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My SerialPortEvent does not receive data using jSSC in a continous loop

I have been trying to use serial communication with my Arduino Uno and have used the library jSSC-2.6.0. I am using a SeriaPortEvent listener to receive bytes from the Serial Port (Arduino) and store them in a linked list.
public synchronized void serialEvent(SerialPortEvent serialPortEvent) {
if (serialPortEvent.isRXCHAR()) { // if we receive data
if (serialPortEvent.getEventValue() > 0) { // if there is some existent data
try {
byte[] bytes = this.serialPort.readBytes(); // reading the bytes received on serial port
if (bytes != null) {
for (byte b : bytes) {
this.serialInput.add(b); // adding the bytes to the linked list
// *** DEBUGGING *** //
System.out.print(String.format("%X ", b));
}
}
} catch (SerialPortException e) {
System.out.println(e);
e.printStackTrace();
}
}
}
}
Now if I send individual data in a loop and don't wait for any response the serialEvent usually prints bytes received, to the Console.
But If I try and wait till there is some data in the linked list the program just keeps on looping and the SerialEvent never adds bytes to the LinkedList, it even does not even register any bytes being received.
This works and the correct bytes are sent by Arduino received by SerialEvent and printed to the Console:
while(true) {
t.write((byte) 0x41);
}
But this method just stucks at this.available() which returns the size of the LinkedList,
as in no data is actually received from the Arduino or receieved by the serialEvent:
public boolean testComm() throws SerialPortException {
if (!this.serialPort.isOpened()) // if port is not open return false
return false;
this.write(SerialCOM.TEST); // SerialCOM.TEST = 0x41
while (this.available() < 1)
; // we wait for a response
if (this.read() == SerialCOM.SUCCESS)
return true;
return false;
}
I have debugged the program and sometimes debugging, the program does work but not always. Also the program only gets stuck when i try and check if there is some bytes in the linkedlist i.e while(available() < 1). Otherwise if I dont check I eventually receive the correct response of bytes from Arduino

Found the answer myself after wasting 4hours. I was better off using the readBytes() method with a byteCount of 1 and timeOut of 100ms just to be on the safe side. So now the read method looks like this.
private byte read() throws SerialPortException{
byte[] temp = null;
try {
temp = this.serialPort.readBytes(1, 100);
if (temp == null) {
throw new SerialPortException(this.serialPort.getPortName(),
"SerialCOM : read()", "Can't read from Serial Port");
} else {
return temp[0];
}
} catch (SerialPortTimeoutException e) {
System.out.println(e);
e.printStackTrace();
}
return (Byte) null;
}

Android, detect socket write failure

Basically the server side sends a keep alive message every 8 minutes, if the write fails it disconnects the client and closes the socket connection. If my android device is awake and the server closes the connection then the read operation on the android device throws an exception as it should and i disconnect from the server. If the device is asleep it doesn't read data at all even with a partial wake lock and a wifilock, i have already given up on that, but my actual problem is when my device comes back from sleep (if i turn the screen on for example) what i do is send a message to the server so i can refresh the data but if my server has already closed the socket my write operation should throw an IOException but for some reason it doesn't. And even the blocking read i have doesn't throw any exception or return -1.
here is my write operation:
public boolean sendData(byte[] data)
{
boolean sent=false;
if(connectedToServer)
{
try
{
myOutputStream.write(data, 0, data.length);
sent= true;
}
catch (IOException e)
{
e.printStackTrace();
unexpectedDisconnectionFromServer();
}
}
return sent;
}
and here is my read operation:
public void startReadingInBackground()
{
while(connectedToServer)
{
try
{
int bytesRead=0;
if(myWifiLock!=null && !myWifiLock.isHeld())
myWifiLock.acquire();
byte val=(byte)myInputStream.read();
myWakeLock.acquire();
if(val==-1)
{
unexpectedDisconnectionFromServer();
if(myWifiLock!=null && myWifiLock.isHeld())
myWifiLock.release();
myWakeLock.release();
return;
}
bytesRead=myInputStream.read(myBuffer, 0, bufferSize);
if(bytesRead<1)
{
unexpectedDisconnectionFromServer();
if(myWifiLock!=null && myWifiLock.isHeld())
myWifiLock.release();
myWakeLock.release();
return;
}
byte[] dataArray=Arrays.copyOfRange(myBuffer,0,bytesRead);
ByteBuffer data=ByteBuffer.allocate(bytesRead+1).put(val).put(dataArray);
myParent.invokeReceiveAction(data, bytesRead + 1);
}
catch (IOException e)
{
if(!myWakeLock.isHeld())
myWakeLock.acquire();
unexpectedDisconnectionFromServer();
e.printStackTrace();
}
finally
{
if(myWifiLock!=null && myWifiLock.isHeld())
myWifiLock.release();
if(myWakeLock!=null && myWakeLock.isHeld())
myWakeLock.release();
}
}
}
and i get the outputstream like so:
Socket mySocket = new Socket(SERVER_IP, SERVER_PORT_TCP );
myOutputStream=mySocket.getOutputStream();

Your write will throw an IOException, eventually. Your mistake is in assuming it is bound to happen on the first write after the disconnect. It won't, for all sorts of reasons including buffering and retries. TCP has to determine that the connection is really dead before it will reject a new write, and it certainly won't do that on the first write after the disconnect.

Bluetooth transfer App stops after using InputStream.read() with no error

I am trying to make a file transfer Bluetooth app work using these sources:
http://developer.android.com/guide/topics/connectivity/bluetooth.html
https://android.googlesource.com/platform/development/+/25b6aed7b2e01ce7bdc0dfa1a79eaf009ad178fe/samples/BluetoothChat/
When I attempt to get the InputStream bytes using InputStream.read() method this way:
public class ConnectedThread extends Thread {
...(some code here)
public void run(){
byte[] buffer = new byte[1024];
int bytes = -1;
//Keep listening to the InputStream while connected
while (true){
try {
bytes = this.mmInStream.read(buffer);
//* this part is not reached
if (bytes==-1){
Log.d("NoData:","-1");
}
}
catch(Exception e){
Log.d("inStream exception:",e.getMessage());
break;
}
}
}
...(some code here)
}
The next part of the code ("if" part in this case) is never reached, nor a Log.D debug output or whatever else I put in following. I just get this message from LogCat:
BluetoothSocket read in: android.net.LocalStocketImpl$SocketInputStream#f7e
b08 len: 1024
To transfer the data from the Client to the Server I am doing this:
public class MainActivity extends Activity {
...(some code here)
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
clientConnect();
//serverConnect();
}
...(some code here)
public void clientConnect(){
Set<BluetoothDevice> devices;
devices = bConfig.getPairedDevices();
if (devices == null){
return;
}
if (devices.size() > 0) {
BluetoothDevice device = devices.iterator().next();
ConnectThread connectTransmit = new ConnectThread(device,bConfig.getBluetoothAdapter(),BluetoothConfig.mUUID);
connectTransmit.start();
Toast.makeText(this, "connected", Toast.LENGTH_SHORT).show();
socket = connectTransmit.mmSocket;
ConnectedThread connectedThread = new ConnectedThread(socket);
//write file bytes to the connected thread, so the thread can receive its own input written bytes later
File file_to_transfer = new File(Environment.getExternalStorageDirectory() + "/txtTransfer.txt");
//get bytes from our File
int size = (int) file_to_transfer.length();
byte[] bytes = new byte[size];
try {
//14b are read succesfully, the whole text file
BufferedInputStream buf = new BufferedInputStream(new FileInputStream(file_to_transfer));
buf.read(bytes,0,bytes.length);
buf.close();
}catch (FileNotFoundException e){
Log.d("FileNotFoundException:",e.getMessage());
}catch (IOException e){
Log.d("IOException:",e.getMessage());
}
//send the data to the server
connectedThread.start();
connectedThread.write(bytes);
//connectedThread.cancel();
}
}
...(some code here)
}
The AcceptThread (Server part of the implementation) works, because when I run the client part to connect and then transfer the data, while debuging in the device the LogCat on the Server part activates and reaches the run method of the thread, where I call the ConnectedThread implementation but then after it "apparently" reads the bytes but it gets stuck on LogCat with no error.
Please let me know what can I do to finish reading the bytes to move to the next part of the flow.
Thank you

You're blocked waiting for more input.
The part labelled ... (some code here) should be inside the read loop, after the test for end of stream. NB If read() returns -1 it doesn't mean 'no data', it means end of stream, and you should close the socket and break out of the read loop. Otherwise you should then go on to process the data you've just read. At present you just read and ignore all input until end of stream, which is pointless. At best you can only process the last partial buffer, and you won't know how long it was.

In my opinion You should verify if something is in buffer before reading.
reading from stream is blocking operation so aplication will hang until somehing data appear.
How can I check if an InputStream is empty without reading from it?

In your client code you should probably keep the connectedThread object alive a while longer. Might be that once the if clause closes and it goes out of scope (not quite sure what happens with GC and all) the write just doesn't happen and your connection is not closed but not used either.
Calling flush() on the mmOutStream inside the connectedThread after the write might help also.
Like #EJP suggested, you should put something inside your read loop.
Edit: For the sake of debugging you could add this.wait(1000); immediately after your write in the client code.

Try changing your run method to this:
public void run(){
byte[] buffer = new byte[1024];
int bytesRead = 0;
final int shortSleepTime = 1000;
final int longSleepTime = 5000;
int emptyReadCounter = 0;
int sleepCounter = 0;
int currentSleepTime = shortSleepTime;
//Keep listening to the InputStream while connected
while (bytesRead >= 0){
try {
// if available() returns 0, there is nothing to read yet
if (this.mmInStream.available() != 0){
bytesRead = this.mmInStream.read(buffer);
// Check if we need to reset the sleep counters
if (emptyReadCounter != 0){
emptyReadCounter = 0;
sleepCounter = 0;
currentSleepTime = shortSleepTime;
// We can also do anything else dependent on just waking up
// from a sleep cycle in this block
}
// Do something with my now full buffer
// Remember not to process more than
// 'bytesRead' bytes from my buffer because the
// rest could be filled with crap left over from
// the last iteration
} else {
// Three consecutive empty reads means sleep
if (emptyReadCounter++ >= 3){
if (currentSleepTime != longSleepTime && sleepCounter++ >= 3){
currentSleepTime = longSleepTime;
}
Thread.sleep(currentSleepTime);
}
}
}
catch(Exception e){
Log.d("inStream exception:",e.getMessage());
break;
}
}
}

Handling two threads with high frequency reads

I'm writing a simple app that constantly reads some data from serial port over bluetooth and then draws that data on 2 charts. I came up with an idea of buffering that data to byte buffer and then reading it from some other part of the code. The problem is that I have to read that data quite frequently (reading only 5 bytes at once) and I have some issues with synchronization of the threads. The serial port reading part is not allowing the printing thread to read anything most of the time. Sometimes it gets through and prints some data. These 2 are the only threads that use buffer as the locking object.
I think I might've missunderstood some basic synchronization principles, but I'm starting to run out of ideas how can I solve this issue.
Reading from serial port part:
public void startReading() {
Thread thread = new Thread(new Runnable() {
#Override
public void run() {
resetBuffer();
read = true;
try {
serialPort.purgePort(SerialPort.PURGE_RXCLEAR);
byte[] buf = new byte[5];
int bytes;
while (read) {
synchronized (buffer) {
try {
bytes = inputStream.blockingRead(buf);
System.out.println(buf);
System.arraycopy(buf, 0, buffer, bufferPos, bytes);
bufferPos += buf.length;
buffer.notifyAll();
} catch (Exception e) {
e.printStackTrace();
}
}
}
} catch (SerialPortException e) {
e.printStackTrace();
}
}
});
thread.start();
}
Printing data part (in loop):
synchronized (buffer) {
while (serialPortConnection.getBufferLength() < 5) {
try {
buffer.wait();
} catch (Exception e) {
e.printStackTrace();
}
}
}
readBytesToStringBuffer();
printLineIfAvailable();

while (read) {
synchronized (buffer) {
try {
bytes = inputStream.blockingRead(buf);
Your problem is not in reading often; it is in blocking. You acquire the monitor on buffer and then enter a blocking I/O call. You spend precious little time outside of that call, thus outside of the synchronized block.
Advice:
First read from port outside of synchronized, then acquire the monitor to transfer the data to a shared structure.

Receiving data from Terminal connected with USB->RS232

I'm developing a java application that need communicate with a terminal connected with a usb-to-rs232 converter!!
Right now I can connect with device and send data! I can be sure that the terminal receive the data sent because a led glow when the terminal receive something!
I'm using JSSC (Link: https://code.google.com/p/java-simple-serial-connector/wiki/jSSC_examples)... but for some reason I never never never receive any data FROM the Terminal.
My code (JSSC code):
public class Main
{
static SerialPort serialPort;
public static void main(String[] args) throws InterruptedException
{
serialPort = new SerialPort("COM7");
try
{
serialPort.openPort();//Open port
serialPort.setParams(9600, 8, 1, 0);//Set params
int mask = SerialPort.MASK_RXCHAR + SerialPort.MASK_CTS + SerialPort.MASK_DSR;//Prepare mask
serialPort.setEventsMask(mask);//Set mask
serialPort.addEventListener(new SerialPortReader());//Add SerialPortEventListener
serialPort.writeByte( (byte)0x02 );
TimeUnit.SECONDS.sleep( 10 );
byte[] b = serialPort.readBytes();
System.out.println( "bytes " + b );
}
catch (SerialPortException ex)
{
System.out.println(ex);
}
}
/*
* In this class must implement the method serialEvent, through it we learn about
* events that happened to our port. But we will not report on all events but only
* those that we put in the mask. In this case the arrival of the data and change the
* status lines CTS and DSR
*/
static class SerialPortReader implements SerialPortEventListener
{
public void serialEvent(SerialPortEvent event)
{
System.out.println( "Event raised!" );
if(event.isRXCHAR())
{//If data is available
if(event.getEventValue() == 10)
{//Check bytes count in the input buffer
//Read data, if 10 bytes available
try
{
byte buffer[] = serialPort.readBytes(10);
}
catch (SerialPortException ex)
{
System.out.println(ex);
}
}
}
else if(event.isCTS())
{//If CTS line has changed state
if(event.getEventValue() == 1)
{//If line is ON
System.out.println("CTS - ON");
}
else
{
System.out.println("CTS - OFF");
}
}
else if(event.isDSR())
{///If DSR line has changed state
if(event.getEventValue() == 1)
{//If line is ON
System.out.println("DSR - ON");
}
else
{
System.out.println("DSR - OFF");
}
}
}
}
}
Can anyone help me with this issue?

Did you intend to use hardware flow control with USB-UART. If yes, try setting DTR followed by RTS. This tells 1st end that 2nd end is ready for communication. Further does 10 bytes are not received or no data is received at all. Also consider another serial port communication library like scm http://www.embeddedunveiled.com/