quaquel / EMAworkbench / 6708238519

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master: 80%

Pull #299

github

Fix MPIEvaluator pool not initializating multiple times

Addressed an issue where initializing the MPIEvaluator pool multiple times with a common initializer was causing a 'BrokenExecutor' error.

Details:
- Observed that using the MPIPoolExecutor twice in a row with an initializer function would lead to a 'BrokenExecutor: cannot run initializer' error on the second run.
- Reproduced the issue with simplified examples to confirm that the problem was due to the initializer function in conjunction with MPIPoolExecutor.
- Decided to remove the common initializer function from the MPIEvaluator to prevent this error.

Changes:
- Removed the global `experiment_runner` and the `mpi_initializer` function.
- Modified the MPIEvaluator's `initialize` method to not use the initializer arguments.
- Updated the `run_experiment_mpi` function to create the `ExperimentRunner` directly, ensuring each experiment execution has its fresh instance.

Examples:

Before:
```python
with MPIEvaluator(model) as evaluator:
    results = evaluator.perform_experiments(scenarios=24)
with MPIEvaluator(model) as evaluator:
    results2 = evaluator.perform_experiments(scenarios=48)

This would fail on the second invocation with a 'BrokenExecutor' error.

with MPIEvaluator(model) as evaluator:
    results = evaluator.perform_experiments(scenarios=24)
with MPIEvaluator(model) as evaluator:
    results2 = evaluator.perform_experiments(scenarios=48)

Now, both invocations run successfully without errors.

TL;DR:
By removing the common initializer, we have resolved the issue with re-initializing the MPIEvaluator pool. Users can now confidently use the MPIEvaluator multiple times in their workflows without encountering the 'BrokenExecutor' error.

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