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In computer science, a fiber is a particularly lightweight thread of execution.

Like threads, fibers share address space; where a distinction exists, it is that fibers use co-operative multitasking while threads use pre-emptive multitasking. Threads often depend on the kernel's thread scheduler to preempt a busy thread and resume another thread; fibers yield themselves to run another fiber while executing. The article on threads contains more on the distinction between threads and fibers.

Contents 1 Fibers and coroutines 2 Advantages and disadvantages 3 Operating system support 4 See also 5 References 6 External links

Fibers describe essentially the same concept as coroutines. The distinction, if there is any, is that coroutines are a language-level construct, a form of control flow, while fibers are a systems-level construct, viewed as threads that happen not to run concurrently. Priority is contentious; fibers may be viewed as an implementation of coroutines^[1], or as a substrate on which to implement coroutines.^[2]

Because fibers multitask cooperatively, thread safety is less of an issue than with preemptively scheduled threads, and the paraphernalia of spinlocks and atomic operations are unnecessary when writing fibered code. However, some libraries may yield a fiber implicitly as a method of conducting non-blocking I/O; as such, some caution is advised. Among the disadvantages are that fibered code may utilise multiprocessor machines less effectively than threaded code.

Less support from operating system is needed for fibers than for threads. They are implemented in modern Unix systems using the library functions getcontext, setcontext and swapcontext in ucontext.h.

On Windows, fibers are created using the ConvertThreadToFiber and CreateFiber calls; a fiber that is currently suspended may be resumed in any thread. Fiber-local storage, analogous to thread-local storage, may be used to create unique copies of variables.^[3]

• getcontext/setcontext library routines

1. ^ A Fiber Class
2. ^ Implementing Coroutines for .NET by Wrapping the Unmanaged Fiber API, Ajai Shankar, MSDN Magazine
3. ^ Fibers, MSDN Library

• GNU Portable threads
• Portable Coroutines