CS621 Slides Week 1-6 Combined

What is Concurrency?

Concurrent tasks can execute in a single or multiprocessing environment.

In a single processing environment, concurrent tasks exist at the same time and execute within the same time period by context switching. In a multiprocessor environment, if enough processors are free, concurrent tasks may execute at the same instant over the same time period. The determining factor for what makes an acceptable time period for concurrency is relative to the application. Concurrent doesn't necessarily mean at the same exact instant. For example, two tasks may occur concurrently within the same second but with each task executing within different fractions of the second.

• There must be an implicit or explicit control over concurrency. It is both hazardous and unsafe when multiple flows of executions simultaneously operate in the same address space without any kind of agreement on ordered access. Two or more activities might access the same data and thus induce data corruption as well as inconsistent or invalid application state.
• Multiple activities that work jointly on a problem need an agreement on their common progress. Both issues represent fundamental challenges of concurrency and concurrent programming.

Concurrency Control Cont…

• Synchronization is a mechanism that controls access on shared resources between multiple activities. It enforces exclusiveness and ordered access on the resource by different activities. • Coordination aims at the orchestration of collaborating activities.

Synchronization · and · Coordination are · two basic · approaches to · tackle this · challenge: