hardbyte
bus.send() fails with `No buffer space available` despite not reaching the timeout
Describe the bug
When sending a lot of packets very quickly to a physical socketcan bus, bus.send() raises a can.exceptions.CanOperationError: Failed to transmit: No buffer space available [Error Code 105] despite the timeout not being reached.
To Reproduce
Send 100 frames to a physical socketcan bus with timeout=1.0 for each frame and no delay between sending the frames.
Expected behavior
can.send() should retry transmission until buffer space is available or the timeout is exceeded.
Additional context
OS and version: Ubuntu 24.04
Python version: 3.12.3
python-can version: 4.6.1
python-can interface/s (if applicable): socketcan (for a CANable 2.0 running CANnectivity)
Traceback and logs
$ ip -d link show pcan-e
12: pcan-e: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UP mode DEFAULT group default qlen 10
link/can promiscuity 0 allmulti 0 minmtu 0 maxmtu 0
can state ERROR-ACTIVE restart-ms 0
bitrate 1024096 sample-point 0.746
tq 5 prop-seg 61 phase-seg1 62 phase-seg2 42 sjw 21 brp 1
gs_usb: tseg1 2..256 tseg2 2..128 sjw 1..128 brp 1..512 brp_inc 1
clock 170000000 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 tso_max_size 65536 tso_max_segs 65535 gro_max_size 65536 parentbus usb parentdev 1-7.3:1.0
$ time python tests/cantest.py
Traceback (most recent call last):
File "/home/gos/gena-sidl/Integration-Tests/env/lib/python3.12/site-packages/can/interfaces/socketcan/socketcan.py", line 889, in _send_once
sent = self.socket.send(data)
^^^^^^^^^^^^^^^^^^^^^^
OSError: [Errno 105] No buffer space available
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/home/gos/gena-sidl/Integration-Tests/tests/cantest.py", line 12, in <module>
bus.send(msg, timeout=1.0)
File "/home/gos/gena-sidl/Integration-Tests/env/lib/python3.12/site-packages/can/interfaces/socketcan/socketcan.py", line 874, in send
sent = self._send_once(data, channel)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/gos/gena-sidl/Integration-Tests/env/lib/python3.12/site-packages/can/interfaces/socketcan/socketcan.py", line 891, in _send_once
raise can.CanOperationError(
can.exceptions.CanOperationError: Failed to transmit: No buffer space available [Error Code 105]
SocketcanBus was not properly shut down
real 0m0.112s
user 0m0.099s
sys 0m0.013s
with the following test script:
#!/usr/bin/env python3
import can
N_PACKETS = 100
bus = can.Bus(interface="socketcan", channel="pcan-e")
data = bytes([0xAB] * 8)
for _ in range(N_PACKETS):
msg = can.Message(arbitration_id=1, is_extended_id=True, data=data)
bus.send(msg, timeout=1.0)
bus.shutdown()
Modifying SocketcanBus._send_once() as follows fixes the issue:
--- a/home/jasper/Downloads/socketcan.py
+++ b/env/lib/python3.12/site-packages/can/interfaces/socketcan/socketcan.py
@@ -883,16 +883,19 @@ class SocketcanBus(BusABC): # pylint: disable=abstract-method
def _send_once(self, data: bytes, channel: Optional[str] = None) -> int:
try:
if self.channel == "" and channel:
# Message must be addressed to a specific channel
sent = self.socket.sendto(data, (channel,))
else:
sent = self.socket.send(data)
except OSError as error:
+ if error.errno == errno.ENOBUFS:
+ return 0
+
raise can.CanOperationError(
f"Failed to transmit: {error.strerror}", error.errno
) from error
return sent
def _send_periodic_internal(
self,
msgs: Union[Sequence[Message], Message],
but I'm not sure if this essentially turns the while-loop in SocketcanBus.send() into a busy-waiting loop.