Controlling Task execution order with ExecutorService

Question

I have a process which delegates asynch tasks to a pool of threads. I need to ensure that certain tasks are executed in order. So for example

Tasks arrive in order<

Answer 1

In Habanero-Java library, there is a concept of data-driven tasks which can be used to express dependencies between tasks and avoid thread-blocking operations. Under the covers Habanero-Java library uses the JDKs ForkJoinPool (i.e. an ExecutorService).

For example, your use case for tasks A1, A2, A3, ... could be expressed as follows:

HjFuture a1 = future(() -> { doA1(); return true; });
HjFuture a2 = futureAwait(a1, () -> { doA2(); return true; });
HjFuture a3 = futureAwait(a2, () -> { doA3(); return true; });

Note that a1, a2, and a3 are just references to objects of type HjFuture and can be maintained in your custom data structures to specify the dependencies as and when the tasks A2 and A3 come in at runtime.

There are some tutorial slides available. You can find further documentation as javadoc, API summary and primers.