I am going through different concurrency model in multi-threading environment (http://tutorials.jenkov.com/java-concurrency/concurrency-models.html)
The article highlights about three concurrency models.
The first concurrency model is what I call the parallel worker model. Incoming jobs are assigned to different workers.
The workers are organized like workers at an assembly line in a factory. Each worker only performs a part of the full job. When that part is finished the worker forwards the job to the next worker.
Each worker is running in its own thread, and shares no state with other workers. This is also sometimes referred to as a shared nothing concurrency model.
The basic idea of functional parallelism is that you implement your program using function calls. Functions can be seen as "agents" or "actors" that send messages to each other, just like in the assembly line concurrency model (AKA reactive or event driven systems). When one function calls another, that is similar to sending a message.
Now I want to map java API support for these three concepts
Assembly Line : Sending an event to messaging system like JMS & using messaging concepts of Queues & Topics.
Functional Parallelism: ForkJoinPool to some extent & java 8 streams. ForkJoin pool is easy to understand compared to streams.
Am I correct in mapping these concurrency models? If not please correct me.
Each of those models says how the work is done/splitted from a general point of view, but when it comes to implementation, it really depends on your exact problem. Generally I see it like this:
- Parallel Workers: a producer creates new jobs somewhere (e.g in a
BlockingQueue) and many threads (via an
ExecutorService) process those jobs in parallel. Of course, you could also use a
CountDownLatch, but that means you want to trigger an action after exactly
Nsubproblems have been processed (e.g you know your big problem may be split in
Nsmaller problems, check the second example here).
- Assembly Line: for every intermediate step, you have a
ExecutorService. On each step the jobs are taken from one
BlickingQueueand put in the next one, to be processed further. To your idea with JMS: JMS is there to connect distributed components and is part of the Java EE and was not thought to be used in a high concurrent context (messages are kept usually on the hard disk, before being processed).
- Functional Parallelism:
ForkJoinPoolis a good example on how you could implement this.