Concurrency is a property of systems in which several processes are executing at the same time.

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Composable concurrency in Java or any other programming language

While I was reading a research paper on concurrency named Software and the Concurrency Revolution (html version). I came across following lines: Unfortunately, although locks work, they pose ...
4
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2answers
75 views

How to handle a one-time startup SQL script

I'm trying to figure out the best way to tackle running a one-time SQL script when a service instance starts up. Here's the scenario: We run multiple Amazon instances of our service in parallel. ...
4
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2answers
86 views

Serializing mutating objects

In our system a media file can have several states: invalid, empty, uploading, ingesting, ready… Depending of the state, information about the media are accessed in different ways. For example, during ...
13
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2answers
268 views

Does Optimistic Concurrency per object imply Serializability if a transaction will never span multiple objects?

Given a system which provides: Optimistic concurrency control / versioning per object (using CAS - Check-and-Set) Transactions that never need to span more then a single object. Snapshot Isolation ...
2
votes
1answer
122 views

What are the advantages of Observables over an iterable of futures?

I recently came across the ReactiveX pattern for asynchronous data-flows. I studied the information provided there and also watched this talk by a Netflix engineer on how they used Observables to ...
15
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8answers
4k views

Why should I know concurrent programming?

Concurrent programming is quite difficult to me: even looking at a basic slide seems challenging to me. It seems so abstract. What are the benefits to knowing Concurrent programming concepts well? ...
16
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1answer
341 views

How does Rust diverge from the concurrency facilities of C++?

I am trying to decide whether Rust fundamentally, sufficiently improves upon the concurrency facilities of C++ that I should spend the time to learn Rust. In light of Stackexchange's format, I should ...
18
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3answers
19k views

UML Diagrams of Multi-Threaded Applications

For single-threaded applications I like to use class diagrams to get an overview of the architecture of that application. This type of diagram, however, hasn’t been very helpful when trying to ...
4
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0answers
67 views

possible to achieve Rust's ownership model with a generic C++ wrapper?

Looking through this article on Rust's concurrency safety: http://blog.rust-lang.org/2015/04/10/Fearless-Concurrency.html I was wondering how many of these ideas can be achieved in C++11 (or ...
2
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1answer
148 views

Event Sourcing + Updates to multiple aggregates

I'm trying to learn about event sourcing for potential application to a booking system I am building - I think I understand the core concepts, but I'm having trouble understanding how to handle cases ...
0
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1answer
90 views

Synchronisation with offline system

I'm designing a system from which I will synchronise business data from mobile device that have an embedded application that generates datas and send them back to the server. Each line synchronised ...
8
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3answers
6k views

Looking for a distributed locking pattern

I need to come up with a custom recursive object locking mechanism\pattern for a distributed system in C#. Essentially, I have a multi-node system. Each node has exclusive write permissions over ...
3
votes
1answer
59 views

Is there use case for implementing a callback if a future is returned?

If I have function which returns a future, is there any reason to also include a callback where the callback is simply called right before the future completes? The only advantage I can think of ...
0
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2answers
100 views

Lock threads or not lock threads?

I have an application (full-stack) that is used millions of times concurrently. Some vital application properties are managed on the client side (at the time it seemed to be the simplest approach to ...
2
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1answer
98 views

Should I use BackgroundWorker in Pipeline pattern?

I am planning the implementation of a Pipeline pattern as seen in this MSDN article. This is a WPF application for which I need to monitor progress of each stage of the pipeline in order to display it ...
2
votes
1answer
80 views

Possible DRY with Pausing Mechanism

Background I am currently working on the architecture for a future software design. The design is one long running task (hours-long) with thousands of sequential calls to various libraries. I ...
1
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4answers
321 views

What is the ninja performance gap, why is it so large, and how can we overcome it?

According to this abstract: The "Ninja gap" [...] is the performance gap between naively written C/C++ code that is parallelism unaware (often serial) and best-optimized code on modern ...
1
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2answers
103 views

Why are the Coffman conditions necessary for a deadlock to occur?

Quoting https://en.wikipedia.org/wiki/Deadlock#Necessary_conditions : A deadlock situation can arise if all of the following conditions hold simultaneously in a system: Mutual exclusion: ...
0
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1answer
63 views

Concurrent languages and non-concurrent dependencies [closed]

We had a bug caused by ruby workers (4 processes, 1 thread each) doing batching records using a legacy mongodb as the store. The race condition was around whether the batch was full or not; with one ...
3
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1answer
32 views

Asynchronous socket.io for lots of concurrent messages

We have a web application which currently operates like this on a typical view/page: the front has to display 100+ "previews" (in the form of base64 images) each of this preview is built on-demand ...
4
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2answers
279 views

Understanding the Single-Writer Principle

The article on the Single-Writer Principle of the Mechanical Sympathy blog explains how bad queues are (performance-wise), because they need to be able to receive messages from multiple produers, and ...
0
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1answer
50 views

Concurrent and atomic updates to multiple properties/variable of an object

I have a class with multiple setters and want to make atomic updates to multiple properties/variables. As far as I can see there are three methods that could work: Call all setters in synchronized ...
0
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0answers
60 views

How to prevent parallel calls to model?

While there is some command running which calls methods on some model, how to prevent concurrent calls for critical places in that model? If multiple requests comes in then they should maintain their ...
4
votes
4answers
173 views

How to prevent user from requesting API method multiple times in parallel?

Let's say we have an app where the users gain points and can exchange them for rewards. The exchange request, in pseudo-code, could look like this: function exchangePointsForReward(userId, rewardId){ ...
42
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6answers
14k views

Is object pooling a deprecated technique?

I am very familiar with the concept of object pooling and I always try to use it as much as possible. Additionally I always thought that object pooling is the standard norm as I have observed that ...
0
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1answer
492 views

akka and futures, which ExecutionContext should be used

Following this blog by @Tomasz Nurkiewicz we can see that 4 different approaches are available for picking the ExecutionContext, when interacting with akka actors, for scala futures to run on. import ...
-1
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1answer
76 views

Approaches to Concurrency [closed]

I’ve been doing some research on the various approaches to concurrency, and I’ve ended up with the following taxonomy: Manual thread based concurrency with locks Asynchronous dispatch queues and ...
2
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0answers
71 views

Handling exceptions in multiple-issue CPUs

From what I read, VLIWs execute instructions in bundles, i.e. the CPU loads a bundle of instructions and dispatches them all at once. This is possible because the compiler scheduled instructions in ...
3
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1answer
141 views

Java concurrency

I am working to solve interesting concurrent problem! Not sure if I understand it correctly since I am little bit confused. The system needs to process the prices, and typically they cannot be ...
0
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1answer
260 views

Ever-running timed tasks

I need to design a piece of software which is invoking some actions regularly. By regularly I mean that there is x things that need to be done at 12.00, y things at 12.30 etc,etc. The times and ...
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2answers
126 views

Don't quite understand check and set in concurrency

I don't entirely understand check and set behaviour.. here is an example: public static void main(String[] args) { List<String> list = Collections.synchronizedList(new ...
6
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3answers
2k views

How to avoid halting of the JVM due to a deadlock in java?

I have read many websites talking about how to avoid and how to design etc. I completely understand those strategies. My question is based on the following preconditions: You have a company with ...
4
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2answers
353 views

Why is Akka good for concurrency?

I am new to Akka and actor framework - I am sure I am missing something obvious, please accept my apologies in advance. I keep reading that one of the main points to choose Akka is the way it manages ...
23
votes
3answers
9k views

Why is multithreading often preferred for improving performance?

I have a question, it's about why programmers seems to love concurrency and multi-threaded programs in general. I'm considering 2 main approaches here: an async approach basically based on signals, ...
2
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3answers
749 views

Accessing shared data without blocking in TPL

I am writing a class that contains data. It exposes methods that allow to query the data, while the data is also being updated from an external source (web service, for example). All the methods ...
2
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3answers
156 views

Long running DB query with concurrent write at the same time [closed]

We have a big table with a lot of data and a select query which takes 3 seconds to run. However we are a highly concurrent environment and each second we get 100 new records in our database. So ...
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0answers
99 views

Terminology - Difference between thread and process and how they manage DB connections

I've been working more with concurrency in Ruby recently, and I keep seeing various articles using "threads" and "process" interchangeably. What are the actual definitions of these terms? Is a ...
9
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3answers
3k views

Parallelism implies concurrency but not the other way round right?

I often read that parallelism and concurrency are different things. Very often the answerers/commenters go as far as writing that they're two entirely different things. Yet in my view they're related ...
1
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1answer
147 views

Does ReaderWriterLockSlim provide thread safety and speed efficiency (compared to a traditional lock) when using a List?

I have a list, to which I write once in every update Loop and then I spawn some tasks which create read that List and create a duplicate to manipulate that data. More or less it's List.ToList() call ...
72
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10answers
10k views

How to explain why multi-threading is difficult

I am a fairly good programmer, my boss is also a fairly good programmer. Though he seems to underestimate some tasks such as multi-threading and how difficult it can be (I find it very difficult for ...
0
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0answers
45 views

Is using synchronization in service layer a bad idea?

I need to implement a mailbox monitor system as a web service. I have follow classes: MailboxMonitor: Contains information such as username, password, pulling interval etc. MailboxMonitorRepository: ...
9
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5answers
2k views

Best-practice to manage concurrency into a basket in a e-commerce website

What is the best practice to manage the case where two customers add in the same time a product whose the stock was only 1 ? Must there be a check in the code of the basket to avoid one of these 2 ...
2
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1answer
143 views

How do I handle online payment for items with single quantity? [duplicate]

I would like to implement a robust way to handle ecommerce payment for items with limited quantity, like for example exclusive paintings. Payment would ideally be accepted via PayPal and credit ...
11
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5answers
846 views

Why is implicit parallelism/concurrency not more widespread? [closed]

Implicit parallelism^ can take a big burden away from many programmers, placing it on the computer. So... why is it is not more widespread at present? ^ Implicit parallelism is to make a computer be ...
5
votes
3answers
1k views

Is REST only limited to optimistic concurrency control?

Context Due to the statelessness of the REST architectural style involving that each requests stands completely alone, leading server to never store any informations about client. Thus, pessimistic ...
3
votes
1answer
105 views

How does condition_variable::notify_one() choose which thread to unblock?

notify_one() of C++ 11 thread library is used to unblock one of the waiting threads. How does it choose which thread to unblock? To begin with, I tried googling but could not find any appropriate ...
1
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1answer
161 views

Generic PHP web interface for handling concurrent updates optimistically

I'm looking in to writing a new PHP based CMS which handles concurrent edits optimistically like source version control rather than pessimistic locking like Wordpress. I want to be able to write some ...
3
votes
1answer
1k views

Difference between Consumer/Producer and Observer/Observable

I am working on the design of an application that consists of three parts: a single thread that watches for certain events happening (file creation, external requests etc.) N worker threads that ...
1
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0answers
134 views

Injecting locking policy into a class

I have a class that does some operations on data, and I want to have different locking schemes (no-lock, simple-lock, and read reader-writer lock) in different situations. Think this main class like ...
28
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5answers
32k views

The difference between “concurrent” and “parallel” execution?

What is the difference between the terms concurrent and parallel execution? I've never quite been able to grasp the distinction. The tag defines concurrency as a manner of running two processes ...