Concurrent computing

Concurrent computing is a model in which multiple tasks make progress during overlapping periods. Tasks may execute simultaneously on separate processors or take turns on one processor.

Operating-system scheduling: Operating-system scheduling selects which processes or threads run and when. Schedulers interleave tasks on a processor or assign them to separate processors.
Process (computing): A process is an executing program with its own address space and operating-system resources. Processes are independent units of work that can progress concurrently.
Event loop: An event loop repeatedly dispatches events and callbacks, often allowing one thread to manage many tasks. Event loops handle overlapping I/O and user activity without blocking on each task.
Sequential computing: Sequential computing performs operations in a defined order, one step after another. It contrasts with tasks whose periods of progress overlap.
Race condition: A race condition occurs when a result depends on the timing or order of concurrent operations. Overlapping tasks can access shared state in an order that changes the outcome.
Thread (computing): A thread is a sequence of execution within a process that shares the process's memory and resources. Multiple threads can perform overlapping work while sharing a process's state.
Asynchronous I/O: Asynchronous I/O lets a program continue working while an input or output operation is pending. It allows computation to overlap with slow device and network operations.
Synchronous programming: Synchronous programming makes an operation wait for a preceding operation to finish before continuing. Synchronous code can constrain overlap, though a concurrent system may include synchronous operations.
Mutual exclusion: Mutual exclusion ensures that only one process or thread at a time accesses a protected resource. It prevents concurrent tasks from entering critical sections together.
Coroutine: A coroutine is a routine that can suspend and resume execution while preserving its state. Coroutines let a program manage many overlapping tasks without requiring a thread for each.

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