Flow detecting scheme in .NET Making Code 128C in .NET Flow detecting scheme

7.9.1 Flow detecting scheme generate, create qr bidimensional barcode none with .net projects barcode pdf417 Weights may be lost becaus qr barcode for .NET e a process holding a non-zero weight may crash or a message destined to a crashed process is carrying a weight. Therefore, due to faulty processes and undeliverable messages carrying weights, it may not be possible for the leader to accumulate the total weight of 1 to declare termination.

In the case of a process crash, the lost weight must be calculated. To solve this problem, the concept of flow invariant is used..

The concept of flow invariant Define H S as the set of .NET qr-codes all healthy processes. Define subsystem H to be part of the system containing all processes in H and communication channels connecting two processes in H.

According to the concept of flow invariant, the weight change of the subsystem during time interval I, during which the system is doing computation, is equal to (weights flowing into H during I) (weights flowing out of H during I). To implement this concept, a variable called neti is assigned to each process Pi belonging to H. This variable records the total weight flowing into and out of the subsystem H.

Initially, i neti = 0. The following flow-detecting rules are defined: Rule 1: Whenever a process Pi which belongs to H receives a message with weight x from another process Pj which does not belong to H, x is added to neti ..

Termination detection Figure 7.11 Healthy and fa visual .net QR Code JIS X 0510 ulty process sets and message flow between them [20].

. WH H WH WH H WH Rule 2: Whenever a process visual .net QR Code Pi which belongs to H sends a message with weight x to a process Pj which does not belong to H, x is subtracted from neti . Let WH be the sum of the weights of all processes in H and all in-transit messages transmitted between processes in H: WH =.

Pi H neti + 1/n where 1/n is the initial w eight held by each process Pi . Let H = S H be the set of faulty processes. The distribution of weights is divided into four parts: WH : weights of processes in H.

WH : weights of processes in H. WH H : weights held by in-transit messages from H to H. WH H : weights held by in-transit messages from H to H.

This is shown in Figure 7.11. WH and WH H are lost and cannot be used in the termination detection.

. 7.9.2 Taking snapshots In distributed systems, du e to the lack of a perfectly synchronized global clock, it is not possible to get a global view of the subsystem H and hence it may not possible to determine WH . We obtain W H , which is an estimated value of WH , by taking snapshots on the subsystem H and by using the above equation for WH . However, note that weights in WH H carried by in-transit messages may join H and change WH .

To obtain a stable value of WH , channels from H to H are disconnected before taking snapshots of H. Once a channel is disconnected, a healthy process can no longer send or receive messages along it. A snapshot on H is the collection of neti s from all processes in H.

A snapshot is said to be consistent if all channels from H to H are disconnected before taking the snapshot (i.e., recording the values of neti ).

. 7.9 Termination detection in a faulty distributed system A snapshot is taken upon a snapshot request by the leader process. The leader uses the information in a consistent snapshot and equation to compute WH to calculate W H . Snapshots are requested when a new faulty process is found or when a new leader is elected.

It should be noted that W H is an estimate of the weight remaining in the system. This is because processes can fail and stop any time and there may not exist any point in real time in the computation where H is the healthy set of processes. Suppose H is the set of healthy processes at some point in time in the computation after taking the snapshot.

If H = H , then W H = WH ; otherwise, W H WH must be true, because of the fail-stop model of processes. This eliminates the possibility of declaring termination falsely. Thus, the leader can safely declare termination after it has collected W H of weight.

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