[Bug]: Timeout Exceptions After 5–10 Minutes When Reading 207 Memory Blocks with S7 Protocol in v0.13.0 (Works in v0.12.0)

[shekhartanwar]

What happened?

Issue
After upgrading to library version 0.13.0, my application, which reads 207 memory blocks from a PLC using the S7 protocol every second, starts throwing timeout exceptions after running for 5–10 minutes. With version 0.12.0, the application runs without issues.

Expected behavior
The application should continuously read all 207 memory blocks every second without timeout exceptions, as it does with version 0.12.0.

Steps to reproduce

1. Use library version 0.13.0.
2. Continuously read 207 memory blocks from a PLC every second.
3. Observe that after 5–10 minutes, timeout exceptions occur.

Additional context
In 0.12.0, I manually divided the 207 memory blocks into ~21 PlcReadRequests (max 20 blocks per request) using batching.
In 0.13.0, batching is handled internally by the library.
No other changes were made to the application code.
This issue blocks me from upgrading to 0.13.0.

Environment
Library version: 0.13.0 (works in 0.12.0)
Protocol: S7
Number of memory blocks: 207
Frequency: 1 read per second

Version

v0.13.0

Programming Languages

• plc4c
• plc4go
• plc4j
• plc4net
• plc4py

Protocols

• AB-Ethernet
• ADS /AMS
• BACnet/IP
• C-Bus
• CANopen
• EtherNet/IP
• Firmata
• IEC-69870
• KNXnet/IP
• Modbus
• OPC-UA
• Profinet
• S7
• S7-light

[sruehl]

try 0.13.1

[chrisdutz]

So I think we added quite a bit of timeout handling in the general core. It might be that some if these are now firing. More than 200DBs every second is quite a lot.

The batching you are referring to, that I added due 0.13.0 is mainly tied to the s7-light driver. Could you please try using that instead? (just change the URL from s7:// to s7-light://

[shekhartanwar]

Hi @chrisdutz Yes s7-light is working fine with v0.13.1, but i am seeing below errors in the logs.

`2025-09-05T07:16:28.254Z ERROR 1 --- [ntLoopGroup-3-1] o.a.p.j.s.c.DefaultNettyPlcConnection : unknown error, close the connection

java.net.SocketException: Connection reset
`

`2025-09-05T07:16:30.242Z ERROR 1 --- [ool-24-thread-1] c.v.p.service.impl.PlcS7Service : Unexpected exception occurred during executing read request

java.util.concurrent.TimeoutException: null`

But it starts working again from next request.

I am using Single PlcConnection for read and write request that happens every second. Should i optimize anything here? Any Suggestions will be helpful.

[chrisdutz]

Well ... does it generally work, or are you just seeing that in the logs and generally everything is working?
In general S7 devices are some times a little "bitchy" ... if they don't like something, they just hang up. So some times a bit might flip or the S7 thinks one flipped and it just hangs up .... especially under heavy network loads, I've seen that happen.

Are you using the connection cache or are you opening a connection for every request? I hope you're using the connection-cache, as that should handle the reconnects and also improve performance quite a bit.

[shekhartanwar]

Well ... does it generally work, or are you just seeing that in the logs and generally everything is working? In general S7 devices are some times a little "bitchy" ... if they don't like something, they just hang up. So some times a bit might flip or the S7 thinks one flipped and it just hangs up .... especially under heavy network loads, I've seen that happen.

Are you using the connection cache or are you opening a connection for every request? I hope you're using the connection-cache, as that should handle the reconnects and also improve performance quite a bit.

I am creating only 1 instance of PlcConnection and using it in all read/write requests, i have created a getConnection() method that whenever called checks if plcConnection.isConnected() then accordingly reconnects if not connected. But at the end, the connection object is Singleton. This connection stays open till it's automatically disconnected.
As fas as i understood, for using Connection Cache, i have to close connection every time so that all other threads can use it.

[chrisdutz]

Hi,

yeah ... well you "technically" close it after doing your thing, but it doesn't really close, it but return it to the cache (and potentially waiting threads).
In your case I guess you have implemented part of the functionality. I just wanted to make sure that you don't expect the connection to be open indeffinitely. If you're checking things and potentially re-creating connections, you should be fine. But I guess your log output is simply the log of an operation failing and your code then creates a new connection the next time.

[glcj]

Hello,
Can you tell me how many bytes (on average) you're reading from each DB, and if it's not a problem, the CPU model with the assigned communications load?
I'm in a remote location without much connectivity, but I have access to a CPU315 2PN/DP.
I'm interested in evaluating that test.
Best regards,

[shekhartanwar]

Hello, Can you tell me how many bytes (on average) you're reading from each DB, and if it's not a problem, the CPU model with the assigned communications load? I'm in a remote location without much connectivity, but I have access to a CPU315 2PN/DP. I'm interested in evaluating that test. Best regards,

I am not sure of PLC Configuration because that is managed by some other team. I read approx. 250 bytes per second from single memory block with different offsets. Correction: Single DB with different offsets.

[shekhartanwar]

Hi,

yeah ... well you "technically" close it after doing your thing, but it doesn't really close, it but return it to the cache (and potentially waiting threads). In your case I guess you have implemented part of the functionality. I just wanted to make sure that you don't expect the connection to be open indeffinitely. If you're checking things and potentially re-creating connections, you should be fine. But I guess your log output is simply the log of an operation failing and your code then creates a new connection the next time.

Hello, I am seeing frequent connection resets with v0.13.1 s7-light driver. It reconnects within 1-2 seconds max, that's why i don't have a problem here, it will be nice to have connection stable.

Please check the logs below.

2025-09-09T03:55:41.993Z ERROR 1 --- [oopGroup-1424-1] o.a.p.j.s.c.DefaultNettyPlcConnection    : unknown error, close the connection
--
java.net.SocketException: Connection reset
at java.base/sun.nio.ch.SocketChannelImpl.throwConnectionReset(Unknown Source) ~[na:na]
at java.base/sun.nio.ch.SocketChannelImpl.read(Unknown Source) ~[na:na]
at io.netty.buffer.PooledByteBuf.setBytes(PooledByteBuf.java:255) ~[netty-buffer-4.1.123.Final.jar!/:4.1.123.Final]
at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:1132) ~[netty-buffer-4.1.123.Final.jar!/:4.1.123.Final]
at io.netty.channel.socket.nio.NioSocketChannel.doReadBytes(NioSocketChannel.java:356) ~[netty-transport-4.1.123.Final.jar!/:4.1.123.Final]
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:151) ~[netty-transport-4.1.123.Final.jar!/:4.1.123.Final]
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:796) ~[netty-transport-4.1.123.Final.jar!/:4.1.123.Final]
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:732) ~[netty-transport-4.1.123.Final.jar!/:4.1.123.Final]
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:658) ~[netty-transport-4.1.123.Final.jar!/:4.1.123.Final]
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:562) ~[netty-transport-4.1.123.Final.jar!/:4.1.123.Final]
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:998) ~[netty-common-4.1.123.Final.jar!/:4.1.123.Final]
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-common-4.1.123.Final.jar!/:4.1.123.Final]
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[netty-common-4.1.123.Final.jar!/:4.1.123.Final]
at java.base/java.lang.Thread.run(Unknown Source) ~[na:na]
2025-09-09T03:55:41.996Z  INFO 1 --- [oopGroup-1424-1] o.a.p.j.s.c.NettyChannelFactory          : Channel is closed, closing worker Group also
2025-09-09T03:55:42.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T03:55:42.092Z  INFO 1 --- [ool-14-thread-1] o.a.plc4x.java.DefaultPlcDriverManager   : Instantiating new PLC Driver Manager with class loader null
2025-09-09T03:55:42.092Z  INFO 1 --- [ool-14-thread-1] o.a.plc4x.java.DefaultPlcDriverManager   : Registering available drivers...
2025-09-09T03:55:42.092Z ERROR 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Plc connect error : Unable to find driver for protocol 's7-light'
2025-09-09T03:55:42.092Z ERROR 1 --- [ool-14-thread-1] c.v.p.watchdog.impl.WatchdogImpl         : Exception occurred while initializing watchdog builder, Message : PLC connection is down
2025-09-09T03:55:42.092Z ERROR 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Exception occurred while executing write request, Message
java.lang.NullPointerException: null
2025-09-09T03:55:42.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T03:55:42.168Z  INFO 1 --- [ool-10-thread-1] o.a.plc4x.java.DefaultPlcDriverManager   : Instantiating new PLC Driver Manager with class loader null
2025-09-09T03:55:42.168Z  INFO 1 --- [ool-10-thread-1] o.a.plc4x.java.DefaultPlcDriverManager   : Registering available drivers...
2025-09-09T03:55:42.168Z ERROR 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Plc connect error : Unable to find driver for protocol 's7-light'
2025-09-09T03:55:42.168Z ERROR 1 --- [ool-10-thread-1] c.v.p.watchdog.impl.WatchdogImpl         : Exception occurred while initializing watchdog builder, Message : PLC connection is down
2025-09-09T03:55:42.168Z ERROR 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Exception occurred while executing write request, Message
java.lang.NullPointerException: null

2025-09-09T03:55:42.655Z  INFO 1 --- [   scheduling-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
--
2025-09-09T03:55:42.655Z  INFO 1 --- [   scheduling-1] o.a.plc4x.java.DefaultPlcDriverManager   : Instantiating new PLC Driver Manager with class loader org.springframework.boot.loader.launch.LaunchedClassLoader@568db2f2
2025-09-09T03:55:42.655Z  INFO 1 --- [   scheduling-1] o.a.plc4x.java.DefaultPlcDriverManager   : Registering available drivers...
2025-09-09T03:55:42.657Z  INFO 1 --- [   scheduling-1] o.a.plc4x.java.DefaultPlcDriverManager   : Registering driver for Protocol s7 (Siemens S7 (Basic))
2025-09-09T03:55:42.657Z  INFO 1 --- [   scheduling-1] o.a.plc4x.java.DefaultPlcDriverManager   : Registering driver for Protocol s7-light (Siemens S7 (Basic) (light))
2025-09-09T03:55:42.659Z  INFO 1 --- [   scheduling-1] o.a.p.j.transport.tcp.TcpChannelFactory  : Configuring Bootstrap with org.apache.plc4x.java.s7light.readwrite.configuration.S7TcpTransportConfiguration@6b245a65
2025-09-09T03:55:42.663Z  INFO 1 --- [oopGroup-1425-1] o.a.p.j.s.r.protocol.S7ProtocolLogic     : S7 Driver running in ACTIVE mode.
2025-09-09T03:55:42.675Z  INFO 1 --- [   scheduling-1] c.v.p.service.impl.PlcS7Service          : PLC Connection Created Successfully isConnected:true

Connection Reset Frequently.

2025-09-09T03:55:42.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
--
2025-09-09T03:55:42.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T03:55:42.655Z  INFO 1 --- [   scheduling-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T03:56:17.996Z  INFO 1 --- [ntContainer#0-4] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:00:29.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:00:29.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:00:29.307Z  INFO 1 --- [ntContainer#0-5] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:01:41.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:01:41.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:01:41.569Z  INFO 1 --- [ntContainer#0-2] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:18:56.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:18:56.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:18:56.323Z  INFO 1 --- [ntContainer#0-5] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:21:37.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:21:37.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:21:37.478Z  INFO 1 --- [ntContainer#0-5] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:27:00.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:27:00.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:27:00.655Z  INFO 1 --- [   scheduling-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:28:26.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:28:26.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:28:26.655Z  INFO 1 --- [   scheduling-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:32:32.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:32:32.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:32:32.655Z  INFO 1 --- [   scheduling-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:34:37.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:34:37.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:34:37.655Z  INFO 1 --- [   scheduling-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:41:01.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:41:01.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:41:01.655Z  INFO 1 --- [   scheduling-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:41:05.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:41:05.168Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:41:05.452Z  INFO 1 --- [ntContainer#0-4] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T04:42:39.042Z  INFO 1 --- [tContainer#0-10] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T05:01:46.092Z  INFO 1 --- [ool-14-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T05:01:46.174Z  INFO 1 --- [ool-10-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...
2025-09-09T05:01:46.644Z  INFO 1 --- [ntContainer#0-3] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection...

I can see error like Unable to find driver for protocol 's7-light' but in multiple retries it's able to find the driver.
I can also observe frequent connection resets throughout the day. This was not the case with 0.12.0 version. Is there anything else can i do here to improve the connection stability?

Is calling plcConnection.isConnected() every second from multiple threads (5-6) put load on PLC?

[shekhartanwar]

I created 2 PlcConnections for READ and WRITE operations and i can see now the connection reset happens only for READ operation.

2025-09-09T08:37:54.827Z  INFO 1 --- [ool-26-thread-2] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection Type READ
--
2025-09-09T08:40:03.822Z  INFO 1 --- [ool-26-thread-2] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection Type READ
2025-09-09T08:40:48.827Z  INFO 1 --- [ool-26-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection Type READ
2025-09-09T08:42:56.822Z  INFO 1 --- [ool-26-thread-2] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection Type READ
2025-09-09T08:42:57.857Z  INFO 1 --- [ool-26-thread-1] c.v.p.service.impl.PlcS7Service          : Creating PLC Connection Type READ

Looks like the READ operation is causing PLC to close the connection.