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

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Programming design on heavy web I/O Django based scrapping application

I've started a project few month ago for closest to real time database operations next to HTTP requests. I choose Django + Celery as a first place, then tried with home made multiprocessing + ...
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0answers
51 views

Strategy for writing a scalable chat server in Java [on hold]

Currently I'm creating a chat server in Java using socket, seems that is the natural choice for a newbie java programmer. What are the strategies that need to be taken in order to scale the chat ...
4
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0answers
124 views

Does REST is 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 ...
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1answer
128 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 ...
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0answers
78 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 ...
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3answers
86 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
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4answers
119 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 ...
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1answer
81 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 ...
9
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1answer
342 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 ...
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1answer
112 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 ...
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1answer
100 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 ...
25
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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 ...
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1answer
105 views

is a DoS attack a good analogy of Dining Philosophers?

Let's say that, instead philosophers, we have TCP/IP connections to a server, and instead forks we have the server's TCP/IP avaliable ports. In this scenario, we don't have a lot of connections ...
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1answer
40 views

What's the best way to implement a real time show board to show results from concurrent result producers in Java?

I'm making a load test tool that launches multiple thread to simulate load on the target server. Each thread executes a predefined set of commands in the structure of TestSuite - TestCase- TestStep ...
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1answer
111 views

Experiences with C++ Async/actor model Library [closed]

I am fairly experienced with async and concurrent programming in c# using event, actor, and task based patterns, but now I have a task in c++ with which I have basic familiarity and it needs some ...
2
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3answers
203 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 ...
5
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2answers
624 views

Where is the evidence for the performance of Node.js?

A lot of developers, especially ones who haven't used Node.js in production, seem to believe that Node.js is faster than other interpreted languages such as PHP, Python, and Ruby. These claims ...
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2answers
91 views

When, if ever, are basic concurrency optimizations generally made?

Lets say I need to preform the following computationally intensive task For i in range(100000000): doComplexCalculationWithNoSideEffects(i) Most people I talk to tell me that basically any ...
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1answer
36 views

How to model parallel processes (in a Bounded Context) with the same data store?

The situation. Let's say a background process puts stuff into data containers. It runs all the time, observes system events, and populates the data accordingly. The user may launch a control panel ...
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2answers
153 views

Scaling locks in high concurrency web apps [closed]

Our web application has a certain resource type that is shared accross multiple users, and may thus be read and written by anyone at anytime. We resorted to the usual suspects, database transactions ...
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3answers
194 views

Is there an algorithm to determine the amount of work needed to keep workers busy?

I wrote a multi-threaded program that randomly generates strings, and after generating, checks to see if the string contains a certain value. Namely, StringGenerator and StringChecker. What I'm trying ...
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1answer
52 views

Locking on data vs locking on functions

In concurrent code, what is the difference between, and the pros and cons of each: Locking on data Locking on functions My understanding is that locking on data is better, and I think I'm doing ...
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2answers
62 views

Lock data in DB while external API call is pending?

I have an interesting situation, and I am looking for the best way to solve it. My app runs like this: 1) The user gets a Promotion Pin from Some Company, and I have a db table with these pins also. ...
2
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1answer
90 views

Can concurrent code (threads, distributed computing, etc.) be directly ported to single-threaded/non-networked platforms?

Take an arbitrary "perfect" multi-threaded program, on an arbitrary multi-threaded platform, using an arbitrary programming language. Assuming that this "perfect" multi-threaded program: is ...
6
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144 views

Which languages have the best support for stackful coroutines? [closed]

Various languages support (some flavor of) coroutines. One way to discriminate coroutines is whether they are stackful or not (terminology based on Ana Lucia de Moura; Roberto Ierusalimschy (2004). ...
2
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2answers
151 views

Alternative locking strategies

I'm having a problem with the design of my application, that neither optimistic nor pessimistic locking tends to solve. Here is a simplified/altered version of the problem that describes the ...
23
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8answers
6k views

Function guaranteed to never return the same value twice [closed]

This is a question I was asked at a job interview, and I can't figure out the answer they were looking for, so I'm hoping someone here might have some ideas. The goal is to write a function that is ...
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80 views

Concurrent Processes - Monitors and Reader/Writers

So this is a general question about the use of monitors in the Reader/Writers problem. I know the monitor procedures for the Readers/Writers problem are used for mutual exclusion to a critical ...
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2answers
107 views

Simultaneous purchase in online shop bypassing limited offer

Our client sells several products in an online shop (our software) for a especially low price on the first purchase. Further purchases of each product will fallback to the regular price. E.g. product ...
6
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0answers
94 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 ...
6
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6answers
1k views

What is the actual reason that locks (sentinels) in OO are hard to reason about? [closed]

In this talk, Rich Hickey introduces Clojure. He gives an Ants demo and talks about his motivations for implementing a Software Transactional Memory (STM) system. His reasoning for STM is that ...
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1answer
301 views

Algorithm to create custom ConcurrentHashMap?

I tried to look into concurrent HashMap source code to look in to how it is implemented. To me it looked very difficult to understand((In no way i am saying its not required :))). I thought if i need ...
2
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2answers
226 views

How do you solve issue of consistency in concurrent and distributed application (built around Bankers Dilemma)?

This is a classic problem which I'm sure has been solved many times by many different people. I don't have any formal training (I've not studied computer science or any other such academic subject) ...
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1answer
118 views

Coordinating a complicated data migration process

A project I'm involved in has suffered a change in scope, and before I set about trying to cook up some homegrown solution, I'm wondering if there is something out there -- some framework, for example ...
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2answers
162 views

Patterns for creating adaptive web crawler throttling

Im running a service that crawls many websites daily. The crawlers are run as jobs processed by a bunch of independent background worker processes, that picks up the jobs as they get enqueued. Now ...
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43 views

Semaphore : one for each shared resource?

Normally semaphores are implemented as integer variables. The value of a semaphore represents initially the number of processes that are allowed to access the shared resource at the same time, which ...
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1answer
134 views

Repurpose MySQL as a mutex

My application needs to perform an operation once every 10 minutes, but that operation is triggered many times more frequently. Occasionally it is triggered three or four times a second in different ...
4
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1answer
223 views

Error Handling Strategies in Multithreaded Environments

TL;DR What error generating and handling strategies do you use in Multithreaded code intended for use by others and why do you use them? If applicable, state what programming paradigm it's useful for. ...
22
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1answer
2k views

Is there a difference between fibers, coroutines and green threads and if that is so what is it?

Today I was reading several articles on the Internet about fibers, coroutines and green threads, and it seems like these concepts have very much in common, but there are slight differences, especially ...
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1answer
302 views

In C++, are acquire-release memory order semantics transitive?

According to cppreference, we can use release-acquire semantics to ensure write-read precedence between two threads as follows: // Thread A 1. Write to X 2. Atomic store to Y with ...
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1answer
202 views

Implementing distributed Semaphore for AWS workload

We have a messaging gateway in AWS (Amazon Cloud) that comprises of a number of nodes (Linux servers) responsible for receiving, routing, despatching and escalating messages (emails, SMS' and voice ...
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1answer
66 views

handling online payment for items with one quantity - design issue

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 ...
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1answer
103 views

Locking database records

What I have right now: A table with lot of records. About 200 users can select a record according to some rules based on the data in each record. There is a high chance that 2 or more users will ...
20
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4answers
2k views

What prevents a race condition on a lock?

I understand the basics of what data races are, and how locks/mutexes/semaphores help prevent them. But what happens if you have a "race condition" on the lock itself? For example, two different ...
3
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1answer
153 views

How to avoid oscillation by async event based systems?

Imagine a system where there are data sources which need to be kept in sync. A simple example is model - view data binding by MVC. Now I intend to describe these kind of systems with data sources and ...
3
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0answers
188 views

How can I make a universal construction more efficient?

A "universal construction" is a wrapper class for a sequential object that enables it to be linearized (a strong consistency condition for concurrent objects). For instance, here's an adapted ...
2
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1answer
338 views

Where to implement thread-safety logic for my queue data structure?

I will immediately confess that I do very little multithreading, so questions of style and organization in this domain a little fresh to me. I've written a data structure (in Python, if that matters) ...
3
votes
1answer
178 views

Can the possibility of a data race be ignored in some cases? (while having concurrent threads) [duplicate]

I am programming a game engine as a hobby project, and I would like to separate physics and drawing into two separate threads. The position vectors of entities are subject to modifications by the ...
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1answer
111 views

Cache concurrency: ensuring latest version in cache

We have a data service app working on object graphs. We place some complex graphs in a (memory) caching tier as a single data item, so as to avoid the length of time to retrieve every individual data ...
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2answers
280 views

Are all race conditions worth fixing? [closed]

I just wrote the following piece of code (in delphi): procedure Update(Value: Integer); begin // If the last update was yesterday, replace yesterday value if CompareDate(FLastUpdate,Now) <> ...