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Object locking can be efficiently implemented by bimodal use of a field reserved in an object. The field is used as a lightweight lock in one mode, while it holds the reference to a heavyweight lock in the other mode. A bimodal object-locking algorithm recently proposed for Java achieves the highest performance in the absence of contention, and is still fast enough when contention occurs.
However, mode transitions inherent in bimodal locking have not yet been fully considered. The above algorithm requires busy-wait in the transition from the light mode (inflation), and does not make the reverse transition (deflation) at all.
We propose a new algorithm that allows both inflation without busy-wait and deflation, but still maintains an almost maximum level of performance in the absence of contention. We also present statistics on the synchronization behavior of real multithreaded Java programs, which indicates that busy-wait in inflation
and absence of deflation can be problematic. An initial implementation of our algorithm shows promising results in terms of increased robustness and improved performance.
By: Tamiya Onodera and Kiyokuni Kawachiya
Published in: ACM SIGPLAN Notices, volume 34, (no 10), pages 223-237 in 1999
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