Semaphores. To avoid busy waiting: when a process has to wait, it will be put in a blocked queue of processes waiting for the same event
|
|
- Darleen Thomas
- 5 years ago
- Views:
Transcription
1 Semaphores Synchronization tool (provided by the OS) that do not require busy waiting A semaphore S is an integer variable that, apart from initialization, can only be accessed through 2 atomic and mutually exclusive operations: wait(s) also P(S) signal(s) also V(S) To avoid busy waiting: when a process has to wait, it will be put in a blocked queue of processes waiting for the same event 1
2 Semaphores Hence, in fact, a semaphore is a record (structure): typedef struct General_Semaphore { count: integer; queue: list of process } semaphore; semaphore S; When a process must wait for a semaphore S, it is blocked and put on the semaphore s queue The signal operation removes (acc. to a fair policy like FIFO) one process from the queue and puts it in the list of ready processes 2
3 Semaphore s operations P(S)or wait(s)[ if (S.count <=0) then //wait until positive {block this process and place this process in S.queue } S.count--; //decrement ] V(S) or signal(s)[ S.count++; //increment remove one process P, if any, from S.queue; place this process P on ready list ] S.count must be initialized to a non-negative integer value (depending on the application) 3
4 Semaphores: observations When a semaphore is created, its value can be initialized to any non-negative integer (0,1,2,3..) When S.count >=0: the number of processes that can execute wait(s) without being blocked = S.count Atomicity and mutual exclusion: no 2 process can be in wait(s) and signal(s) (on the same S) at the same time (even with multiple CPUs) Hence the blocks of code defining wait(s) and signal(s) are, in fact, critical sections No other operations are allowed on a semaphore 4
5 Semaphores: observations The critical sections defined by wait(s) and signal(s) are very short: typically 10 instructions Solutions: uniprocessor: disable interrupts during these operations (ie: for a very short period). This does not work on a multiprocessor machine. multiprocessor: use previous software or hardware schemes. The amount of busy waiting should be small. 5
6 Binary semaphores Semaphores that allow arbitrary non-negative values are called counting semaphores or general semaphores We also have binary semaphores similar to counting semaphores except that count is Boolean valued (0 or 1) counting semaphores can be implemented by binary semaphores... generally more difficult to use than counting semaphores (eg: they cannot be initialized to an integer k > 1) 6
7 Binary semaphores waitb(s):[ if (S.value == 0 ) { block this process; place this process in S.queue; } S.value=0; ] signalb(s):[ S.value=1; remove one process P, if any from S.queue place this process P on ready list; ] Binary Semaphore S; {init 0 or 1} 7
8 Binary sempahore using busy wait S initially 0 or 1 Wait(S): [while (S == 0 )do skip; S = 0;] Signal(S): [S = 1;] 8
9 Using semaphores for solving critical section problems For n processes Initialize S.count to 1 Then only 1 process is allowed into CS (mutual exclusion) To allow k processes into CS, we initialize S.count to k Process Pi: repeat wait(s); CS signal(s); RS forever wait(s): wait until semaphore becomes +ve; atomically decrement signal(s): atomically increment semaphore value; wake up one process if any 9
10 Mutual exclusion Only 1 train can cross the pass at a time Each train will execute wait(s) prior to entering Each train will execute signal(s) after leaving the pass 10
11 Using semaphores to synchronize processes We have 2 processes: Parent (P1) and child (P2) Statement S2 in P2 needs to be performed before statement S1 in P1 Then define a semaphore synch Initialize synch to 0 Proper synchronization is achieved by having in P2: Thread_exit();{ S2; signal(synch);} And having in P1: Thread_join(){ wait(synch); S1;} 11
12 Hiking trail Child has to wait for parent to first cross the ridge Child executes wait(s) S initialized to 0 Parent executes signal(s) 12
13 Binary semaphore in pthreads Binary semaphore initialized to 1 also called mutex Type pthread_mutex_t #include <pthread.h> pthread_mutex_t lock; int pthread_mutex_lock(pthread_mutex_t *lock); int pthread_mutex_unlock(pthread_mutex_t *lock); 13
14 Implementing general semaphore using binary semaphores Binary semaphore entry,mutex =1; Binary semaphore delay=0; Int c ={non-negative integer}; wait(c)[ wait(entry); wait(mutex); c=c-1 If c<0 { signal(mutex); wait(delay); } else signal(mutex); signal(entry); ] signal(c)[ wait(mutex) c++; If c==0 {signal (delay);} signal(mutex) ] Why is entry semaphore needed? 14
15 The producer/consumer problem A producer process produces information that is consumed by a consumer process Ex1: a print program produces characters that are consumed by a printer Ex2: a compiler produces object modules from a series of steps pipelined gcc : cpp cc as ld We need a buffer to hold items that are produced and eventually consumed A common paradigm for cooperating processes 15
16 P/C: unbounded buffer We assume first an unbounded buffer consisting of a linear array of elements in points to the next item to be produced out points to the next item to be consumed 16
17 P/C: unbounded buffer We need a semaphore S to perform mutual exclusion on the buffer: only 1 process at a time can access the buffer We need another semaphore N to synchronize producer and consumer on the number N (= in - out) of items in the buffer an item can be consumed only after it has been created 17
18 P/C: unbounded buffer The producer is free to add an item into the buffer at any time: it performs wait(s) before appending and signal(s) afterwards to prevent customer access It also performs signal(n) after each append to increment N The consumer must first do wait(n) to see if there is an item to consume and use wait(s)/ signal(s) to access the buffer 18
19 Producer consumer problem int c; bin semaphore mutex=1; gen semaphore empty=0; int buf[]; int in, out=0; Producer Process do { read v; wait(mutex); produce(v); signal(mutex); signal (empty); } while (TRUE); produce(v){ b[in]=v; in++; } Consumer Process do { wait(empty); wait(mutex;) w=consume(); signal (mutex); } while (TRUE); consume(){ W=b[out]; out++; return w;} 19
20 P/C: unbounded buffer Remarks: Putting signal(empty) inside the CS of the producer (instead of outside) has no effect since the consumer must always wait for both semaphores before proceeding The consumer must perform wait(empty) before wait(mutex), otherwise deadlock occurs if consumer enter CS while the buffer is empty Using semaphores is a difficult art... 20
21 P/C: finite circular buffer of size k can consume only when number N of (consumable) items is at least 1 (now: N!=in-out) can produce only when number E of empty spaces is at least 1 21
22 P/C: finite circular buffer of size k As before: we need a semaphore S to have mutual exclusion on buffer access we need a semaphore N to synchronize producer and consumer on the number of consumable items In addition: we need a semaphore E to synchronize producer and consumer on the number of empty spaces 22
23 Producer consumer problem int const k= 50; bin semaphore mutex=1; gen semaphore empty=0; gen semaphore full=k; int buf[k]; int in, out=0; Producer Process do { wait(full); read v; wait(mutex); produce(v); signal(mutex); signal (empty); } while (TRUE); produce(v){ b[in]=v; in= (in+1) mod k; } Consumer Process do { wait(empty); wait(mutex;) w=consume(); signal (mutex); signal(full); } while (TRUE); consume(){ W=b[out]; out=(out +1) mod k; return w;} 23
24 Readers and writers problem Many readers and many writer processes Constraint: many readers can be in the CS (no other writer) Only 1 writer in the CS (no other reader or writer) 24
25 Readers writers problem semaphore wrt, mutex=1; int No_Of_readers = 0; Writer Process wait(wrt); Write signal (wrt); Reader Process wait(mutex); Entry condition. signal (mutex); Read wait(mutex); Exit condition. signal(mutex); 25
26 The Dining Philosophers Problem 5 philosophers who only eat and think each need to use 2 forks for eating we have only 5 forks A classical synchron. problem Illustrates the difficulty of allocating resources among process without deadlock and starvation 26
27 The Dining Philosophers Problem Each philosopher is a process One semaphore per fork: fork: array[0..4] of semaphores Initialization: fork[i].count:=1 for i:=0..4 A first attempt: Deadlock if each philosopher start by picking his left fork! Process Pi: repeat think; wait(fork[i]); wait(fork[i+1 mod 5]); eat; signal(fork[i+1 mod 5]); signal(fork[i]); forever 27
28 The Dining Philosophers Problem A solution: admit only 4 philosophers at a time that tries to eat Then 1 philosopher can always eat when the other 3 are holding 1 fork Hence, we can use another semaphore T that would limit at 4 the numb. of philosophers sitting at the table Initialize: T.count:=4 Process Pi: repeat think; wait(t); wait(fork[i]); wait(fork[i+1 mod 5]); eat; signal(fork[i+1 mod 5]); signal(fork[i]); signal(t); forever 28
29 Problems with semaphores semaphores provide a powerful tool for enforcing mutual exclusion and coordinate processes But wait(s) and signal(s) are scattered among several processes. Hence, difficult to understand their effects Usage must be correct in all the processes One bad (or malicious) process can fail the entire collection of processes 29
30 Monitors Are high-level language constructs that provide equivalent functionality to that of semaphores but are easier to control Found in many concurrent programming languages Concurrent Pascal, Modula-3, C++, Java... Can be implemented by semaphores... 30
31 Monitor Is a software module containing: one or more procedures an initialization sequence local data variables Characteristics: local variables accessible only by monitor s procedures a process enters the monitor by invoking one of it s procedures only one process can be in the monitor at any one time 31
32 Monitor The monitor ensures mutual exclusion: no need to program this constraint explicitly Hence, shared data are protected by placing them in the monitor The monitor locks the shared data on process entry Process synchronization is done by the programmer by using condition variables that represent conditions a process may need to wait for before executing in the monitor 32
33 Schematic view of a Monitor
34 Condition Variables condition x, y; Two operations are allowed on a condition variable: x.wait() a process that invokes the operation is suspended until x.signal() x.signal() resumes one of processes (if any) that invoked x.wait() If no x.wait() on the variable, then it has no effect on the variable
35 Monitor with Condition Variables Condition Variable: a queue of threads waiting for something inside a critical section Key idea: make it possible to go to sleep inside critical section by atomically releasing lock prior to block Contrast to semaphores: Can t wait inside critical section
36 Producer/Consumer problem Two types of processes: producers consumers Synchronization is now confined within the monitor append(.) and take(.) are procedures within the monitor: are the only means by which P/C can access the buffer If these procedures are correct, synchronization will be correct for all participating processes ProducerI: repeat produce v; Append(v); forever ConsumerI: repeat Take(v); consume v; forever 36
37 Monitor for the bounded P/C problem Monitor needs to hold the buffer: buffer: array[0..k-1] of items; needs two condition variables: notfull: csignal(notfull) indicates that the buffer is not full notempty: csignal(notempty) indicates that the buffer is not empty needs buffer pointers and counts: nextin: points to next item to be appended nextout: points to next item to be taken count: holds the number of items in buffer 37
38 Monitor for the bounded P/C problem Monitor boundedbuffer: const k 50; buffer: array[k] of items; nextin:=0, nextout:=0, count:=0: integer; notfull, notempty: condition; Append(v): if (count==k) cwait(notfull); buffer[nextin]= v; nextin:= nextin+1 mod k; count++; csignal(notempty); Take(v): if (count==0) cwait(notempty); v:= buffer[nextout]; nextout= nextout+1 mod k; count--; csignal(notfull); 38
39 Condition Variables Choices If process P invokes x.signal(), and process Q is suspended in x.wait(), what should happen next? Both Q and P cannot execute in parallel. If Q is resumed, then P must wait Options include Signal and wait P waits until Q either leaves the monitor or it waits for another condition Signal and continue Q waits until P either leaves the monitor or it waits for another condition Both have pros and cons language implementer can decide Monitors implemented in Concurrent Pascal compromise P executing signal immediately leaves the monitor, Q is resumed Implemented in other languages including Mesa, C#, Java
40 Review: Mesa vs. Hoare Monitors Need to be careful about precise definition of signal and wait. Consider a piece of our producer code: We did this. What assumptions we had to make? if (count==k) { cwait(notfull); // If full, sleep } buffer[nextin]=v; // Get next item sometimes we may need to do this while (count==k) { cwait(notfull); // If full, sleep } buffer[nextin]=v; // Get next item Answer: depends on the type of scheduling Hoare-style (most textbooks): Signaler gives up lock, CPU to waiter; waiter runs immediately Waiter gives up lock, processor back to signaler when it exits critical section or if it waits again Mesa-style (most real operating systems): Signaler keeps lock and processor Waiter placed on ready queue with no special priority Practically, need to check condition again after wait
41 Pthread condition variables pthread_condition_t xc; pthread_mutex_t lock; Pthread_cond_wait(xc,lock); Pthread_cond_signal(xc); Pthread_mutex_t Pthread_cond_t cv_mutex; waitfor_dad_cv; Dad() {. pthread_cond_signal(&waitfor_dad_cv) } Child() { pthread_cond_wait(&cv_mutex,&waitfor_dad_cv) }; 41
Semaphores. Semaphores. Semaphore s operations. Semaphores: observations
Semaphores Synchronization tool (provided by the OS) that do not require busy waiting A semaphore S is an integer variable that, apart from initialization, can only be accessed through 2 atomic and mutually
More informationClassic Problems of Synchronization
Classic Problems of Synchronization Bounded-Buffer Problem s-s Problem Dining Philosophers Problem Monitors 2/21/12 CSE325 - Synchronization 1 s-s Problem s s 2/21/12 CSE325 - Synchronization 2 Problem
More informationLecture Topics. Announcements. Today: Concurrency (Stallings, chapter , 5.7) Next: Exam #1. Self-Study Exercise #5. Project #3 (due 9/28)
Lecture Topics Today: Concurrency (Stallings, chapter 5.1-5.4, 5.7) Next: Exam #1 1 Announcements Self-Study Exercise #5 Project #3 (due 9/28) Project #4 (due 10/12) 2 Exam #1 Tuesday, 10/3 during lecture
More informationLesson 6: Process Synchronization
Lesson 6: Process Synchronization Chapter 5: Process Synchronization Background The Critical-Section Problem Peterson s Solution Synchronization Hardware Mutex Locks Semaphores Classic Problems of Synchronization
More informationLecture 6. Process Synchronization
Lecture 6 Process Synchronization 1 Lecture Contents 1. Principles of Concurrency 2. Hardware Support 3. Semaphores 4. Monitors 5. Readers/Writers Problem 2 1. Principles of Concurrency OS design issue
More informationProcess Synchronization
Process Synchronization Part II, Modified by M.Rebaudengo - 2013 Silberschatz, Galvin and Gagne 2009 Classical Problems of Synchronization Consumer/Producer with Bounded-Buffer Problem s and s Problem
More informationChapter 5: Process Synchronization. Operating System Concepts Essentials 2 nd Edition
Chapter 5: Process Synchronization Silberschatz, Galvin and Gagne 2013 Chapter 5: Process Synchronization Background The Critical-Section Problem Peterson s Solution Synchronization Hardware Mutex Locks
More informationProcess Synchronization
Process Synchronization Mandar Mitra Indian Statistical Institute M. Mitra (ISI) Process Synchronization 1 / 28 Cooperating processes Reference: Section 4.4. Cooperating process: shares data with other
More informationConcurrency. Chapter 5
Concurrency 1 Chapter 5 2 Concurrency Is a fundamental concept in operating system design Processes execute interleaved in time on a single processor Creates the illusion of simultaneous execution Benefits
More informationCS370 Operating Systems
CS370 Operating Systems Colorado State University Yashwant K Malaiya Fall 2017 Lecture 12 Slides based on Text by Silberschatz, Galvin, Gagne Various sources 1 1 FAQ 2 Mutex vs Semaphore Mutex is binary,
More informationLearning Outcomes. Concurrency and Synchronisation. Textbook. Concurrency Example. Inter- Thread and Process Communication. Sections & 2.
Learning Outcomes Concurrency and Synchronisation Understand concurrency is an issue in operating systems and multithreaded applications Know the concept of a critical region. Understand how mutual exclusion
More informationProcess Coordination
Process Coordination Why is it needed? Processes may need to share data More than one process reading/writing the same data (a shared file, a database record, ) Output of one process being used by another
More informationSynchronization. CS 475, Spring 2018 Concurrent & Distributed Systems
Synchronization CS 475, Spring 2018 Concurrent & Distributed Systems Review: Threads: Memory View code heap data files code heap data files stack stack stack stack m1 m1 a1 b1 m2 m2 a2 b2 m3 m3 a3 m4 m4
More informationConcurrency and Synchronisation
Concurrency and Synchronisation 1 Learning Outcomes Understand concurrency is an issue in operating systems and multithreaded applications Know the concept of a critical region. Understand how mutual exclusion
More informationCHAPTER 6: PROCESS SYNCHRONIZATION
CHAPTER 6: PROCESS SYNCHRONIZATION The slides do not contain all the information and cannot be treated as a study material for Operating System. Please refer the text book for exams. TOPICS Background
More informationChapter 6: Process Synchronization
Chapter 6: Process Synchronization Objectives Introduce Concept of Critical-Section Problem Hardware and Software Solutions of Critical-Section Problem Concept of Atomic Transaction Operating Systems CS
More informationInterprocess Communication By: Kaushik Vaghani
Interprocess Communication By: Kaushik Vaghani Background Race Condition: A situation where several processes access and manipulate the same data concurrently and the outcome of execution depends on the
More informationChapter 6: Process Synchronization
Chapter 6: Process Synchronization Chapter 6: Synchronization 6.1 Background 6.2 The Critical-Section Problem 6.3 Peterson s Solution 6.4 Synchronization Hardware 6.5 Mutex Locks 6.6 Semaphores 6.7 Classic
More informationSemaphores. Jinkyu Jeong Computer Systems Laboratory Sungkyunkwan University
Semaphores Jinkyu Jeong (jinkyu@skku.edu) Computer Systems Laboratory Sungkyunkwan University http://csl.skku.edu EEE3052: Introduction to Operating Systems, Fall 2017, Jinkyu Jeong (jinkyu@skku.edu) Synchronization
More informationChapter 6: Process Synchronization
Chapter 6: Process Synchronization Chapter 6: Process Synchronization Background The Critical-Section Problem Peterson s Solution Synchronization Hardware Mutex Locks Semaphores Classic Problems of Synchronization
More informationConcurrency and Synchronisation
Concurrency and Synchronisation 1 Sections 2.3 & 2.4 Textbook 2 Making Single-Threaded Code Multithreaded Conflicts between threads over the use of a global variable 3 Inter- Thread and Process Communication
More informationChapter 6: Synchronization. Chapter 6: Synchronization. 6.1 Background. Part Three - Process Coordination. Consumer. Producer. 6.
Part Three - Process Coordination Chapter 6: Synchronization 6.1 Background Concurrent access to shared data may result in data inconsistency Maintaining data consistency requires mechanisms to ensure
More informationChapter 7: Process Synchronization. Background. Illustration
Chapter 7: Process Synchronization Background The Critical-Section Problem Synchronization Hardware Semaphores Classical Problems of Synchronization Critical Regions Monitors Synchronization in Solaris
More informationChapter 5: Process Synchronization
Chapter 5: Process Synchronization Silberschatz, Galvin and Gagne 2013 Operating System Concepts 9th Edition Chapter 5: Process Synchronization Background The Critical-Section Problem Peterson s Solution
More informationChapter 5: Process Synchronization. Operating System Concepts 9 th Edition
Chapter 5: Process Synchronization Silberschatz, Galvin and Gagne 2013 Chapter 5: Process Synchronization Background The Critical-Section Problem Peterson s Solution Synchronization Hardware Mutex Locks
More informationProcess Synchronization: Semaphores. CSSE 332 Operating Systems Rose-Hulman Institute of Technology
Process Synchronization: Semaphores CSSE 332 Operating Systems Rose-Hulman Institute of Technology Critical-section problem solution 1. Mutual Exclusion - If process Pi is executing in its critical section,
More informationProcess Synchronization
Chapter 7 Process Synchronization 1 Chapter s Content Background The Critical-Section Problem Synchronization Hardware Semaphores Classical Problems of Synchronization Critical Regions Monitors 2 Background
More informationChapter 7: Process Synchronization. Background
Chapter 7: Process Synchronization Background The Critical-Section Problem Synchronization Hardware Semaphores Classical Problems of Synchronization Critical Regions Monitors Synchronization in Solaris
More informationProcess Synchronization(2)
EECS 3221.3 Operating System Fundamentals No.6 Process Synchronization(2) Prof. Hui Jiang Dept of Electrical Engineering and Computer Science, York University Semaphores Problems with the software solutions.
More informationBackground. Module 6: Process Synchronization. Bounded-Buffer (Cont.) Bounded-Buffer. Background
Module 6: Process Synchronization Background Background The Critical-Section Problem Synchronization Hardware Semaphores Classical Problems of Synchronization Critical Regions Monitors Synchronization
More informationChapter 5: Process Synchronization. Operating System Concepts 9 th Edition
Chapter 5: Process Synchronization Silberschatz, Galvin and Gagne 2013 Chapter 5: Process Synchronization Background The Critical-Section Problem Peterson s Solution Synchronization Hardware Mutex Locks
More informationProcess Synchronization(2)
CSE 3221.3 Operating System Fundamentals No.6 Process Synchronization(2) Prof. Hui Jiang Dept of Computer Science and Engineering York University Semaphores Problems with the software solutions. Not easy
More informationCOP 4225 Advanced Unix Programming. Synchronization. Chi Zhang
COP 4225 Advanced Unix Programming Synchronization Chi Zhang czhang@cs.fiu.edu 1 Cooperating Processes Independent process cannot affect or be affected by the execution of another process. Cooperating
More informationProcess Management And Synchronization
Process Management And Synchronization In a single processor multiprogramming system the processor switches between the various jobs until to finish the execution of all jobs. These jobs will share the
More informationSynchronization Classic Problems
CS 4410 Operating Systems Synchronization Classic Problems Summer 2013 Cornell University 1 Today What practical problems can we solve with semaphores? Bounded-Buffer Problem Producer-Consumer Problem
More informationProcesses. Rafael Ramirez Dep Tecnologia Universitat Pompeu Fabra
Processes Rafael Ramirez Dep Tecnologia Universitat Pompeu Fabra Processes Process Concept Process Scheduling Operation on Processes Cooperating Processes Interprocess Communication Process Concept Early
More informationHigh-level Synchronization
Recap of Last Class High-level Synchronization CS 256/456 Dept. of Computer Science, University of Rochester Concurrent access to shared data may result in data inconsistency race condition. The Critical-Section
More informationProcess Synchronization(2)
EECS 3221.3 Operating System Fundamentals No.6 Process Synchronization(2) Prof. Hui Jiang Dept of Electrical Engineering and Computer Science, York University Semaphores Problems with the software solutions.
More informationOperating Systems. Operating Systems Summer 2017 Sina Meraji U of T
Operating Systems Operating Systems Summer 2017 Sina Meraji U of T More Special Instructions Swap (or Exchange) instruction Operates on two words atomically Can also be used to solve critical section problem
More informationChapter 7: Process Synchronization!
Chapter 7: Process Synchronization Background The Critical-Section Problem Synchronization Hardware Semaphores Classical Problems of Synchronization Monitors 7.1 Background Concurrent access to shared
More informationChapter 5: Process Synchronization
Chapter 5: Process Synchronization Silberschatz, Galvin and Gagne 2013 Chapter 5: Process Synchronization Background The Critical-Section Problem Peterson s Solution Synchronization Hardware Mutex Locks
More informationCSE 4/521 Introduction to Operating Systems
CSE 4/521 Introduction to Operating Systems Lecture 7 Process Synchronization II (Classic Problems of Synchronization, Synchronization Examples) Summer 2018 Overview Objective: 1. To examine several classical
More informationConcurrency(I) Chapter 5
Chapter 5 Concurrency(I) The central themes of OS are all concerned with the management of processes and threads: such as multiprogramming, multiprocessing, and distributed processing. The concept of concurrency
More informationSynchronization Principles
Synchronization Principles Gordon College Stephen Brinton The Problem with Concurrency Concurrent access to shared data may result in data inconsistency Maintaining data consistency requires mechanisms
More informationProcess Synchronization
Process Synchronization Daniel Mosse (Slides are from Silberschatz, Galvin and Gagne 2013 and Sherif Khattab) Chapter 5: Process Synchronization Background The Critical-Section Problem Peterson s Solution
More informationChapter 6: Process Synchronization. Operating System Concepts 9 th Edit9on
Chapter 6: Process Synchronization Operating System Concepts 9 th Edit9on Silberschatz, Galvin and Gagne 2013 Objectives To present the concept of process synchronization. To introduce the critical-section
More informationCS 537 Lecture 8 Monitors. Thread Join with Semaphores. Dining Philosophers. Parent thread. Child thread. Michael Swift
CS 537 Lecture 8 Monitors Michael Swift Two Classes of Synchronization Problems Uniform resource usage with simple scheduling constraints No other variables needed to express relationships Use one semaphore
More informationProf. Hui Jiang Dept of Computer Science and Engineering York University
0./ ' )-, ' ' # # 2 H; 2 7 E 7 2 $&% ( Prof. Hui Jiang ept of omputer Science and Engineering York University )+* Problems with the software solutions. Not easy to generalize to more complex synchronization
More informationAnnouncement. Due data of HW#4 is on Sunday. Due data of Exercise # 5 is on Friday. Two more office hours on this weekend for HW#4.
Announcement Due data of HW#4 is on Sunday. Due data of Exercise # 5 is on Friday. Two more office hours on this weekend for HW#4. Saturday 3-4 pm Sunday 6-7 pm Operating Systems: Internals and Design
More informationProcess Synchronization
TDDI04 Concurrent Programming, Operating Systems, and Real-time Operating Systems Process Synchronization [SGG7] Chapter 6 Copyright Notice: The lecture notes are mainly based on Silberschatz s, Galvin
More informationProcess Synchronization
Process Synchronization Concurrent access to shared data in the data section of a multi-thread process, in the shared memory of multiple processes, or in a shared file Although every example in this chapter
More informationProcess Synchronization. CISC3595, Spring 2015 Dr. Zhang
Process Synchronization CISC3595, Spring 2015 Dr. Zhang 1 Concurrency OS supports multi-programming In single-processor system, processes are interleaved in time In multiple-process system, processes execution
More informationOperating Systems. Designed and Presented by Dr. Ayman Elshenawy Elsefy
Operating Systems Designed and Presented by Dr. Ayman Elshenawy Elsefy Dept. of Systems & Computer Eng.. AL-AZHAR University Website : eaymanelshenawy.wordpress.com Email : eaymanelshenawy@yahoo.com Reference
More informationCS370 Operating Systems
CS370 Operating Systems Colorado State University Yashwant K Malaiya Spring 1018 L11 Synchronization Slides based on Text by Silberschatz, Galvin, Gagne Various sources 1 1 FAQ Multilevel feedback queue:
More informationSynchronization. Peter J. Denning CS471/CS571. Copyright 2001, by Peter Denning
Synchronization Peter J. Denning CS471/CS571 Copyright 2001, by Peter Denning What is synchronization? Requirement that one process stop to wait to pass a point until another process sends a signal. The
More information1. Motivation (Race Condition)
COSC4740-01 Operating Systems Design, Fall 2004, Byunggu Yu Chapter 6 Process Synchronization (textbook chapter 7) Concurrent access to shared data in the data section of a multi-thread process, in the
More information1 Process Coordination
COMP 730 (242) Class Notes Section 5: Process Coordination 1 Process Coordination Process coordination consists of synchronization and mutual exclusion, which were discussed earlier. We will now study
More informationModule 6: Process Synchronization
Module 6: Process Synchronization Background The Critical-Section Problem Synchronization Hardware Semaphores Classical Problems of Synchronization Critical Regions Monitors Synchronization in Solaris
More informationChapter 6: Synchronization. Operating System Concepts 8 th Edition,
Chapter 6: Synchronization, Silberschatz, Galvin and Gagne 2009 Outline Background The Critical-Section Problem Peterson s Solution Synchronization Hardware Semaphores Classic Problems of Synchronization
More informationIntroduction to Operating Systems
Introduction to Operating Systems Lecture 4: Process Synchronization MING GAO SE@ecnu (for course related communications) mgao@sei.ecnu.edu.cn Mar. 18, 2015 Outline 1 The synchronization problem 2 A roadmap
More informationLecture 6 (cont.): Semaphores and Monitors
Project 1 Due Thursday 10/20 Lecture 6 (cont.): Semaphores and Monitors CSE 120: Principles of Operating Systems Alex C. Snoeren Higher-Level Synchronization We looked at using locks to provide mutual
More informationChapter 6: Process Synchronization. Operating System Concepts 8 th Edition,
Chapter 6: Process Synchronization, Silberschatz, Galvin and Gagne 2009 Module 6: Process Synchronization Background The Critical-Section Problem Peterson s Solution Synchronization Hardware Semaphores
More informationConcept of a process
Concept of a process In the context of this course a process is a program whose execution is in progress States of a process: running, ready, blocked Submit Ready Running Completion Blocked Concurrent
More informationEI 338: Computer Systems Engineering (Operating Systems & Computer Architecture)
EI 338: Computer Systems Engineering (Operating Systems & Computer Architecture) Dept. of Computer Science & Engineering Chentao Wu wuct@cs.sjtu.edu.cn Download lectures ftp://public.sjtu.edu.cn User:
More informationCS 162 Operating Systems and Systems Programming Professor: Anthony D. Joseph Spring Lecture 8: Semaphores, Monitors, & Condition Variables
CS 162 Operating Systems and Systems Programming Professor: Anthony D. Joseph Spring 2004 Lecture 8: Semaphores, Monitors, & Condition Variables 8.0 Main Points: Definition of semaphores Example of use
More informationChapter 5: Process Synchronization
Chapter 5: Process Synchronization Silberschatz, Galvin and Gagne 2013! Chapter 5: Process Synchronization Background" The Critical-Section Problem" Petersons Solution" Synchronization Hardware" Mutex
More informationSemaphore. Originally called P() and V() wait (S) { while S <= 0 ; // no-op S--; } signal (S) { S++; }
Semaphore Semaphore S integer variable Two standard operations modify S: wait() and signal() Originally called P() and V() Can only be accessed via two indivisible (atomic) operations wait (S) { while
More informationSynchronization. CSE 2431: Introduction to Operating Systems Reading: Chapter 5, [OSC] (except Section 5.10)
Synchronization CSE 2431: Introduction to Operating Systems Reading: Chapter 5, [OSC] (except Section 5.10) 1 Outline Critical region and mutual exclusion Mutual exclusion using busy waiting Sleep and
More informationMultitasking / Multithreading system Supports multiple tasks
Tasks and Intertask Communication Introduction Multitasking / Multithreading system Supports multiple tasks As we ve noted Important job in multitasking system Exchanging data between tasks Synchronizing
More informationChapter 5 Concurrency: Mutual Exclusion. and. Synchronization. Operating Systems: Internals. and. Design Principles
Operating Systems: Internals and Design Principles Chapter 5 Concurrency: Mutual Exclusion and Synchronization Seventh Edition By William Stallings Designing correct routines for controlling concurrent
More informationCSE 120. Fall Lecture 6: Semaphores. Keith Marzullo
CSE 120 Principles of Operating Systems Fall 2007 Lecture 6: Semaphores Keith Marzullo Announcements Homework #2 out Homework #1 almost graded... Discussion session on Wednesday will entertain questions
More informationProcess Synchronization
Process Synchronization Chapter 6 2015 Prof. Amr El-Kadi Background Concurrent access to shared data may result in data inconsistency Maintaining data consistency requires mechanisms to ensure the orderly
More informationSynchronization Basic Problem:
Synchronization Synchronization Basic Problem: If two concurrent processes are accessing a shared variable, and that variable is read, modified, and written by those processes, then the variable must be
More informationProcess Synchronization
CS307 Process Synchronization Fan Wu Department of Computer Science and Engineering Shanghai Jiao Tong University Spring 2018 Background Concurrent access to shared data may result in data inconsistency
More informationChapter 5 Concurrency: Mutual Exclusion and Synchronization
Operating Systems: Internals and Design Principles Chapter 5 Concurrency: Mutual Exclusion and Synchronization Seventh Edition By William Stallings Designing correct routines for controlling concurrent
More informationIntroduction to OS Synchronization MOS 2.3
Introduction to OS Synchronization MOS 2.3 Mahmoud El-Gayyar elgayyar@ci.suez.edu.eg Mahmoud El-Gayyar / Introduction to OS 1 Challenge How can we help processes synchronize with each other? E.g., how
More informationProcess Co-ordination OPERATING SYSTEMS
OPERATING SYSTEMS Prescribed Text Book Operating System Principles, Seventh Edition By Abraham Silberschatz, Peter Baer Galvin and Greg Gagne 1 PROCESS - CONCEPT Processes executing concurrently in the
More informationConcurrency: Deadlock and Starvation. Chapter 6
Concurrency: Deadlock and Starvation Chapter 6 Deadlock Permanent blocking of a set of processes that either compete for system resources or communicate with each other Involve conflicting needs for resources
More informationSemaphores (by Dijkstra)
CSCI 4401 Principles of Operating Systems I Process Synchronization II: Classic Problems Vassil Roussev vassil@cs.uno.edu Semaphores (by Dijkstra) A higher-level way of doing synchronization between threads/processes
More informationMore Synchronization; Concurrency in Java. CS 475, Spring 2018 Concurrent & Distributed Systems
More Synchronization; Concurrency in Java CS 475, Spring 2018 Concurrent & Distributed Systems Review: Semaphores Synchronization tool that provides more sophisticated ways (than Mutex locks) for process
More informationCS3502 OPERATING SYSTEMS
CS3502 OPERATING SYSTEMS Spring 2018 Synchronization Chapter 6 Synchronization The coordination of the activities of the processes Processes interfere with each other Processes compete for resources Processes
More informationSynchronization. Race Condition. The Critical-Section Problem Solution. The Synchronization Problem. Typical Process P i. Peterson s Solution
Race Condition Synchronization CSCI 315 Operating Systems Design Department of Computer Science A race occurs when the correctness of a program depends on one thread reaching point x in its control flow
More informationCS370 Operating Systems
CS370 Operating Systems Colorado State University Yashwant K Malaiya Fall 2017 Lecture 11 Slides based on Text by Silberschatz, Galvin, Gagne Various sources 1 1 FAQ Multilevel Feedback Queue: Q0, Q1,
More informationDealing with Issues for Interprocess Communication
Dealing with Issues for Interprocess Communication Ref Section 2.3 Tanenbaum 7.1 Overview Processes frequently need to communicate with other processes. In a shell pipe the o/p of one process is passed
More informationProcess Synchronization
CSC 4103 - Operating Systems Spring 2007 Lecture - VI Process Synchronization Tevfik Koşar Louisiana State University February 6 th, 2007 1 Roadmap Process Synchronization The Critical-Section Problem
More informationCS510 Operating System Foundations. Jonathan Walpole
CS510 Operating System Foundations Jonathan Walpole Monitors 2 Programming Complexity There are many ways to introduce bugs using locks and semaphores - forget to lock somewhere in the program - forget
More informationCSE Traditional Operating Systems deal with typical system software designed to be:
CSE 6431 Traditional Operating Systems deal with typical system software designed to be: general purpose running on single processor machines Advanced Operating Systems are designed for either a special
More informationOperating Systems ECE344
Operating Systems ECE344 Ding Yuan Announcement & Reminder Lab 0 mark posted on Piazza Great job! One problem: compilation error I fixed some for you this time, but won t do it next time Make sure you
More informationOS Process Synchronization!
OS Process Synchronization! Race Conditions! The Critical Section Problem! Synchronization Hardware! Semaphores! Classical Problems of Synchronization! Synchronization HW Assignment! 3.1! Concurrent Access
More informationChapter 5: Process Synchronization. Operating System Concepts 9 th Edition
Chapter 5: Process Synchronization Silberschatz, Galvin and Gagne 2013 Chapter 5: Process Synchronization Background The Critical-Section Problem Peterson s Solution Synchronization Hardware Mutex Locks
More informationConcurrency and Synchronisation. Leonid Ryzhyk
Concurrency and Synchronisation Leonid Ryzhyk Textbook Sections 2.3 & 2.5 2 Concurrency in operating systems Inter-process communication web server SQL request DB Intra-process communication worker thread
More informationReminder from last time
Concurrent systems Lecture 3: CCR, monitors, and concurrency in practice DrRobert N. M. Watson 1 Reminder from last time Implementing mutual exclusion: hardware support for atomicity and inter-processor
More informationCS3733: Operating Systems
Outline CS3733: Operating Systems Topics: Synchronization, Critical Sections and Semaphores (SGG Chapter 6) Instructor: Dr. Tongping Liu 1 Memory Model of Multithreaded Programs Synchronization for coordinated
More informationOpera&ng Systems ECE344
Opera&ng Systems ECE344 Lecture 6: Synchroniza&on (II) Semaphores and Monitors Ding Yuan Higher- Level Synchroniza&on We looked at using locks to provide mutual exclusion Locks work, but they have some
More informationCS420: Operating Systems. Process Synchronization
Process Synchronization James Moscola Department of Engineering & Computer Science York College of Pennsylvania Based on Operating System Concepts, 9th Edition by Silberschatz, Galvin, Gagne Background
More informationCS370 Operating Systems
CS370 Operating Systems Colorado State University Yashwant K Malaiya Spring 1019 L12 Synchronization Slides based on Text by Silberschatz, Galvin, Gagne Various sources 1 1 FAQ Critical section: shared
More informationChapter 2 Processes and Threads. Interprocess Communication Race Conditions
Chapter 2 Processes and Threads [ ] 2.3 Interprocess communication 2.4 Classical IPC problems 2.5 Scheduling 85 Interprocess Communication Race Conditions Two processes want to access shared memory at
More informationParalleland Distributed Programming. Concurrency
Paralleland Distributed Programming Concurrency Concurrency problems race condition synchronization hardware (eg matrix PCs) software (barrier, critical section, atomic operations) mutual exclusion critical
More informationChapter 6 Process Synchronization
Chapter 6 Process Synchronization Cooperating Process process that can affect or be affected by other processes directly share a logical address space (threads) be allowed to share data via files or messages
More informationThreads. Concurrency. What it is. Lecture Notes Week 2. Figure 1: Multi-Threading. Figure 2: Multi-Threading
Threads Figure 1: Multi-Threading Figure 2: Multi-Threading Concurrency What it is 1. Two or more threads of control access a shared resource. Scheduler operation must be taken into account fetch-decode-execute-check
More information