I have one simple question regarding Java TimerTask. How do I pause/resume two TimerTask tasks based on a certain condition? For example I have two timers that run between each other. When a certain condition has been met inside the task of first timer, the first timer stops and starts the second timer, and the same thing happens when a certain condition has been met inside the task of second timer. The class below shows exactly what I mean:
public class TimerTest {
Timer timer1;
Timer timer2;
volatile boolean a = false;
public TimerTest() {
timer1 = new Timer();
timer2 = new Timer();
}
public void runStart() {
timer1.scheduleAtFixedRate(new Task1(), 0, 1000);
}
class Task1 extends TimerTask {
public void run() {
System.out.println("Checking a");
a = SomeClass.getSomeStaticValue();
if (a) {
// Pause/stop timer1, start/resume timer2 for 5 seconds
timer2.schedule(new Task2(), 5000);
}
}
}
class Task2 extends TimerTask{
public void run() {
System.out.println("Checking a");
a = SomeClass.getSomeStaticValue();
if (!a) {
// Pause/stop timer2, back to timer1
timer1.scheduleAtFixedRate(new Task1(), 0, 1000);
}
// Do something...
}
}
public static void main(String args[]) {
TimerTest tt = new TimerTest();
tt.runStart();
}
}
So my question is, how do I pause timer1 while running timer2 and vice versa while timer2 is running? Performance and timing is my main concern as this needs to be implemented inside another running thread. By the way I am trying to implement these concurrent timers on Android.
Thanks for your help!
From TimerTask.cancel():
Note that calling this method from
within the run method of a repeating
timer task absolutely guarantees that
the timer task will not run again.
So once cancelled, it won't ever run again. You'd be better off instead using the more modern ScheduledExecutorService (from Java 5+).
Edit: The basic construct is:
ScheduledExecutorService exec = Executors.newSingleThreadScheduledExecutor();
exec.scheduleAtFixedRate(runnable, 0, 1000, TimeUnit.MILLISECONDS);
but looking into it there's no way of cancelling that task once its started without shutting down the service, which is a bit odd.
TimerTask might be easier in this case but you'll need to create a new instance when you start one up. It can't be reused.
Alternatively you could encapsulate each task as a separate transient service:
final ScheduledExecutorService exec = Executors.newSingleThreadScheduledExecutor();
Runnable task1 = new Runnable() {
public void run() {
a++;
if (a == 3) {
exec.shutdown();
exec = Executors.newSingleThreadScheduledExecutor();
exec.scheduleAtFixedRate(task2, 0, 1000, TimeUnit.MILLISECONDS)
}
}
};
exec.scheduleAtFixedRate(task1, 0, 1000, TimeUnit.MILLISECONDS);
easiest solution i found: just add a boolean in the run code in the timer task, like so:
timer.schedule( new TimerTask() {
public void run() {
if(!paused){
//do your thing
}
}
}, 0, 1000 );
If you have already canceled one timer, you can't re-start it, you'll have to create a new one.
See this answer, it contains a video and the source code how I did something similar.
Basically there are two method: pause and resume
In pause:
public void pause() {
this.timer.cancel();
}
In resume:
public void resume() {
this.timer = new Timer();
this.timer.schedule( aTask, 0, 1000 );
}
That makes the perception of pause/resume.
If your timers perform different actions based on the state of the application you may consider use the StatePattern
Fist define a abstract state:
abstract class TaskState {
public void run();
public TaskState next();
}
And provide as many states as you like. The key is that one state leads you to another.
class InitialState extends TaskState {
public void run() {
System.out.println( "starting...");
}
public TaskState next() {
return new FinalState();
}
}
class FinalState extends TaskState {
public void run() {
System.out.println("Finishing...");
}
public TaskState next(){
return new InitialState();
}
}
And then you change the state in your timer.
Timer timer = new Timer();
TaskState state = new InitialState();
timer.schedule( new TimerTask() {
public void run() {
this.state.run();
if( shouldChangeState() ) {
this.state = this.state.next();
}
}
}, 0, 1000 );
Finally, if what you need is to perform the same thing, but at different rates, you may consider using the TimingFramework. It is a bit more complex but let's you do cool animations, by allowing the painting of certain component take place at different rates ( instead of being linear )
In my opinion, this is somewhat misguided. If your code needs time guarantees, you can't use Timer anyway, nor would you want to. "This class does not offer real-time guarantees: it schedules tasks using the Object.wait(long) method."
The answer, IMHO, is that you don't want to pause and restart your timers. You just want to suppress their run methods from doing their business. And that's easy: you just wrap them in an if statement. The switch is on, they run, the switch is off, they miss that cycle.
Edit: The question has shifted substantially from what it was originally, but I'll leave this answer in case it helps anyone. My point is: if you don't care when your event fires in the N millisecond span (just that it doesn't EXCEED once every N milliseconds), you can just use conditionals on the run methods. This is, in fact, a very common case, especially when N is less than 1 second.
Reviewing your source code, here are the changes ( which pretty much validate my previous answer )
In task1:
// Stop timer1 and start timer2
timer1.cancel();
timer2 = new Timer(); // <-- just insert this line
timer2.scheduleAtFixedRate(new Task2(), 0, 1000);
and in task2:
// Stop timer2 and start timer1
timer2.cancel();
timer1 = new Timer(); // <-- just insert this other
timer1.scheduleAtFixedRate(new Task1(), 0, 1000);
It runs on my machine:
Android won't reuse a TimerTask that has already been scheduled once. So it's necessary to reinstantiate both the Timer and TimerTask, for example like this in a Fragment:
private Timer timer;
private TimerTask timerTask;
public void onResume ()
{
super.onResume();
timer = new Timer();
timerTask = new MyTimerTask();
timer.schedule(timerTask, 0, 1000);
}
public void onPause ()
{
super.onPause();
timer.cancel(); // Renders Timer unusable for further schedule() calls.
}
I am able to stop a timer and a task using following code:
if(null != timer)
{
timer.cancel();
Log.i(LOG_TAG,"Number of cancelled tasks purged: " + timer.purge());
timer = null;
}
if(task != null)
{
Log.i(LOG_TAG,"Tracking cancellation status: " + task.cancel());
task = null;
}
Timer timer1;
private boolean videoCompleteCDR=false;
private boolean isVideoPlaying=false;
int videoTime=0;
private int DEFAULT_VIDEO_PLAY_TIME = 30;
#Override
public View onCreate(){
isVideoPlaying = true; //when server response is successfully
}
#Override
public void onPause() {
super.onPause();
if(isVideoPlaying ) {
if(this.timer1 !=null) {
this.timer1.cancel();
}
}
}
#Override
public void onResume() {
super.onResume();
if(isVideoPlaying && !videoCompleteCDR) {
callTimerTask();
}
}
#Override
public void onHiddenChanged(boolean hidden) {
super.onHiddenChanged(hidden);
if (!hidden) {
printLog( "GameFragment visible ");
if(isVideoPlaying && !videoCompleteCDR) {
callTimerTask();
}
} else {
printLog("GameFragment in visible ");
if(isVideoPlaying) {
if(this.timer1 !=null) {
this.timer1.cancel();
}
}
}
}
private void callTimerTask() {
// TODO Timer for auto sliding
printLog( "callTimerTask Start" );
timer1 = new Timer();
timer1.schedule(new TimerTask() {
#Override
public void run() {
if (getActivity() != null) {
getActivity().runOnUiThread(new Runnable() {
#Override
public void run() {
if (getActivity() == null) {
return;
}
videoTime++;
if(DEFAULT_VIDEO_PLAY_TIME ==videoTime){
videoCompleteCDR=true;
Log.e("KeshavTimer", "callTimerTask videoCompleteCDR called.... " +videoTime);
destroyTimer();
}
Log.e("KeshavTimer", "callTimerTask videoTime " +videoTime);
}
});
} else {
printLog("callTimerTask getActivity is null ");
}
}
}, 1000, 1000);
// TODO 300, 2000;
}
private void destroyTimer(){
this.timer1.cancel();
}
Related
I have an application in Java where I need to schedule a TimerTaskwhich will be executed after 500ms , however if a certain event occurs, I must reset the timer for this task (so that we must wait another 500ms for it to execute). I have a timer declared for the whole class. I use the following code:
public static void main(String[] args) {
if (curr_pck == my_pck) {
timer.cancel();
timer.purge();
timer = new Timer();
timer.schedule(new TimerTask() {
#Override
public void run() {
myTask();
}
}, 500);
}
}
public static void myTask() {
timer.cancel();
timer.purge();
timer = new Timer();
timer.schedule(new TimerTask() {
#Override
public void run() {
myTask();
}
}, 500);
//EXECUTE CODE WHICH ISN'T RELEVANT TO THE QUESTION
}
I know that if I use timer.cancel() I can't reuse the timer object, however I thought reinitialising it in the line timer = new Timer() should solve this issue. Is there any way around this?
EXCEPTION on line timer.schedule(new TimerTask() { inside myTask() function:
java.lang.IllegalStateException: Timer already cancelled.
Create a class Timerr with the appropriate methods. Then access it as if it were a normal timer.
public class Timerr
{
private Timer timer;
public Timerr()
{
timer = new Timer();
start();
}
public void start()
{
timer.schedule(new TimerTask()
{
#Override
public void run()
{
System.out.println("hi");
}
}, 500);
}
public void reset()
{
timer.cancel();
timer.purge();
start();
}
}
Create instance
private Timerr timer = new Timerr();
Do your reset
if(condition)
{
timerr.reset();
}
You may want to check out Java's Swing timer. It works somewhat differently and you may have to write an internal class or an actionlistener, but the Swing timer includes .stop() and .restart(), which seem like they would work better in your application.
I'm just trying to change the color of my drawn circle with a timer. I have implemented following code into my "onCreate" method:
Timer t = new Timer();
t.scheduleAtFixedRate(new TimerTask() {
#Override
public void run() {
runOnUiThread(new Runnable() {
#Override
public void run() {
Drawing.switchColor();
}
});
}
},
1000,
1000);
The method switchColor() does the following action:
public static void switchColor() {
Random r = new Random(30);
int random = r.nextInt();
if(random < 10) {
p.setColor(Color.GREEN);
}
else if(random >10 && random < 20) {
p.setColor(Color.BLUE);
}
else {
p.setColor(Color.RED);
}
}
When I run this, the color stays at it's default.
Does anyone know whether I have to use a handler within or a different timer model?
Thanks in advance!
I now found a suitable solution:
//-------------------Part 1 of AddCircleTimer------------------------
//Declare the timerAddCircle
timerAddCircle = new Timer();
timerAddCircle.schedule(new TimerTask() {
#Override
public void run() {
TimerMethodAddCircle();
}
}, 1000, 1000);
//-------------------Part 2 of AddCircleTimer------------------------
private void TimerMethodAddCircle()
{
//This method is called directly by the timer and runs in the same thread as the timer.
//We call the method that will work with the UI through the runOnUiThread method.
this.runOnUiThread(Timer_Add);
}
private Runnable Timer_Add = new Runnable() {
public void run() {
//This method runs in the same thread as the UI.
//Do something to the UI thread here
Drawing.addCircle();
d.invalidate();
}
};
//-------------------END Part 2 of AddCircleTimer------------------------
This works very fine and I can use it for even more timers and different methods!
Thanks to all!
Your t.start() is missing, either in onCreate, onStart, or onResume, depending on when you want to start your timer.
boolean timing = true; /* this is a global attribute and its only here for context */
Timer t = new Timer();
t.schedule(new TimerTask() {
#Override
public void run() {
Platform.runLater(() -> {
new Thread(() -> {
if (!timing) {
try {
tt.cancel(); /* I want to cancel this if timming is false*/
} catch (Exception e) {
e.printStackTrace();
}
} else {
update();
}
}).run();
});
}
}, 10, 10);
I want to know if is possible to cancel that particular TimerTask inside of itself, please note that "tt" is only an example, I didn't know what else to call it. thanks.
Timers have their own background threads. Unless your tasks take a very long time to run, you do not need to create a new thread within the #run() method of the task (and you should not).
You can cancel subsequent executions of the timer by making the instance final:
final Timer t = new Timer();
t.schedule(new TimerTask() {
#Override
public void run() {
// Do work.
if (!timing) {
t.cancel();
}
}
});
(Exception handling omitted for brevity.)
If you only want to cancel the task itself (allowing other tasks scheduled by the timer to continue running), it's a trivial call to the #cancel() method of the task instance:
if (!timing) {
this.cancel();
}
You should also ensure that your timing variable is declared volatile. If you don't, the value could be cached in each thread, and you won't be able to observe changes.
How about you make a new method to cancel the Timer?
private void cancelTimer(Timer t)
{
t.cancel();
}
You also need to make the Timer final.
Hi I am using a timer for 2 tasks, which will monitor a set of IP address
public input ()
{
timer.schedule(task, 0, 8);
timer_second.schedule(task_monitor, 0, 5);
}
and I have 2 Timer Task
private final TimerTask task = new TimerTask() {
#Override
public void run() {
}
}
private final TimerTask task2 = new TimerTask() {
#Override
public void run() {
}
}
But as per my code logic, input () can be called more than one time , and if i call second time i get IllegalStateException: Task already scheduled or cancelled
Which seems to be obvious, but my logic is input can be called by different IP's and i have to monitor all such IP's using the 2 Timer Task
How should I avoid This ??
Please Help !!!!!
Thanks in advance
I'm currently using a Timer and TimerTask to perform some work every 30 seconds.
My problem is that after each time I do this work I want to increment the interval time of the Timer.
So for example it starts off with 30 seconds between the timer firing but I want to add 10 seconds to the interval then so that the next time the Timer takes 40 seconds before it fires.
Here is my previous code:
public void StartScanning() {
scanTask = new TimerTask() {
public void run() {
handler.post(new Runnable() {
public void run() {
wifiManager.startScan();
scanCount++;
if(SCAN_INTERVAL_TIME <= SCAN_MAX_INTERVAL){
SCAN_INTERVAL_TIME = SCAN_INTERVAL_TIME + SCAN_INCREASE_INTERVAL;
t.schedule(scanTask, 0, SCAN_INTERVAL_TIME);
}
}
});
}};
Log.d("SCAN_INTERVAL_TIME ** ", "SCAN_INTERVAL_TIME ** = " + SCAN_INTERVAL_TIME);
t.schedule(scanTask, 0, SCAN_INTERVAL_TIME);
}
REFACTORED CODE
#Override
public void StartScanning() {
t.schedule(new ScanTask(),SCAN_INTERVAL_TIME);
}
class ScanTask extends TimerTask{
#Override
public void run() {
wifiManager.startScan();
scanCount++;
if(SCAN_INTERVAL_TIME < SCAN_MAX_INTERVAL)
SCAN_INTERVAL_TIME = SCAN_INTERVAL_TIME + SCAN_INCREASE_INTERVAL;
t.schedule(new ScanTask(), SCAN_INTERVAL_TIME);
}
}
It works now but is creating a new ScanTask() every time wasteful?
Here is how I would do it:
1) Schedule the task for a single execution rather than a repeated one
2) At the end of the execution (possibly in a finally block), schedule a new single execution of the task, with a longer delay. Note that you must create a new instance of the task, otherwise the timer will complain (IllegalStateException). That means that you can't use an anonymous inner class anymore.