Camel threads(1,10) processor only holds 1 thread in its threadpool and does not grow.

Resolution

Why isn't my thread pool growing to maxpoolsize?

The Camel threads processor is delegating to the java.util.concurrent.ThreadPoolExecutor. The ThreadPoolExecutor poolsize is controlled by the interaction of corePoolSize, maximumPoolSize AND the QueueSize. From the javadoc for ThreadPoolExecutor (http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/ThreadPoolExecutor.html) explains it best:

Queuing

Any BlockingQueue may be used to transfer and hold submitted tasks. The use of this queue interacts with pool sizing:
- If fewer than corePoolSize threads are running, the Executor always prefers adding a new thread rather than queuing.
- If corePoolSize or more threads are running, the Executor always prefers queuing a request rather than adding a new thread.
- If a request cannot be queued, a new thread is created unless this would exceed maximumPoolSize, in which case, the task will be rejected.

By default the Camel Threads component maxQueuesize is 1000.

It is possible to change the maxQueueSize as follows

.threads(1,10,"vm1").maxQueueSize(1)

There are also other approaches to changing the the configuration of the thread pools used within camel by using the "default thread pool profile" or using a custom thread pool. These are all explained in http://fusesource.com/docs/esbent/7.1/camel_eip/BasicPrinciples-Thread.html