Project: Processes and Resource Management

Project: Processes and Resource Management

Textbook: pages 482-491

Lubomir Bic

Operating Systems

Assignment• Design/implement a simplified process and resource

manager• Required functionalities:

– process: create/destroy– resource: request/release– time-out interrupt– multi-unit resources (5.1. page 490 of textbook)– extensive error checking

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Operating Systems

• Problem: we do not have the actual processes or hardware• Solution: your terminal (or test files) represent

– currently running process, and– the hardware causing interrupts

Overall Organization

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Operating Systems

• Write presentation/test shell– it reads command from terminal or test file– it invokes kernel function– it displays reply (on terminal or to output file)

• which process is running• any errors

Overall Organization

your terminal/test files

repeat get f, par invoke f(par) get reply display reply

Process andResource Manager

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Operating Systems

Presentation/test shell Example:

*Process Init is running. . .shell> cr A 1*Process A is runningshell> cr B 2*Process B is runningshell> cr C 1*Process B is runningshell> req R1,1*Process B is blocked; Process A is running. . .

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Operating Systems

Process states and operations• Process states: ready, running, blocked

• Possible Operations:– Create: (none) ready– Destroy: running/ready/blocked (none)– Request: running blocked– Release: blocked ready– Time_out: running ready– Scheduler: ready running/running ready

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Operating Systems

Process Control Block (PCB)• PID• CPU state — not used• Memory — not used• Open_Files — not used• Other_resources• Status: Type & List• Creation_tree: Parent/Children• Priority: 0, 1, 2 (Init, User, System)

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The Ready List (RL)• 3-level priority list

2 = “system”

1 = “user”

0 = “init”• Priorities don’t change• Every process (PCB) is either on the RL on a blocked list

Operating Systems 8

Operating Systems

Create a processCreate(initialization parameters){

create PCB data structureinitialize PCB using parameterslink PCB to creation treeinsert(RL, PCB)Scheduler() }

• Init process is created at start-up & can create first system or user process

• Any new or released process is inserted at the end of the queue (RL)

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Operating Systems

Destroy a processDestroy (pid) {

get pointer p to PCB using pidKill_Tree(p)Scheduler() }

Kill_Tree(p) {for all child processes q Kill_Tree(q)free resourcesdelete PCB and update all pointers }

• Process can be destroyed by any of its ancestors or by itself (exit)

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Operating Systems

Representation of Resources

• There is a fixed set of resources• Resource Control Block (RCB)

– RID– Status: counter for number of free units– Waiting_List: list of blocked processes

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Operating Systems

Request resource (1-unit resources)Request(rid) { r = Get_RCB(rid); if (r->Status == 'free') { r->Status = 'allocated‘; insert(self->Other_Resources, r); } else { self->Status.Type = 'blocked'; self->Status.List = r; remove(RL, self); insert(r->Waiting_List, self); Scheduler(); }

• all requests are satisfied in strict FIFO order

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Operating Systems

Release resource (1-unit resources)Release(rid) { r = Get_RCB(rid); remove(self->Other_Resources, r); if (r->Waiting_List == NIL} { r->Status = 'free'; } else { remove(r->Waiting_List, q); q->Status.Type = 'ready'; q->Status.List = RL; insert(q->Other_Resources, r); insert(RL, q);

Scheduler(); }}

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Operating Systems

Scheduling

• 3-level priority scheduler• Use preemptive round-robin scheduling within level• Time sharing is simulated by function call• Init process serves a dual purpose:

– dummy process: lowest priority/never blocked– root of process creation tree

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Operating Systems

Scheduler• Called at the end of every kernel call(1) Scheduler() {(2) find highest priority process p(3) if (self->priority < p->priority ||(4) self->Status.Type != 'running' ||(5) self == NIL) (5) preempt(p, self) }

Condition (3): called from create or releaseCondition (4): called from request or time-outCondition (5): called from destroyPreemption: • Change status of p to running (status of self already changed

to ready/blocked)• Context switch—output name of running process

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Operating Systems

Time-out Interrupts• Simulate time-sharing

Time_out() { find running process q; remove(RL, q); q->Status.Type = 'ready'; insert(RL, q);

Scheduler();}

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Operating Systems

Presentation/Test Shell• Mandatory Commands

– init– cr <name> <priority> – de <name>– req <resource name> <# of units> – rel <resource name> <# of units> – to

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Operating Systems

Presentation/Test Shell

• Optional commands (examples):– list all processes and their status– list all resources and their status– provide information about a given process – provide information about a given resource

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Operating Systems

Summary of tasks• Design/implement the process and resource manager

– data structures and functions• Design/implement a driver program (shell)

– command language and interpreter• Instantiate the manager to include at start-up:

– A Ready List with 3 priorities– A single process, Init– 4 resources labeled: R1, R2, R3, R4 (each Ri has i units))

• Submit your program for testing, submit documentation for evaluation

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Sample test 1cr x 2 cr y 1 to cr z 2 to req R1 1 to req R1 1 de z rel R1 1 de x

init x x x x z z x z x x init 20

Sample test 2cr x 1 cr p 1 cr q 1 cr r 1 to req R2 1 to req R3 3 to req R4 3 to to req R3 1 req R4 2 req R2 2 to de q to to init x x x x p p q q r r x p q r x x x p x 21