DispatchersDefault

DispatchersDefault, commonly referred to in code as Dispatchers.Default, is the default CoroutineDispatcher provided by the Kotlin Coroutines library for CPU‑bound work. It represents a shared pool of background threads separate from the main thread and is used automatically when no dispatcher is specified for a coroutine.

On the JVM, DispatchersDefault is backed by a thread pool sized to efficiently utilize available CPU cores. The pool uses a work-stealing scheduler to balance CPU‑bound tasks across threads and is initialized lazily when first used. The underlying thread count is designed to scale with hardware while avoiding excessive thread creation.

Usage is straightforward for CPU‑intensive tasks: launch a coroutine with a context of Dispatchers.Default or wrap blocking computations with withContext(Dispatchers.Default). If you do not specify a dispatcher, coroutines are scheduled on DispatchersDefault by default.

DispatchersDefault is distinct from other dispatchers in the Kotlin Coroutines family. Dispatchers.IO provides a separate pool optimized for I/O-bound operations with a larger, unbounded thread pool, while Dispatchers.Main targets the main thread in UI applications. In general, Dispatchers.Default should not be used for long‑running or blocking I/O tasks.

Configuration and caveats: The parallelism of the Default dispatcher can be overridden via the system property kotlinx.coroutines.default.parallelism. Blocking calls inside this pool should be avoided; for blocking or long‑running I/O, Dispatchers.IO is preferred. Across platforms (JVM, Android, Native, JS), implementation details and threading semantics may vary, but the core purpose—efficient CPU-bound task execution—remains consistent.