parallel

Concurrency - doing more than one thing at a time Multihreading - a form of concurrency that uses multiple threads of execution parallel processing - does lot of work by dividing it up among multiple threads hat run concurrently

• two threads have accesto same address space, and if we don't enforce atomicity by a thread by synchronization context

A critical section is a piece of code that accesses a shared resource, usually a variable or data structure.

• A race condition (or data race [NM92]) arises if multiple threads of execution enter the critical section at roughly the same time; both attempt to update the shared data structure, leading to a surprising (and perhaps undesirable) outcome.

• An indeterminate program consists of one or more race conditions; the output of the program varies from run to run, depending on which threads ran when. The outcome is thus not deterministic, something we usually expect from computer systems.

• To avoid these problems, threads should use some kind of mutual exclusion primitives; doing so guarantees that only a single thread ever enters a critical section, thus avoiding races, and resulting in deterministic program outputs.