Most high-performance software transactional memories (STM) use optimistic invisible reads. Consequently, a transaction might have an inconsistent view of the objects it accesses unless the consistency of the view is validated whenever the view changes. Although all STMs usually detect inconsistencies at commit time, a transaction might never reach this point because an inconsistent view can provoke arbitrary behavior in the application (e.g., enter an infinite loop). In this paper, we formally introduce a lazy snapshot algorithm that verifies at each object access that the view observed by a transaction is consistent. Validating previously accessed objects is not necessary for that, however, it can be used on-demand to prolong the view's validity. We demonstrate both formally and by measurements that the performance of our approach is quite competitive by comparing other STMs with an STM that uses our algorithm.

https://doc.rero.ch/record/18139/files/Riegel_Torvald_-_A_Lazy_Snapshot_Algorithm_with_Eager_Validation_20100430.pdf

A Lazy Snapshot Algorithm with Eager Validation

Blockchain-based platforms, such as Ethereum, allow transactions in blocks to call user-defined scripts named smart contracts In the blockchain network, after being generated by a miner, a block will be validated many times by the peers who accept it Hence by enabling concurrency on smart contracts, especially validation, we can improve the efficiency and the throughput of those platforms

Enabling Concurrency on Smart Contracts Using Multiversion Ordering

Innovative Research and Applications in Next-Generation High Performance Computing

Today, rapid advancement and innovation of technology has changed the perspective and the way information precedes. The utilization of self-service interactive kiosks through the concept of touch screens have been becoming a massive trend used intensively, especially in e-commerce and medical healthcare. Thus, this research will investigate and innovate the current interactive kiosk to provide immediate responses and reliable information incorporating an intelligent conversational agent (CA). A CA also widely known as chatbots is a computer program to simulate the conversations between human and machine. Our goal is to design and develop a framework for revolutionizing medical kiosk via the incorporation of an intelligent chatbots. This research intends to escalate the productivity and efficiency in medical institutions by offering the capabilities to provide immediate reply as well as initiating a conversation, similar to conversing with the experienced customer service assistant. Latest innovations in natural language processing (NLP), machine learning and deep learning in the field of artificial intelligence (AI) ensure smarter decision making in providing accurate, reliable and up-to-date information. The future MedKiosks is reliant on the AI, specifically the machine learning and deep learning to unveil the correlations, algorithms, patterns and anomalies to improve chatbots knowledge base. Moreover the experiment would be hosted by positioning the MedKiosk in the hospital for real-time data collections.

MedKiosk: An embodied conversational intelligence via deep learning

Existing dynamic deadlock avoidance techniques have four main drawbacks: limited capability, offline avoidance algorithm, passive avoidance strategy and poor usability. To solve these problems, we propose a user-friendly, online and active avoidance technique, called Slider, to avoid multiple types of deadlocks. The key idea of Slider is that deadlocks will not happen if critical sections are executed serially. Slider interferes in thread scheduling to ensure that at any time only one thread is in the critical state. We design Slider to avoid all deadlocks except self-deadlocks caused by mutexes or rwlocks in pthread interface. We implement Slider as a pre-loadable library so that it can be applied directly to existing applications. We do four experiments to evaluate avoidance capability, performance overhead and scalability of Slider, comparing with three state-of-the-art avoidance techniques. Experimental results show Slider can correctly avoid multiple types of deadlocks in an online, active, efficient and scalable way.

Slider: an online and active deadlock avoider by serial execution of critical sections

Software transactional memory (STM) has evolved as an alternative for traditional lock-based process synchronization. It promises greater degree of concurrency and faster execution. This paper proposes a simple, lightweight, and yet efficient implementation of OFTM. The major contribution of the paper is in proposing a new STM algorithm that uses simple data structure. This does not require any contention manager toward ensuring progress condition, atomicity, and serializability of transactions besides maintaining data consistency. Experimental simulation on random data set establishes the merit of the proposed solution.

A Lightweight Implementation of Obstruction-Free Software Transactional Memory

Software transactional memory (STM) is one of the techniques used towards achieving non-blocking process synchronization in multi-threaded computing environment. In spite of its high potential, one of the major limitations of transactional memory (TM) is that in order to ensure data consistency as well as progress condition, TM often forces transactions to abort. This paper proposes a new concurrency control mechanism. It starts with the existing TM implementations for obstruction freedom and eventually builds a new STM methodology. The primary objective is to reduce aborting of transactions in some typical scenarios. A programming model is described for a chain of update transactions that share the same data object among themselves. Using the proposed approach, any new update transaction appended in this chain need not wait for the earlier transactions to finish. The proposed STM allows wait-free, non-blocking implementation of a mix of read and multiple update transactions on the same shared data object with higher throughput.

/pdf/a-new-concurrency-control-mechanism-for-multi-threaded-44ct652k73.pdf

A new concurrency control mechanism for multi-threaded environment using transactional memory

In this paper, we propose a novel checkpoint-based multi-versioning concurrency control system (CMS) for software transactional memory (STM). A checkpoint is defined to refer a set of versions. CMS maintains a list of live read-only transactions for every checkpoint. An appropriate object versioning technique decides on how many older versions are to be kept or to be removed. Moreover, the proposed method does not require any global synchronization point, such as centralized logical clock for versioning. Due to its efficient garbage-collecting mechanism, CMS is suitable for both read and write-dominated workload. We formally prove that CMS complies useless-prefix garbage collection (UP-GC). On the basis of number of memory accesses for searching consistent version, CMS performs better in comparison with conventional multi-version permissive STM.

CMS: Checkpoint-Based Multi-versioning System for Software Transactional Memory

This paper addresses the synchronization aspect for multiple concurrent threads in a Remote Healthcare System (RHS) under development. Resources like data files are shared by multiple stakeholders and users including doctors, trained paramedic staff, patient party or even Government agencies collecting statistical and demographic data. In the system under trial, medical kiosks are setup at distant places where patients visit and their complaints are recorded by trained caregivers. Later, doctor accesses such data from the system, makes a diagnosis and suggests prescriptions accordingly. In such a set-up, it is quite often that more than one users access the same shared resource simultaneously. In conventional lock-based process synchronization, such concurrent processes are blocked by the process holding a lock over the files. The major contribution of this paper is to use checkpoint-based multi-versioning Software Transactional Memory for our application domain to achieve non-blocking process synchronization. With help of multi-versioning technique the proposed method is also able to reduce number of expensive remote validations as well as transactional aborts. Experimental verification finds that proposed method yields higher throughput in comparison to clairvoyant type multi-version concurrency control mechanism.

Checkpoint based multi-version concurrency control mechanism for remote healthcare system

Software transactional memory (STM) is a promising approach for concurrency control in parallel computing environment. The non-blocking progress implementations for STM forces transactions to abort. Although this is primarily done to ensure block-freedom, it may lead to poor system performance. This paper proposes a new Abort-Free STM methodology (AFTM) to achieve abort-free execution so that a group of processes, which are contending for a common set of concurrent objects can commit in finite number of steps. The proposed STM allows wait-free, non-blocking execution of multiple read and write transactions on shared data object without aborting any of the transactions. The important properties of AFTM have been proved towards establishing its advantages.

Ammlan Ghosh

Papers

A Lightweight Implementation of Obstruction-Free Software Transactional Memory

A new concurrency control mechanism for multi-threaded environment using transactional memory

CMS: Checkpoint-Based Multi-versioning System for Software Transactional Memory

Checkpoint based multi-version concurrency control mechanism for remote healthcare system

Abort-Free STM: A Non-blocking Concurrency Control Approach Using Software Transactional Memory