56.9 Java Executor Concurrency

So far in this chapter we have looked exclusively at directly creating and managing Java threads. While acceptable for simple multi-threading tasks, this can prove to be inadequate when working with complex situations involving large number of threads. There is, for example, a system overhead involved in starting and stopping threads. An app that creates and destroys large number of threads is, therefore, at risk of exhibiting degraded performance. The basic threading API also does not provide pre-built options for scheduling or repeating task execution, or for returning results from a task.

The shortcomings of working directly with threads can be overcome by making use of the Executor classes of the Java Concurrent framework (part of the java.util.concurrent package). This framework allows for a pool of active threads to be created and manages how tasks are assigned to those threads. This allows existing threads to be reused for other tasks without...