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Operating System Process Synchronization

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Haziq Naeem

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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ACKNOWLEDGEMENT We have no words to express our deepest gratitude to ALLAH who blessed and enabled us to complete this project. Its great privilege to mention the feelings of obligations towards our affectionate parents and department, who prayed, encouraged and inspired us for higher education and are supporting financially and morally throughout our studies. We find it very difficult to select the appropriate words to express our gratitude to our teacher Prof. Umar and his useful encouragement and dynamic supervision. Course Instructor: -----------------------------------
DECLARATION We hereby declare that this project report entitled “Process Synchronization” is written by us and is our own effort and that no part has been copied and taken from any other source. Submitted by Signature with Date Haziq Naeem (107) ---------------------------------------- Muhammad Adeel (83) ----------------------------------------
TABLE OF CONTENTS Sr# Contents Page# 1 Introduction 1 2 Synchronization 2 2.1 Critical Section Problem 2 2.2 Locks 4 2.3 Petersons Solution 5 2.4 Semaphores 5 2.5 Major Problems of Synchronization 6 3 Windows vs Linux Synchronization 8 4 Activity Chart 9 5 Conclusion 9 6 References 9
FIGURES TABLE Fig# Contents Page# 1 Synchronization 1 2 Synchronization 2 3 Critical Section Problem 3 4 Locks 4 5 Petersons Solution 5 6 Major Problems of Synchronization 7 7 Major Problems of Synchronization 7 8 Major Problems of Synchronization 8 9 Activity Chart 9
1. Introduction 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 are mutually synchronized with each other. 2. Synchronization Access to two or more processes to share data can result in data inconsistency. for this a mechanism 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 are mutually synchronized with each other.
(Figure 1) Example: Synchronizing Traffic In a one way tunnel the tunnel can only be used when no oncoming traffic is present and when the traffic is already flowing in the right way.
(Figure 2) Problems:  Deadlock: Two or more than two process waiting for an event  Starvation: Indefinite blocking. Process that required resource which is never allocated. 2.1. Critical SectionProblem Only one process executed at a time in critical section. Only one process is allowed to start or execute in its critical section. So every process 1st request permission to entering in critical section. Three section involved in critical section: i. Entering Section ii. Exit Section iii. Remainder Section If 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 section problem. Solutions of Critical Section Problem:
Three kinds of solutions involved in critical section problem i. Mutual Exclusion ii. Progress iii. Bounded Waiting i. Mutual Exclusion One 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 critical section, then A2 not allowed to interfere in it. ii. Progress If no process executed in its critical section, then those process only requested to execute in its critical section which are in remainder section and the rest are placed in queue. iii. Bounded Waiting When a process makes request or a process request granted to enter in a critical section then a limit or bound exists on the number of times that the other processes are allowed to enter its critical section. For example, a process AB requested to enter in its critical section bounded waiting restricted that this process enter only two times in its critical section after request made and before request granted to its critical section Another example of bounded waiting is the limits of downloading on websites 2.2. Locks Lock means to prevent someone to do something. Any solution to critical section problem requires some form of lock. Acquire: Before entering its critical section Release: After exits the critical section A software tool is built for this known as “Mutex Lock”. Also known as spin lock.
(Figure 4) Synchronization Hardware: Many systems 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 Solution It 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.
(Figure 5) 2.4. Semaphores Semaphores is a variable that is used to manage or control access to a common resource by multiple processes in a similar or concurrent system. It is basically a synchronization tool. Two operations are involved in it. Wait and Signal represented as P() and V(). Wait: increasing the value of its arguments as soon as it will become non minus Signal: decreasing the value of its arguments as an individual operation Properties:  It is very simple  Works with many processes  Each critical section has different semaphores  Can have same critical section with same semaphores Types of semaphores: i. Counting Semaphores ii. Binary Semaphores i. Binary Semaphores It is a type of semaphores used to implement bounded concurrency The value of binary semaphores can only range from 0 to 1. ii. Counting Semaphores A type of semaphores which is also known as mutex. It is used to implement mutual exclusion value of counting semaphores over an unrestricted range. For example Bank account 2.5. MajorProblems of Synchronization There are three major problems of synchronization
i. Bound Buffer Problems ii. Reader-Writer Problem iii. Dinning Philosophers Problem i. Bound Buffer Problem In bound buffer there are two concepts involved. Producer and consumer This 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 delete or remove data one by one If buffer is full then more data can’t be stored and consumer not able 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 consumer removes 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 puts any data in buffer the consumer awakes. The solution of this problem is semaphores and improper solution will result as a deadlock. ii. Readers-Writers Problem Readers: Don’t perform any updates only read the data Writers: Performing both reading and writing Problem is that multiple readers to read the data but only one writer can access data at that time. iii. Dining Philosophers Problems Invented by E.W. Dijkstra. Problem: Imagine there are five philosophers who only eat and think. They are sitting on a circular table to eat spaghetti and have only five chopsticks to eat. Each philosopher thins and when he felt hungry he picks up chopsticks and eat spaghetti, after finish eating he puts down the chopsticks and starts to think again.
(Figure 6) Analysis of problem: (Figure 7) Solution:
(Figure 8) 3. Windows vs Linux Synchronization Windows Linux Uses interrupts to protect access to global resources on unipolar systems Disables interrupts to implement short critical sections Provides dispatcher objects which may act as semaphores Provides semaphores Uses spin locks on multiprocessor systems Provides spin locks 4. Activity Chart
(Figure 9) 5. Conclusion Synchronization is a mechanism for the mutual understanding between two or more processes. It Includes critical section problems, locks, Peterson’s solution, semaphores and major problems 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 prevent from deadlocks and starvation, due to this mechanism the data integrity and consistency increases, it collaborates data and improve the efficiency of the work. 6. References Critical Section: http://web.stanford.edu/class/cs140/cgi-bin/lecture.php?topic=locks https://cseweb.ucsd.edu/classes/fa05/cse120/lectures/120-l5.pdf Semaphores: https://en.wikipedia.org/wiki/Semaphore_(programming) http://www.personal.kent.edu/~rmuhamma/OpSystems/Myos/semaphore.htm https://en.wikibooks.org/wiki/Operating_System_Design/Processes/Semaphores Dining Philosophers Problems: https://www.cs.mtu.edu/~shene/NSF-3/e-Book/MUTEX/TM-example-philos-1.html Locks: http://cse.stfx.ca/~mlin/cs375/lectures/syn3.ppt Imp of Sync: http://users.csc.calpoly.edu/~fkurfess/Courses/COMP-346/W00/Slides/05-ProcSync.ppt
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Operating System Process Synchronization

  • 1. ACKNOWLEDGEMENT We have no words to express our deepest gratitude to ALLAH who blessed and enabled us to complete this project. Its great privilege to mention the feelings of obligations towards our affectionate parents and department, who prayed, encouraged and inspired us for higher education and are supporting financially and morally throughout our studies. We find it very difficult to select the appropriate words to express our gratitude to our teacher Prof. Umar and his useful encouragement and dynamic supervision. Course Instructor: -----------------------------------
  • 2. DECLARATION We hereby declare that this project report entitled “Process Synchronization” is written by us and is our own effort and that no part has been copied and taken from any other source. Submitted by Signature with Date Haziq Naeem (107) ---------------------------------------- Muhammad Adeel (83) ----------------------------------------
  • 3. TABLE OF CONTENTS Sr# Contents Page# 1 Introduction 1 2 Synchronization 2 2.1 Critical Section Problem 2 2.2 Locks 4 2.3 Petersons Solution 5 2.4 Semaphores 5 2.5 Major Problems of Synchronization 6 3 Windows vs Linux Synchronization 8 4 Activity Chart 9 5 Conclusion 9 6 References 9
  • 4. FIGURES TABLE Fig# Contents Page# 1 Synchronization 1 2 Synchronization 2 3 Critical Section Problem 3 4 Locks 4 5 Petersons Solution 5 6 Major Problems of Synchronization 7 7 Major Problems of Synchronization 7 8 Major Problems of Synchronization 8 9 Activity Chart 9
  • 5. 1. Introduction 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 are mutually synchronized with each other. 2. Synchronization Access to two or more processes to share data can result in data inconsistency. for this a mechanism 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 are mutually synchronized with each other.
  • 6. (Figure 1) Example: Synchronizing Traffic In a one way tunnel the tunnel can only be used when no oncoming traffic is present and when the traffic is already flowing in the right way.
  • 7. (Figure 2) Problems:  Deadlock: Two or more than two process waiting for an event  Starvation: Indefinite blocking. Process that required resource which is never allocated. 2.1. Critical SectionProblem Only one process executed at a time in critical section. Only one process is allowed to start or execute in its critical section. So every process 1st request permission to entering in critical section. Three section involved in critical section: i. Entering Section ii. Exit Section iii. Remainder Section If 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 section problem. Solutions of Critical Section Problem:
  • 8. Three kinds of solutions involved in critical section problem i. Mutual Exclusion ii. Progress iii. Bounded Waiting i. Mutual Exclusion One 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 critical section, then A2 not allowed to interfere in it. ii. Progress If no process executed in its critical section, then those process only requested to execute in its critical section which are in remainder section and the rest are placed in queue. iii. Bounded Waiting When a process makes request or a process request granted to enter in a critical section then a limit or bound exists on the number of times that the other processes are allowed to enter its critical section. For example, a process AB requested to enter in its critical section bounded waiting restricted that this process enter only two times in its critical section after request made and before request granted to its critical section Another example of bounded waiting is the limits of downloading on websites 2.2. Locks Lock means to prevent someone to do something. Any solution to critical section problem requires some form of lock. Acquire: Before entering its critical section Release: After exits the critical section A software tool is built for this known as “Mutex Lock”. Also known as spin lock.
  • 9. (Figure 4) Synchronization Hardware: Many systems 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 Solution It 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.
  • 10. (Figure 5) 2.4. Semaphores Semaphores is a variable that is used to manage or control access to a common resource by multiple processes in a similar or concurrent system. It is basically a synchronization tool. Two operations are involved in it. Wait and Signal represented as P() and V(). Wait: increasing the value of its arguments as soon as it will become non minus Signal: decreasing the value of its arguments as an individual operation Properties:  It is very simple  Works with many processes  Each critical section has different semaphores  Can have same critical section with same semaphores Types of semaphores: i. Counting Semaphores ii. Binary Semaphores i. Binary Semaphores It is a type of semaphores used to implement bounded concurrency The value of binary semaphores can only range from 0 to 1. ii. Counting Semaphores A type of semaphores which is also known as mutex. It is used to implement mutual exclusion value of counting semaphores over an unrestricted range. For example Bank account 2.5. MajorProblems of Synchronization There are three major problems of synchronization
  • 11. i. Bound Buffer Problems ii. Reader-Writer Problem iii. Dinning Philosophers Problem i. Bound Buffer Problem In bound buffer there are two concepts involved. Producer and consumer This 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 delete or remove data one by one If buffer is full then more data can’t be stored and consumer not able 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 consumer removes 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 puts any data in buffer the consumer awakes. The solution of this problem is semaphores and improper solution will result as a deadlock. ii. Readers-Writers Problem Readers: Don’t perform any updates only read the data Writers: Performing both reading and writing Problem is that multiple readers to read the data but only one writer can access data at that time. iii. Dining Philosophers Problems Invented by E.W. Dijkstra. Problem: Imagine there are five philosophers who only eat and think. They are sitting on a circular table to eat spaghetti and have only five chopsticks to eat. Each philosopher thins and when he felt hungry he picks up chopsticks and eat spaghetti, after finish eating he puts down the chopsticks and starts to think again.
  • 12. (Figure 6) Analysis of problem: (Figure 7) Solution:
  • 13. (Figure 8) 3. Windows vs Linux Synchronization Windows Linux Uses interrupts to protect access to global resources on unipolar systems Disables interrupts to implement short critical sections Provides dispatcher objects which may act as semaphores Provides semaphores Uses spin locks on multiprocessor systems Provides spin locks 4. Activity Chart
  • 14. (Figure 9) 5. Conclusion Synchronization is a mechanism for the mutual understanding between two or more processes. It Includes critical section problems, locks, Peterson’s solution, semaphores and major problems 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 prevent from deadlocks and starvation, due to this mechanism the data integrity and consistency increases, it collaborates data and improve the efficiency of the work. 6. References Critical Section: http://web.stanford.edu/class/cs140/cgi-bin/lecture.php?topic=locks https://cseweb.ucsd.edu/classes/fa05/cse120/lectures/120-l5.pdf Semaphores: https://en.wikipedia.org/wiki/Semaphore_(programming) http://www.personal.kent.edu/~rmuhamma/OpSystems/Myos/semaphore.htm https://en.wikibooks.org/wiki/Operating_System_Design/Processes/Semaphores Dining Philosophers Problems: https://www.cs.mtu.edu/~shene/NSF-3/e-Book/MUTEX/TM-example-philos-1.html Locks: http://cse.stfx.ca/~mlin/cs375/lectures/syn3.ppt Imp of Sync: http://users.csc.calpoly.edu/~fkurfess/Courses/COMP-346/W00/Slides/05-ProcSync.ppt