add graceful shutdown example

examples/graceful_shutdown.py

@@ -0,0 +1,80 @@
+import asyncio
+import signal
+import sys
+
+import nats
+
+
+def sig_cb(shutdown_event: asyncio.Event):
+    print("received shutdown signal")
+    # Setting shutdown event to true, so other listeners can close
+    shutdown_event.set()
+
+
+async def nats_consumer(shutdown_event: asyncio.Event):
+    # Connect to NATS!
+    try:
+        nc = await nats.connect(
+            servers=["nats://127.0.0.1:4222"],
+            # Setting max rc attempts in order to prevent termination block
+            max_reconnect_attempts=3,
+        )
+    except Exception as e:
+        print(e)
+        return
+
+    # Callback for sub
+    async def cb(msg):
+        print("received: ", msg)
+
+    # Receive messages on 'foo'
+    await nc.subscribe("foo", cb=cb)
+
+    # Wait until shutdown event is set to release resources
+    await shutdown_event.wait()
+
+    await nc.drain()
+    print("gracefully closed nats consumer")
+
+
+async def nats_producer(shutdown_event: asyncio.Event):
+    # Connect to NATS!
+    try:
+        nc = await nats.connect(
+            servers=["nats://127.0.0.1:4222"],
+            # Setting max rc attempts in order to prevent termination block
+            max_reconnect_attempts=3,
+        )
+    except Exception as e:
+        print(e)
+        return
+
+    while not shutdown_event.is_set():
+        await nc.publish("foo", b"bar")
+        await asyncio.sleep(1)
+
+    await nc.drain()
+    print("gracefully closed nats producer")
+
+
+async def main(shutdown_event: asyncio.Event):
+    nats_consumer_task = asyncio.create_task(nats_consumer(shutdown_event))
+    nats_producer_task = asyncio.create_task(nats_producer(shutdown_event))
+
+    await asyncio.gather(*[nats_consumer_task, nats_producer_task])
+
+    sys.exit(0)
+
+
+if __name__ == "__main__":
+    # Creating shutdown event to notify child routines of a shutdown
+    shutdown_event = asyncio.Event()
+    try:
+        loop = asyncio.new_event_loop()
+        # Setting signals handlers to catch termination and interruption events
+        loop.add_signal_handler(signal.SIGTERM, sig_cb, shutdown_event)
+        loop.add_signal_handler(signal.SIGINT, sig_cb, shutdown_event)
+        loop.run_until_complete(main(shutdown_event))
+        loop.close()
+    except KeyboardInterrupt:
+        print("interrupted by ctrl+c")