Definitions & Scenarios

Acknowledgements  This tutorial is based in part on Concurrency: State Models & Java Programming by Jeff Magee and Jeff Kramer.

Acknowledgements  Tutorial Authors/Creators: Zhen Li, Eileen Kraemer, Zhe Zhao Computer Science Department The University of Georgia

 Concurrent Program  Process & Thread  Thread Life Cycle

Sequential v. Concurrent  Programs consist of subprograms or procedures simpler sets of activities that together make up the overall program  Sequential program Subprograms are executed one after the other in fixed order, determined by program’s input  Concurrent program The execution of subprograms may overlap in time

 Computational activities that overlap in time may occur in parallel, or be interleaved. Concurrent Program Parallelism Interleaved

 In a concurrent program, computational activities are permitted to overlap in time. Concurrent Program Parallelism Interleaved

 In a concurrent program, computational activities are permitted to overlap in time. Concurrent Program Parallelism Interleaved

Process  The execution of a sequential program or subprogram  A unit of sequential execution  A concurrent program consists of multiple processes.

Process Parallelism Interleaved Three processes in each figure

Thread  A method of implementing concurrency Parallelism Interleaved Two different implementations

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield suspend resume alive

Thread Life Cycle created terminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle created terminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle created terminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle created terminated Ready (Runnable) running Waiting (Non-runnable) stop dispatch yield resume alive suspend

Thread Life Cycle created terminated Ready (Runnable) running Waiting (Non-runnable) stop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) Waiting (Non-runnable) stop startstop dispatch resume alive suspend running

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop start dispatch yield resume alive suspend

Thread Life Cycle created terminated Ready (Runnable) running Waiting (Non-runnable) stop start dispatch yield resume alive suspend

Thread Life Cycle created terminated Ready (Runnable) running Waiting (Non-runnable) stop dispatch yield resume alive suspend

Thread Life Cycle created terminated Ready (Runnable) running Waiting (Non-runnable) stop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop dispatch yield resume alive suspend

Thread Life Cycle createdterminated Ready (Runnable) running Waiting (Non-runnable) stop startstop dispatch yield resume alive suspend

 Shared Objects  Conditional Synchronization  Resource Allocation

Shared Object  Multiple threads have computational activities on the same object  Ornamental Garden Garden East Turnstile West Turnstile

A Naïve Implementation Garden East Turnstile West Turnstile population thread shared object

A Naïve Implementation

Problem

Race Condition  A common flaw in implementing a concurrent program with shared objects  Final results depend on the execution sequence of threads  Therac-25 accident

Mutual Exclusion  Access to shared objects should be mutually exclusive in time

Solution  Lock for atomic operation

Solution  Lock for atomic operation

Review  Definitions Concurrency Process & Thread Thread Life Cycle  Scenarios Shared Objects – Race Conditions