Questions tagged [synchronization]

Questions about techniques for enforcing an agreed order of events between several concurrently executing threads. Specific synchronization mechanisms include mutexes (locks), condition variables, semaphores and monitors.

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143 views

How to use Parallel Semaphores for Dining Philosophers Problem

I am in an intro to OS class and we are learning about mutual exclusion and semaphores. One classical problem we learned about was the dining philosophers problem. My professor touched on the ...
1 vote
1 answer
80 views

Tigers and elephants can't drink water from a pond simultaneously, while more than one tiger or more than one elephants can drink water simultaneously

Below is a question on synchronization mechanism which was asked in an interview in Indian Statistical Institute, M.Tech CS. I got hold of it from here. There is a forest where there are tigers and ...
3 votes
1 answer
852 views

Does starvation freedom imply progress?

The above answer taken from the book https://www.amazon.com/Operating-Systems-Sibsankar-Haldar/dp/8131730220 says starvation freedom may not imply progress as processes can be deadlocked. I think ...
0 votes
1 answer
28 views

Verification of atomic primitives using Petri Net Models

I want to verify semantics of a library of atomic primitives that I wrote. The idea is, only if the semantics of all the primitives are consistent with each other, an application that uses them could ...
6 votes
2 answers
7k views

Difference between Lamport timestamps and Vector clocks

Lamport timestamps and vector clocks sound like almost the same thing. Both are used to determine the order of events in a distributed system. What are their key differences?
1 vote
0 answers
48 views

Meaning of pulse driven sequential logic?

I am trying to understand the meaning of this scheme, providing a sort of classification of sequential logic circuits. This taken from https://www.electronics-tutorials.ws/sequential/seq_1.html Does ...
1 vote
1 answer
86 views

Does Dekkers solutions to critical section problem ensure progress?

I was reading concurrency control section from Operating Systems book by William Stallings. In this book, he gives three attempts by Dekker to give solution to critical section problem: Attempt 1 <...
0 votes
1 answer
209 views

Prove correctness of a solution to the critical section problem in general?

I was wondering if there is any formal, general way to prove the correctness of a candidate solution to the critical section problem in synchronization. For example, in the image enclosed, I have ...
0 votes
1 answer
68 views

What will you do if multiple users access your application at the same time?

I'm an experienced Software Engineer but very weak in concurrency because of no prior experience in that. I've been interviewing with several companies in which I was asked similar kinds of questions ...
0 votes
0 answers
18 views

Partition in a tree shaped distributed network

We are given a synchronic undirected tree shaped network, with $n$ indexed nodes. We know that there is at least one node with at least $\log_k n$ neighbors, $k>1000$, and $k$ is given. We need to ...
1 vote
1 answer
45 views

Synchronization in Distributed Systems

If there is no global clock in Distributed systems , then what is the solution for synchronization in DS ? Also , no global clock in DS is a direct consequence of the fact that the only communication ...
7 votes
2 answers
11k views

Understanding N process Peterson's algorithm

The intuitive informal description of two process Peterson's algorithm for process 0 can be given as follows: ...
0 votes
1 answer
29 views

How to reconcile the different definitions of asynchrony?

There are 3 definitions of asynchrony that I know of: In event-based programming, asynchrony refers to the execution of tasks in a non-sequential way, which may involve creating another thread. For ...
6 votes
2 answers
20k views

Minimum number of processes for the deadlock?

A system has 6 identical resources and $N$ processes competing for them. Each process can request at most two requests. Which one of the following values of $N$ could lead to a deadlock? 1 2 3 4 My ...
1 vote
0 answers
65 views

Starvation and Livelock

I think Option C is false. Following is my thought process: Starvation in general mean Process is waiting indefinitely for the resource or to get scheduled etc. [A/c to Galvin Book]. So, here in this ...
0 votes
0 answers
55 views

Simultaneous buffer access in the bounded buffer problem

Galvin and various other resources only allow either the producer or the consumer to access the buffer at a time, the common code is as follows: ...
7 votes
2 answers
2k views

Bounded waiting and starvation free in critical section problem

i have 4 question regarding relation between starvation and bounded waiting. 1.Does starvation-freedom imply deadlock-freedom? My Answer-: From here, definition of starvation free is Freedom ...
0 votes
2 answers
4k views

Peterson's vs. Bakery Algorithm

From my CS course, the Peterson's Algorithm and the Bakery Algorithm both are solutions which satisfy the 3 requirements of any solution to the critical section problem. a) What are their adv/disadv ...
-1 votes
1 answer
54 views

Operating system , synchronization

Consider the methods used by processes P1 and P2 for accessing their critical sections whenever needed, as given below. The initial values of shared boolean variables S1 and S2 are randomly assigned. ...
1 vote
0 answers
29 views

Race Condition in Mesa Monitor

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0 votes
1 answer
71 views

Process synchronization problem

The atomic fetch-and-set x,y instruction unconditionally sets the memory location x to 1 and fetches the old value of x in y without allowing any intervening access to the memory location x. Consider ...
1 vote
0 answers
58 views

Bakery algorithm: How does it work with single-writer safe registers?

I'm trying to understand the bakery algorithm and read that the Bakery algorithm uses single-writer safe registers. But I am not able to understand the correctness of bakery algorithm with safe ...
52 votes
3 answers
27k views

Contrasting Peterson’s and Dekker’s algorithms

I am trying to understand the algorithms by Peterson and Dekker which are very similar and display a lot of symmetries. I tried to formulate the algorithms in informal language like follows: ...
1 vote
2 answers
358 views

Does pre-emption of a process occur when that process is busy waiting?

I was reading about Peterson's Solution for Synchronisation. Let's assume the two shared variables to be int bool flag[2] and ...
6 votes
3 answers
453 views

Emulations of atomic registers and read-modify-write (RMW) primitives in message-passing systems

The ABD algorithm in paper: Sharing Memory Robustly in Message-Passing Systems can emulate single-writer multi-reader atomic registers in message-passing systems, in the presence of processor or link ...
0 votes
1 answer
130 views

Can timestamp be used in synchronization of processes having Race Condition?

I am wondering whether timestamp can be used to solve process synchronization problem, when race condition occurs? Below is an algorithm for entry as well as exit sections for every process who wants ...
1 vote
0 answers
132 views

How to prove that an algorithm has no deadlock

I need to mathematically prove that this algorithm is deadlock-free: ...
1 vote
0 answers
62 views

How to do atomic operations on systems that don't support it?

I need to sync data with WebDAV and other similar backend that do not have a concept of atomic operations. In some cases, I might need to read a file, change its content and write it back. And of ...
3 votes
1 answer
266 views

Is it possible to write a wait free leader election algorithm?

I want to understand if there exists an algorithm which is wait free and operates on non-shared memory, asynchronously. Finally I want to know how to derive the consensus number of this algorithm. ...
2 votes
0 answers
36 views

Does this state certify to be called as a deadlock?

I came across following problem: Barrier is a synchronization construct where a set of processes synchronizes globally i.e., each process in the set arrives at the barrier and waits for all others ...
11 votes
3 answers
4k views

Why are most mutex implementations unfair?

My understanding is that most popular implementations of a mutex (e.g. std::mutex in C++) do not guarantee fairness -- that is, they do not guarantee that in instances of contention, the lock will be ...
0 votes
4 answers
225 views

Compiler instructions to sync core caches: are they really needed?

I have read reviews of this book, and quote the following from one of the reviews (emphasis mine): Other than straining your eyes with old-styled C++, you can read such misconceptions in the book ...
0 votes
0 answers
37 views

Any good source explaining multiprocessor synchronization techniques and their implementation

I need to study how synchronization is done in a multiprocessor operating system, but I am unable to find a good source. I have read about it in the book "Modern Operating System" by Tanenbaum, but I ...
2 votes
1 answer
651 views

Why do OS and DBMS have their own synchronisation mechanisms, when OS can alone do it and it sits at the bottom of DB?

I know that synchronization is important in the OS, but why do we need a separate topic synchronization and concurrency in the DBMS? The OS concentrates on program synchronization while the DBMS ...
2 votes
2 answers
2k views

Increment and Decrement on binary semaphores when their values are $1$ and $0$ respectively?

What happens if we increment binary semaphore $x$ when it is equal to $1$. E.g A process executes $V(x)$ when $x==1$; What are the possible cases then- Process would be blocked till $x$ becomes $0$. ...
6 votes
6 answers
6k views

Does Deadlock imply Starvation

If there is a deadlock between the processes does that mean that there is starvation also? My Thinking: deadlock is no process using that resources , but starvation is like not giving chance to only ...
1 vote
1 answer
157 views

Can 2-philosophers problem be analogous to dining philosophers problem?

Two philosophers A and B, two forks numbered "1", "2"; A needs both "1" and "2" for eating, so does B. Is this theoretical a dining philosopher problem? I'm questioning about the forks philosopher A ...
0 votes
0 answers
144 views

How to design synchronisation algorithm to combine two automata?

I have two automata of states, transition and events (Etat, Transition, evenements) and I want to create a function that create the synchronized product between those two automata. For instance, given ...
1 vote
0 answers
113 views

Do we really need a mutex in this case?

Wikipedia's solution for multi Producer-Consumer problem uses both mutexes and semaphores. ...
4 votes
1 answer
865 views

Lamport logical clock: what does partial mean in the concept of `Partial ordering`?

In lamport's paper[1], he define two concept The partial ordering and The totally ordering. What does partial mean in ...
3 votes
1 answer
190 views

Lamport logical clock: why event occurs in a process with smaller pid is treated earlier?

In lamport's paper1, he define global local timestamp, which is composed of process id and local lamport timestamp. This timestamp is used to order all the events in a distributed system. The rule ...
4 votes
2 answers
482 views

Can we have a strictly monotonically increasing/decreasing sequence generated by a distributed system?

Just what the title says. Can we have a strictly monotonically increasing/decreasing sequence generated by a distributed system (without a single point of failure)? My current thoughts are that this ...
1 vote
0 answers
59 views

semaphore for two groups of processes

Can someone help me giving a pseudo code to this problem : There are two groups of processes , A and B. Maximum 3 Processes from group A or group B(only from one group) can use the given resource . ...
1 vote
0 answers
147 views

bakery algorithm, switching up the condition

I'm currently studying the Bakery Algorithm. I understand it for what it is but now I want to switch it up a bit. If we changed the < in the 2nd ...
3 votes
1 answer
89 views

FLP Impossiblity Result assumption of $C_1 = e'(C_0)$

FLP86's famous proof regarding impossibility of async distributed processes with a single fault assumes in the proof of the third lemma the existence of an event $e'$ such that the neighbor ...
5 votes
3 answers
2k views

Implementing wait-free consensus with queues

Using Herlihy's model and definition of the wait-free hierarchy, a queue (a shared object with enqueue and dequeue) has consensus number 2, because we can initialize the queue with some value, and the ...
4 votes
1 answer
509 views

Are Test and set primitives as powerful as semaphores?

I get confused because i don't know if it is possible to use Test and Set primitives in case where more then one process can be enter in critical section at the same time.
1 vote
0 answers
46 views

Does the following piece of code lead to a deadlock?

Process X ...
1 vote
0 answers
125 views

Is Dekker's algorithm not k-bounded for any finite k?

Consider this version of the algorithm, for only 2 processes, 0 and 1: ...
2 votes
1 answer
1k views

semaphore implementation with test and set

I'm trying to understand the algorithm for implementing semaphores on SMP system using test and set instruction described here: https://people.mpi-sws.org/~druschel/courses/os/lectures/proc4.pdf (and ...