read(-1) blocking?
Opened this issue · 6 comments
GHamblin commented
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 commented
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 commented
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()
…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?
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mikewadsten commented
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 commented
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: ?
…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.
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You are receiving this because you authored the thread.
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<#65 (comment)>,
or unsubscribe
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mikewadsten commented
So begin = stdin.buffer.read(-1) should be a line by itself, followed by an
if begin: ?
Yes, exactly.
GHamblin commented
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:
…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>
.