How can channel input be handled in a prioritized fashion? Is there anything equivalent
to Scala's "reactWithin(0) { ... case TIMEOUT }" construct?
I wrote a Subscription class that delivers prioritized messages on a set interval. It's not an ideal general case way to consume prioritized messages, but I'll post it for posterity. I think a custom RequestReplyChannel would be a better option for certain other cases. Implementation of PriorityQueue is left as an exercise to the reader.
class PrioritySubscriber<T> : BaseSubscription<T>
{
private readonly PriorityQueue<T> queue;
private readonly IScheduler scheduler;
private readonly Action<T> receive;
private readonly int interval;
private readonly object sync = new object();
private ITimerControl next = null;
public PrioritySubscriber(IComparer<T> comparer, IScheduler scheduler,
Action<T> receive, int interval)
{
this.queue = new PriorityQueue<T>(comparer);
this.scheduler = scheduler;
this.receive = receive;
this.interval = interval;
}
protected override void OnMessageOnProducerThread(T msg)
{
lock (this.sync)
{
this.queue.Enqueue(msg);
if (this.next == null)
{
this.next =
this.scheduler.Schedule(this.Receive, this.interval);
}
}
}
private void Receive()
{
T msg;
lock (this.sync)
{
msg = this.queue.Dequeue();
if (this.queue.Count > 0)
{
this.next =
this.scheduler.Schedule(this.Receive, this.interval);
}
}
this.receive(msg);
}
}
Related
I have a use case where I have a set of items, DiagnosticRuns, that are submitted to my cluster. I want to process them serially (to avoid conflicts). I am trying to use a Hazelcast Queue protected by a Lock to make sure the items are processed one at a time. Hazelcast is running in embedded mode in my cluster. If I register an ItemListener with the Queue, is it safe to call take() on the Queue from within the itemAdded() method? For example:
#Component
public class DistributedQueueListener
{
public static final String DIAGNOSTICS_RUN_QUEUE_NAME = "diagnosticRun";
#Autowired
private HazelcastInstance hazelcast;
#Autowired
private ProductVersioningService productVersioningService;
private IQueue<DiagnosticRun> diagnosticRunQueue;
private ILock diagnosticRunLock;
private String diagnosticRunListenerId;
#PostConstruct
public void init()
{
diagnosticRunQueue = hazelcast.getQueue(DIAGNOSTICS_RUN_QUEUE_NAME);
diagnosticRunLock = hazelcast.getLock("diagnosticRunLock");
diagnosticRunListenerId = diagnosticRunQueue.addItemListener(new DiagnosticRunListener(), false);
}
#PreDestroy
public void stop()
{
diagnosticRunQueue.removeItemListener(diagnosticRunListenerId);
}
public class DiagnosticRunListener implements ItemListener<DiagnosticRun>
{
#Override
public void itemAdded(ItemEvent<diagnosticRun> item)
{
diagnosticRunLock.lock(5, TimeUnit.SECONDS);
try
{
DiagnosticRun diagnosticRun = diagnosticRunQueue.poll();
if(diagnosticRun != null)
{
productVersioningService.updateProductDeviceTable(diagnosticRun);
}
}
finally
{
diagnosticRunLock.unlock();
}
}
#Override
public void itemRemoved(ItemEvent<diagnosticRun> item)
{
}
}
}
I'm not sure whether it's threadsafe to call take() on the Queue from that location and thread.
If that is not allowed, I'll have to set up my own long-running loop to poll() the Queue. I'm not sure what's the best way to set up a long-running thread in a Spring Boot application. Assuming the method above does not work, would the below code be threadsafe? Or is there a better way to do this?
#Component
public class DistributedQueueListener
{
public static final String DIAGNOSTIC_RUN_QUEUE_NAME = "diagnosticRun";
#Autowired
private HazelcastInstance hazelcast;
#Autowired
private ProductVersioningService productVersioningService;
private IQueue<diagnosticRun> diagnosticRunQueue;
private ILock diagnosticRunLock;
private ExecutorService executorService;
#PostConstruct
public void init()
{
diagnosticRunQueue = hazelcast.getQueue(DIAGNOSTIC_RUN_QUEUE_NAME);
diagnosticRunLock = hazelcast.getLock("diagnosticRunLock");
executorService = Executors.newFixedThreadPool(1);
executorService.submit(() -> listenToDiagnosticRuns());
}
#PreDestroy
public void stop()
{
executorService.shutdown();
}
private void listenToDiagnosticRuns()
{
while(!executorService.isShutdown())
{
diagnosticRunLock.lock(5, TimeUnit.SECONDS);
try
{
DiagnosticRun diagnosticRun = diagnosticRunQueue.poll(1L, TimeUnit.SECONDS);
productVersioningService.updateProductDeviceTable(diagnosticRun);
}
catch(InterruptedException e)
{
logger.error("Interrupted polling diagnosticRun queue", e);
}
finally
{
diagnosticRunLock.unlock();
}
}
}
}
First I'll qualify that I'm not exactly an expert on which threads these are executed on and when so some may disagree but here're my thoughts on this so anyone please chime in as this looks to be an interesting case. Your first solution mixes the Hazelcast event threading with it's operation threading. In fact you're triggering three operations to be invoked as a result of the single event. If you put some arbitrary latency in your call to updateProcductDeviceTable, you'll see that eventually, it will slow down but resume up again after some time. This will cause your local event queue to pile up while operations are invoked. You could put everything you're doing in a separate thread which you can "wake" up on #itemAdded or if you can afford to have a bit of latency, do what you're doing on your second solution. I would, however, make a couple changes in
listenToDiagnosticsRuns() method:
private void listenToDiagnosticRuns()
{
while(!executorService.isShutdown())
{
if(diagnosticRunQueue.peek() != null)
{
diagnosticRunLock.lock(5, TimeUnit.SECONDS);
try
{
DiagnosticRun diagnosticRun = diagnosticRunQueue.poll(1L, TimeUnit.SECONDS);
if(diagnosticRun != null)
{
productVersioningService.updateProductDeviceTable(diagnosticRun);
}
}
catch(InterruptedException e)
{
logger.error("Interrupted polling diagnosticRun queue", e);
}
finally
{
diagnosticRunLock.unlock();
}
} // peek != null
else
{
try
{
Thread.sleep(5000);
}
catch (InterruptedException e)
{
//do nothing
}
}
}
}
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);
}
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 :))
Just recently a few colleagues of mine helped out with narrowing down a memory leak. One of the problems was found in Microsoft's code. This is from reflector showing that the enumerator will leak.
Here the count property calls getenumerator but never checks for Idisposable:
public int Count
{
get
{
if (this.isDisposed)
{
throw new ObjectDisposedException(name);
}
int num = 0;
IEnumerator enumerator = this.GetEnumerator();
while (enumerator.MoveNext())
{
num++;
}
return num;
}
}
This is the ManagementObjectCollection's GetEnumerator just to show the type returned is a ManagementObjectEnumerator.
public ManagementObjectEnumerator GetEnumerator()
{
if (this.isDisposed)
{
throw new ObjectDisposedException(name);
}
if (!this.options.Rewindable)
{
return new ManagementObjectEnumerator(this, this.enumWbem);
}
IEnumWbemClassObject ppEnum = null;
int errorCode = 0;
try
{
errorCode = this.scope.GetSecuredIEnumWbemClassObjectHandler(this.enumWbem).Clone_(ref ppEnum);
if ((errorCode & 0x80000000L) == 0L)
{
errorCode = this.scope.GetSecuredIEnumWbemClassObjectHandler(ppEnum).Reset_();
}
}
catch (COMException exception)
{
ManagementException.ThrowWithExtendedInfo(exception);
}
if ((errorCode & 0xfffff000L) == 0x80041000L)
{
ManagementException.ThrowWithExtendedInfo((ManagementStatus) errorCode);
}
else if ((errorCode & 0x80000000L) != 0L)
{
Marshal.ThrowExceptionForHR(errorCode);
}
return new ManagementObjectEnumerator(this, ppEnum);
}
This showing that it is disposable:
public class ManagementObjectEnumerator : IEnumerator, IDisposable
{
// Fields
private bool atEndOfCollection;
private uint cachedCount;
private IWbemClassObjectFreeThreaded[] cachedObjects;
private int cacheIndex;
private ManagementObjectCollection collectionObject;
private IEnumWbemClassObject enumWbem;
private bool isDisposed;
private static readonly string name;
// Methods
static ManagementObjectEnumerator();
internal ManagementObjectEnumerator(ManagementObjectCollection collectionObject, IEnumWbemClassObject enumWbem);
public void Dispose();
protected override void Finalize();
public bool MoveNext();
public void Reset();
// Properties
public ManagementBaseObject Current { get; }
object IEnumerator.Current { [TargetedPatchingOptOut("Performance critical to inline this type of method across NGen image boundaries")] get; }
}
Though enumerators that are disposable are disposed of properly by foreach statements (http://msdn.microsoft.com/en-us/library/aa664754(v=vs.71).aspx), this does not mean that the only case where the enumerator will be used is in a foreach loop.
I know that you can skip the count property and roll your own mechanism for getting the number of objects in the collection by using the enumerator yourself but the question I have is how much unmanaged memory does this leak?
How can I cancel a thread from another class fetching/refreshing location. I am able to cancel a thread from within the same class. But I am unable to do this across classes. Declaring the GPSThread static did not help. Can anyone please guide?
Class1:
public class GPSListener {
/* Other instantiation code */
Dialog busyDialog1 = new Dialog("Refreshing Location...",
new String [] { "Cancel" },
new int [] { Dialog.CANCEL},
Dialog.CANCEL,
Bitmap.getPredefinedBitmap(Bitmap.HOURGLASS))
{
public void fieldChanged(Field field1, int context1)
{
GPSHandler.requestStop();
busyDialog1.cancel();
}
};
public String refreshCoordinates() {
String test = "nothing";
if (GPSHandler.isStopRequested())
{
GPSHandler.stopRequested = false;
return null;
}
GPSHandler.getInstance().setListener(this);
GPSHandler.getInstance().requestLocationUpdates();
if (GPSHandler.isStopRequested())
{
GPSHandler.stopRequested = false;
return null;
}
busyDialog1.setEscapeEnabled(false);
busyDialog1.show();
return test;
}
public void onLocationReceived(Coordinates location) {
lblLatitude.setText(Double.toString(location.getLatitude()));
lblLongitude.setText(Double.toString(location.getLongitude()));
busyDialog1.cancel();
}
}
Class 2:
public class GPSHandler {
private GPSThread _gpsThread;
private Coordinates _location;
private boolean _gotLocation;
private GPSListener _listener;
/** this class will be a Singleton, as the device only has one GPS system */
private static GPSHandler _instance;
/** #return the Singleton instance of the GPSHandler */
public static GPSHandler getInstance() {
if (_instance == null) {
_instance = new GPSHandler();
}
return _instance;
}
public static boolean stopRequested = false;
public synchronized static void requestStop() {
stopRequested = true;
}
public synchronized static boolean isStopRequested() {
return stopRequested;
}
/** not publicly accessible ... use getInstance() */
private GPSHandler() {
}
/** call this to trigger a new location fix */
public void requestLocationUpdates() {
if (_gpsThread == null || !_gpsThread.isAlive()) {
_gpsThread = new GPSThread();
_gpsThread.start();
}
}
public void setListener(GPSListener listener) {
// only supports one listener this way
_listener = listener;
}
private void setLocation(final Coordinates value) {
_location = value;
if (value.getLatitude() != 0.0 || value.getLongitude() != 0.0) {
_gotLocation = true;
if (_listener != null) {
// this assumes listeners are UI listeners, and want callbacks on the UI thread:
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
_listener.onLocationReceived(value);
}
});
}
}
}
private class GPSThread extends Thread {
private void getLocationFromGoogle() {
try {
int cellID = GPRSInfo.getCellInfo().getCellId();
int lac = GPRSInfo.getCellInfo().getLAC();
String urlString2 = "http://www.google.com/glm/mmap";
// Open a connection to Google Maps API
ConnectionFactory connFact = new ConnectionFactory();
ConnectionDescriptor connDesc;
connDesc = connFact.getConnection(urlString2);
HttpConnection httpConn2;
httpConn2 = (HttpConnection)connDesc.getConnection();
httpConn2.setRequestMethod("POST");
// Write some custom data to Google Maps API
OutputStream outputStream2 = httpConn2.openOutputStream();//getOutputStream();
writeDataGoogleMaps(outputStream2, cellID, lac);
// Get the response
InputStream inputStream2 = httpConn2.openInputStream();//getInputStream();
DataInputStream dataInputStream2 = new DataInputStream(inputStream2);
// Interpret the response obtained
dataInputStream2.readShort();
dataInputStream2.readByte();
final int code = dataInputStream2.readInt();
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
Dialog.alert(code + "");
}
});
if (code == 0) {
final double latitude = dataInputStream2.readInt() / 1000000D;
final double longitude = dataInputStream2.readInt() / 1000000D;
setLocation(new Coordinates(latitude, longitude, 0.0f));
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
Dialog.alert(latitude+"-----"+longitude);
}
});
dataInputStream2.readInt();
dataInputStream2.readInt();
dataInputStream2.readUTF();
} else {
System.out.println("Error obtaining Cell Id ");
}
outputStream2.close();
inputStream2.close();
} catch (Exception e) {
System.out.println("Error: " + e.getMessage());
}
}
private void tryGetLocationFromDevice() {
_gotLocation = false;
try {
Criteria myCriteria = new Criteria();
myCriteria.setCostAllowed(false);
LocationProvider myLocationProvider = LocationProvider.getInstance(myCriteria);
try {
Location myLocation = myLocationProvider.getLocation(300);
setLocation(myLocation.getQualifiedCoordinates());
} catch ( InterruptedException iex ) {
System.out.println(iex.getMessage());
} catch ( LocationException lex ) {
System.out.println(lex.getMessage());
}
} catch ( LocationException lex ) {
System.out.println(lex.getMessage());
}
if (!_gotLocation) {
getLocationFromGoogle();
}
}
public void run() {
int bbMapsHandle = CodeModuleManager.getModuleHandle("net_rim_bb_lbs"); // OS 4.5 - 6.0
int bbMapsHandle60 = CodeModuleManager.getModuleHandle("net_rim_bb_maps"); // OS 6.0
if (bbMapsHandle > 0 || bbMapsHandle60 > 0) {
tryGetLocationFromDevice();
} else {
getLocationFromGoogle();
}
}
}
private void writeDataGoogleMaps(OutputStream out, int cellID, int lac) throws IOException {
DataOutputStream dataOutputStream = new DataOutputStream(out);
dataOutputStream.writeShort(21);
dataOutputStream.writeLong(0);
dataOutputStream.writeUTF("en");
dataOutputStream.writeUTF("Android");
dataOutputStream.writeUTF("1.0");
dataOutputStream.writeUTF("Web");
dataOutputStream.writeByte(27);
dataOutputStream.writeInt(0);
dataOutputStream.writeInt(0);
dataOutputStream.writeInt(3);
dataOutputStream.writeUTF("");
dataOutputStream.writeInt(cellID);
dataOutputStream.writeInt(lac);
dataOutputStream.writeInt(0);
dataOutputStream.writeInt(0);
dataOutputStream.writeInt(0);
dataOutputStream.writeInt(0);
dataOutputStream.flush();
}
}
Your GPSThread object is currently declared as a private inner class within GPSHandler. If you want to stop execution (or indeed do anything with it) from outside the scope of GPSHandler you will need to mark it as public. You will also need to provide some public mechanism (e.g. a stop() method) to cancel the thread execution.
The most common way of doing this is to have a boolean flag inside your thread (e.g shouldStop) which is checked within your main execution loop inside run() to see if it should stop. When the stop() method is called shouldStop is set to true and your Thread will stop.
Here's a good example: How to stop threads in Java?
There's two groups of changes you should make.
Change the Stop Requested Flag
First, remember that encapsulation is a good thing in Object-Oriented languages. The isStopRequested() method, or stopRequested variable of the GPSHandler should not be used outside of that class. Your UI's GPSListener should not attempt to use either of those. I would change your GPSHandler to use this:
private static boolean stopRequested = false;
public synchronized static void requestStop() {
stopRequested = true;
}
private synchronized static boolean isStopRequested() {
return stopRequested;
}
Only requestStop() should be public. It looks like you made stopRequested public to allow the GPSListener to reset it. If it needs resetting, let the class that owns that variable do the resetting. For example, in GPSHandler:
/** call this to trigger a new location fix */
public void requestLocationUpdates() {
if (_gpsThread == null || !_gpsThread.isAlive()) {
// reset this stop flag:
stopRequested = false;
_gpsThread = new GPSThread();
_gpsThread.start();
}
}
requestLocationUpdates() is really the method that starts the thread, so it should be where stopRequested gets reset to false.
Also, another reason that you should not make stopRequested public and allow other classes to use it is that this is not generally thread-safe. One of the reasons to wrap stopRequested with the requestStop() and isStopRequested() methods is to add thread-safety. There's many ways to do that, but those two methods achieve thread-safety by being marked with the synchronized keyword.
Change How/Where You Check the Flag
After you make these fixes, you need to change where you check if a stop has been requested. You don't really want to check isStopRequested() in the refreshCoordinates() method. That method involves almost no work. Even though it starts the process of getting a location fix, that only starts a thread, but the actual work of getting the location is done on a background thread (your GPSThread). If requestStop() is called, it's very unlikely that it will be called in the middle of refreshCoordinates(), so that's not where you should check it.
Check isStopRequested() multiple times within the GPSHandler class's methods tryGetLocationFromDevice() and getLocationFromGoogle(). Those are the methods that perform slow processing. Those are the ones you might want to interrupt in the middle. So, something like this:
private void getLocationFromGoogle() {
try {
int cellID = GPRSInfo.getCellInfo().getCellId();
int lac = GPRSInfo.getCellInfo().getLAC();
String urlString2 = "http://www.google.com/glm/mmap";
if (isStopRequested()) return;
// Open a connection to Google Maps API
ConnectionFactory connFact = new ConnectionFactory();
ConnectionDescriptor connDesc;
connDesc = connFact.getConnection(urlString2);
HttpConnection httpConn2;
httpConn2 = (HttpConnection)connDesc.getConnection();
httpConn2.setRequestMethod("POST");
// Write some custom data to Google Maps API
OutputStream outputStream2 = httpConn2.openOutputStream();//getOutputStream();
writeDataGoogleMaps(outputStream2, cellID, lac);
if (isStopRequested()) return;
// Get the response
InputStream inputStream2 = httpConn2.openInputStream();//getInputStream();
DataInputStream dataInputStream2 = new DataInputStream(inputStream2);
// Interpret the response obtained
dataInputStream2.readShort();
dataInputStream2.readByte();
if (isStopRequested()) return;
final int code = dataInputStream2.readInt();
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
Dialog.alert(code + "");
}
});
And in tryGetLocationFromDevice(), you could do this (make sure to add the member variable and new method below):
private LocationProvider _locationProvider; // must be a member variable!
public void requestStop() {
if (_locationProvider != null) {
// this will interrupt the _locationProvider.getLocation(300) call
_locationProvider.reset();
}
}
private void tryGetLocationFromDevice() {
_gotLocation = false;
try {
Criteria myCriteria = new Criteria();
myCriteria.setCostAllowed(false);
_locationProvider = LocationProvider.getInstance(myCriteria);
try {
Location myLocation = _locationProvider.getLocation(300);
setLocation(myLocation.getQualifiedCoordinates());
} catch ( InterruptedException iex ) {
// this may be caught if stop requested!!!!
System.out.println(iex.getMessage());
} catch ( LocationException lex ) {
System.out.println(lex.getMessage());
}
} catch ( LocationException lex ) {
System.out.println(lex.getMessage());
}
if (!_gotLocation && !isStopRequested()) {
getLocationFromGoogle();
}
}
Then, call the GPSThread.requestStop() method from the outer GPSHandler.requestStop() method:
public synchronized static void requestStop() {
stopRequested = true;
if (_gpsThread != null) {
_gpsThread.requestStop();
}
}
I used 101 samples of Rx Framework ( http://rxwiki.wikidot.com/101samples#toc47 ) last example and created a class like below and usage like in the test function.
private void Test()
{
var order = new Order();
order.ObservableOrder.Subscribe(
ord => Console.WriteLine("Order progress "), // subscribe to onnext event
ex => Console.WriteLine("Paid error " + ex.Message), // subscribe to error event
() => Console.WriteLine("Paid oncompleted ") // subscribe to completed event
); // Subscribe
order.Start();
}
public class Order
{
private readonly Subject<Order> _subject = new Subject<Order>();
public IObservable<Order> ObservableOrder { get { return _subject.AsObservable(); } }
public void RaiseError() {
_subject.OnError(new Exception("test exception"));
}
public void RaiseCompleted() {
_subject.OnCompleted();
}
public void RaiseProgress() {
_subject.OnNext(this);
}
public void Start() {
for (int i = 0; i < 5; i++)
this.RaiseProgress();
this.RaiseError(); // either error is raised
this.RaiseCompleted(); // or completed is raised
}
}
My requirement is how to write a base class ( or some kind of factory ) to
make it easy to use this for 20-30 classes which does similar things ( like they need to
send progress, oncompleted and on error events ) Also how can I also send some data back to
on progress and oncompleted events ( like we send exception into onerror event )
OnCompleted() accepts no arguments, which obviously can't be changed.
You have a few choices:
You can create a payload class that has both the process and the final payload in it. class OrderProgress { double Process; OrderResult Result; }
You can expose another subject, Progress, which you can subscribe to in addition to ObservableOrder.
If you want to keep Start reentrant, you could have it return an object that exposed both a Progress and OrderProgress observable.
Edit: Including example code (of my second option):
private void Test()
{
var order = new Order();
order.ObservableProgress.Subscribe(
prog => Console.WriteLine("Order progress " + prog.ToString()
);
order.ObservableOrder.Subscribe(
ord => Console.WriteLine("Order progress"),
ex => Console.WriteLine("Paid error " + ex.Message),
() => Console.WriteLine("Paid oncompleted")
);
order.Start();
}
public class Order
{
private readonly Subject<Order> _subject = new Subject<Order>();
private readonly Subject<double> _progressSubject = new Subject<double>();
public IObservable<Order> ObservableOrder
{
get { return _subject.AsObservable(); }
}
public IObservable<double> ObservableProgress
{
get { return _progressSubject.AsObservable(); }
}
public void RaiseError() {
_subject.OnError(new Exception("test exception"));
}
public void RaiseCompleted() {
_subject.OnNext(this);
_subject.OnCompleted();
_progressSubject.OnCompleted();
}
public void RaiseProgress(double progress) {
_progressSubject.OnNext(progress);
}
public void Start() {
for (int i = 0; i < 5; i++)
this.RaiseProgress((double)i / 5D);
this.RaiseError(); // either error is raised
this.RaiseCompleted(); // or completed is raised
}
}