Read Locks Research Articles

Automated Refactoring for Stampedlock

StampedLock, proposed in JDK 1.8, provides many interesting features, such as optimistic read locks and upgrading/downgrading locks to improve the design of concurrent programs instead of employing pure read/write locks. Existing refactorings have proposed algorithms to convert locks, but there are a few refactorings that use these promising features of StampedLock. To illustrate a possible refactoring, this paper first shows three code transformations based on StampedLock. Then, this paper presents CLOCK, an automated refactoring tool that helps developers convert the synchronized lock into the StampedLock. An algorithm for reentrance analysis is proposed for the precondition validation. The write lock, read lock, optimistic read lock, and upgrading/downgrading lock are inferred and refactored. CLOCK is evaluated with the SPECjbb2005 benchmark and two real-world applications, Xalan and FOP. A total of 66 classes are modified by searching approximately 395KSLOC and applying the refactoring, achieving an average of 22 classes per benchmark. The experimental results show that CLOCK can help developers with refactoring for StampedLock and save developer effort.

Automation of data acquisition Surface Plasmon Resonance (SPR) based on LabVIEW

Evanescent wave is the result of Attenuated Total Reflection (ATR), Surface Plasmon Resonance (SPR) occurs at a specific angle on condition ATR. When a beam is passed through a prism, the beam will experience a reflection on the part of the prism which is in contact with the sample. The result of this reflection to be captured by the detector, On the condition of SPR weaken the intensity of the reflected beam of laser light that occurs because the refracted exponentially away from the boundary of the medium. The LabVIEW-based program has been created that can be used as a tool for experimental SPR, using Motor SHOT 602 and Lock-In Amplifier (SR510). Programs that have been made already equipped with the condition automation starts of movement Motor 2 (Prism), Motor 1 (Detectors), Readings Voltage detectors by Lock-In Amplifier (SR510) and storage of results (time, a position of the motor 1 and 2, the voltage read Lock in Amplifier). Automation program is made by studying the way of the light at Surface Plasmon Resonance (SPR), to determine the relationship between the rotational angle of motor prism and the rotational angle of motor, it can be used for control the position of the sample on the prism and the detector in a program based on LabVIEW.

Mostly-optimistic concurrency control for highly contended dynamic workloads on a thousand cores

Future servers will be equipped with thousands of CPU cores and deep memory hierarchies. Traditional concurrency control (CC) schemes---both optimistic and pessimistic---slow down orders of magnitude in such environments for highly contended workloads. Optimistic CC (OCC) scales the best for workloads with few conflicts, but suffers from clobbered reads for high conflict workloads. Although pessimistic locking can protect reads, it floods cache-coherence backbones in deep memory hierarchies and can also cause numerous deadlock aborts. This paper proposes a new CC scheme, mostly-optimistic concurrency control (MOCC), to address these problems. MOCC achieves orders of magnitude higher performance for dynamic workloads on modern servers. The key objective of MOCC is to avoid clobbered reads for high conflict workloads, without any centralized mechanisms or heavyweight interthread communication. To satisfy such needs, we devise a native, cancellable reader-writer spinlock and a serializable protocol that can acquire, release and re-acquire locks in any order without expensive interthread communication. For low conflict workloads, MOCC maintains OCC's high performance without taking read locks. Our experiments with high conflict YCSB workloads on a 288-core server reveal that MOCC performs 8× and 23× faster than OCC and pessimistic locking, respectively. It achieves 17 million TPS for TPC-C and more than 110 million TPS for YCSB without conflicts, 170× faster than pessimistic methods.

On Deferred Constraints in Distributed Database Systems

An atomic commit protocol (ACP) is a distributed algorithm used to ensure the atomicity property of transactions in distributed database systems. Although ACPs are designed to guarantee atomicity, they add a significant extra cost to each transaction execution time. This added cost is due to the overhead of the required coordination messages and log writes at each involved database site to achieve atomicity. For this reason, the continuing research efforts led to a number of optimizations that reduce the aforementioned cost. The most commonly adopted optimizations in the database standards and commercial database management systems are those designed around the early release of read locks of transactions. In this type of optimizations, certain participating sites may start releasing the read locks held by transactions before they are fully terminated across all participants. Hence, greatly enhancing concurrency among executing transactions and, consequently, the overall system performance. However, this type of optimizations introduces possible “execution infections” in the presence of deferred consistency constraints; a devastating complication that may lead to non-serializable executions of transactions. Thus, this type of optimizations could be considered useless, given the importance of preserving the consistency of the database in presence of deferred constraints, unless this complication is resolved in a practical and efficient manner. This is the essence of the “unsolicited deferred consistency constraints validation” mechanism presented in this paper.

ASEP: a secure and flexible commit protocol for MLS distributed database systems

The classical Early Prepare (EP) commit protocol, used in many commercial systems, is not suitable for use in multi-level secure (MLS) distributed database systems that employ a locking protocol for concurrency control. This is because EP requires that read locks are not released by a participant during their window of uncertainty; however, it is not possible for a locking protocol to provide this guarantee in a MLS system (since the read lock of a higher-level transaction on a lower-level data object must be released whenever a lower-level transaction wants to write the same data). The only available work in the literature, namely the Secure Early Prepare (SEP) protocol, overcomes this difficulty by aborting those distributed transactions that release their low-level read locks prematurely. We see this approach as being too restrictive. One of the major benefits of distributed processing is its robustness to failures, and SEP fails to take advantage of this. In this paper, we propose the Advanced Secure Early Prepare (ASEP) commit protocol to solve the above problem, together with a number of language primitives that can be used as system calls in distributed transactions. These primitives permit features like partial rollback and forward recovery to be incorporated within the transaction model, and allow a distributed transaction to proceed even when a participant has released its low-level read locks prematurely. This not only offers flexibility, but can also be used, if desired, by a sophisticated programmer to trade off consistency for atomicity of the distributed transaction.

Access synchronization and deadlock-analysis in database systems: An implementation-oriented approach

In this paper a simple method for access synchronization in large database systems is developed, on the basis of which an efficient deadlock detection procedure can be given. The described methods can easily be implemented; it seems that the resulting overhead is comparatively small. The method can, with minor modifications, be extended to a two-level lockout mechanism that provides for read locks as well as for write locks.