Concurrency Testing

• Defect-based

  • Will focus on specific types of concurrency bugs

• Long-duration / Random Testing

  • Rely on the fact that concurrency errors occur very rarely

• Model-based Testing

  • Use MBT tools that support modeling of concurrent behavior

• Manual Delays

  • Use delays (e.g. Thread.sleep()) to enforce specific schedules

Blocking -> Starvation, Suspension

Non-Blocking -> Atomicity violation

• Livelock

• Starvation

• Suspension

• Order Violation

• Priority Inversion

• Atomcity Violation

• Intermittent/nondeterministic failures that only occur rarely

• Non-deterministic behaviour

  • different outcome for same test

  • hard to reproduce failures

  • hard to analyze

• Correcting concurrency bugs often requires redesign instead of simple code changes

• Mutual Exklusion: shared resource

• Hold and Wait: process holding a resource and process waiting for it

• No Preemption: resource can only be released by process holding it

• Circular Wait: set of processes {P1, P2, …, Pn} such that P1 waits for P2, …, Pn waits for P1

Thread repeatedly obtains resource but never completes execution before losing it

thread ready to execute, but delayed because other threads hold necessery resource

thread waiting too long before it can access shared resource

fault caused by nondeterministic ordering of multiple interleaved operations

-> Race Condition - special form: shared resources not protected from simultaneous access

higher priority operation of one thread forced to wait for execution of lower priority of another thread

execution of one thread interrupts execution of another thread