Hi,

I've utilized Consumer/Producer pattern together with CompletionService
from java.util.concurrent package.

Delegator class delegates (in its thread) tasks to producers by use of
CompletionService:

 CompletionService cs = ....
 while(true) {
      Task task = receive();
       Future<Result> f = cs.submit(task);
 }

Consumer class (in its thread) uses CompletionService to handle with
results of task execution

 while(true) {
     Futute<Result> f = cs.take();
     handle(f);
 }

But it also needs to know some details connected with the executed
Task. These details cannot be given in the Result object of /taken/
Future<Result> task, since sometimes task execution could cause
exception and then the associated Result object is /null/.

What I tried to do was to use shared Map object, in which Future
objects get associated with their tasks by Delegator:

  Future<Result> f = cs.submit(task);
  tasks.put(f, task)

but in between Consumer may take Future object which has no task
assiociated in tasks map.

Any solution to that ? Is there anything like BlockingHashMap ?

Regards,
Maciej