read(-1) blocking?

[GHamblin]

It appears that sometimes stdin.buffer.read(-1) is blocking. Is there any way to determine if something is in the buffer before attempting to read from it?

[mikewadsten]

Hi,

Would you be able to provide a simplified piece of example code which demonstrates this issue? Also, can you tell us which XBee product and firmware version you are seeing this on?

[GHamblin]

Here is the function that's causing me issues. It will hang until I send it a newline. The data it receives from the device is already terminated with a new line, But it blocks until I manually send it a newline. Thanks for looking into this. I am a Python noob, so I may have also done something wrong without realizing it. def subscribe_test(client_id=CLIENT_ID, hostname=SERVER, topic=SUB_TOPIC, blocking=False): """ Connects to the MQTT server subscribes to a topic and waits for messages coming from that topic. :param client_id: Unique identifier for the device connected. :param hostname: Host name to connect to. :param topic: Name of the topic to subscribe. :param blocking: `True` to block the client waiting for messages, `False` to poll for messages. """ # Connect to the MQTT server. client = MQTTClient(client_id, hostname) client.KEEP_QOS0 = False client.NO_QUEUE_DUPS = True client.MSG_QUEUE_MAX = 2 client.set_callback(sub_cb) print("- Connecting to '%s'... " % hostname, end="") if not client.connect(clean_session=False): print("New session being set up") client.subscribe(b"/Machines/100002/cmd", qos=1, resubscribe=True) print("[OK]") # Subscribe to topic. # print("- Subscribing to topic '%s'... " % "/Machines/100002/cmd", end="") # client.subscribe("/Machines/100002/cmd") print("[OK]") # Wait for messages. print("Waiting for input lines") loops = 0 while True: client.check_msg() if (begin = stdin.buffer.read(-1)): data = stdin.buffer.readline() data = begin + data if len(data) > 20: publish_message(client, topic, data) # Need to sleep to avoid 100% CPU usage. utime.sleep_ms(200) loops += 1 if loops > 7500: client.ping() loops = 0 while client.is_conn_issue(): # If the connection is successful, the is_conn_issue # method will not return a connection error. client.reconnect() else: client.resubscribe() client.check_msg() client.send_queue()

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On Mon, Feb 22, 2021 at 9:42 AM Mike Wadsten ***@***.***> wrote: Hi, Would you be able to provide a simplified piece of example code which demonstrates this issue? Also, can you tell us which XBee product and firmware version you are seeing this on? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#65 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA45DCWC4DGLYWKNUVVEAUDTAKCPBANCNFSM4X7QPUJQ> .

[mikewadsten]

if (begin = stdin.buffer.read(-1)):

That is not (or should not be) valid Python/MicroPython. I take it you're coming from C or C++ (or similar language). Variable assignments in Python are not expressions, and you cannot do this. https://www.quora.com/Why-does-the-Python-assignment-not-return-a-value

If you send Ctrl-C while the program is hung, what line does the resulting traceback point to? That will tell you (and us) where it is hanging.

[GHamblin]

Thanks. I'll try ^C and get back to you. So begin = stdin.buffer.read(-1) should be a line by itself, followed by an if begin: ?

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On Tue, Feb 23, 2021 at 2:35 PM Mike Wadsten ***@***.***> wrote: if (begin = stdin.buffer.read(-1)): That is not (or should not be) valid Python/MicroPython. I take it you're coming from C or C++ (or similar language). Variable assignments in Python are not expressions, and you cannot do this. https://www.quora.com/Why-does-the-Python-assignment-not-return-a-value If you send Ctrl-C while the program is hung, what line does the resulting traceback point to? That will tell you (and us) where it is hanging. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#65 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA45DCXRABRFGE23UB4FG43TAQNSNANCNFSM4X7QPUJQ> .

[mikewadsten]

So begin = stdin.buffer.read(-1) should be a line by itself, followed by an
if begin: ?

Yes, exactly.

[GHamblin]

Here's the result of the ^C. And yes I have had a long relationship with C in the embedded world. Traceback (most recent call last): File "main", line 139, in <module> =subscribe_test(blocking=False ) File "main", line 96, in subscribe_test = utime.sleep_ms(200) KeyboardInterrupt:

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On Tue, Feb 23, 2021 at 2:35 PM Mike Wadsten ***@***.***> wrote: if (begin = stdin.buffer.read(-1)): That is not (or should not be) valid Python/MicroPython. I take it you're coming from C or C++ (or similar language). Variable assignments in Python are not expressions, and you cannot do this. https://www.quora.com/Why-does-the-Python-assignment-not-return-a-value If you send Ctrl-C while the program is hung, what line does the resulting traceback point to? That will tell you (and us) where it is hanging. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#65 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA45DCXRABRFGE23UB4FG43TAQNSNANCNFSM4X7QPUJQ> .