JavaFX Concurrency and Tasks (running threads in Task) - multithreading

Question

I am new to JavaFx/Concurrency so I read the tutorial over at Concurrency in JavaFX but I am still a little confused about the implementation of background threads in a JavaFX Gui.
I'm trying to write a small GUI that interfaces with some serial devices (using JSSC-2.8) and that updates the GUI based on the responses from those devices. But, there's a lag between when the message is written and when the device responds, and using Thread.sleep() for an arbitrary amount of time wasn't a reliable way for me program it. So instead I want to use wait() and notify() methods from the concurrency package (with all the appropriate synchronizations), but I am not sure how to implement it. What I initially did is create another Thread, inside the Task, that would write the messages and wait for the responses, and using some bindings, would update the GUI. I've included my code at the end. Here is a short form of the pseudocode I am trying to implement:
start Task:
connect to serial devices
synchronized loop:
send messages
wait() for event to fire
notify()
But what's been happening is, as soon as I call the wait(), the entire application idles and then when notify() is called (after the response fires and event), it doesn't continue where it left off in the recipe() loop, or the startTdk() loop for that matter, it's just idle. Have I implements the threads wrong? When I am calling the wait(), is it a possibility that I cause the EventDispatch or JavaFX Application Thread to pause?
I hope the question is clear, if there are any clarifications needed I can update the post.
public class OmicronRecipe extends Service<String> implements Runnable{
private final String SEPERATOR=";";
private final Tdk tdk;
private final Pvci pvci;
private final SimpleStringProperty data = new SimpleStringProperty("");
private final Float MAX_V = 26.0f,UHV=1e-8f;
private boolean isTdkOn=false, isPvciOn=false;
private String power;
private Float temp,press,maxT, setT;
private int diffMaxT,diffP,diffPow, diffT, index=0;
public OmicronRecipe(){
tdk = new Tdk("COM4");
pvci = new Pvci("COM5");
}
private synchronized void recipe(){
while (true){
try {
sendMessages();
data.set(power+SEPERATOR+temp+SEPERATOR+press);
calcDiffs();
if (diffPow < 0){
if(diffMaxT < 0){
if(diffT < 0){
if (diffP < 0){
if(!rampPow()){
//Max Power reached
}
}else{
//Wait for pressure drop
}
}
}else{
//Wait until quit
}
}else{
//Max power reached
}
Thread.sleep(5000);
} catch (InterruptedException ex) {
Logger.getLogger(OmicronRecipe.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
private synchronized boolean rampPow(){
boolean isRamped=false;
Float setPow = tdk.getSetPow(index), curPow;
setT = tdk.getSetT(index);
curPow = Float.parseFloat(power);
if(curPow.compareTo(setPow) < 0){
do{
curPow += 0.1f;
tdk.sendMessage("PV "+curPow+"\r");
try {
wait();
} catch (InterruptedException ex) {
Logger.getLogger(OmicronRecipe.class.getName()).log(Level.SEVERE, null, ex);
}
curPow = Float.parseFloat(power);
}while(curPow.compareTo(setPow) < 0);
index++;
isRamped=true;
}
return isRamped;
}
public synchronized boolean connect(){
if(!isTdkOn && !isPvciOn){
isTdkOn = tdk.connect();
isPvciOn = pvci.connect();
}
return isTdkOn && isPvciOn;
}
public synchronized boolean disconnect(){
if(tdk!=null && pvci !=null){
isTdkOn = tdk.disconnect();
isPvciOn = pvci.disconnect();
}
return !isTdkOn && !isPvciOn;
}
public synchronized StringProperty getData(){
return data;
}
public void setMaxT(Float maxT){
this.maxT = maxT;
}
private synchronized void calcDiffs(){
Float pow = Float.parseFloat(power);
diffPow = pow.compareTo(MAX_V);
diffMaxT = temp.compareTo(maxT);
diffT = temp.compareTo(100f);
diffP = press.compareTo(UHV);
}
private synchronized void setListeners(){
tdk.getLine().addListener((ov,t, t1)-> {
synchronized (this){
System.out.println("New Power: "+t1);
power = t1;
this.notify();
}
});
pvci.getLine().addListener((ov,t,t1) ->{
synchronized (this){
String[] msg = t1.split(SEPERATOR);
if(msg.length == 2){
switch(msg[0]){
case "temperature":
System.out.println("Temperaute");
temp = Float.parseFloat(msg[1]);
break;
case "pressure":
System.out.println("Pressure");
press = Float.parseFloat(msg[1]);
break;
default:
System.out.println("Nothing; Something went wrong");
break;
}
}
this.notify();
}
});
}
private synchronized void sendMessages(){
try {
tdk.sendMessage("PV?\r");
this.wait();
pvci.sendMessage("temperature");
this.wait();
pvci.sendMessage("pressure");
this.wait();
} catch (InterruptedException ex) {
Logger.getLogger(OmicronRecipe.class.getName()).log(Level.SEVERE, null, ex);
}
}
private synchronized boolean startTdk(){
boolean isOut=false;
if(isTdkOn){
try {
tdk.sendMessage("ADR 06\r");
this.wait();
System.out.println("Power: "+power);
if(power.equals("OK")){
tdk.sendMessage("OUT?\r");
this.wait();
if(power.equals("OFF")){
tdk.sendMessage("OUT ON\r");
this.wait();
isOut = power.equals("ON");
}
else{
isOut = power.equals("ON");
}
}
} catch (InterruptedException ex) {
Logger.getLogger(OmicronRecipe.class.getName()).log(Level.SEVERE, null, ex);
}
}
return isOut;
}
#Override
protected Task<String> createTask() {
return new Task<String>() {
#Override
protected String call() throws IOException{
new Thread(new OmicronRecipe()).start();
return "";
}
};
}
#Override
public void run() {
if (connect()){
setListeners();
if(startTdk()){
recipe();
}
}
}
}
I won't include the Pvci class, because it just a copy of the Tdk class but with specific message sequences to talk with that machine.
public class Tdk {
private SerialPort tdkPort;
private final String portName;
private StringBuilder sb = new StringBuilder("");;
private final StringProperty line = new SimpleStringProperty("");
private final HashMap<Float,Float> calibMap;
private ArrayList<Float> list ;
private boolean isEnd=false;
public Tdk(String portName){
this.portName = portName;
System.out.println("TDK at "+portName);
calibMap = new HashMap();
setMap();
}
public synchronized boolean connect(){
tdkPort = new SerialPort(portName);
try {
System.out.println("Connecting");
tdkPort.openPort();
tdkPort.setParams(9600,
SerialPort.DATABITS_8,
SerialPort.STOPBITS_1,
SerialPort.PARITY_NONE);
tdkPort.setEventsMask(SerialPort.MASK_RXCHAR);
tdkPort.addEventListener(event -> {
if(event.isRXCHAR()){
if(event.getPortName().equals(portName)){
try {
if(!isEnd){
int[] str = tdkPort.readIntArray();
if(str!=null)
hexToString(str);
}
if(isEnd){
System.out.println("Here: "+sb.toString());
isEnd=false;
String d = sb.toString();
sb = new StringBuilder("");
line.setValue(d);
}
} catch (SerialPortException e) {
Logger.getLogger(Tdk.class.getName()).log(Level.SEVERE, null, e);
}
}
}
});
} catch (SerialPortException e) {
Logger.getLogger(Tdk.class.getName()).log(Level.SEVERE, null, e);
}
return tdkPort !=null && tdkPort.isOpened();
}
public synchronized boolean disconnect(){
if(tdkPort!=null) {
try {
tdkPort.removeEventListener();
if (tdkPort.isOpened())
tdkPort.closePort();
} catch (SerialPortException e) {
Logger.getLogger(Tdk.class.getName()).log(Level.SEVERE, null, e);
}
System.out.println("Disconnecting");
}
return tdkPort.isOpened();
}
public synchronized void sendMessage(String message){
try {
tdkPort.writeBytes(message.getBytes());
} catch (SerialPortException e) {
Logger.getLogger(Tdk.class.getName()).log(Level.SEVERE, null, e);
}
}
private void setMap(){
calibMap.put(1.0f, 25.0f);
calibMap.put(7.0f, 125.0f);
calibMap.put(9.8f, 220.0f);
list = new ArrayList(calibMap.keySet());
}
public Float getSetPow(int index){
return list.get(index);
}
public Float getSetT(int index){
return calibMap.get(list.get(index));
}
public synchronized StringProperty getLine(){
return line;
}
private synchronized void hexToString(int[] hexVal){
for(int i : hexVal){
if(i != 13){
sb.append((char)i);
}else{
isEnd=true;
}
}
System.out.println("Turning: "+Arrays.toString(hexVal)+" to String: "+sb.toString()+" End: "+isEnd);
}

Answer 1

Freeze
Your UI freezes most probably because you are waiting on the FX Apllication Thread, to solve this there are different approaches:
JavaFX Application Thread
You can delegate some work to the FX Application Thread, therefore see Platform.runLater
Not everything can be run on this thread, but for example, in your DeviceController, you can wait until the message appears and then call Platform.runLater() and update the field (you should therefor oc hand the field over to the controller).
DataBinding
What you are describing can also be realised with DataBinding.
With this you could define a SimpleStringProperty, which is bound to your UI Label (.bind() Method). If the controller must fire its message you can set the StringProperty and the UI will update itself.
The scenario you described could be used like this:
start Task:
connect to serial devices
synchronized loop:
send messages
wait() for event to fire
**updateDate the DataBounded fields**
We are taught that, Concurrency notify/wait
Concurrency on level wait()/notify() is very low level. You should try to work with higher level synchronisation methods or helpers (where people have already solved your problems :))