[Bug]: S7 protocol leaks memory

[michele-tramonti]

What happened?

i'm using plc4j version 0.13.0, connecting to S7_400.
sometimes (I'm not able to identify the specific reason or pattern) i see this error in log:

[2025-09-04 15:51:56] [info] Recent access records:
[2025-09-04 15:51:56] [info] Created at:
[2025-09-04 15:51:56] [info] #011io.netty.buffer.PooledByteBufAllocator.newDirectBuffer(PooledByteBufAllocator.java:410)
[2025-09-04 15:51:56] [info] #011io.netty.buffer.AbstractByteBufAllocator.directBuffer(AbstractByteBufAllocator.java:188)
[2025-09-04 15:51:56] [info] #011io.netty.buffer.UnsafeByteBufUtil.copy(UnsafeByteBufUtil.java:454)
[2025-09-04 15:51:56] [info] #011io.netty.buffer.PooledUnsafeDirectByteBuf.copy(PooledUnsafeDirectByteBuf.java:216)
[2025-09-04 15:51:56] [info] #011io.netty.buffer.AbstractByteBuf.copy(AbstractByteBuf.java:1194)
[2025-09-04 15:51:56] [info] #011org.apache.plc4x.java.s7.readwrite.protocol.S7HMuxImpl.encode(S7HMuxImpl.java:136)
[2025-09-04 15:51:56] [info] #011org.apache.plc4x.java.s7.readwrite.protocol.S7HMuxImpl.encode(S7HMuxImpl.java:1)
[2025-09-04 15:51:56] [info] #011io.netty.handler.codec.MessageToMessageCodec$2.encode(MessageToMessageCodec.java:85)
[2025-09-04 15:51:56] [info] #011io.netty.handler.codec.MessageToMessageEncoder.write(MessageToMessageEncoder.java:90)
[2025-09-04 15:51:56] [info] #011io.netty.handler.codec.MessageToMessageCodec.write(MessageToMessageCodec.java:130)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:891)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:875)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:984)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:868)
[2025-09-04 15:51:56] [info] #011io.netty.handler.codec.MessageToByteEncoder.write(MessageToByteEncoder.java:113)
[2025-09-04 15:51:56] [info] #011io.netty.handler.codec.ByteToMessageCodec.write(ByteToMessageCodec.java:108)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:891)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:875)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:984)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:868)
[2025-09-04 15:51:56] [info] #011io.netty.handler.codec.MessageToMessageEncoder.write(MessageToMessageEncoder.java:113)
[2025-09-04 15:51:56] [info] #011io.netty.handler.codec.MessageToMessageCodec.write(MessageToMessageCodec.java:130)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:891)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:875)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:984)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:868)
[2025-09-04 15:51:56] [info] #011io.netty.handler.codec.MessageToMessageEncoder.write(MessageToMessageEncoder.java:113)
[2025-09-04 15:51:56] [info] #011io.netty.handler.codec.MessageToMessageCodec.write(MessageToMessageCodec.java:130)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:891)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.invokeWriteAndFlush(AbstractChannelHandlerContext.java:956)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:982)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:950)
[2025-09-04 15:51:56] [info] #011io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:1000)
[2025-09-04 15:51:56] [info] #011io.netty.channel.DefaultChannelPipeline.writeAndFlush(DefaultChannelPipeline.java:974)
[2025-09-04 15:51:56] [info] #011org.apache.plc4x.java.spi.Plc4xNettyWrapper$1.sendToWire(Plc4xNettyWrapper.java:100)
[2025-09-04 15:51:56] [info] #011org.apache.plc4x.java.spi.internal.DefaultSendRequestContext.handle(DefaultSendRequestContext.java:108)
[2025-09-04 15:51:56] [info] #011org.apache.plc4x.java.spi.internal.DefaultSendRequestContext.handle(DefaultSendRequestContext.java:1)
[2025-09-04 15:51:56] [info] #011org.apache.plc4x.java.s7.readwrite.protocol.S7ProtocolLogic.lambda$42(S7ProtocolLogic.java:1535)
[2025-09-04 15:51:56] [info] #011org.apache.plc4x.java.spi.transaction.RequestTransactionManager$TransactionOperation.run(RequestTransactionManager.java:225)
[2025-09-04 15:51:56] [info] #011java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
[2025-09-04 15:51:56] [info] #011java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[2025-09-04 15:51:56] [info] #011java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
[2025-09-04 15:51:56] [info] #011java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
[2025-09-04 15:51:56] [info] #011java.base/java.lang.Thread.run(Thread.java:829)

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

[glcj]

Hello,
I have 0.13.0-SNAPSHOT running 24/7, with some sporadic disconnection, but never a memory consumption error.
Can you tell me your use case so I can replicate the problem? Next week I'll have access to an S7-400 (417) in the office.
I usually use the profiler to detect a memory leak; if you can use the "jconsole" and take a screenshot, that might help.
Best regards,

[chrisdutz]

And if you're not relying on the subscription support, you can try the s7-light driver.

[michele-tramonti]

Thanks glcj for your reply. My use case is as follows: I have a Spring Boot application running on a Tomcat server, with a service method called every 10 seconds that reads some values ​​from the S7 PLC, saving them to the database, and sends other values ​​to the PLC by reading them from the database. The peculiarity of this method is that it is internally separated into three sequential parts, each of which opens and closes (with a Java try-with) the connection to the PLC.

thank you chrisdutz for your reply, I hadn't thought about it: maybe I can try

[daniells92]

Hello,
we have the same issue.
plc4j version 0.12.0 connected to a S7_300.
The application runs 24/7.
It reads every second from the PLC and writes event based every few seconds.
Sometimes it takes 1-2 weeks until an OutOfMemmoryError, sometimes it's over one month.
Seems like it directly allocates memory and never releases it.

2025-07-21 08:49:33,460  INFO | plc4x-tm-thread-2    | o.a.p.java.spi.transaction.RequestTransactionManager    | java.lang.OutOfMemoryError: Cannot reserve 4194304 bytes of direct buffer memory (allocated: 2118267416, limit: 2122317824)
2025-07-21 08:49:42,987  WARN | scheduling-1         | de.myApp.plcbridge.s7.S7Reader                | Could not execute read request!
java.util.concurrent.ExecutionException: org.apache.plc4x.java.api.exceptions.PlcProtocolException: Error reading
	at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:396)
	at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2073)
	at de.myApp.plcbridge.s7.S7Reader.readFromPlc(S7Reader.java:66)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at org.springframework.scheduling.support.ScheduledMethodRunnable.runInternal(ScheduledMethodRunnable.java:130)
	at org.springframework.scheduling.support.ScheduledMethodRunnable.lambda$run$2(ScheduledMethodRunnable.java:124)
	at io.micrometer.observation.Observation.observe(Observation.java:498)
	at org.springframework.scheduling.support.ScheduledMethodRunnable.run(ScheduledMethodRunnable.java:124)
	at org.springframework.scheduling.config.Task$OutcomeTrackingRunnable.run(Task.java:85)
	at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:54)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
	at java.base/java.util.concurrent.FutureTask.runAndReset(FutureTask.java:358)
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:305)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
	at java.base/java.lang.Thread.run(Thread.java:1583)
Caused by: org.apache.plc4x.java.api.exceptions.PlcProtocolException: Error reading
	at org.apache.plc4x.java.s7.readwrite.protocol.S7ProtocolLogic.lambda$18(S7ProtocolLogic.java:314)
	at java.base/java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:863)
	at java.base/java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:841)
	at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:510)
	at java.base/java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:2194)
	at org.apache.plc4x.java.s7.readwrite.protocol.S7ProtocolLogic$TransactionErrorCallback.accept(S7ProtocolLogic.java:2202)
	at org.apache.plc4x.java.s7.readwrite.protocol.S7ProtocolLogic$TransactionErrorCallback.accept(S7ProtocolLogic.java:1)
	at org.apache.plc4x.java.spi.Plc4xNettyWrapper.lambda$8(Plc4xNettyWrapper.java:253)
	at org.apache.plc4x.java.spi.netty.NettyHashTimerTimeoutManager.lambda$0(NettyHashTimerTimeoutManager.java:55)
	at io.netty.util.HashedWheelTimer$HashedWheelTimeout.run(HashedWheelTimer.java:713)
	at io.netty.util.concurrent.ImmediateExecutor.execute(ImmediateExecutor.java:34)
	at io.netty.util.HashedWheelTimer$HashedWheelTimeout.expire(HashedWheelTimer.java:701)
	at io.netty.util.HashedWheelTimer$HashedWheelBucket.expireTimeouts(HashedWheelTimer.java:787)
	at io.netty.util.HashedWheelTimer$Worker.run(HashedWheelTimer.java:501)
	... 1 common frames omitted
Caused by: java.util.concurrent.TimeoutException: null
	at org.apache.plc4x.java.spi.netty.NettyHashTimerTimeoutManager.lambda$0(NettyHashTimerTimeoutManager.java:54)
	... 6 common frames omitted`

[sruehl]

make sure to use -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/tmp/somedir" to capture more details on what the offenders are

[daniells92]

here is a heap dump from last week when the issue occured:

heapdump-1757318542419.zip