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November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 1Instructor: Dr. Khalil
Synchronization Tools for Distributed Operating System
Survey Paper
• Team Members:Mazen HammadChuck MannVrushali Nidgundi Hong Zhang
• Course:CSE 8343 Advanced Operating Systems
• Professor:Dr. Mohamed Khalil
(Group 2)
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 2Instructor: Dr. Khalil
Outline
• Mutual Exclusion• Atomicity• Concurrency• Semaphores• Message Passing• Deadlock Handling
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 3Instructor: Dr. Khalil
Mutual Exclusion• Mutual-exclusion guarantees that certain sections of
code (critical sections) will not be executed by more than one process simultaneously. These sections of code usually access shared variables in a common store or access shared hardware.
• The standard solution to kernel-level mutual-exclusion in uniprocessor systems is to momentarily disable interrupts to guarantee that the process accessing the sensitive data will not be preempted before the access has been completed. This solution is not available for multiprocessor systems, since processes on these are truly concurrent.
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 4Instructor: Dr. Khalil
Mutual Exclusion (Continued)
• A critical section of code is framed by an entry section at the beginning and an exit section at the end; these sections act to grab and release the “lock” on that section.
• One safety property of mutual exclusion is, no more than one process should have its program counter (PC) in the critical code at the same time.
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 5Instructor: Dr. Khalil
Mutual Exclusion (Continued)
Different algorithms for implementing mutual exclusion • Centralized Approach: One of the processes in the
system is chosen to coordinate the entry to the critical section.
• Fully Distributed Approach: This algorithm is based on the event ordering scheme.
• Token Passing Approach: Another method of providing mutual exclusion is to circulate a token among the processes in the system.
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 6Instructor: Dr. Khalil
Atomicity
• Atomic transaction is a program that must be executed atomically. That is, either all the operations associated with it are executed to completion, or none are performed.
• The two phase commit protocol is used to ensure atomicity.
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 7Instructor: Dr. Khalil
Concurrency
Different concurrency control schemes are
modified so that they can be used in a
distributed environment:• Locking Protocols• Timestamping
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 8Instructor: Dr. Khalil
Distributed Semaphores
• Semaphores provide a basic synchronization mechanism in uni and multi processor systems
• Supporting semaphores in distributed systems has not received much attention
• Implementation of semaphores very difficult in a distributed system
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 9Instructor: Dr. Khalil
Distributed Semaphores (Continued)
• Distributed Semaphore is a semaphore-like mechanism
• It does not require shared memory• Implemented using conditional synchronous
message-passing mechanism
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 10Instructor: Dr. Khalil
Distributed Semaphores (Continued)
Synchronization is achieved using LEMMA (MESSAGE QUEUE STABILITY) approach and is used to ensure consistency in distributed database systems
Once the Lemma equation is satisfied then the following things are also satisfied:– A proxy message will not be queued indefinitely– A request message will not be queued indefinitely– Every P request message eventually reaches the
semaphore holder– Two or more nodes will not form a cycle while waiting for a
semaphore– A node’s request for P and V will not form a cycle
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 11Instructor: Dr. Khalil
Message Passing
• Minimum set of primitives needed for processes to conduct message passing are:– Send (destination, message)– Receive (source, message)
• Process A sends message to process B with send primitive designating B as destination
• Process B receives message with receive primitive designating A as the source
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 12Instructor: Dr. Khalil
Message Passing
Shared Data
Send Message
Process A
Recv Message
Process B
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 13Instructor: Dr. Khalil
Common Synchronization Combinations
• Blocking send and blocking receive– Rendezvous – Both sender and receiver are
blocked until the message is delivered– Example – Remote Procedure Calls (RPCs)
• Nonblocking send and blocking receive– Sender can send messages to several different
recipient processes– Receiver that must obtain data from message
before it can do useful work waits for the data
• Nonblocking send and nonblocking receive– Neither process waits but recipient should poll
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 14Instructor: Dr. Khalil
Synchronization with Receive MessagesT
ime
Nonblocking Blocking Timeout
pvm_trecv()pvm_recv()pvm_nrecv()Function Called
Time Expired
Message Arrives
Waiting
Waiting
Running
Running
Running
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 15Instructor: Dr. Khalil
Synchronization Point
• Group barrier synchronizes a group of processes at a point in time
• Indirect message passing via daemons• Each early member process in a group
performs a virtual blocking receive• Last member process performs a virtual
nonblocking send to all the other processes
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 16Instructor: Dr. Khalil
Synchronization with a Group BarrierT
ime
Process 1 Process 2 Process 3
barrier call
barrier call
Synchronization Point
barrier call
Waiting
Waiting
Running
Running
RunningRunning
Note: Syntax of barrier call is pvm_barrier(“g2”,3) where the group name is g2 and the number of processes to rendezvous is 3.
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 17Instructor: Dr. Khalil
Deadlock Handling
Processes compete for resources
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 18Instructor: Dr. Khalil
Deadlock Characterization& Handling Approaches
• Deadlock will happen if four conditions hold simultaneously– Mutual exclusion– Hold and wait– No preemption– Circular wait
• Deadlock Handling Approaches– Prevention– Avoidance– Detection– Recovery
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 19Instructor: Dr. Khalil
Deadlock Prevention
Ensure at least one of these conditions cannot hold• Mutual Exclusion - Not required for sharable
resources, must hold for non-sharable resources• Hold and Wait - Whenever a process requests a
resource, it does not hold any other resources.• No Preemption - Preempt resources held by a
process, which is requesting another resource that cannot be immediately allocated to it.
• Circular Wait - Impose a total ordering of all resource types, and require that each process requests resources in an increasing order of enumeration.
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 20Instructor: Dr. Khalil
Deadlock Avoidance
• Wound-Wait Scheme (Preemptive)
Process P0 requests a resource held by process P1,
P0 will be allowed to wait only if it has a larger timestamp
than P1, i.e. P0 is younger than P1. Otherwise, P1 is rolled
back (P1 is wound by P0).
• Wait-Die Scheme (Non-preemptive)
Process P0 requests a resource held by process P1,
P0 will be allowed to wait only if it has a smaller
timestamp than P1, i.e. P0 is older than P1. Otherwise, P0
is rolled back (dies).
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 21Instructor: Dr. Khalil
Deadlock Detection
• Centralized Approach• Fully Distributed Approach
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 22Instructor: Dr. Khalil
Recovery from Deadlock
• Process Termination– Abort all deadlocked processes– Abort one process at a time until the deadlock cycle is
eliminated– In which order to abort
• Resource Preemption– Selecting a victim - minimize cost– Rollback - return to some safe state, restart process from
that state– Avoid starvation - same process may always be picked as
victim, include number of rollbacks in cost factor
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 23Instructor: Dr. Khalil
References
[1] Comer, D. (2000), Internetworking with TCP/IP: Principles, Protocols, and Architectures, 4th Ed., Prentice-Hall, Upper Saddle River, NJ.
[2] Coulouris, G.; Dollimore, J.; Kindberg, T. (2001), Distributed Systems: Concepts and Design, 3rd Ed., Addison-Wesley, Reading, Mass.
[3] El-Rewini, H. (2003), Classroom Lectures, CSE 8380 - Parallel and Distributed Processing, Southern Methodist University, Spring 2003.
[4] El-Rewini, H. and Lewis, T. (1998), Distributed and Parallel Computing, Manning & Prentice Hall, Greenwich, CT.
[5] Fiorini, P. "Distributed Deadlock", University of Southern Maine, Portland, ME.
[6] Holliday, J. and Abbadi, A. “Distributed Deadlock Detection”, Encyclopedia of Distributed Computing, Kluwer Academic Publishers.
[7] Silberschatz, A. and Galvin, P. (1998), "Operating System Concepts", 5th Ed., Addison-Wesley, Read-ing Mass.
[8] Stallings, W. (2001), "Operating Systems: Internals and Design Principles", 4th Ed., Prentice-Hall, Up-per Saddle River, NJ.
[9] Tanenbaum, A. and van Steen, M. (2002), "Distributed Systems: Principles and Paradigms", Prentice-Hall, Upper Saddle River, NJ.
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 24Instructor: Dr. Khalil
Questions & Discussion
November 22, 2003SMU School of Engineering
Group 2: Hammad, Mann, Nidgundi, & ZhangCSE 8343 Advanced Operating Systems
Slide 25Instructor: Dr. Khalil
Thank You!