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“Static lock capabilities for deadlock freedom” by Colin S. Gordon, Michael D. Ernst, and Dan Grossman. University of Washington Department of Computer Science and Engineering technical report UW-CSE-11-10-01, (Seattle, WA, USA), Oct. 2011.
We present a technique — lock capabilities — for statically verifying that multithreaded programs with locks will not deadlock. Most previous work is built around a strict total order on all locks held simultaneously by a thread, but such an invariant often does not hold with fine-grained locking, especially when data-structure mutations change the order locks are acquired. Lock capabilities support idioms that use fine-grained locking, such as mutable binary trees, circular lists, and arrays where each element has a different lock.
Lock capabilities do not enforce a total order and do not prevent external references to data-structure nodes. Instead, the technique reasons about static capabilities, where a thread already holding locks can attempt to acquire another lock only if its capabilities allow it. Acquiring one lock may grant a capability to acquire further locks, and in data-structures where heap shape affects safe locking orders, we can use the heap structure to induce the capability-granting relation. Deadlock-freedom follows from ensuring that the capability-granting relation is acyclic. Where necessary, we restrict aliasing with a variant of unique references to allow strong updates to the capability-granting relation, while still allowing other aliases that are used only to acquire locks while holding no locks.
We formalize our technique as a type-and-effect system, demonstrate it handles realistic challenging idioms, and use syntactic techniques (type preservation) to show it soundly prevents deadlock.
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BibTeX entry:
@techreport{GordonEG2011,
author = {Colin S. Gordon and Michael D. Ernst and Dan Grossman},
title = {Static lock capabilities for deadlock freedom},
institution = {University of Washington Department of Computer Science
and Engineering},
number = {UW-CSE-11-10-01},
address = {Seattle, WA, USA},
month = oct,
year = {2011}
}
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