CODEWITHSUNDEEP
javamultithreading
Delphian
Delphian

Reputation: 1760

What does it mean to create a thread with Executors.newScheduledThreadPool(n)?

When I create the ExecutorService, I use one of the factories to create threads, for example, we have 3 threads:

Executors.newScheduledThreadPool (3)

What happens with resources and memory, when we use the factory? These threads already exist or they create when I start the tasks? What does it mean to create a thread (native code)?

Upvotes: 0

Views: 118

Answers (1)

shazin
shazin

Reputation: 21883

It will create and return a ScheduledThreadPoolExecutor with the following characteristics 

This class specializes ThreadPoolExecutor implementation by

 1. Using a custom task type, ScheduledFutureTask for
    tasks, even those that don't require scheduling (i.e.,
    those submitted using ExecutorService execute, not
    ScheduledExecutorService methods) which are treated as
    delayed tasks with a delay of zero.

 2. Using a custom queue (DelayedWorkQueue) based on an
    unbounded DelayQueue. The lack of capacity constraint and
    the fact that corePoolSize and maximumPoolSize are
    effectively identical simplifies some execution mechanics
    (see delayedExecute) compared to ThreadPoolExecutor
    version.

    The DelayedWorkQueue class is defined below for the sake of
    ensuring that all elements are instances of
    RunnableScheduledFuture.  Since DelayQueue otherwise
    requires type be Delayed, but not necessarily Runnable, and
    the workQueue requires the opposite, we need to explicitly
    define a class that requires both to ensure that users don't
    add objects that aren't RunnableScheduledFutures via
    getQueue().add() etc.

 3. Supporting optional run-after-shutdown parameters, which
    leads to overrides of shutdown methods to remove and cancel
    tasks that should NOT be run after shutdown, as well as
    different recheck logic when task (re)submission overlaps
    with a shutdown.

 4. Task decoration methods to allow interception and
    instrumentation, which are needed because subclasses cannot
    otherwise override submit methods to get this effect. These
    don't have any impact on pool control logic though.

For your question

These threads already exist or they create when I start the tasks?

There will be Threads created and pooled for the size of corePoolSize which is 3 in this case.

Upvotes: 2

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