Questions tagged [concurrency]
Questiont about issues of concurrency such as synchronization and deadlocks.
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Why is shared register's consensus number 1?
I'm trying to understand the consensus number concept. It is trivially clear that a shared register doesn't create any problem when there is only one thread using it. By why does its consensus number ...
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34 views
Concurrent Garbage-Collectiong/Compacting Memory Allocator
I'm developing an algorithm for concurrent heap garbage collection/compaction. It will be used in low latency systems that need to scale well to a lot of clients, e.g. web servers.
I thought about an ...
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1answer
20 views
What is the difference between a lock convoy and lock/thread contention?
From wikipedia on lock convoy:
A lock convoy occurs when multiple threads of equal priority contend repeatedly for the same lock. Unlike deadlock and livelock situations, the threads in a lock convoy ...
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21 views
Strategies for event-driven concurrency
Is there any good formal investigation or at least definition of different strategies of event-driven concurrent programming?
I've read that there exist readiness based (pull based) and completion ...
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1answer
34 views
Count number of ways in which atomic operation(s) of n different processes can be interleaved
PROBLEM: Count the number of ways in which atomic operation(s) of n different processes can be interleaved. A process may crash mid way before completion.
Suppose there are a total of n different ...
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1answer
75 views
Estimating P in Amdahl's Law theoretically and in practice
In parallel computing, Amdahl's law is mainly used to predict the theoretical maximum speedup for program processing using multiple processors. If we denote the speed up by S then Amdahl’s law is ...
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11 views
parallelized data structure
I'm searching a data structure that supports O(1) concurrent insertions (thread number is known in advance) and iteration over its elements (insertion order doesn't need to be preserved).
While one ...
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1answer
86 views
Difference between consensus number n and consensus number infinite
In book Concurrent Programming: Algorithms, Principles, and Foundations of Michel Raynal, in Section 16.5.1, Theorem 75 says
Compare&swap objects have infinite consensus number.
and in ...
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24 views
Unconditionally fair, weakly fair, and strongly fair scheduling
I am trying to understand the difference between weakly fair and strongly fair scheduling.
For example, what scheduling policy would ensure that a process delayed at its first await statement will ...
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29 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 ...
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58 views
Why is the Black-White Bakery Algorithm considered bounded?
As stated in Lamport's papers for the bakery algorithm he states that the ticket numbers are unbounded specifically
The range of values of number is unbounded.
and
Fortunately, practical ...
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1answer
42 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
<...
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2answers
120 views
Why the most dominant programming languages didn't follow CSP thread model?
I was trying to ask this question in StackOverflow, but later realized that this question is more relevant to general computer science, not specific engineering problems. If you think it's not, please ...
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2answers
98 views
Is this a deadlock?
Consider we have two processes P1 and P2. There are also two semaphores M and N which are initialized to zero. Here's how they execute:
...
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0answers
35 views
n thread consensus queues
Its generally agreed that wait free queues have a consensus number of 2.
But what about this following code for a consensus protocol for a queue.
How is it that this does not go against the idea above?...
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0answers
73 views
How to prove that an algorithm has no deadlock
I need to mathematically prove that this algorithm is deadlock-free:
...
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1answer
176 views
What is google docs solution to handling multiple users editing and reading at the same time?
I have always been curious as to how google solved the solution of real time collaboration in their google docs product where they allow multiple users to edit and read the same document in real time.
...
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1answer
26 views
Distributed algorithm can be executed in a single process
Looking at a "Distributed" algorithm from a textbook on distributed algorithms (e.g. Building a spanning tree, Broadcast/Convergecast.) I found that one can implement it using Golang's concurrency ...
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0answers
35 views
Concurrent Element-wise Reduction Algorithm (multi-threaded) (C++)
I'd like to implement a high-performance implementation of a multi-threaded reduction, element-wise, on x86 CPUs. Without loss of generality, assume the reduction operation is a sum of integers (so, ...
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23 views
Comparing wait-signal alternatives for synchronizing two piece of programs
I came across following problem:
A certain computation generates two arrays a and b such that ...
2
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1answer
68 views
Designing solution to critical section problem with two semaphores vs single semaphore
I came across following problem:
Let two processes P1 and P2 are there:
...
2
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0answers
24 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 ...
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3answers
1k views
Whats exact definition of 'atomicity' in programming?
the definition of 'atomicity' says that a transaction should be able to be terminated without being touched or manipulated by possibly concurrent running actions during its process. But does that also ...
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1answer
67 views
Are two CCS processes equivalent with respect to weak bisimilarity if and only if they satisfy exactly the same set of HML formulas?
I was skimming this recent paper and I was struck by the following statement:
two processes are equivalent with respect to weak bisimilarity if and only if they satisfy exactly the same set of HML ...
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1answer
170 views
Can a schedule be conflict serializable but not serializable?
A schedule is called conflict serializable if it can be transformed into a serial schedule by swapping non-conflicting operations. Then,
My question is: Can a schedule be conflict serializable but ...
4
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1answer
259 views
What is a counterexample for Lamport's distributed mutual exclusion algorithm with non-FIFO message queues?
Lamport's distributed mutual exclusion algorithm (also described here) solves mutual exclusion problem for $N$ processes with $3(N-1)$ messages per request ("take and release lock" cycle).
It ...
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0answers
47 views
Prove that set of operations form a commutative Monoid
this is my first post on this exchange.
I am looking for some help with defining a proof that a set of operations I have designed forms a commutative monoid.
(Disclaimer: I am not sure that I have ...
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2answers
45 views
System restarted before transaction is committed
Consider the following log sequence of two transactions on a bank account, with initial balance 12000, that transfer 2000 to a mortgage payment and then apply a 5% interest.
...
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1answer
101 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 ...
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0answers
77 views
How can I implement locking a range of values in a sorted sequence?
I am trying to write a general purpose locking algorithm which allows me to lock a range of contiguous values in a sorted array. To start with, these could be exclusive locks - so two concurrent locks ...
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1answer
1k views
Thoughts on definition for disadvantage of concurrent processing?
I'm a Computer Science student currently learning about concurrent processing. I found the benefits and disadvantages in my book vague, did some online research and put together a more detailed way of ...
2
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2answers
68 views
What is the formal statement of the dining philosopher's problem?
I've read about it in a few places and I'm not sure I get it.
Are the philosopher's allowed to act simultaneously?
Do they each take 1 action simultaneously, then go on to their next action?
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0answers
61 views
Do we really need a mutex in this case?
Wikipedia's solution for multi Producer-Consumer problem uses both mutexes and semaphores.
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1answer
566 views
Which Peterson’s Solution is right?
I have seen two different Peterson’s Solution to mutual exclusion, one is from Modern Operating Systems:
...
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152 views
how to find the depth of a concurrency bug
How to find the depth of a concurrency bug
The below program runs on two separate threads and shares the variable x. Variables t1 and t2 are local to their threads. The program has a concurrency bug ...
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1answer
37 views
Can Multiprocessor Systems Implement Both Temporal Multithreading and Simultaneous Multithreading?
I am aware that multiprocessor systems often implement simultaneous multithreading in order to allow multiple threads to run on different CPUs. I am also aware that uni-core systems often implement ...
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1answer
84 views
What is the Difference Between Many-to-Many (M:M) Threading and Hybrid (M:N) Threading?
I have been researching threading and come across several websites which all say contradicting statements about which and how many thread models exist. Some websites say there are only three: 1:1, M:1 ...
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1answer
197 views
What fraction of all combinations is guaranteed to be deadlock free?
I found this question in the exercise of Tanenbaum (operating systems):
Two processes, $A$ and $B$,each need three records $1, 2, \text{ and } 3$ in a database. If $A$ asks for them in the
order $...
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0answers
63 views
How to Optimise Each Multithreading Technique? (Cooperative/Preemptive/Simultaneous)
I am currently in the process of writing an IB Extended Essay on the efficacy of multithreading on increasing the performance of applications. So far, I have been able to deduce that there are three ...
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1answer
71 views
Checking claim in paper “A Read-Only Transaction Anomaly Under Snapshot Isolation” by Alan Fekete et al
In the 2004 paper "A Read-Only Transaction Anomaly Under Snapshot Isolation" by Alan Fekete et al. (which can be found here and here) the authors state:
We also note that any execution of T1 and T2 ...
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1answer
47 views
How to keep track of changes done to concurrent stacks?
I am writing a small RPN calculator that works on some stacks concurrently. For example, if I have two functions:
...
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1answer
23 views
Are process-safe mutexes shared between OSes?
I understand you can use process wide mutexes, but does this still apply if you have an additional virtualized operating system provisioned?
For example, take two OSes: ...
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2answers
1k views
Serializability and the Lost Update Problem
Serializability is the strongest consistency level with regard to the execution of two concurrent transactions T1 and T2. That is, if T1 and T2 independently change the application between consistent ...
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1answer
135 views
Erlang- Creating a function which only adds/subtracts positive integers
I want to create a function which allows me to input a list, and then add all of the positive numbers from the list together, leaving any that are negative.
([3,1,-1])
For example only 3 and 1 would ...
2
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1answer
79 views
What are good resources for self teaching parallel/concurrent/multithreaded programming techniques? [closed]
I’m having a hard time finding anything thorough. I have found some courses with titles like "parallel and concurrent programming in Java", but I'm looking to learn general techniques, not their use ...
4
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1answer
110 views
Task scheduling algorithm that limits concurrency
My prof introduced us an algorithm with semaphores that was used to solve the "dining philosophers" problem.
The algo is ok, apart from that it limits concurrency.
What does mean that it "limits ...
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1answer
157 views
Concurrency and fairness
I'm studying the concurrency in programming and the atomic instructions.
What i have not understood is the concept of "fairness" applied to this matter.
Can you give me an hint ?
