Method SerialInputStream.read(byte[] bytes) returns 0 even though data is available for reading

Question

I encountered a problem from library nrjavaserial when we comunicate with com-port for emulating NMEA device: when calling the RXTXPort#SerialInputStream.read(byte[] bytes) method, the result is 0. The bytes parameter is never empty, bytes are read. Presumably the problem can also be caused by the int a = nativeavailable();(RXTXPort#1467) method, which returns 0, so Minimum = 1, with the consequence that in the readArray(b, off, Minimum)(RXTXPort#1492) method the result is 0. Here is the code from the library itself where the problem occurs: `public synchronized int read( byte b[], int off, int len ) throws IOException { ..... int Minimum = len;

        if( threshold==0 )
        {
        /*
         * If threshold is disabled, read should return as soon
         * as data are available (up to the amount of available
         * bytes in order to avoid blocking)
         * Read may return earlier depending on the receive time
         * out.
         */
            int a = nativeavailable(); // i think main problem is here a = 0
            if( a == 0 )
                Minimum = 1;
            else
                Minimum = Math.min( Minimum, a );
        }
....
        IOLockedMutex.readLock().lock();
        try
        {
            waitForTheNativeCodeSilly();
            result = readArray( b, off, Minimum);//result = 0
            if (debug_read_results)
                z.reportln( "RXTXPort:SerialInputStream:read(" + b.length + " " + off + " " + len + ") returned " + result + " bytes" /*+ new String(b) */);
            return( result );
        }`

It is important to note that the problem is not static, i.e. periodic, sometimes it can read normally, and sometimes the problem pops up and it can hang for a few minutes.

My code:

byte[] buffer = new byte[4096];
  
  inputStream = serialPort.getInputStream();
  
  while (!isInterrupted())
  {
  
    // problem is here, it returns 0 sometimes ->
     int bytesRead = inputStream.read(buffer); ////RXTXPort#SerialInputStream.read(byte[] bytes)
    
    if (bytesRead == -1)
      break;
    
   ..........
    
    Thread.currentThread().sleep(500);`

What is the problem and is it definitely related to my code?