[Jsr308-statements] use cases for the annotations on code blocks and statements

[Eugene Kuleshov]

Hi,

  I would like to start collecting possible use cases for the 
annotations on code blocks and statements.

  Doug Lea gave great example for parallel execution [1]. In short the 
idea is to allow to transform the following code to improve execution 
characteristics:

   @ParallelAccumulator int sum = 0;
   @Parallelizable for(Student s : students) sum += s.credit;

  Decisions on those transformations can be delayed till execution and 
transformation could take into the account characteristics of the actual 
environment. In some cases runtime may allow to execute certain methods 
in parallel:

   @Parallelizable {
      methodA();
      ....
      methodX();
   }

  Further exploiting this idea to the distributed computing, if 
"students" collection in the above example is partitioned across several 
nodes, it is useful to transfer loop code block to the nodes holding 
particular subsets of collection and at the end return result back to 
the caller for aggregation. And things like that can be also done by the 
code transformations, unloading source code complexity from the developer.

  Another example is continuations. There are at least two continuation 
engines for Java that allow to suspend and resume method execution in 
the middle of method (RIFE [2] and Javaflow [3]) that allows very 
compact and readable code for defining execution floe. They both are 
using special method naming convention to control transformations for 
the execution flow. It would be better to use annotations for that purpose.

  Thoughts, comments and other use cases and examples are really 
appreciated.

  regards,
  Eugene

[1] https://lists.csail.mit.edu/pipermail/jsr308/2007-February/000152.html
[2] http://rifers.org/wiki/display/RIFECNT/Home
[3] http://jakarta.apache.org/commons/sandbox/javaflow/