This document discusses synchronization between processes. It defines synchronization as the mutual understanding between two or more processes when sharing system resources. It describes critical section problems, solutions like locks, Peterson's solution, and semaphores. It also covers major synchronization problems like bounded buffer, reader-writer, and dining philosophers. Windows uses interrupts to protect shared resources while Linux uses semaphores. Synchronization is important for preventing deadlocks and data inconsistencies to improve efficiency.

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Operating System Process Synchronization

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  ACKNOWLEDGEMENTWe have nowords to express our deepest gratitude to ALLAH whoblessed and enabled us to complete this project. Its great privilege tomention the feelings of obligations towards our affectionate parentsand department, who prayed, encouraged and inspired us for highereducation and are supporting financially and morally throughout ourstudies.We find it very difficult to select the appropriate words to express ourgratitude to our teacher Prof. Umar and his useful encouragement anddynamic supervision.Course Instructor:-----------------------------------
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  DECLARATIONWe hereby declarethat this project report entitled “Process Synchronization” is written by usand is our own effort and that no part has been copied and taken from any other source.Submitted by Signature with DateHaziq Naeem (107) ----------------------------------------Muhammad Adeel (83) ----------------------------------------
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  TABLE OF CONTENTSSr#Contents Page#1 Introduction 12 Synchronization 22.1 Critical Section Problem 22.2 Locks 42.3 Petersons Solution 52.4 Semaphores 52.5 Major Problems of Synchronization 63 Windows vs Linux Synchronization 84 Activity Chart 95 Conclusion 96 References 9
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  FIGURES TABLEFig# ContentsPage#1 Synchronization 12 Synchronization 23 Critical Section Problem 34 Locks 45 Petersons Solution 56 Major Problems of Synchronization 77 Major Problems of Synchronization 78 Major Problems of Synchronization 89 Activity Chart 9
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  1. IntroductionSynchronization isthe mutual understanding between two processes or more.In simple words synchronization means sharing system resources. i.e. Track of a train, they aremutually synchronized with each other.2. SynchronizationAccess to two or more processes to share data can result in data inconsistency. for this amechanism is used called “Synchronization”.Synchronization is the mutual understanding between two processes or more.In simple words synchronization means sharing system resources. i.e. Track of a train, they aremutually synchronized with each other.
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  (Figure 1)Example:Synchronizing TrafficIna one way tunnel the tunnel can only be used when no oncoming traffic is present and whenthe traffic is already flowing in the right way.
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  (Figure 2)Problems: Deadlock:Two or more than two process waiting for an event Starvation: Indefinite blocking. Process that required resource which is neverallocated.2.1. Critical SectionProblemOnly one process executed at a time in critical section. Only one process is allowed to start orexecute in its critical section. So every process 1st request permission to entering in criticalsection.Three section involved in critical section:i. Entering Sectionii. Exit Sectioniii. Remainder SectionIf one process started working, other processes will have to wait until first will finished.(Figure 3)We discuss the critical section problem now we will discuss the solution of critical sectionproblem.Solutions of Critical Section Problem:
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  Three kinds ofsolutions involved in critical section problemi. Mutual Exclusionii. Progressiii. Bounded Waitingi. Mutual ExclusionOne processes execute no other process will interfere in it.For example, if a process named A1 and other Process named A2. If A1 executes in its criticalsection, then A2 not allowed to interfere in it.ii. ProgressIf no process executed in its critical section, then those process only requested to execute inits critical section which are in remainder section and the rest are placed in queue.iii. Bounded WaitingWhen a process makes request or a process request granted to enter in a critical section then alimit or bound exists on the number of times that the other processes are allowed to enter itscritical section.For example, a process AB requested to enter in its critical section bounded waiting restrictedthat this process enter only two times in its critical section after request made and before requestgranted to its critical sectionAnother example of bounded waiting is the limits of downloading on websites2.2. LocksLock means to prevent someone to do something. Any solution to critical section problemrequires some form of lock.Acquire: Before entering its critical sectionRelease: After exits the critical sectionA software tool is built for this known as “Mutex Lock”. Also known as spin lock.
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  (Figure 4)Synchronization Hardware:Manysystems provide the support of hardware for critical section. Uniprocessors can disable interrupts:System clock kept updated by interrupts Modern machines are non-interrupt able:Allow us to test and modify content of a word or to swap contents of two words.2.3. Peterson’s SolutionIt is a software based solution to critical section problem. Provides good algorithm description of solving. Describe the complexities in designing software (three critical section solutions). Could not be work on modern non-interrupt able machines.The solution is for two processes. Load and store instructions are non-interrupt able.
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  (Figure 5)2.4. SemaphoresSemaphoresis a variable that is used to manage or control access to a common resource bymultiple processes in a similar or concurrent system.It is basically a synchronization tool. Two operations are involved in it. Wait and Signalrepresented as P() and V().Wait: increasing the value of its arguments as soon as it will become non minusSignal: decreasing the value of its arguments as an individual operationProperties: It is very simple Works with many processes Each critical section has different semaphores Can have same critical section with same semaphoresTypes of semaphores:i. Counting Semaphoresii. Binary Semaphoresi. Binary SemaphoresIt is a type of semaphores used to implement bounded concurrencyThe value of binary semaphores can only range from 0 to 1.ii. Counting SemaphoresA type of semaphores which is also known as mutex. It is used to implement mutual exclusionvalue of counting semaphores over an unrestricted range.For example Bank account2.5. MajorProblems of SynchronizationThere are three major problems of synchronization
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  i. Bound BufferProblemsii. Reader-Writer Problemiii. Dinning Philosophers Problemi. Bound Buffer ProblemIn bound buffer there are two concepts involved. Producer and consumerThis problem explains these two processes which share common buffer used as a queue.Producer produce the data take it into the buffer and again started Whereas Consumer deleteor remove data one by one If buffer is full then more data can’t be stored and consumer notable to remove data from an empty buffer.The solution for producer is to discard data or go to sleep if the buffer is full. If consumerremoves something into the buffer, then notifies the producer will start again to fill the buffer.Now for consumer, if consumer finds buffer empty then it can go to sleep. When producer putsany data in buffer the consumer awakes.The solution of this problem is semaphores and improper solution will result as a deadlock.ii. Readers-Writers ProblemReaders: Don’t perform any updates only read the dataWriters: Performing both reading and writingProblem is that multiple readers to read the data but only one writer can access data at thattime.iii. Dining Philosophers ProblemsInvented by E.W. Dijkstra.Problem:Imagine there are five philosophers who only eat and think. They are sitting on a circular tableto eat spaghetti and have only five chopsticks to eat. Each philosopher thins and when he felthungry he picks up chopsticks and eat spaghetti, after finish eating he puts down the chopsticksand starts to think again.
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  (Figure 6)Analysis ofproblem:(Figure 7)Solution:
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  (Figure 8)3. Windowsvs Linux SynchronizationWindows LinuxUses interrupts to protect access toglobal resources on unipolar systemsDisables interrupts to implementshort critical sectionsProvides dispatcher objects whichmay act as semaphoresProvides semaphoresUses spin locks on multiprocessorsystemsProvides spin locks4. Activity Chart
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  (Figure 9)5. ConclusionSynchronizationis a mechanism for the mutual understanding between two or more processes.It Includes critical section problems, locks, Peterson’s solution, semaphores and majorproblems of synchronization.As very thing has positive and negative sights, synchronization has more positive ones.It is a major technique / mechanism used in the operating systems. It gives access to preventfrom deadlocks and starvation, due to this mechanism the data integrity and consistencyincreases, it collaborates data and improve the efficiency of the work.6. ReferencesCritical Section:http://web.stanford.edu/class/cs140/cgi-bin/lecture.php?topic=lockshttps://cseweb.ucsd.edu/classes/fa05/cse120/lectures/120-l5.pdfSemaphores:https://en.wikipedia.org/wiki/Semaphore_(programming)http://www.personal.kent.edu/~rmuhamma/OpSystems/Myos/semaphore.htmhttps://en.wikibooks.org/wiki/Operating_System_Design/Processes/SemaphoresDining Philosophers Problems:https://www.cs.mtu.edu/~shene/NSF-3/e-Book/MUTEX/TM-example-philos-1.htmlLocks:http://cse.stfx.ca/~mlin/cs375/lectures/syn3.pptImp of Sync:http://users.csc.calpoly.edu/~fkurfess/Courses/COMP-346/W00/Slides/05-ProcSync.ppt
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