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Merged
kevinherron merged 8 commits into from
Mar 14, 2026
Merged

Lazy-initialize SerialPort in transport classes #145

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c936caa
Lazy-initialize SerialPort in transport classes
kevinherron Mar 14, 2026
d9f1de4
Add tests for SerialPort behavior and exception handling
kevinherron Mar 14, 2026
8a345ff
Build and test on multiple OS
kevinherron Mar 14, 2026
be8f630
Add OS-specific tests for cross-platform port descriptor behavior
kevinherron Mar 14, 2026
0b57bae
Potential fix for pull request finding
kevinherron Mar 14, 2026
0fc296b
Potential fix for pull request finding
kevinherron Mar 14, 2026
9b1f952
Potential fix for pull request finding
kevinherron Mar 14, 2026
893f6b9
Potential fix for pull request finding
kevinherron Mar 14, 2026
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5 changes: 4 additions & 1 deletion .github/workflows/maven.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,10 @@ on:

jobs:
build:
runs-on: ubuntu-latest
runs-on: ${{ matrix.os }}
strategy:
matrix:
os: [ubuntu-latest, macos-latest, windows-latest]
steps:
- uses: actions/checkout@v4

Expand Down
94 changes: 69 additions & 25 deletions ...serial/src/main/java/com/digitalpetri/modbus/serial/client/SerialPortClientTransport.java
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,8 @@
import com.digitalpetri.modbus.ModbusRtuResponseFrameParser.Accumulated;
import com.digitalpetri.modbus.ModbusRtuResponseFrameParser.ParserState;
import com.digitalpetri.modbus.client.ModbusRtuClientTransport;
import com.digitalpetri.modbus.exceptions.ModbusConnectException;
import com.digitalpetri.modbus.exceptions.ModbusException;
import com.digitalpetri.modbus.internal.util.ExecutionQueue;
import com.digitalpetri.modbus.serial.SerialPortTransportConfig;
import com.fazecast.jSerialComm.SerialPort;
Expand All @@ -27,67 +29,97 @@ public class SerialPortClientTransport implements ModbusRtuClientTransport {

private final ExecutionQueue executionQueue;

private final SerialPort serialPort;
private volatile SerialPort serialPort;

private final SerialPortTransportConfig config;

public SerialPortClientTransport(SerialPortTransportConfig config) {
this.config = config;

serialPort = SerialPort.getCommPort(config.serialPort());

serialPort.setComPortParameters(
config.baudRate(),
config.dataBits(),
config.stopBits(),
config.parity(),
config.rs485Mode());

executionQueue = new ExecutionQueue(config.executor());
}

/**
* Return the underlying {@link SerialPort} used by this transport.
*
* <p>The serial port is lazily instantiated on first access.
*
* @return the configured {@link SerialPort} instance.
* @throws ModbusException if the serial port could not be created.
*/
public SerialPort getSerialPort() {
return serialPort;
public SerialPort getSerialPort() throws ModbusException {
SerialPort sp = this.serialPort;
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if (sp == null) {
synchronized (this) {
sp = this.serialPort;
if (sp == null) {
try {
sp = SerialPort.getCommPort(config.serialPort());
sp.setComPortParameters(
config.baudRate(),
config.dataBits(),
config.stopBits(),
config.parity(),
config.rs485Mode());
this.serialPort = sp;
} catch (Exception e) {
throw new ModbusException(
"failed to get comm port '%s'".formatted(config.serialPort()), e);
}
}
}
}
return sp;
}

@Override
public synchronized CompletableFuture<Void> connect() {
if (serialPort.isOpen()) {
SerialPort sp;
try {
sp = getSerialPort();
} catch (ModbusException e) {
return CompletableFuture.failedFuture(
new ModbusConnectException(e.getMessage(), e));
}

if (sp.isOpen()) {
return CompletableFuture.completedFuture(null);
} else {
if (serialPort.openPort()) {
if (sp.openPort()) {
frameParser.reset();

// note: no-op if already added from previous connect()
serialPort.addDataListener(new ModbusRtuDataListener());
sp.addDataListener(new ModbusRtuDataListener());

return CompletableFuture.completedFuture(null);
} else {
return CompletableFuture.failedFuture(
new Exception(
new ModbusConnectException(
"failed to open port '%s', lastErrorCode=%d"
.formatted(config.serialPort(), serialPort.getLastErrorCode())));
.formatted(config.serialPort(), sp.getLastErrorCode())));
}
}
}

/**
* {@inheritDoc}
*
* <p>The returned {@link CompletionStage} may complete exceptionally with a {@link
* ModbusException} if the serial port could not be closed.
*/
@Override
public synchronized CompletableFuture<Void> disconnect() {
if (serialPort.isOpen()) {
if (serialPort.closePort()) {
SerialPort sp = this.serialPort;
if (sp != null && sp.isOpen()) {
if (sp.closePort()) {
frameParser.reset();

return CompletableFuture.completedFuture(null);
} else {
return CompletableFuture.failedFuture(
new Exception(
new ModbusException(
"failed to close port '%s', lastErrorCode=%d"
.formatted(config.serialPort(), serialPort.getLastErrorCode())));
.formatted(config.serialPort(), sp.getLastErrorCode())));
}
} else {
return CompletableFuture.completedFuture(null);
Expand All @@ -96,11 +128,23 @@ public synchronized CompletableFuture<Void> disconnect() {

@Override
public boolean isConnected() {
return serialPort.isOpen();
SerialPort sp = this.serialPort;
return sp != null && sp.isOpen();
}

/**
* {@inheritDoc}
*
* <p>The returned {@link CompletionStage} may complete exceptionally with a {@link
* ModbusException} if the transport is not connected or if writing to the serial port fails.
*/
@Override
public CompletionStage<Void> send(ModbusRtuFrame frame) {
SerialPort sp = this.serialPort;
if (sp == null || !sp.isOpen()) {
return CompletableFuture.failedFuture(new ModbusException("not connected"));
}

ByteBuffer buffer = ByteBuffer.allocate(256);

try {
Expand All @@ -114,10 +158,10 @@ public CompletionStage<Void> send(ModbusRtuFrame frame) {

int totalWritten = 0;
while (totalWritten < data.length) {
int written = serialPort.writeBytes(data, data.length - totalWritten, totalWritten);
int written = sp.writeBytes(data, data.length - totalWritten, totalWritten);
if (written == -1) {
int errorCode = serialPort.getLastErrorCode();
throw new Exception(
int errorCode = sp.getLastErrorCode();
throw new ModbusException(
"failed to write to port '%s', lastErrorCode=%d"
.formatted(config.serialPort(), errorCode));
}
Expand Down
77 changes: 54 additions & 23 deletions ...serial/src/main/java/com/digitalpetri/modbus/serial/server/SerialPortServerTransport.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,8 @@
import com.digitalpetri.modbus.ModbusRtuRequestFrameParser;
import com.digitalpetri.modbus.ModbusRtuRequestFrameParser.Accumulated;
import com.digitalpetri.modbus.ModbusRtuRequestFrameParser.ParserState;
import com.digitalpetri.modbus.exceptions.ModbusConnectException;
import com.digitalpetri.modbus.exceptions.ModbusException;
import com.digitalpetri.modbus.exceptions.UnknownUnitIdException;
import com.digitalpetri.modbus.internal.util.ExecutionQueue;
import com.digitalpetri.modbus.serial.SerialPortTransportConfig;
Expand Down Expand Up @@ -35,66 +37,95 @@ public class SerialPortServerTransport implements ModbusRtuServerTransport {

private final ExecutionQueue executionQueue;

private final SerialPort serialPort;
private volatile SerialPort serialPort;

private final SerialPortTransportConfig config;

public SerialPortServerTransport(SerialPortTransportConfig config) {
this.config = config;

serialPort = SerialPort.getCommPort(config.serialPort());

serialPort.setComPortParameters(
config.baudRate(),
config.dataBits(),
config.stopBits(),
config.parity(),
config.rs485Mode());

executionQueue = new ExecutionQueue(config.executor());
}

/**
* Return the underlying {@link SerialPort} used by this transport.
*
* <p>The serial port is lazily instantiated on first access.
*
* @return the configured {@link SerialPort} instance.
* @throws ModbusException if the serial port could not be created.
*/
public SerialPort getSerialPort() {
return serialPort;
public SerialPort getSerialPort() throws ModbusException {
SerialPort sp = this.serialPort;
Comment thread
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if (sp == null) {
synchronized (this) {
sp = this.serialPort;
if (sp == null) {
try {
sp = SerialPort.getCommPort(config.serialPort());
sp.setComPortParameters(
config.baudRate(),
config.dataBits(),
config.stopBits(),
config.parity(),
config.rs485Mode());
this.serialPort = sp;
} catch (Exception e) {
throw new ModbusException(
"failed to get comm port '%s'".formatted(config.serialPort()), e);
}
}
}
}
return sp;
}

@Override
public CompletionStage<Void> bind() {
if (serialPort.isOpen()) {
SerialPort sp;
try {
sp = getSerialPort();
} catch (ModbusException e) {
return CompletableFuture.failedFuture(new ModbusConnectException(e));
}

if (sp.isOpen()) {
return CompletableFuture.completedFuture(null);
} else {
if (serialPort.openPort()) {
if (sp.openPort()) {
frameParser.reset();

serialPort.addDataListener(new ModbusRtuDataListener());
sp.addDataListener(new ModbusRtuDataListener());

return CompletableFuture.completedFuture(null);
} else {
return CompletableFuture.failedFuture(
new Exception(
new ModbusConnectException(
"failed to open port '%s', lastErrorCode=%d"
.formatted(config.serialPort(), serialPort.getLastErrorCode())));
.formatted(config.serialPort(), sp.getLastErrorCode())));
}
}
}

/**
* {@inheritDoc}
*
* <p>The returned {@link CompletionStage} may complete exceptionally with a {@link
* ModbusException} if the serial port could not be closed.
*/
@Override
public CompletionStage<Void> unbind() {
if (serialPort.isOpen()) {
if (serialPort.closePort()) {
SerialPort sp = this.serialPort;
if (sp != null && sp.isOpen()) {
if (sp.closePort()) {
frameParser.reset();

return CompletableFuture.completedFuture(null);
} else {
return CompletableFuture.failedFuture(
new Exception(
new ModbusException(
"failed to close port '%s', lastErrorCode=%d"
.formatted(config.serialPort(), serialPort.getLastErrorCode())));
.formatted(config.serialPort(), sp.getLastErrorCode())));
}
} else {
return CompletableFuture.completedFuture(null);
Expand Down Expand Up @@ -157,10 +188,10 @@ private void onFrameReceived(ModbusRtuFrame requestFrame) {
pdu.get(data, 1, pdu.remaining());
crc.get(data, data.length - 2, crc.remaining());

SerialPort sp = SerialPortServerTransport.this.serialPort;
int totalWritten = 0;
while (totalWritten < data.length) {
int written =
serialPort.writeBytes(data, data.length - totalWritten, totalWritten);
int written = sp.writeBytes(data, data.length - totalWritten, totalWritten);
if (written == -1) {
logger.error("Error writing frame to serial port");

Expand Down
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