Self-Stabilizing Systems

Physicalsystemswhichrightthemselvesafterbeingdisturbedevokeourcuriosity becausewe wantto understand howsuchsystemsareableto reactto unexpected stimuli. Themechanismsareallthe morefascinatingwhensystemsarecomposed of small, simple units, and the ability of the system to self-stabilize emerges out of its components. Faithful computer simulations of such physical systems exhibit the self-stabilizing property, but in the realm of computing, particularly for distributed systems, wehavegreaterambition. We imaginethat all manner of software, ranging from basic communication protocols to high-level applications, could enjoy self-corrective properties. Self-stabilizing software o?ers a unique, non-traditional approach to the c- cial problem of transient fault tolerance. Many successful instances of modern fault-tolerant networks are based on principles of self-stabilization. Surprisingly, the most widely accepted technical de?nition of a self-stabilizing system does not refer to faults: it is the property that the system can be started in any i- tial state, possibly an "e;illegal state,"e; and yet the system guarantees to behave properly in ?nite time. This, and similar de?nitions, break many traditional approaches to program design, in which the programmer by habit makes - sumptions about initial conditions. The composition of self-stabilizing systems, initially seen as a daunting challenge, has been transformed into a mana- able task, thanks to an accumulation of discoveries by many investigators. - search on various topics in self-stabilization continues to supply new methods for constructing self-stabilizing systems, determines limits and applicability of the paradigm of self-stabilization, and connects self-stabilization to related areas of fault tolerance anddistributed computing.