Nebenläufigkeitsprobleme

Concurrency (German: Nebenläufigkeit) refers to the ability of a system to perform multiple tasks in overlapping time periods. Concurrency focuses on structuring a program so that it can manage multiple tasks that make progress, while parallelism is a form of execution in which tasks run simultaneously, typically on multi-core hardware.

Two common models are shared-memory concurrency, where multiple threads or lightweight processes access a common address space, and message-passing concurrency, where components communicate by exchanging messages. Synchronization primitives such as mutexes, semaphores, monitors, and barriers coordinate access to shared data and manage the ordering of events.

Concurrency introduces nondeterminism and potential errors such as data races when two tasks access the same data without proper synchronization, deadlocks when two or more tasks wait for each other indefinitely, and livelocks. Correctness often relies on formal reasoning or disciplined design; debugging tools and race detectors can help.

Common techniques include mutual exclusion, atomic operations, critical sections, and higher-level abstractions such as monitors, transactional memory, or actor-based models. Designing granularity of locking, choosing suitable synchronization, and minimizing shared state are important considerations.

Concurrency improves responsiveness, throughput, and resource utilization, especially in interactive applications and servers that must handle multiple requests. It also increases complexity, making portability and maintainability more challenging. Many languages and runtimes provide built-in support for concurrency, including Java, C++, Go, and Erlang.