Concurrent programming language
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Concurrent programming languages are those that provide linguistic mechanisms for creating concurrent or multi-threaded programs. This in contrast to languages such as C, which only support concurrency through the use of libraries or operating system features.
Concurrent programming languages can essentially be divided into two classes:
- Shared-state languages, in which separate threads of execution can access the same data directly. This style of concurrent programming requires the application of some form of locking (e.g. mutexes, semaphores, or monitors) to ensure that only a single thread is manipulating the shared data at any one time. This form of concurrency can be difficult to reason about, and is prone to errors as a result of improperly coordinated locks. The Java programming language is an example of the shared-state style.
- Message-passing languages, in which data is strictly encapsulated within a thread of execution, and can only be modified by passing messages to the responsible thread. Messages can be asynchronous (aka "send and pray"), as in Erlang, or may use a rendezvous style in which the sender blocks until the message is received, as in Occam. The inspiration for this style of language is theoretical work on concurrency such as Milner's Pi-Calculus and Hoare's CSP. Message-passing concurrency tends to be far easier to reason about than shared-state concurrency, and is typically considered a more robust form of concurrent programming.
Examples
- Ada
- Alef - originally used as a programming language for the Plan 9 from Bell Labs operating system.
- ChucK - concurrent, on-the-fly programming language for audio
- Cilk
- Comega
- Concurrent Pascal (by Brinch-Hansen)
- E
- Erlang
- Java
- Joule
- Limbo - the successor to Alef, used in the Inferno (operating system).
- Mozart/Oz - a "multi-paradigm" language that supports both shared-state and message-passing concurrency.
- Occam - influenced heavily by Communicating Sequential Processes.
- Pict - essentially an executable implementation of Milner's Pi-Calculus.
- Promise (programming)
- SR
Note that many of these languages are intended more as research languages (e.g. Pict) than as languages for production use. However, several of the examples (such as Ada, Erlang, Java, Limbo, and Occam) have seen widespread industrial use at various times in the last 20 years.