What is "concurrency"

Concurrency \Con*cur"ren*cy\, n. Concurrence.

n. 1 The property or an instance of being concurrent; something that happens at the same time as something else. 2 (context computer science English) a property of systems where several processes execute at the same time

Concurrency, concurrent, or concurrence may refer to:

• Concurrence, a legal term referring to the need to prove both actus reus and mens rea
• Concurring opinion (also called a "concurrence"), a legal opinion which supports the conclusion, though not always the reasoning, of the majority.
• Concurrency (computer science), the property of program, algorithm, or problem decomposition into order-independent or partially-ordered units.
• Concurrency (road), an instance of one physical road bearing two or more different route numbers
• Concurrent DOS, Digital Research's multiuser multitasking operating system, with "Concurrent" once being their registered trademark
• Concurrent estate, a concept in property law
• Concurrent computing, the overlapping execution of multiple interacting computational tasks
• Concurrent lines, a mathematical term for multiple lines or curves intersecting at a single point
• Concurrent enrollment, the process in which high school students enroll at a university or college usually to attain college credit
• Concurrent resolution, a legislative measure passed by both the United States Senate and the United States House of Representatives
• Concurrent sentences, in criminal law, periods of imprisonment that are served simultaneously
• Concurrent Design Facility, an assessment center of the European Space Agency using concurrent engineering methods
• Concurrence (quantum computing), a measure of quantum entanglement used in quantum information theory

In computer science, concurrency is the decomposability property of a program, algorithm, or problem into order-independent or partially-ordered components or units. This means that even if the concurrent units of the program, algorithm, or problem are executed out-of-order or in partial order, the final outcome will remain the same. This allows for parallel execution of the concurrent units, which can significantly improve overall speed of the execution in multi-processor and multi-core systems.

A number of mathematical models have been developed for general concurrent computation including Petri nets, process calculi, the Parallel Random Access Machine model, the Actor model and the Reo Coordination Language.

A concurrency in a road network is an instance of one physical road bearing two or more different highway, motorway, or other route numbers. When two freeways share the same right-of-way, it is sometimes called a common section or commons. Other terminology for a concurrency includes overlap, coincidence, duplex (two concurrent routes), triplex (three concurrent routes), multiplex (any number of concurrent routes), dual routing or triple routing.

Concurrent numbering can become very common in countries that allow it. Where multiple routes must pass through a single mountain crossing, or through a major city, it is often economically and practically advantageous for them all to be accommodated on a single physical road. In some countries, however, concurrent numbering is avoided by posting only one route number on road signs; these routes disappear at the start of the concurrency and reappear when it ends. Criticism of concurrencies include environmental intrusion, as well as being considered a factor in road accidents.