The appendix B.3 deals with an inexistent (as of SI 2.x) class SimpleTaskScheduler:
"By default Spring Integration uses the SimpleTaskScheduler implementation...."
Also, the Section 7.1.4 the pooler executor is explained in terms of that appendix:
"If no 'task-executor' is provided, the consumer's handler will be invoked in the caller's thread. Note that the "caller" is usually the default TaskScheduler (see Section B.3, "Configuring the Task Scheduler")."
Apart from deleting the SimpleTaskScheduler references, an explanation about the mentioned "default TaskScheduler" is needed (I can't find anything related in the Scheduling chapter of the Spring Framework reference.)