tailieunhanh - Building Secure and Reliable Network Applications phần 6

được gọi là CORBA, dựa trên một số trong những ý tưởng được giới thiệu bởi ANSA, và đã nổi lên như một tiêu chuẩn được chấp nhận rộng rãi cho phản đối định hướng tính toán phân viên, và do đó ngăn cản tiến bộ. | Chapter 13 Guaranteeing Behavior in Distributed Systems 257 Interestingly we have now solved our problem because we can use the non-dynamically uniform multicast protocol to distribute new views within the group. In fact this hides a subtle point to which we will return momentarily namely the way to deal with ordering properties of a reliable multicast particularly in the case where the sender fails and the protocol must be terminated by other processes in the system. However we will see below that the protocol has the necessary ordering properties when it operates over stream connections that guarantee FIFO delivery of messages and when the failure handling mechanisms introduced earlier are executed in the same order that the messages themselves were initially seen . if process Pi first received multicast m0 before multicast m1 then Pi retransmits m0 before m1 . View-Synchronous Failure Atomicity We have now created an environment within which a process that joins a process group will receive the membership view for that group as of the time it was added to the group and will subsequently observe any changes that occur until it crashes or leaves the group provided only that the GMS continues to report failure information. Such a process may now wish to initiate multicasts to the group using the reliable protocols presented above. But suppose that a process belonging to a group fails while some multicasts from it are pending When can the other members be certain that they have seen all of its messages so that they can take over from it if the application requires that they do so Figure 13-26 Although m was sent when p0 belonged to G it reaches p2 and p3 after a view change reporting that p0 has failed. The red and blue delivery events thus differ in that the recipients will observe a different view of the process group at the time the message arrives. This can result in inconsistency if for example the membership of the group is used to subdivide the .