Add an example which breaks shielded proc waits

examples/multiple_streams_one_portal.py

@@ -0,0 +1,45 @@
+import trio
+import tractor
+
+
+log = tractor.log.get_logger('multiportal')
+
+
+async def stream_data(seed=10):
+    log.info("Starting stream task")
+
+    for i in range(seed):
+        yield i
+        await trio.sleep(0)  # trigger scheduler
+
+
+async def stream_from_portal(p, consumed):
+
+    async for item in await p.run(stream_data):
+        if item in consumed:
+            consumed.remove(item)
+        else:
+            consumed.append(item)
+
+
+async def main():
+
+    async with tractor.open_nursery(loglevel='info') as an:
+
+        p = await an.start_actor('stream_boi', enable_modules=[__name__])
+
+        consumed = []
+
+        async with trio.open_nursery() as n:
+            for i in range(2):
+                n.start_soon(stream_from_portal, p, consumed)
+
+        # both streaming consumer tasks have completed and so we should
+        # have nothing in our list thanks to single threadedness
+        assert not consumed
+
+        await an.cancel()
+
+
+if __name__ == '__main__':
+    trio.run(main)