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arXiv · 2602.04013

Pending Conflicts Make Progress Impossible

Petr Kuznetsov·Pierre Sutra·Guillermo Toyos-Marfurt
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Abstract

In this work, we study progress conditions for commutativity-aware, linearizable implementations of shared objects. Motivated by the observation that commuting operations can be executed in parallel, we introduce conflict-obstruction-freedom: a process is guaranteed to complete its operation if it runs for long enough without encountering step contention with conflicting (non-commuting) operations. This condition generalizes obstruction-freedom and wait-freedom by allowing progress as long as step contention is only induced by commuting operations. We prove that conflict-obstruction-free universal constructions are impossible to implement in the asynchronous read-write shared memory model. This result exposes a fundamental limitation of conflict-aware universal constructions: the mere invocation of conflicting operations imposes a synchronization cost. Progress requires eventual resolution of pending conflicts.

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Petr Kuznetsov, Pierre Sutra, Guillermo Toyos-Marfurt. 2026-02-03. Pending Conflicts Make Progress Impossible. https://arxiv.org/abs/2602.04013

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