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ε-STM
ε-STM is the first software transactional memory supporting elastic transactions. Elastic transactions are a variant of the transactional model. Upon conflict detection, an elastic transaction might drop what it did so far within a separate transaction that immediately commits, and initiate a new transaction which might itself be elastic.
Elastic transactions are a complementary alternative to traditional transactions, particularly appealing when implementing search structures. Both forms of transactions can safely be combined within the same application. ε-STM implementation is faster than a state-of-the-art software transactional memory in various workloads and with a speedup of 36% on average. It also presents a speedup over lock-based solutions of 89% on average.
The figure on the right-hand side shows that ε-STM multiplies regular STM peak performance by a factor of 4 on an 8-core machine for searching and modifying a 216-sized linked list, but, more importantly, tolerates contention. Indeed it scales better as the ratio of updating transactions grows and the level of parallelism grows. Here is the simple API, ε-STM provides to the user:
- BEGIN(elastic);
- BEGIN(normal);
- END;
- READ(x);
- WRITE(x,v).
The simplicity of using ε-STM comes from the very few information the programmer has to provide. The programmer has to indicate whether his(her) transaction is normal or elastic and no extra-information (i.e., release action, or on-abort-action) is necessary.