Chap. 2 in Java Compose barcode data matrix in Java Chap. 2

Chap. 2 using jdk todraw 2d data matrix barcode on web,windows application Barcodes for Mobile Applications Process Management .anaging .ultiple Users One additional fall Data Matrix ECC200 for Java out from these types of operating systemS should be noted. As we have said, a process is a program I"IJlUUng in a computer and comprises a code area and a data area. The code area is never modified.

Tbe!e is no :reason that in that same computer, another process could not be created. using the same program but simply carrying another name. In fact, since its code area would be identical to that of the first process, the code area would not have to be duplicated; both processes would map into the same code area in physical IDeIDOJ:Y, ~ shown in F~ 2-~4.

,. "~A. PROGRAM INO TERMINAL TERMIIIAL TERMINAL. Fipre 2-14 MIIIIiuser opeadaL Let us incmduce one IDCR concept, 1hat of the home termintzl. When a process is aeated by an operator. it is Cleated by that operator typing in a rormmmd at a terminal.

The process tbeD lcnowS that tamjnaJ as i1s home terminal aDd may Jeter to it as such.. Consider a progtam tomcat datamatrix 2d barcode written to pezform a task (maybe an inquiry task) to support ODe and ODly ODe tfmrinaJ, which is i1s home tamjnaJ. The program file is ,stcnd as an object file on disk and is IIiImed INQ. " ODe operator could walk up to tmninaJ 1 (in FIgIR 2-14) and type.

RUN lNQINAME INQAI and tile Process INQA would be Cleated." A copy of tile code ccmespondiDg to program lNQ would be made available to p.roc:ess INQA, and a data area image for process INQA would be created on disk.

The operator can now use process INQA for inquiry pirposes. As die process executes. pages requD:ed by it Will be paged in aDd mapped as pmiously described.

. Transaction-Processing Systems Chap. 2 A second operator c Data Matrix 2d barcode for Java an walk up to terminal 2 and enter a similar command:. RUN lNQINAME lNQBI and process INQB wi applet gs1 datamatrix barcode ll be created as was lNQA, except that a second copy of lNQ"s code does not need to be paged into physical memory if lNQB is running in the same computer as lNQA (that is, the terminals are on the same computer, or the CPU is specified in the RUN command). Process lNQB will use the same code area as lNQA. Of course, a separate data area is aeated for process lNQB.

This can continue vinDally without limit, allowing more and more simultaneous users of the same single-user program by creaIing more and more uniquely named pr0cesses using the same program. All such processes lUDDing in a common computer will use a common memory-residen.t copy of the code, but each will have its own data area.

In fact, the sum total of memory used by many sing1e-user processes is about the same as the JDeIDOr)r used by one lirge rimltiUser process since the separate data areas are required anyway. The duplication of common data areas and the additional multiprocess oved1ead (e.g.

, PCBs) are periJaps offset by the simpler code requiIed.. Additional ConsideratioIts The creation of a l jboss DataMatrix aIge number ofprocesses does not come without problems, and there are some instances in wbich it is desiIable to design a process to handle a number of users. Among these considerations are the following: -. Each process requ ires a PCB and other system stmctu.res, such as file control blocks, that ue aIlocared from vecy valuable common buffer space in the system data area. "Ibis imposes a pacticallimit cmthe number of prOcesses that can exist in one computer at any one time.

Typical CODtempOImy systemS can support from 100 to a few bundred COJlCUDeIlt processes. If large buffers ue RqUiIed for each user, II users will mquire II buffers if each process is siDglo-user. This could result in excessive page faulting.

A multiuser process could get by with a smaller buffer pool, wbich it c:J.ynamically allocates to users as needed, so page faultiag would be redaced or etinrinated. IDterproc:ess messages ue time cons"""ng in multicomputer sysIeJiIs.

Typical interpIoc:ess message times mage from 1 JDSeC. to SO JDSeC. In some applications.

it is possible to batch traDsactiODs iD one process before sencfing.tbem. to 8DOCber proceSs, thus saviDgmany intetpIocess messages.

In this case, it may be desirable to have a piQcess ccmtto1 many users so it can aa:amulaie a batch in a Ielatively short period of time. Orherwise, data-base updating and othetfuneticms dependent on these traDsactiODs might drag. The act ofprocessfi"itcbing addsopaating system ovedlead.

Typical overl1eads run from O.s DJSeC. to 10 DJSeC.

When processes are switched, the old active piOc:ess must be switched to waiting and pedJaps added to the timer list, the new active process must be removed from the =rdy list, and maps must be ~hed..
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