CODEWITHSUNDEEP
javathreadpoolthreadpoolexecutor
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One Two Three

Reputation: 23497

meaning of 'core pool size' in ScheduledThreadPoolExecutor's constructor

I'm new to ScheduledThreadPoolExecutor (as I usually use the simple Timer, but people have been advising against it), and I don't quite understand what would be the appropriate integer value to pass to the ScheduledThreadPoolExecutor(int) constructor.

Could anyone explain this?

Thank you

Upvotes: 16

Views: 10737

Answers (2)

Antoniossss
Antoniossss

Reputation: 32507

In case of ScheduledThreadPoolExecutor, corePoolSize is maximum number of threads that will be created to perform scheduled actions. This thread pool is fixed-sized and idle threads are kept alive.

DrunkenRabbit's answer is simply ivalid because ScheduledThreadPoolsExecutor docs says explicitly that (There will be no thread count spikes at all):

While this class inherits from ThreadPoolExecutor, a few of the inherited tuning methods are not useful for it. In particular, because it acts as a fixed-sized pool using corePoolSize threads and an unbounded queue, adjustments to maximumPoolSize have no useful effect.

Now as for the value, reasonable number would be number of CPU cores that application is running on.

Upvotes: 13

drunkenRabbit
drunkenRabbit

Reputation: 394

Essentially, the corePoolSize is the number of Threads to maintain in the pool.

eg. if you expect 10 concurrent requests on a regular basis, but peaks of 20. The corePoolSize should be 10 and max as 20. This way the executor will create up to 10 new threads, even if idle threads are available for use.

As stated in the JavaDocs

Core and maximum pool sizes

A ThreadPoolExecutor will automatically adjust the pool size (see getPoolSize()) according to the bounds set by corePoolSize (see getCorePoolSize()) and maximumPoolSize (see getMaximumPoolSize()). When a new task is submitted in method execute(java.lang.Runnable), and fewer than corePoolSize threads are running, a new thread is created to handle the request, even if other worker threads are idle. If there are more than corePoolSize but less than maximumPoolSize threads running, a new thread will be created only if the queue is full. By setting corePoolSize and maximumPoolSize the same, you create a fixed-size thread pool. By setting maximumPoolSize to an essentially unbounded value such as Integer.MAX_VALUE, you allow the pool to accommodate an arbitrary number of concurrent tasks. Most typically, core and maximum pool sizes are set only upon construction, but they may also be changed dynamically using setCorePoolSize(int) and setMaximumPoolSize(int).

Upvotes: 0

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