Project 4 DME

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Project 4 DME
Project 4

• When two or more tasks in a distributed system do
  not share memory or a clock and compete for the
  use of system resources, there is a requirement
  for a mechanism to enforce mutual exclusion.
• Consequently, algorithms for mutual exclusion and
  deadlock must depend upon the exchange of
  messages without relying upon common memory
  semaphores.
• Project 4 is designed to help you understand
• mutual exclusion in a distributed system.
• clock and messaging synchronization.
• the client/server relationship with sharable
  resources.
• concepts of task communication and
  synchronization.

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Tasks and Messaging
Project 4

• Task 0 Shell Task
• Port 0
• Task 10 Bank Task
• Port 10
• Tasks 1-9 ATM Tasks
• Ports 1-9 communicate with shell
• Ports 11-19 communicate with Bank and DME
• Tasks 11-19 DME Tasks
• Ports 21-29

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The Bank
Project 4
All communications via GETMESSAGE(int from, int
to, MSG msg) POSTMESSAGE(int from, int to, char
msg)
BANK (Task 10)
ACCOUNT account100
Port 10
message Success -message Error bbalance
account balance
b d, n s,a t x w,
Balance request Deposit Open new account
Select account Request balances Delete
account Withdrawal
atm,a,b atm,a,d, atm,a,n, atm,a,x atm,a
,w, atm,9999,t
Balance request Deposit Open new account
Delete account Withdrawal Accounts summary
Ports 11-19
Port 0
Ports 1-9
b,a d,a, n,a, x,a w,a, t,9999
Balance request Deposit Open new account
Delete account Withdrawal Summary
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DME Queuing Task
Project 4
5
DME Example
Project 4
Request
Reply
0
P0
0
P1
0
P2
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DME Guidelines
Project 4

• Read and understand Stallings Chapter 15, section
  3.
• Validate that Project 4 shell commands and tasks
  (OS345p4.c and OS345bank.c) operate with your
  operating system and verify the ATM/Bank
  operations work for individual ATM/Bank requests.
  Validate that your counting semaphore
  implementation from Project 2 works properly.
  ATM requests from your shell must be queued up in
  the message buffers awaiting access to the Bank
  critical section.
• Several other shell commands are included in
  OS345p4.c which should help in the debug process.
  The lm command displays all the messages
  currently in the message buffers. Verify that
  this works properly.
• Lower the priority of your ATM tasks below the
  shell and implement your distributed mutual
  exclusion peering solution. Validate with
  individual requests from the command line that
  the system still works.
• Execute the shell commands test1 and test2 to
  validate that the Bank is accessed by only one
  ATM task at a time. (The validation should be
  obvious!)

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Project 4 Grading Criteria
Project 4

• REQUIRED
• Successfully integrate OS345p4.c and OS345bank.c
  into your operating system. (2 pts)
• Implement a DME solution for critical section
  access to the bank using the DME peer tasks to
  arbitrate ATM Requests and Releases. (8 pts)
• Successfully pass test1 with the ATM tasks at a
  low priority. (4 pts)
• Successfully pass test2 with the ATM tasks at a
  low priority. (6 pts)

• BONUS
• 2 points bonus for early pass-off (at least one
  day before due date.)
• 2 points bonus for implementing a more
  stressful stress test.
• -8 points for using a common semaphore or shared
  memory/clock for the DME solution.
• 2 points penalty for each school day late.