Fix island-based evolution not distributing programs across islands #392
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Fix issue #391 by ensuring children are placed in the intended target island instead of inheriting the parent's island. Add target_island to SerializableResult, capture sampling_island in the worker, and pass result.target_island into database.add when inserting child programs. Update tests to reflect the fixed behavior (children go to the target island) and add regression tests that demonstrate the old buggy behavior when target_island is not provided and the correct behavior when it is.
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Summary
Fixes issue #391 where all evolved programs were placed in Island 0 instead of being distributed across configured islands.
Root Cause
When sampling from an empty island,
sample_from_island()falls back to sampling from any available program (typically from Island 0). Children then inherited their parent's island viadatabase.add(), creating a feedback loop where all programs ended up in Island 0.Fix
target_islandfield toSerializableResultsampling_islandfrom the snapshot in the resultProcessParallelControllerpassestarget_islandtodatabase.add()when processing resultsThis ensures children are placed in the intended target island, not the parent's island.
Changes
openevolve/process_parallel.py: Addedtarget_islandto result and pass it todatabase.add()tests/test_island_child_placement.py: Comprehensive tests for island placement behaviorTest Plan
Closes #391
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