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scheduleAtFixedRate vs scheduleWithFixedDelay

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How does scheduleAtFixedRate work?

scheduleAtFixedRate. Creates and executes a periodic action that becomes enabled first after the given initial delay, and subsequently with the given period; that is executions will commence after initialDelay then initialDelay+period, then initialDelay + 2 * period, and so on.

What is ScheduledExecutorService?

ScheduledExecutorService is an ExecutorService which can schedule tasks to run after a delay, or to execute repeatedly with a fixed interval of time in between each execution. Tasks are executed asynchronously by a worker thread, and not by the thread handing the task to the ScheduledExecutorService .

What is Scheduledfuture?

A delayed result-bearing action that can be cancelled. Usually a scheduled future is the result of scheduling a task with a ScheduledExecutorService .


Try adding a Thread.sleep(1000); call within your run() method... Basically it's the difference between scheduling something based on when the previous execution ends and when it (logically) starts.

For example, suppose I schedule an alarm to go off with a fixed rate of once an hour, and every time it goes off, I have a cup of coffee, which takes 10 minutes. Suppose that starts at midnight, I'd have:

00:00: Start making coffee
00:10: Finish making coffee
01:00: Start making coffee
01:10: Finish making coffee
02:00: Start making coffee
02:10: Finish making coffee

If I schedule with a fixed delay of one hour, I'd have:

00:00: Start making coffee
00:10: Finish making coffee
01:10: Start making coffee
01:20: Finish making coffee
02:20: Start making coffee
02:30: Finish making coffee

Which one you want depends on your task.


Visualize time series of invocation scheduleAtFixedRate method. Next executions will start immediately if the last one takes longer than period. Otherwise, it will start after period time.

time series of invocation scheduleAtFixedRate method

Time series of invocation scheduleWithFixedDelay method. Next execution will start after delay time between termination of one execution and the commencement of the next, regardless of its execution time

time series of invocation scheduleWithFixedDelay method

Hope can help you


The scheduleAtFixedRate() method creates a new task and submits it to the executor every period, regardless of whether or not the previous task finished.

On the other hand, the scheduleWithFixedDelay() method creates a new task after the previous task has finished.


If you read the Java Doc it will be clearer

ScheduledFuture scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) Creates and executes a periodic action that becomes enabled first after the given initial delay, and subsequently with the given period; that is executions will commence after initialDelay then initialDelay+period, then initialDelay + 2 * period, and so on.

ScheduledFuture scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) Creates and executes a periodic action that becomes enabled first after the given initial delay, and subsequently with the given delay between the termination of one execution and the commencement of the next.


There is one catch in scheduleAtFixedRate if first thread is taking too long and not ended in given duration then second conscutive thread will not start once the first task will get finsished and will not imediately get started while the first thread has comepleted their task and gievn duration has been elapsed. JVM Will decide when the next task will get executed .

I think that will help you to choose method Becuase due to this i got big problem