Coordination of Parallel Tasks in Access to Resource Groups by Adaptive Conflictless Scheduling

Abstract

Conflictless task scheduling is dedicated for environment of parallel task processing with high contention of limited amount of resources. For tasks that each one requires group of resources presented solution can prepare schedule of tasks execution without occurrence of any resource conflict. As a task it can be used any selected sequence of operation that for execution requires access for resource group, to which access is controlled by conflictless scheduling. Any resource group required by task has own FIFO queue, where tasks are waiting for access of those resources. Queues are emptying according to prepared conflictless schedule in such a way that there is no starvation of waiting tasks. Presented scheduling concept for tasks and resource group bases on resource representation model which allows to efficient detect a resource conflict using dedicated data structures like task classes and conflict matrix and algorithms which allows to prepare adaptive conflictless schedule. Prepared conflictless schedule adapts to current environment state like number of resource groups and tasks in their queues and also waiting times of tasks. Prepared schedule ensures task execution without resource conflicts and therefore there is no tasks deadlock. As example of environments where conflictless scheduling can be applied is transaction processing in databases or OLTP systems, processes or threads competing for resources. In transaction processing environment deadlock elimination by using proposed conflictless scheduling reduces the number of transaction rollbacks.