I am using a while loop with a timer.
The thing is that the timer is not used in every loop.
It is used only the first time. After the first time the statements included inside the loop are executed without the delay that i have set.
How is this even possible since the timer is included inside the while loop.
Any solutions ?
int count = 1;
while (count <= 10) {
final Handler handler = new Handler();
Timer t = new Timer();
t.schedule(new TimerTask() {
public void run() {
handler.post(new Runnable() {
public void run() {
// Stuff the while loop executes
}
});
}
}, 20000);
count++;
}
The TimerTask kicks off a new Thread and then the loop proceeds as normal.
The execution of the thread does not cause a delay to the execution of the code in your loop.
It's because you're queueing up 10 toasts all to execute in one hour. Each iteration of your loop takes only a fraction of a millisecond or maybe a tad bit more than that. To enqueue them properly, you could do 3600000 * count instead of 3600000 each time.
This is a terrible way to do it though. You should use AlarmManager for stuff like this.
You're scheduling 10 TimerTasks to execute after an hour, at the same time. So all 10 tasks are being executed after 1 hour, which makes it seem like 1 execute since all the Toast messages display at the same time. To schedule tasks at a fixed delay, with the first task starting in 1 hour, use this method:
Timer t = new Timer();
t.schedule(task, 3600000, 3600000);
This will execute until you call t.cancel().
Related
How can I get the time left in a util.Timer?
What I want to do is to add a progressbar that displays time left until the timer starts over.
This is what I've got this far:
int seconds = 8;
java.util.Timer timer = new Timer();
timer.schedule( new TimerTask(){
public void run(){
// Do something
// Add a progressbar that displays time left until the timer "starts over".
},0,(long) (seconds*1000));
You would need a second timer to refresh the gui in a specific interval.
Another way to achieve this, would be to activate a single timer every second and update the counting in the ui. If the time is up, call your specific action.
A simple expample with console output only:
TimerTask task = new TimerTask()
{
int seconds = 8;
int i = 0;
#Override
public void run()
{
i++;
if(i % seconds == 0)
System.out.println("Timer action!");
else
System.out.println("Time left:" + (seconds - (i %seconds)) );
}
};
Timer timer = new Timer();
timer.schedule(task, 0, 1000);
It's output would be:
Time left:7
Time left:6
Time left:5
Time left:4
Time left:3
Time left:2
Time left:1
Timer action!
Time left:7
Time left:6
Time left:5
Time left:4
Time left:3
Time left:2
Time left:1
Timer action!
Time left:7
Time left:6
...
Then simply change the System.out's with your code to update the progress bar. Remember: java.util.Timer starts its own Thread. Swing is not thread safe, so you need to put every gui changing code into SwingUtilities.invokeLater()!
If you're not doing any long running tasks, every time your timer reachs the 8 seconds mark, you may want to use javax.swing.Timer directly. It uses the EDT and not its own Thread, so you don't need to synchronize your calls to Swing components with SwingUtilities.invokeLater().
Also see:
javax.swing.Timer vs java.util.Timer inside of a Swing application
All you need to do is declare a long variable timeleft in your MainActivity.
long timeleft;
Then, when you create a new Timer, set the "onTick" override to update the timeleft variable each "onTick" (which in the following example is 1000 milliseconds )
timer = new CountDownTimer(time, 1000) {
#Override
public void onTick(long millisecondsUntilFinished) {
timeleft = millisecondsUntilFinished;
}
}
Your app can access then the variable timeleft every time you need to check how much time is left.
I'm trying to perform a task every 5 minute.
The task need to start from: xx:00, xx:05, xx:10, xx:15 and so on so if the time is xx:37 the task will start in xx:40.
I'm used the following code to do that:
Date d1 = new Date();
d1.setMinutes(d1.getMinutes() + 5 - d1.getMinutes()%5);
d1.setSeconds(0);
this.timer.schedule(new Send(), d1, TEN_MINUTES/2);
Send looks like that:
class Send extends TimerTask
{
public void run()
{
if(SomeCondition)
{
Timestamp ts1 = new Timestamp(new java.util.Date().getTime());
SendToDB(ts1);
}
}
}
So the result should be records that if you % the minutes the result would be 0.
But the records time I have is:
*05:35:00
*07:44:40
*07:54:40
*09:05:31
*09:50:00
As you can see the first task start perfectly but then something went wrong.
My guess is that the task calculateds the 5 minute jump after the previous task is finished so the task run time effects, but it's just a guess.
The time a task takes to execute will delay the schedule. From the docs for schedule:
If an execution is delayed for any reason (such as garbage collection or other background activity), subsequent executions will be delayed as well.
You will be better off using scheduleAtFixedRate.
Alternatively, you might try using a simple Thread with a loop to repeatedly perform the task. The last step in the loop can be to sleep the necessary time until you want to start the task again. Assuming that no one iteration of the loop takes five minutes, this will eliminate cumulative delays.
public void run() {
long start = System.currentTimeMillis();
while (shouldRun()) {
doTask();
long next = start + FIVE_MINUTES;
try {
Thread.sleep(next - System.currentTimeMillis());
start = next;
} catch (InterruptedException e) {
. . .
}
}
}
This will start each iteration at the next five-minute interval and will not accumulate delays due to the running time of doTask() or any system delays. I haven't looked at the sources, but I suspect that this is close to what's in Timer.scheduleAtFixedRate.
Why dont you use a Task scheduler or simply a sleep command in a loop which lets the thread sleep for 5 minutes then continue.
An alternative would be to use a Timer class
I would probably make use of ScheduleExecutorService.scheduleAtFixedRate which is a more modern approach than using a Timer and would allow for having multiple worker threads in case there are many tasks being scheduled.
I am trying to run a line of code every second by using System.currentTimeMillis();.
The code:
while(true){
long var = System.currentTimeMillis() / 1000;
double var2 = var %2;
if(var2 == 1.0){
//code to run
}//If():
}//While
The code which I want to run, runs multiple times because var2 is set to 1.0 multiple times due to the infinite whole loop. I just want to run the code line when var2 is first set to 1.0, and then every time again when var2 becomes 1.0 after 0.0.
If you want to busy wait for the seconds to change you can use the following.
long lastSec = 0;
while(true){
long sec = System.currentTimeMillis() / 1000;
if (sec != lastSec) {
//code to run
lastSec = sec;
}//If():
}//While
A more efficient approach is to sleep until the next second.
while(true) {
long millis = System.currentTimeMillis();
//code to run
Thread.sleep(1000 - millis % 1000);
}//While
An alternative is to use a ScheduledExecutorService
ScheduledExecutorService ses = Executors.newSingleThreadScheduledExecutor();
ses.scheduleAtFixedRate(new Runnable() {
#Override
public void run() {
// code to run
}
}, 0, 1, TimeUnit.SECONDS);
// when finished
ses.shutdown();
The advantage of this approach is that
you can have a number of tasks with different periods sharing the same thread.
you can have non-repeating delay or asynchronous tasks.
you can collect the results in another thread.
you can shutdown the thread pool with one command.
I'd use the java executor libraries. You can create a ScheduledPool that takes a runnable and can run for any time period you want. For example
Executors.newSingleThreadScheduledExecutor().scheduleAtFixedRate(new MyRunnable(), 0, 5, TimeUnit.SECONDS);
Will run the MyRunnable class every 5 seconds. MyRunnable must implement Runnable. The trouble with this is that it will (efficiently) create a new thread each time which may or may not be desirable.
You should have to use java.util.Timer and java.util.TimerTask class.
Using Thread.sleep(); would be perfect for your case.
while(true)
{
Thread.sleep(1000); // Waiting before run.
// Actual work goes here.
}
preferred way:
ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();
Then pass in Runnables like:
scheduler.scheduleWithFixedDelay(myRunnable, initDelay, delay, TimeUnit.MILLISECONDS);
I wouldn't use the Timer. Schedulers are built to handle problems that Timers can cause. Also, the Thread.sleep is good for a simple program that you're writing quickly for proof of concept type things but I wouldn't use it in the enterprise world.
I am using a while loop with a timer.
The thing is that the timer is not used in every loop.
It is used only the first time. After the first time the statements included inside the loop are executed without the delay that i have set.
How is this even possible since the timer is included inside the while loop.
Any solutions ?
int count = 1;
while (count <= 10) {
final Handler handler = new Handler();
Timer t = new Timer();
t.schedule(new TimerTask() {
public void run() {
handler.post(new Runnable() {
public void run() {
// Stuff the while loop executes
}
});
}
}, 20000);
count++;
}
The TimerTask kicks off a new Thread and then the loop proceeds as normal.
The execution of the thread does not cause a delay to the execution of the code in your loop.
It's because you're queueing up 10 toasts all to execute in one hour. Each iteration of your loop takes only a fraction of a millisecond or maybe a tad bit more than that. To enqueue them properly, you could do 3600000 * count instead of 3600000 each time.
This is a terrible way to do it though. You should use AlarmManager for stuff like this.
You're scheduling 10 TimerTasks to execute after an hour, at the same time. So all 10 tasks are being executed after 1 hour, which makes it seem like 1 execute since all the Toast messages display at the same time. To schedule tasks at a fixed delay, with the first task starting in 1 hour, use this method:
Timer t = new Timer();
t.schedule(task, 3600000, 3600000);
This will execute until you call t.cancel().
I need to run some code for a predefined length of time, when the time is up it needs to stop. Currently I am using a TimerTask to allow the code to execute for a set amount of time but this is causing endless threads to be created by the code and is just simply not efficient. Is there a better alternative?
Current code;
// Calculate the new lines to draw
Timer timer3 = new Timer();
timer3.schedule(new TimerTask(){
public void run(){
ArrayList<String> Coords = new ArrayList<String>();
int x = Float.valueOf(lastFour[0]).intValue();
int y = Float.valueOf(lastFour[1]).intValue();
int x1 = Float.valueOf(lastFour[2]).intValue();
int y1 = Float.valueOf(lastFour[3]).intValue();
//Could be the wrong way round (x1,y1,x,y)?
Coords = CoordFiller.coordFillCalc(x, y, x1, y1);
String newCoOrds = "";
for (int j = 0; j < Coords.size(); j++)
{
newCoOrds += Coords.get(j) + " ";
}
newCoOrds.trim();
ClientStorage.storeAmmendedMotion(newCoOrds);
}
}
,time);
If you are using Java5 or later, consider ScheduledThreadPoolExecutor and Future. With the former, you can schedule tasks to be run after a specified delay, or at specified intervals, thus it takes over the role of Timer, just more reliably.
The Timer facility manages the execution of deferred ("run this task in 100 ms") and periodic ("run this task every 10 ms") tasks. However, Timer has some drawbacks, and ScheduledThreadPoolExecutor should be thought of as its replacement. [...]
A Timer creates only a single thread for executing timer tasks. If a timer task takes too long to run, the timing accuracy of other TimerTasks can suffer. If a recurring TimerTask is scheduled to run every 10 ms and another TimerTask takes 40 ms to run, the recurring task either (depending on whether it was scheduled at fixed rate or fixed delay) gets called four times in rapid succession after the long-running task completes, or "misses" four invocations completely. Scheduled thread pools address this limitation by letting you provide multiple threads for executing deferred and periodic tasks.
Another problem with Timer is that it behaves poorly if a TimerTask throws an unchecked exception. The Timer thread doesn't catch the exception, so an unchecked exception thrown from a TimerTask terminates the timer thread. Timer also doesn't resurrect the thread in this situation; instead, it erroneously assumes the entire Timer was cancelled. In this case, TimerTasks that are already scheduled but not yet executed are never run, and new tasks cannot be scheduled.
From Java Concurrency in Practice, section 6.2.5.
And Futures can be constrained to run at most for the specified time (throwing a TimeoutException if it could not finish in time).
Update
If you don't like the above, you can make the task measure its own execution time, as below:
int totalTime = 50000; // in nanoseconds
long startTime = System.getNanoTime();
boolean toFinish = false;
while (!toFinish)
{
System.out.println("Task!");
...
toFinish = (System.getNanoTime() - startTime >= totalTime);
}
[...] Currently I am using a TimerTask to allow the code to execute for a set amount of time [...]
The timer task will never stop the currently running task. In fact, it's only purpose is to restart the task over and over again.
There is no easy way of solving this without tight cooperation with the executing task. The best way is to let the task monitor it's own execution, and make sure that it returns (terminates) when its time is up.
If by stopping you mean the program has to exit, the solution is to create a thread for your processing and mark it as daemon, start it and in the main thread sleep for the time required, then simply return from the main() method.
Scratch that if by stopping, you mean just to stop the processing.
It should also be noted that generally you only need to create one Timer(). From the code snippet I would guess you are creating multiple Timer() objects.
The time in the schedule method is the time to run at, not how long to run for.
Consider putting a start time before the for loop & putting a break in the for loop if you have exceeded the time limit.
long startedAt = System.currentTimeMillis();
long finishedCorrectly = true;
for (int j = 0; j < Coords.size(); j++) {
newCoOrds += Coords.get(j) + " ";
if ((System.currentTimeMillis() - startedAt) > MAX_TIME_TO_RUN) {
finishedCorrectly = false;
break;
}
}