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

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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 ...
2
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3answers
610 views

Sharing buffer between multiple threads part 2

This is a follow up to my previous not answered question, so I try to make it more clear: last question. I have a n-size buffer that is filled up from an external source, it has 2 main methods get() ...
2
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3answers
208 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 ...
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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) <> ...
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2answers
2k views

How can we handle multiple instances of a method through a single class instance

How can we handle multiple instances of a method through a single class instance(Single constructor call)? To elaborate, I have a handler class which has two methods lets say verifyUser(String JSON) ...
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1answer
280 views

Editing files without race conditions?

I have a CSV file that needs to be edited by multiple processes at the same time. My question is, how can I do this without introducing race conditions? It's easy to write to the end of the file ...
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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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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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3answers
90 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 ...
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3answers
2k views

How can I multiprocess my program?

I wrote a program which scrape internet sites. It is pretty straigtforward because it process link one by one. With the limiting factor of the internet speed, the process is rather slow. I wonder, ...
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2answers
303 views

Are there any advantages of using separate RDBMS for reports?

My production database is SQL Server 2008 R2 Express. It has limited features and I am testing it in a production environment. To better handle reporting queries in a highly concurrent environment, I ...
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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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2answers
155 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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1answer
462 views

Handling or preventing conflicts in a multi-user system

I have a web application that is accessed by multiple users from different locations worldwide. Let's say I have an "edit" form for a specific document and two (or more) users are editing the document ...
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1answer
719 views

Static objects and concurrency in a web application

I'm developing small Java Web Applications on Tomcat server and I'm using MySQL as my database. Up until now I was using a connection singleton for accessing the database but I found out that this ...
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3answers
854 views

3 threads printing numbers of different range

This question was asked in an Electronic Arts interview: There are 3 threads. The first thread prints the numbers 1 to 10. The second thread prints the numbers 11 to 20. The third thread prints the ...
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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
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. ...
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1answer
303 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
833 views

Java BufferedReader vs Separate Producer consumer thread

I have a very big file delimited by some sequence of characters '*L*I*N*E'. The file will be of the order of 250G. And each line comes around 600bytes to 1000 bytes. I will be performing the following ...
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2answers
652 views

How can I avoid concurrent access in PostgreSQL?

I would like to have your opinion, how I can handle the case when PDO engine and Hibernate engine "talk" to the same db? There is a PHP application as frontend, and a Java doing some job after user ...
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1answer
757 views

Model-View-Controller and client-side concurrency responsibility

In a web application that has a significant ajax component, where is the best place for the client-side concurrency responsibility to lie? We're trying to use MVC on both the server application (LAMP ...
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2answers
219 views

Descriptive Locking and Concurrency

I'm thinking about how one would go about designing a descriptive concurrency model for an OOP language that helps simplify concurrency scenarios for programmers (no easy task, concurrency is hard). ...
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1answer
174 views

Programming language and database concurrent locking primitives

I am writing an article about both programming language locking primitives (which are really wrappers for OS primitives) and database locking primitives. Are there any short wide-spread titles for ...
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1answer
82 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 ...
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1answer
116 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
112 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 ...
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1answer
203 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
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
218 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 ...
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1answer
149 views

Design question about a concurrent forking server

I'm in the early stages of designing a client/server application. The clients will be batch programs that read a file of customer contact data (name, address, email address, phone no's) and pass ...
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2answers
278 views

Requiring multithreading/concurrency for implementation of scripting language

Here's the deal: I'm looking at designing my own scripting/interpreted language for fun. I'm only in the planning stages right now; I want to make sure I have a very strong hold on exactly how I will ...
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0answers
79 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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0answers
81 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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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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3answers
206 views

If mutual exclusion is not implemented, how would we detect a race condition?

Suppose we are in a distributed environment, and mutual exclusion is not implemented yet. So how would we be able to detect race conditions? When I researched, use of non-blocking algorithms was ...
0
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3answers
2k views

Super Fast File Storage Engine

I basically have one big gigantic table (about 1.000.000.000.000 records) in a database with these fields: id, block_id, record id is unique, block_id is not unique, it contains about 10k (max) ...
0
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3answers
607 views

Multiple threads and single output source

For the sake of an exercise, say you have an input file with a series of lines of text with the objective of reversing their respective character sequences. Now introduce 5 threads that will each do ...
0
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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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5answers
921 views

Examples of concurrent iterating scenarios needed

I'm trying to wrap my head around different concurrency solutions to several threads iterating over the same collection but I'm having difficulty coming up with good realistic (but preferably easy to ...
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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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1answer
302 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 ...
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1answer
122 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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1answer
137 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 ...
0
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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 ...
0
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1answer
435 views

Apple Dispatch Queue vs Threads

I've heard a lot about apple's famous dispatch queues and the GCD but today was the first time I decided to understand exactly what is going on, so I started reading Concurrency Programming Guide and ...
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1answer
320 views

Concurrency checking with Last Change Time

I have an app with the following three tables Email (emailNumber, Address) Recipients (reportNumber, emailNumber, lastChangeTime, status) Report (reportNumber, reportName) I have a C# application ...
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0answers
55 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 ...
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2answers
189 views

How bad would it be to obtain a lock on every object?

Imagine a hypothetical programming environment that is largely like Java or .NET, i.e. object-oriented, garbage-collected, etc., but with one small change: Every time you call a method on an object, ...
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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 ...