I will explain implementation of ThreadPoolExecutor.class here!
ThreadPoolExecutor class has four constructors, using which one can obtain ThreadPoolExecutor instance.
(1)
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
Executors.defaultThreadFactory(), defaultHandler);
}
(2)
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
threadFactory, defaultHandler);
}
(3)
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
RejectedExecutionHandler handler) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
Executors.defaultThreadFactory(), handler);
}
(4)
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler) {
if (corePoolSize < 0 ||
maximumPoolSize <= 0 ||
maximumPoolSize < corePoolSize ||
keepAliveTime < 0)
throw new IllegalArgumentException();
if (workQueue == null || threadFactory == null || handler == null)
throw new NullPointerException();
this.corePoolSize = corePoolSize;
this.maximumPoolSize = maximumPoolSize;
this.workQueue = workQueue;
this.keepAliveTime = unit.toNanos(keepAliveTime);
this.threadFactory = threadFactory;
this.handler = handler;
}
Out of 4 constructors mentioned above, if you observer, both 1 & 2, variable defaultHandler is passed to create the instance. So, what is defaultHandler?
private static final RejectedExecutionHandler defaultHandler =
new AbortPolicy();
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
throw new RejectedExecutionException("Task " + r.toString() +" rejected from " + e.toString());
}
defaultHandler throws RejecctedExecutionException whenever there is no thread available to execute the job.
If you want to have metric logs for thread rejection execution exception, it is recommended to create a separate implementation for RejectedExecutionHandler.
This can be done as mentioned below.
(a) Create RejectedExecutionHandlerImpl class
public class RejectedExecutionHandlerImpl implements RejectedExecutionHandler {
@Override
public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
// log rejection metrics here
}
}
(b) Create ThreadPoolExecutor
RejectedExecutionHandlerImpl rejectionHandler = new RejectedExecutionHandlerImpl();
ThreadFactory threadFactory = Executors.defaultThreadFactory();
ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor(minThreadCount, maxThreadCount, threadAliveTime, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(poolQueueSize), threadFactory, rejectionHandler);
