio.create_task(task(1, js.p0))
+t2 = asyncio.create_task(task(2, js.p1))
+print("t1", t1.done(), t2.done())
+print("end")
+`);
+
+// Wait for p1 to fulfill so t2 can continue.
+await globalThis.p1;
+
+// Wait a little longer so t2 can complete.
+await new Promise((resolve, reject) => {
+    setTimeout(resolve, 10);
+});
+
+mp.runPython(`
+print("restart")
+print("t1", t1.done(), t2.done())
+`);

tests/ports/webassembly/asyncio_create_task.mjs.exp

@@ -0,0 +1,14 @@
+start
+t1 False False
+end
+task start 1
+task start 2
+task await 1 123
+task await 1 123
+task end 1
+setTimeout resolved
+task await 2 456
+task await 2 456
+task end 2
+restart
+t1 True True

tests/ports/webassembly/asyncio_sleep.mjs

@@ -0,0 +1,25 @@
+// Test asyncio.sleep(), both at the top level and within a task.
+
+const mp = await (await import(process.argv[2])).loadMicroPython();
+
+await mp.runPythonAsync(`
+import time
+import asyncio
+
+print("main start")
+t0 = time.time()
+await asyncio.sleep(0.25)
+dt = time.time() - t0
+print(0.2 <= dt <= 0.3)
+
+async def task():
+    print("task start")
+    t0 = time.time()
+    await asyncio.sleep(0.25)
+    dt = time.time() - t0
+    print(0.2 <= dt <= 0.3)
+    print("task end")
+
+asyncio.create_task(task())
+print("main end")
+`);

tests/ports/webassembly/asyncio_sleep.mjs.exp

@@ -0,0 +1,6 @@
+main start
+True
+main end
+task start
+True
+task end

tests/run-tests.py

@@ -681,6 +681,17 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
         elif args.target == "webassembly":
             skip_tests.add("basics/string_format_modulo.py")  # can't print nulls to stdout
             skip_tests.add("basics/string_strip.py")  # can't print nulls to stdout
+            skip_tests.add("extmod/asyncio_basic2.py")
+            skip_tests.add("extmod/asyncio_cancel_self.py")
+            skip_tests.add("extmod/asyncio_current_task.py")
+            skip_tests.add("extmod/asyncio_exception.py")
+            skip_tests.add("extmod/asyncio_gather_finished_early.py")
+            skip_tests.add("extmod/asyncio_get_event_loop.py")
+            skip_tests.add("extmod/asyncio_heaplock.py")
+            skip_tests.add("extmod/asyncio_loop_stop.py")
+            skip_tests.add("extmod/asyncio_new_event_loop.py")
+            skip_tests.add("extmod/asyncio_threadsafeflag.py")
+            skip_tests.add("extmod/asyncio_wait_for_fwd.py")
             skip_tests.add("extmod/binascii_a2b_base64.py")
             skip_tests.add("extmod/re_stack_overflow.py")
             skip_tests.add("extmod/time_res.py")