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Some Concurrency & Parallelism Operators (CIAO)

• Objective: express (independent) And-parallelism, concurrency (dependent And-Parallelism), and fairness
• Independent And-Parallelism:
  • A \&> H - sends out goal A, returns in H a handler
  • H <& - gets results of goal pointed by H, or executes it
  • A & B - performs a parallel ``fork'' of A and B, waits for the execution of both to finish
  • Last one can be implemented using the other two:

    A & B :- B \&> H, call(A), H <& .

  • The bindings made in the shared variables are not guaranteed to be seen until the threads join
  • Full support for backtracking
• Concurrency:
  • A & - Sends out goal A, bindings in the variables of A (tells) will be exported to other workers sharing them
  • A && - ``Fair'' version of the &/1 operator: if there is no idle worker, it creates one to execute A (``threads'')
  • wait(X) - Suspends the execution until X is bound (also, d_wait(X))
  • ask(C) - Suspends the execution until the constraint C is satisfied
  • A @ Id - Placement operator: goal A is to be executed on worker Id (which may be remote).