Diff for Concurrency (computer science)

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== Concurrency (computer science) ==

'''Concurrency''' in [[computer science]] is the ability of a system to execute multiple tasks or processes in overlapping time intervals, but not necessarily simultaneously. It is a fundamental concept in [[operating system]]s, [[database]]s, [[distributed computing]], and [[multithreading|multithreaded programming]]. Concurrency enables programs to handle multiple events, improve resource utilization, and increase throughput, but introduces challenges such as [[race condition]]s, [[deadlock]]s, and [[livelock]]s.

Concurrency differs from [[parallel computing]]: parallelism strictly requires simultaneous execution (often on multiple [[central processing unit|processors]]), whereas concurrency is about managing multiple tasks that may interleave on a single core. A system can be concurrent but not parallel — for example, a [[single-core processor]] running multiple threads via time‑slicing.

== Key concepts ==

* [[Process (computing)|Process]] – an independent execution unit with its own memory space.
* [[Thread (computing)|Thread]] – a lightweight unit of execution that shares memory with other threads in the same process.
* [[Synchronization (computer science)|Synchronization]] – mechanisms (e.g., [[mutex]]es, [[semaphore (programming)|semaphore]]s, [[monitor (synchronization)|monitor]]s) to coordinate access to shared resources.
* [[Race condition]] – an undesirable outcome when the system’s behavior depends on the timing of non‑atomic operations.
* [[Deadlock]] – a state where two or more processes are each waiting for the other to release a resource.
* [[Livelock]] – a situation where processes repeatedly change states in response to each other, but make no progress.
* [[Non‑blocking algorithm]] – a lock‑free design that ensures progress even if some threads are delayed.

== History ==

The study of concurrency began in the 1960s with the advent of [[time‑sharing operating system]]s, where multiple users interacted with a single computer concurrently. Pioneering work by [[Edsger Dijkstra]] introduced semaphores and the concept of [[mutual exclusion]] (1965). [[C.A.R. Hoare]]’s [[Communicating Sequential Processes]] (1978) and [[Robin Milner]]’s [[Calculus of Communicating Systems]] later formalized concurrent computation.

In the 1990s, the rise of [[multithreading]] in mainstream operating systems and programming languages (e.g., [[Java (programming language)|Java’s]] built‑in threads) made concurrency a practical concern for everyday developers. The explosion of [[multi‑core processor]]s in the 2000s shifted focus toward exploiting parallelism while still managing concurrency safely.

== Challenges and approaches ==

Concurrent programs are notoriously difficult to design and debug due to [[non‑deterministic]] execution. Common pitfalls include [[priority inversion]], [[dining philosophers problem|resource starvation]], and [[memory consistency]] issues. Solutions range from low‑level [[lock]]ing primitives to high‑level [[actor model]]s (e.g., [[Erlang (programming language)|Erlang]]) and [[software transactional memory]] (e.g., in [[Clojure]]).

Many languages now offer built‑in concurrency abstractions, such as [[goroutine]]s in [[Go (programming language)|Go]] or [[async/await]] in [[Python (programming language)|Python]] and [[JavaScript]].

[[Category:Computer science]]
[[Category:Concurrency (computer science)]]
[[Category:Programming paradigms]]