EXCLUSION (Mutual)
| Collection | International Encyclopedia of Systems and Cybernetics |
|---|---|
| Year | 2004 |
| Vol. (num.) | 2(1) |
| ID | ◀ 1211 ▶ |
| Object type | Discipline oriented |
In a network of computers, “the property that the steps of one operation cannot be interleaved with steps of another” (P. DENNING, 1991, p.111).
According to P. DENNING: “One of the most fundamental requirements in all… (networks of computers) is that certain operations be indivisible: the operations must be carried out in some definite order, one at a time, even when different computers request them simultaneously. If, contrary to this requirement, the instructions of one operation were interleaved with those of another, the results would be unpredictable. Deposits and withdrawels could be lost; confirmed reservations might disappear, parallel processing computers could produce invalid outputs.
- “Because indivisible operations are not allowed to be in progress simultaneously, we say that they are mutually exclusive” (Ibid).
It can be seen that the simultaneity problem is all-pervasive.
As simultaneity destroys perfect causal determinism, no perfect algorithm seems possible in parallel operation.