Hao Cheng

1
Simulator Project
Objective 3
Get_Srcipt Logon_Service Next_pgm
Get_memory Alloc_seg Loader
11 functions Dealloc_pgm
Dealloc_seg Merge_seg End_ServiceAbend_Serv
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• Hao Cheng
• haocheng_at_cs.ucf.edu
• 11-01-15

2
Objective 3

• multi-users/terminals
• process control block
• program loader
• memory allocation
• data structure
• program flow
• function descriptions

3
process model

• 5 users logon
• user programs
• logon.dat script.dat

4
termtable pcb_type
5
program files

• editor.dat, user.dat per type
• 5 users - 19 programs (obj3)
• multi-programs per file
• read in the execution order

6
freemem
Memory allocation strategy First Fit
Getmemory, Alloc_seg, Dealloc_pgm, Deallog_seg
7
Cpu()

• Cpu() is only called by itself or XPGM()
• XPGM is called by Dispatcher() or

So in Obj3, the Cpu() will never be called.
8
END - PGEND

• PGEND
• read from logon.dat
• Get_instr Cpu()

9
program flow (obj3)
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Logon(U001) Logon(U002) Logon(U004)
Logon(U005) Logon(U003) END(U001)...
11
Logon_Service

• Allocates and Initializes the PCB
• PCB stored in termtable
• Get_Script - Initialize the process script and
  pgmid.
• Next_pgm(PCB) - Allocate and Load the next
  program.

12
Get_Script

• from script.dat
• file pointer scriptfp
• allocate entries for pcb-gtscript
• load script into pcb-gtscript
• read till LOGOFF

13
Next_pgm

• for this pcb, if some programs are already
  executed, release those resources.
• if (pcb-gtfirstrb ! NULL) return. (for I/O)
• if next script logoff, output return.
• Else
• Get_memory request memory resource
• Load program into allocated memory
• pcb-gtstatus R

14
Get_Memory Alloc_seg

• allocate segment table (program files)
• initialize every new allocated entries
• For each segment
• call alloc_seg() to reserve space in MEM
• Look up the freeMEM for the first fit available
  block in MEM and then update freeMEM
  appropriately alloc_seg().
• Get the returned base address membase
• Compact_men (obj6)

15
Loader

• for each segment
• get instructions from program files (get_instr)
• load instr_type into MEM according to segment
  table.
• Display_pgm

16
Memory

• dealloc_pgm, dealloc_seg, merge_seg
• free every allocated segment table and return the
  occupied MEM into freeMEM
• finally scan the freeMEM and if there are
  adjacent blocks, merge into a big one.

17
End_Service

• End_Service
• output END OF PROGRAM
• If (pcb-gtfirstrb NULL) Next_pgm(pcb)
• first IORB, always NULL in obj3.

18
Questions?