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

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2answers
97 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 ...
5
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2answers
124 views

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 ...
2
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1answer
90 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 ...
12
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2answers
258 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
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1answer
78 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 ...
2
votes
1answer
118 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
67 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 ...
0
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0answers
52 views

Design of thread pool reuse with Executors.newFixedThreadPool in Java [migrated]

In my application I have a code, which should run every hour on a new items and execute some expensive operation with multi threading. Code fragment: int i = 1; //noinspection InfiniteLoopStatement ...
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4answers
316 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
92 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
62 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
30 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
votes
2answers
251 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
46 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
votes
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
155 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
votes
1answer
329 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
votes
1answer
70 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
votes
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
259 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 ...
1
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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
votes
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
votes
2answers
332 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
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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
699 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
139 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 ...
1
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0answers
93 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
vote
1answer
137 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
votes
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
43 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
votes
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
140 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
838 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
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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
99 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
vote
1answer
155 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
127 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 ...
26
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5answers
31k 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 ...
1
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3answers
2k views

Can multiple synchronized methods in same object run concurrently

As far as i know when there are multiple synchronized methods(both static and instance) in a class, java allows only one such method to run at a time. But what if a thread acquires lock on an object ...
4
votes
4answers
440 views

Testing concurrency/thread-safety

A program I have wrote uses multiple threads and I believe my program is thread-safe but how can I really know? I've read a number of examples online and none of them describe how to test the code is ...
9
votes
1answer
451 views

When asynchronous tasks make a bad UX

I'm writing a COM add-in that's extending an IDE that desperately needs it. There are many features involved, but let's narrow it down to 2 for the sake of this post: There's a Code Explorer ...
1
vote
1answer
643 views

How to concurrently write data in Java without locking?

How to implement a multi-threaded program in which each thread needs to write/output some data (in any order of course) but without the locking overhead that is involved with files or a particular ...
-2
votes
1answer
454 views

Crawler - programming language choice [closed]

I'm currently developing a web crawler. The first version was developed in Node.js and runs pretty well. The issues that I encountered with Node.js are in no particular order: slow URL and ...
16
votes
5answers
7k views

What are the best resources for learning about concurrency and multi-threaded applications? [closed]

I realised I have a massive knowledge gap when it comes to multi-threaded applications and concurrent programming. I've covered some basics in the past, but most of it seems to be gone from my mind, ...
25
votes
3answers
3k views

How much work should I place inside a lock statement?

I am a junior developer working on writing an update for software that receives data from a third-party solution, stores it in a database, and then conditions the data for use by another third-party ...
1
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2answers
233 views

How do I find a good middle way to make this library safe for concurrent operations

I've made a little library called SignalR.EventAggregatorProxy Before I push it into 1.0 state I need to fix so it works safely with concurrent operations. Easiest way is lock all operations but ...