Any examples showing how to use parallel search without using Script-based objects?

[yurivict]

The example golomb-ruler.cpp uses IntMinimizeScript::run() with the threads argument passed through the SizeOptions object.

But are there examples showing how to use parallel search with bare engine objects? For example:

  BAB<Solver> e;
  while (auto s = e.next()) {
     ...
  }

[Dekker1]

Script objects are probably the best way (and maybe the only recommended way) of interacting with the search process in Gecode. It might be worth reconsidering implementing your goals as part of a custom Script class instead of trying to re-invent the wheel.

But to point you in the direction of the information: threads is an option of the Search Engine, not an option for the Script. You can find a lot of information about how engines work and everything else about search in Chapter 9 (Search) of Modelling and Programming with Gecode. When working with Gecode this should generally be your first resource.

Just in case you are looking for more examples, there is also no harm in looking at how the script you mentioned is implemented:

• IntMinimizeScript is declared here.
• It's actual "run" method can be found here

[zayenz]

As @Dekker1 says, the threads is an option that is passed through to the search engine using Search::Options that can be passed to a search engine to configure it.

Here is a small example on how to use search options to set up a parallel search using 3 threads and additionally letting the search engine take ownership of the root node.

  Gecode::Search::Options options;
  // Use 3 threads.
  options.threads = 3;
  // Take ownership of the root node passed into the search engine
  options.clone = false;
  auto* root = new Sudoku(instance);
  Gecode::DFS<Sudoku> engine(root, options);
  while (auto* solution = engine.next()) {
    solution->print(std::cout);
    delete solution;
  }

The threads argument is documented in Section 9.3.1 in MPG.

[yurivict]

Thanks Mikael, this code snippet is exactly what I was looking for.

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The reason I avoided IntMinimizeScript is that it does more than I need. For example, it prints solutions unconditionally.