tailieunhanh - Software Fault Tolerance Techniques and Implementation phần 10

Đầu vào biến thể Thiết lập trạng thái = NIL Nhận kết quả biến thể, R, và lòng khoan dung, một ngẫu nhiên chọn một đầu ra biến thể, x Xây dựng tính khả thi thiết lập FS = {x, ri ∈ R x - ri ≤ A, i = 1, ., n} là tính khả thi thiết lập có sản phẩm nào? Không Có Thiết lập trạng thái = NO KẾT QUẢ ĐÚNG (ngoại lệ) chính thức đa số cử tri | Adjudicating the Results 301 Figure Formal majority voter operation. FormalMajorityVoter input_vector e r This Decision Mechanism determines the correct or adjudicated result r given the input vector input_vector of variant results and the maximum allowed distance e via the Formal Majority adjudication algorithm. Set Status NIL r NIL FS NIL Receive Variant Results input_vector e Was a Result Received from each Variant No Set Status NO CORRECT RESULT Exception Go To Out 302 Software Fault Tolerance Techniques and Implementation Yes Continue Randomly Select a Variant Output x. Construct the Feasibility Set FS where FS x y in input_vector x - y z Is FS empty No Set r Randomly Selected Value in FS Set Status SUCCESS Yes Set Status NO CORRECT RESULT Exception Out Return r Status FormalMajorityVoter Example An example of the formal majority voter operation is shown in Figure . Suppose we have a fault-tolerant component with three variants n 3. If the results of the variants are r r2 r1 then the input vector to the voter is . Input vector e Comparison - e - e K FS Randomly select from FS as the result r Output r and status SUCCESS Figure Example of formal majority voter. Adjudicating the Results 303 Suppose the variant result selected as the focal point X is r2. The other variant results are checked to see if they are within the tolerance E of X. IX - r J I - I IX - r31 - I X Since q matches X r2 within s the FS fj r2 . One of these values say is randomly selected from FS as the adjudicated result. Discussion The formal majority voter expects a result from each variant and when all variant results are not present the voter can fail. A way to avoid this type of failure is to make the formal majority .