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Preemptive single server in Java Develop Data Matrix in Java Preemptive single server




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1. Preemptive single server use none none development toassign none with none Microsoft SQL Server td -. (L, + L,,)t$ (1 - Lp - L,,)(l - L,,). (6-32). 2. Nonpreemptive single server 1. -. 1.,rs d - (1 - none for none Lp - L,,)(1 - L,,). (6-33). Processing Environment Chap. 6 For a multiproc none for none essor load sharing system with c processors:. 3. Preemptive multiserver (L, + LJJcpots none none c(c!)[l - (Lp + LJJlc]2(1 - Lltlc). 6-34) (. 4. Nonpreemptive multiserver t. d -. L,cPots c(c!)(l none for none - L,lc)[1 - (Lp + LJJlc](l - Lltlc). (6-35). in the above equations,. Po-1 = ~(L")nln ! + (L")C/[l - L"lc]c!. (6-36). L" = Lp + Lit f or the preemptive case and L, for the nonpreemptive case. Note tbatLp, Lit, andL, in these equations comprise the total system load rathertban the average server load, as used in Appendix 2 and chapter 4. Of course, in all cases of a preemptive system, the actual process service time which is added to the dispatch time to obtain full delay time must be divided by (I-LiJ to ac:count for preemptive processing by the higher priority processes (see Appendix 2 and chapter 4).

If the system is a single priority system, Lit in the above equations becomes zero, with the conesponding simplifications. ..

Contempcmay TP none none applications me organized as autonomous processes, each with their own scope of respcmsibility aad all passiDg dam to each OCher via messages. In some cases, these mtapJOc:ess messages can Iepieseut a significant podion of the load on a TP system. .

. Tbeze are several ways in which the messaging facility ~ be implemeated. AD are suitable for distributecl systems, but cme-the mailbox-is suitable oaly for single computer or mu1tiproc:essor systems.

These 1ecImiques are described brle1ly below. However, the only IeSUlt of practical interest to the perfOlDJ8DCe 8D8lyst is the bouom-liDe time requited to pass a message from one process to another..

Global message network. W"ltb this implementation, any process can send a message to any otber process in the system without any specific effort on the part of one process to establish a path to the adler process. This tecImique is geaemIly applied to muhic:omputer systemS.

AD the sending precess needs to know is the Dame of the receiving process. The operating system knows the name of all J"l"OCeSSC"S in the system and their. Chap. 6 Operating System wh~ts. It assum none none es the responsibility for the message, ~ua1ly moving j~ into a system-allocated buffer. It then routes it over the bus (or network, if necessary) to the computer in which the receiving process is 11lDDing and queues it to the message queue for.

that process. E ven if the receiving process is l"UIlDing in the same computer as the sending process, this full procedure is often followed, except that the bus transfer is null, i.e.

, shortcuts are. not taken. This type of me ssaging facility is used by Tandem. Directed message paths. In other implementations, there are no general messaging facilities provided by the operating system.

Rather, it is the responsibility of one process to establish a message path to another process via operating system facilities. Once established, the operating system knows of this path, and message transfer is similar to that used for global messaging. This philosophy is found in the UNIX pipe structure and is used by Synt:rex (Eatontown, New Jersey) in its distributed word-processing product.

File system. The TP file system can also be used to pass messages between processes. A message file can be opened by two processes and can be used by one process to write messages to the other.

The receiving process is alerted to the receipt of a message via an event flag and can read that message from its file. On the surface, this can sound very time-coDsummg-writing to and reading from disk. However, disk traDsfers are cached in memory (in a cache similar to the memory cache described in the previous section).

If messages are read shortly after they are written, they will still be in memory; the message time is equivalent to the above teclmiques. If they are not lead for awhile, they are ilushed to disk to Dee up valuable memory space. .

Since the file system allows transpalent access to all files across the system, this messaging concept supports distributed systems. This tecImique is used by S1ratus in its.
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