This article examines ZIO fibers, which are lightweight, user-space threads managed within the ZIO runtime as opposed to OS threads. It highlights the characteristics that set fibers apart, primarily their cooperative scheduling that allows fibers to run until they yield control. This drastically reduces the overhead associated with OS threads, enabling massive concurrency with minimal resource consumption. The piece also discusses the significance of correctly configuring thread pools to achieve actual parallelism while emphasizing the distinction between concurrency and parallelism. A practical example demonstrates how these concepts manifest in code, laying the groundwork for future discussions on structured concurrency.
Fibers in ZIO are lightweight, user space threads, essentially "green threads" managed by the ZIO runtime, not the OS. They are extremely cheap to create and can scale in the tens of thousands without the memory overhead of OS threads.
Unlike a native JVM thread that maps one-to-one with an OS thread, a fiber is a pure Scala construct. In short, ZIO fibers let you write code that looks threaded, but many fibers share a limited number of actual OS threads.
The key difference is scheduling: OS threads use preemptive scheduling, whereas fibers use cooperative scheduling, meaning they run until they voluntarily yield control.
This means fibers avoid many concurrency hazards since they don't interrupt each other at random points, but a badly-behaved fiber could starve others.
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