I have a thread which is in charge of doing some processes. I want make it so that these processing would be done every 3 seconds. I've used the code below but when the thread starts, nothing happens.
I assumed that when I define a task for my timer it automatically execute the ScheduledTask within time interval but it doesn't do anything at all.
What am I missing?
class temperatureUp extends Thread
{
#Override
public void run()
{
TimerTask increaseTemperature = new TimerTask(){
public void run() {
try {
//do the processing
} catch (InterruptedException ex) {}
}
};
Timer increaserTimer = new Timer("MyTimer");
increaserTimer.schedule(increaseTemperature, 3000);
}
};
A few errors in your code snippet:
You extend the Thread class, which is not really good practice
You have a Timer within a Thread? That doesnt make sense as the a Timer runs on its own Thread.
You should rather (when/where necessary), implement a Runnable see here for a short example, however I cannot see the need for both a Thread and Timer in the snippet you gave.
Please see the below example of a working Timer which will simply increment the counter by one each time it is called (every 3seconds):
import java.util.Timer;
import java.util.TimerTask;
public class Test {
static int counter = 0;
public static void main(String[] args) {
TimerTask timerTask = new TimerTask() {
#Override
public void run() {
System.out.println("TimerTask executing counter is: " + counter);
counter++;//increments the counter
}
};
Timer timer = new Timer("MyTimer");//create a new Timer
timer.scheduleAtFixedRate(timerTask, 30, 3000);//this line starts the timer at the same time its executed
}
}
Addendum:
I did a short example of incorporating a Thread into the mix. So now the TimerTask will merely increment counter by 1 every 3 seconds, and the Thread will display counters value sleeping for 1 seconds every time it checks counter (it will terminate itself and the timer after counter==3):
import java.util.Timer;
import java.util.TimerTask;
public class Test {
static int counter = 0;
static Timer timer;
public static void main(String[] args) {
//create timer task to increment counter
TimerTask timerTask = new TimerTask() {
#Override
public void run() {
// System.out.println("TimerTask executing counter is: " + counter);
counter++;
}
};
//create thread to print counter value
Thread t = new Thread(new Runnable() {
#Override
public void run() {
while (true) {
try {
System.out.println("Thread reading counter is: " + counter);
if (counter == 3) {
System.out.println("Counter has reached 3 now will terminate");
timer.cancel();//end the timer
break;//end this loop
}
Thread.sleep(1000);
} catch (InterruptedException ex) {
ex.printStackTrace();
}
}
}
});
timer = new Timer("MyTimer");//create a new timer
timer.scheduleAtFixedRate(timerTask, 30, 3000);//start timer in 30ms to increment counter
t.start();//start thread to display counter
}
}
import java.util.Timer;
import java.util.TimerTask;
public class ThreadTimer extends TimerTask{
static int counter = 0;
public static void main(String [] args) {
Timer timer = new Timer("MyTimer");
timer.scheduleAtFixedRate(new ThreadTimer(), 30, 3000);
}
#Override
public void run() {
// TODO Auto-generated method stub
System.out.println("TimerTask executing counter is: " + counter);
counter++;
}
}
In order to do something every three seconds you should use scheduleAtFixedRate (see javadoc).
However your code really does nothing because you create a thread in which you start a timer just before the thread's run stops (there is nothing more to do). When the timer (which is a single shoot one) triggers, there is no thread to interrupt (run finished before).
class temperatureUp extends Thread
{
#Override
public void run()
{
TimerTask increaseTemperature = new TimerTask(){
public void run() {
try {
//do the processing
} catch (InterruptedException ex) {}
}
};
Timer increaserTimer = new Timer("MyTimer");
//start a 3 seconds timer 10ms later
increaserTimer.scheduleAtFixedRate(increaseTemperature, 3000, 10);
while(true) {
//give it some time to see timer triggering
doSomethingMeaningful();
}
}
I think the method you've used has the signature schedule(TimerTask task, long delay) . So in effect you're just delaying the start time of the ONLY execution.
To schedule it to run every 3 seconds you need to go with this method schedule(TimerTask task, long delay, long period) where the third param is used to give the period interval.
You can refer the Timer class definition here to be of further help
http://docs.oracle.com/javase/1.4.2/docs/api/java/util/Timer.html
Timer & TimerTask are legacy
The Timer & TimerTask classes are now legacy. To run code at a certain time, or to run code repeatedly, use a scheduled executor service.
To quote the Timer class Javadoc:
Java 5.0 introduced the java.util.concurrent package and one of the concurrency utilities therein is the ScheduledThreadPoolExecutor which is a thread pool for repeatedly executing tasks at a given rate or delay. It is effectively a more versatile replacement for the Timer/TimerTask combination, as it allows multiple service threads, accepts various time units, and doesn't require subclassing TimerTask (just implement Runnable). Configuring ScheduledThreadPoolExecutor with one thread makes it equivalent to Timer.
Executor framework
In modern Java, we use the Executors framework rather than directly addressing the Thread class.
Define your task as a Runnable or Callable. You can use compact lambda syntax seen below. Or you can use conventional syntax to define a class implementing the Runnable (or Callable) interface.
Ask a ScheduledExecutorService object to execute your Runnable object’s code every so often.
ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor() ;
Runnable task = () -> {
System.out.println( "Doing my thing at: " + Instant.now() );
};
long initialDelay = 0L ;
long period = 3L ;
TimeUnit timeUnit = TimeUnit.SECONDS ;
scheduledExecutorService.submit( task , initialDelay, period , timeUnit ) ;
…
scheduledExecutorService.shutdown() ; // Stops any more tasks from being scheduled.
scheduledExecutorService.awaitTermination() ; // Waits until all currently running tasks are done/failed/canceled.
Notice that we are not directly managing any Thread objects in the code above. Managing threads is the job of the executor service.
Tips:
Always shutdown your executor service gracefully when no longer needed, or when your app exits. Otherwise the backing thread pool may continue indefinitely like a zombie 🧟♂️.
Consider wrapping your task's working code in a try-catch. Any uncaught exception or error reaching the scheduled executor service results in silently halting the further scheduling of any more runs.
Related
I want to delay doing something, along the lines of setting a countdown timer that will "do a thing" after a certain amount of time.
I want the rest of my program to keep running while I wait, so I tried making my own Thread that contained a one-minute delay:
public class Scratch {
private static boolean outOfTime = false;
public static void main(String[] args) {
Thread countdown = new Thread() {
#Override
public void run() {
try {
// wait a while
System.out.println("Starting one-minute countdown now...");
Thread.sleep(60 * 1000);
// do the thing
outOfTime = true;
System.out.println("Out of time!");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
countdown.start();
while (!outOfTime) {
try {
Thread.sleep(1000);
System.out.println("do other stuff here");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
While this worked, more-or-less, it seemed like there should be a better way of doing this.
After some searching, I found a bunch of questions like these but they don't really address what I'm trying to do:
How do I schedule a task to run at periodic intervals?
How i can run my TimerTask everyday 2 PM
How to run certain task every day at a particular time using ScheduledExecutorService?
Java execute task with a number of retries and a timeout
I don't need anything this complicated; I just want to do a single thing after a certain amount of time while letting the rest of the program still run.
How should I go about scheduling a one-time task to "do a thing"?
While the java.util.Timer used to be a good way to schedule future tasks, it is now preferable1 to instead use the classes in the java.util.concurrent package.
There is a ScheduledExecutorService that is designed specifically to run a command after a delay (or to execute them periodically, but that's not relevant to this question).
It has a schedule(Runnable, long, TimeUnit) method that
Creates and executes a one-shot action that becomes enabled after the given delay.
Using a ScheduledExecutorService you could re-write your program like this:
import java.util.concurrent.*;
public class Scratch {
private static final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
public static void main(String[] args) {
System.out.println("Starting one-minute countdown now...");
ScheduledFuture<?> countdown = scheduler.schedule(new Runnable() {
#Override
public void run() {
// do the thing
System.out.println("Out of time!");
}}, 1, TimeUnit.MINUTES);
while (!countdown.isDone()) {
try {
Thread.sleep(1000);
System.out.println("do other stuff here");
} catch (InterruptedException e) {
e.printStackTrace();
}
}
scheduler.shutdown();
}
}
One of the nice things you get by doing things this way is the ScheduledFuture<?> object you get back from calling schedule().
This allows you to get rid of the extra boolean variable, and just check directly whether the job has run.
You can also cancel the scheduled task if you don't want to wait anymore by calling its cancel() method.
1See Java Timer vs ExecutorService? for reasons to avoid using a Timer in favor of an ExecutorService.
Thanks it worked for me. I used scheduler to schedule a task at a batchinterval calculated at runtime.
manualTriggerBatchJob.setSchedulingProperties(pblId, batchInterval);
ScheduledExecutorService scheduledExecutorService =
Executors.newScheduledThreadPool(5);
#SuppressWarnings("unchecked")
ScheduledFuture scheduledFuture =
scheduledExecutorService.schedule(manualTriggerBatchJob,
batchIntervalInMin,TimeUnit.MILLISECONDS);
I'm trying to launch a thread that needs to execute a task every second.
So what I did from now is making a loop on this code:
// execute my task
..
lastScan.setTime(lastScan.getTime() + 1000);
long timeToSleep = (lastScan.getTime() - new Date().getTime());
try {
Thread.sleep(timeToSleep);
} catch (InterruptedException e) {
e.printStackTrace();
}
This works, but I was wondering if there is something more elegant, and maybe more safe, for example a function that awake my thread when the current Date reach a given time.
Thanks in advance for your suggestions.
Try using ScheduledExecutorService:
ScheduledExecutorService es = Executors.newScheduledThreadPool(10); //number of threads
From there, the class has different methods for passing Runnable objects for which you can run on a timed delay in a separate thread
Have a look at the Java Timer class, this will help you do a timed loop more elegantly.
I would go with :
ScheduledThreadPoolExecutor
Scheduled Pool
You can use Timer and TimerTask,
This is a sample code that prints the same line every 5 seconds
import java.util.Calendar;
import java.util.Timer;
import java.util.TimerTask;
public class TimeReminder {
Timer timer;
public TimeReminder(int seconds) {
timer = new Timer(); //At this line a new Thread will be created
timer.schedule(new RemindTask(), Calendar.getInstance().getTime(), seconds * 1000);
}
class RemindTask extends TimerTask {
#Override
public void run() {
System.out.println("ReminderTask is completed by Java timer");
}
}
public static void main(String args[]) {
new TimeReminder(5);
System.out.println("Timertask is scheduled with Java timer.");
}
}
I have this piece of code:
Timeout s = new Timeout();
Timer timer = new Timer();
timer.schedule(s, 1000L); // fires after 1 second
How can I launch the following piece of code as a thread by itself? Would I need to pass the timer and Timeout to a Runnable and then start it? What happens if the thread's Run() ends before the timer is fired?
I am thinking of doing this instead:
ScheduledExecutorService ses = Executors.newScheduledThreadPool(1);
Timeout s = new Timeout(); // Timeout is a runnable
ses.schedule(s, 10, TimeUnit.SECONDS);
but how do I exit the thread after the timeout? I run out of thread after a while
Thanks
I'm not exactly sure what you're asking, but I'll give it a shot.
How can I launch the following piece of code as a thread by itself?
In short...
Timeout.java
public class Timeout extends TimerTask {
boolean isDone = false;
#Override
public void run() {
// TODO something
synchronized(this) {
isDone=true;
this.notifyAll();
}
}
public synchronized void join() throws InterruptedException {
while(!this.isDone)
this.wait();
}
}
TimeoutRunner.java
public class TimerRunner implements Runnable {
#Override
public void run() {
Timeout timeout = new Timeout();
Timer timer = new Timer();
timer.schedule(timeout, 1000L);
try {
timeout.join();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
timer.cancel();
}
}
}
Run the TimeoutRunner using:
new Thread(new TimeoutRunner()).start();
The join method will block the thread until the timeout task has completed execution. At that time you can close the Timer. This is, however, a lot of thread creation, and IMO bad programming.
When you create a Timer instance, a thread is created to execute the Timeout#run() method. The timer has it's own run method that blocks until your task is ready for execution. After the given timeout period elapses, the timer unblocks and executes your timeout.
Your TimeoutRunner thread will block until the timeout operation completes. Only then can this thread die.
The Timer class is very limited. You need to create a new instance for every task. In my option, the ScheduledExecutorService is a better option. Keep the ScheduledExecutorService open for as long as you plan on executing tasks. If you need something like a scheduled cached thread pool, feel free to use this class from one of my open-source projects (Scheduler). This works great with a cached thread pool.
In my case I created a object and planned to release it after 20 minutes(accuracy is not necessary). I know by using java.util.Timer I can create a timer.But I just want it run once. After that,the timer should stop and been released too.
Is there any way just like setTimeOut() in javascript?
Thanks.
int numberOfMillisecondsInTheFuture = 10000; // 10 sec
Date timeToRun = new Date(System.currentTimeMillis()+numberOfMillisecondsInTheFuture);
Timer timer = new Timer();
timer.schedule(new TimerTask() {
public void run() {
// Task here ...
}
}, timeToRun);
Modify above so that you can schedule a job 20 minutes in future.
Use Timer::schedule(TimerTask, long) or look into the ScheduledThreadPoolExecutor or ScheduledExecutorService classes.
You can start a new thread and call sleep with the number of milliseconds to wait, then execute your instructions (on either thread). See http://download.oracle.com/javase/1.4.2/docs/api/java/lang/Thread.html for reference, and look at the various online thread tutorials if you need more help.
java.util.Timer has a cancel method in it:
http://download.oracle.com/javase/6/docs/api/java/util/Timer.html#cancel%28%29
However, as far as I know, in timer if you do not specify a period, scheduled task will run only once.
package com.stevej;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class StackOverflowMain {
public static void main(String[] args) {
ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(1);
Runnable myAction = new Runnable() {
#Override
public void run() {
System.out.println("Hello (2 minutes into the future)");
}
};
executor.schedule(myAction, 2, TimeUnit.MINUTES);
}
}
For my MIDI player, I wanted to print 10 times in a second to get an accuracy of the timing but, the program consume quite a large amount of memory, how do I fix the code?
public void tick(int seconds) {
timer = new Timer();
timer.schedule(new tickcount(), seconds * 100);
}
class tickcount extends TimerTask {
public void run() {
if(sequencer != null) {
System.out.println("sec"+sequencer.getMicrosecondPosition()/1000000);
timer = null;
tick(1);
} else {
timer.cancel();
}
}
}
I don't really see how this code could be causing any kind of large memory consumption, unless it has to do with the incredible rate at which it'll be creating new threads.
At any rate, you should use a ScheduledExecutorService... Timer is kind of outdated (though even using it, you shouldn't be creating a new Timer each time your task runs). If you want the code in your tickcount task to run once every 0.1 seconds, you could do it like this:
private final ScheduledExecutorService scheduler =
Executors.newSingleThreadScheduledExecutor();
private Future<?> timingTask;
public void tick(long milliseconds) {
timingTask = scheduler.scheduleAtFixedRate(new Runnable() {
public void run() {
System.out.println("sec"+sequencer.getMicrosecondPosition()/1000000);
}
}, 0, milliseconds, TimeUnit.MILLISECONDS);
}
Here, the tick method will start your timer running, calling the Runnable every milliseconds ms, starting immediately. It also assigns a Future<?> to a field... this allows you to call timingTask.cancel(true) to cancel the scheduled task from running prior to setting sequencer to null.
Other than creating Timer object every time in tick() method call use a global timer object instance and reuse it