Trying to wrap my head around Java concurrency and am having a tough time understanding the relationship between thread pools, threads, and the runnable "tasks" they are executing.
If I create a thread pool with, say, 10 threads, then do I have to pass the same task to each thread in the pool, or are the pooled threads literally just task-agnostic "worker drones" available to execute any task?
Either way, how does an Executor/ExecutorService assign the right task to the right thread?
Typically, thread pools are implemented with one producer-consumer queue that all of the pool threads wait on for tasks. The Executor does not have to assign tasks, all it has to do is push them onto the queue. Some thread, a 'task-agnostic worker drone', will pop the task, execute its 'run()' method and, when complete, loop round to wait on the queue again for more work.
If I create a thread pool with, say, 10 threads, then do I have to pass the same task to each thread in the pool, or are the pooled threads literally just task-agnostic "worker drones" available to execute any task?
More or less the latter. Any given task gets assigned to the next available thread.
Either way, how does an Executor/ExecutorService assign the right task to the right thread?
There is no such thing as the "right" thread. The task (i.e. the Runnable) needs to be designed so that it doesn't matter which thread runs it. This is not normally an issue ... assuming that your application properly synchronizes access / updates to data that is potentially used by more than one threads.
