If, on the other hand, the overrun is caused by the finite buffer capacity of the network chip, sayn packets, the sender can sendn packets, followed by a substantial gap (or the protocol can be defined to require an acknowledgement after everyn packets).. [Картинка: any2fbimgloader66]. At first it may not be obvious why three voters are needed at each stage. After all, one voter could also detect and pass though the majority view. However, a voter is also a component and can also be faulty. Suppose, for example, thatV1malfunctions. The input toB1will then be wrong, but as long as everything else works,B2andB3 will produce the same output andV4,V5, andV6will all produce the correct result into stage three. A fault in V1 is effectively no different than a fault inB1. In both casesB1produces incorrect output, but in both cases it is voted down later.. 1. To increase reliability by having independent backups of each file. If one server goes down, or is even lost permanently, no data are lost. For many applications, this property is extremely desirable.. Fig. 6-12. Behavior of two processes. The horizontal axis is time. (a) Strictly consistent memory. (b) Memory that is not strictly consistent.. If all these conditions are met and processes use acquire and release properly (i.e., in acquire-release pairs), the results of any execution will be no different than they would have been on a sequentially consistent memory. In effect, blocks of accesses to shared variables are made atomic by the acquire and release primitives to prevent interleaving.. Shared variables that are not annotated as belonging to one of the above categories are treated as in conventional page-based DSM systems: only one copy of each writable page is permitted, and it is moved from process to process on demand. Read-only pages are replicated as needed.. Atupleis like a structure in C or a record in Pascal. It consists of one or more fields, each of which is a value of some type supported by the base language. For C-Linda, field types include integers, long integers, and floatingpoint numbers, as well as composite types such as arrays (including strings) and structures, (but not other tuples). Figure 6-36 shows three tuples as examples.. This operation “searches” the tuple space for a tuple consisting of the string “abc”, the integer, 2, and a third field containing any integer (assuming thati is an integer). If found, the tuple is removed from the tuple space and the variable i is assigned the value of the third field. The matching and removal are atomic, so if two processes execute the samein operation simultaneously, only one of them will succeed, unless two or more matching tuples are present. The tuple space may even contain multiple copies of the same tuple.. In addition to the memory managers for mapped files and other specialized objects, there is also a default memory manager for “ordinary” paged memory. When a process allocates a region of virtual address space using theallocate call, it is in fact mapping an object managed by the default manager. This manager provides zero-filled pages as needed. It uses a temporary file for swap space, rather than a separate swap area as UNIX does.. To see how capability transport works, consider Fig. 8-19(a). Here we see two processes,A andB, with 3 capabilities and 1 capability, respectively. All are RECEIVE capabilities. Numbering starts at 1 since entry 0 is the null port. One of the threads inA is sending a message toB containing capability 3.. Once the emulation library gets control, it examines the registers to determine which system call was invoked. It then makes an RPC to another process, the UNIX server, to do the work. When it is finished, the user program is given control again. This transfer of control need not go through the kernel.. 9.2.4. Traps, Exceptions, and Interrupts. TheactorPriority call allows a process to read the priority of another process, and optionally, to reset it to a new value. Although Chorus is generally location transparent, it is not perfect. Some calls, including this one, work only when the target process is on the caller’s machine. In other words, it is not possible to get or reset the priority of a distant process.. Step 4:client asks the ticket-granting server for a PAC usable by S.