Singlethreaded

Single-threaded refers to a program that executes all tasks on a single thread of execution, meaning there is one call stack, one program counter, and operations are performed one after another. There is no concurrent execution of code within the same process; context switches between threads do not occur because there is only one thread. Memory access is inherently sequential, reducing the complexity associated with data races and synchronization.

Most modern systems are multi-threaded by default, but single-threaded programs may still rely on asynchronous I/O or cooperative multitasking to overlap work without parallel threads. In such models, the program can initiate an I/O operation and continue processing other events, while the I/O completes and its callback is scheduled by an event loop.

Common environments include JavaScript in web browsers, which follows a single-threaded event loop for executing scripts, with web workers available for parallel tasks. Node.js uses a single-threaded event loop for JavaScript code, with asynchronous I/O and a thread pool for certain operations. Some embedded systems and early GUI frameworks also use single-threaded models.

Advantages and drawbacks: Simplicity and predictability; no data races; easier debugging. Drawbacks include limited CPU parallelism, potential UI freezing if operations are long-running, and reliance on asynchronous patterns to maintain responsiveness.

See also: concurrency, multi-threading, event-driven programming, asynchronous I/O.