Jason Baik created AMQ-6396:
-------------------------------
Summary: JVM property
org.apache.activemq.transport.nio.SelectorManager.maximumPoolSize has no impact
Key: AMQ-6396
URL: https://issues.apache.org/jira/browse/AMQ-6396
Project: ActiveMQ
Issue Type: Improvement
Components: Transport
Affects Versions: 5.14.0
Reporter: Jason Baik
Priority: Minor
http://activemq.apache.org/nio-transport-reference.html makes it sound as if
the number of threads in the SelectorManager's ThreadPoolExecutor can be capped
with the JVM property:
org.apache.activemq.transport.nio.SelectorManager.maximumPoolSize.
{code}
protected ExecutorService createDefaultExecutor() {
ThreadPoolExecutor rc = new
ThreadPoolExecutor(getDefaultCorePoolSize(), getDefaultMaximumPoolSize(),
getDefaultKeepAliveTime(), TimeUnit.SECONDS, new
LinkedBlockingQueue<Runnable>(),
new ThreadFactory() {
private long i = 0;
@Override
public Thread newThread(Runnable runnable) {
Thread t = new Thread(runnable, "ActiveMQ NIO Worker " +
(i++));
t.setDaemon(true);
return t;
}
}, new ThreadPoolExecutor.CallerRunsPolicy());
return rc;
}
{code}
However, this is not true since an unbounded LinkedBlockingQueue is being used
with the the executor. The size of the thread pool will never grow past the
core pool size as per ThreadPoolExecutor's Javadoc:
{quote}
If there are more than corePoolSize but less than maximumPoolSize threads
running, a new thread will be created *only if the queue is full*.
{quote}
I think it's better not to include in the maximumPoolSize property in the
documentation since it can confuse users into thinking that the pool size
should be capped using the maximumPoolSize property, although in reality it's
the corePoolSize property that does that.
Personally this confused me greatly and wasted me a lot of time while
stress-testing the MQTT NIO connector for my company. The broker would
constantly hit a live lock and spawn only 10 threads for the NIO transport,
even if I set the maximumPoolSize to a larger number.
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