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Fix StackOverflowError due to non-commuting TransitionFunctionImpl.combineWith - #281
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swissiety merged 3 commits intoSep 23, 2026
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marcus-h
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Apr 23, 2026
marcus-h
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…mbineWith According to the theory, the combineWith operation of the TransitionFunctionImpl class has to be, among other things, commuative. This can result in a StackOverflowError (see VectorTest.testNoStackOverflowDueToNonCommutativeCombineWith for a reproducer). Excerpt from the stack trace: ... at wpds.impl.PostStar.update(PostStar.java:335) at wpds.impl.PostStar$HandleNormalListener.onOutTransitionAdded(PostStar.java:227) at wpds.impl.WeightedPAutomaton.addWeightForTransition(WeightedPAutomaton.java:329) at sync.pds.solver.SyncPDSSolver$4.addWeightForTransition(SyncPDSSolver.java:194) at wpds.impl.PostStar.update(PostStar.java:335) at wpds.impl.PostStar$HandleNormalListener.onOutTransitionAdded(PostStar.java:227) at wpds.impl.WeightedPAutomaton.addWeightForTransition(WeightedPAutomaton.java:329) at sync.pds.solver.SyncPDSSolver$4.addWeightForTransition(SyncPDSSolver.java:194) at wpds.impl.PostStar.update(PostStar.java:335) at wpds.impl.PostStar$HandleNormalListener.onOutTransitionAdded(PostStar.java:227) at wpds.impl.WeightedPAutomaton.addWeightForTransition(WeightedPAutomaton.java:329) at sync.pds.solver.SyncPDSSolver$4.addWeightForTransition(SyncPDSSolver.java:194) at wpds.impl.PostStar.update(PostStar.java:335) at wpds.impl.PostStar$HandleNormalListener.onOutTransitionAdded(PostStar.java:227) at wpds.impl.WeightedPAutomaton.addWeightForTransition(WeightedPAutomaton.java:329) at sync.pds.solver.SyncPDSSolver$4.addWeightForTransition(SyncPDSSolver.java:194) at wpds.impl.PostStar.update(PostStar.java:335) ... When combining the two paths in doSth, a new TransitionFunctionImpl is created where the statement sequences are merged but the stateChangeStatement from one of the path is used. The latter causes the PostStar.update <-> WeightedPAutomaton.addWeightForTransition "ping-pong". In order to fix this, store stateChangeStatement(s) from both paths in a set. Implementation note: a LinkedHashSet is used so the getStateChangeStatement() can be easily implemented (whether the method itself is "meaningful" is debatable, though).
swissiety
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Apr 27, 2026
Address review: storing every TransitionFunctionImpl's state change statement in a LinkedHashSet costs a set per weight, although only combineWith ever produces more than one statement. TransitionFunctionImpl keeps its single Statement field again, and the new package-private CombinedTransitionFunctionImpl holds the set. combineWith only builds a combined function when the merged set has at least two statements, so combining a function with itself still yields an equal plain TransitionFunctionImpl. A combined function compares its statements as a set, ignoring the order in which they were combined. Combining with ONE (in either order) keeps the combined statements.
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