Questions tagged [concurrency]
In computer science, concurrency is a property of systems in which multiple computations can be performed in overlapping time periods. The computations may be executing on multiple cores in the same chip, preemptively time-shared threads on the same processor, or executed on physically separated processors.
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Producer/Consumer implementation
I am using Netty embedded within Grails to process and display incoming SNMP messages. Since Netty 4 doesn't come with a built-in ChannelExecutionHandler I had to ...
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Implemenation for concurrent file access (read/write)
I am developing an application that works with files and folder on a network share (similar to the windows explorer). The application is used by multiple users and provides some commands for modifying ...
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A multi-thread Producer Consumer, where a Consumer has multiple Producers (C++17)
EDID: Thank you very much for your feedback. I updated the code and opened a new post for the updated version. See here.
This post is loosely based on A multi-threaded Producer Consumer with C++11.
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Python Port Scanner 2.0
A few months ago I put up a port scanner for review. Now, I've updated it with some new Python knowledge and integraing the feedback I got.
Some things I specifically think might be wrong with it or ...
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C++20 Thread Pool
I've implemented a thread pool using C++20. I'm fairly new to concurrently/multi-threaded programming and wanted to work on a project that I could learn from while also getting to know some of the new ...
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Concurrent/parallel ForEachAsync - proper handling of exceptions and cancellations
I've created an asynchronous parallel ForEach mechanism so I could enumerate an enumerable by N degrees of concurrency and process an action for each item. ...
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Creating a concurrent/parallel ForEachAsync that can fail immediately or wait until enumeration is complete
I needed an asynchronous parallel ForEach mechanism so I could enumerate an enumerable by N degrees of concurrency and process an action for each item. Searching ...
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A multi-threaded Producer Consumer with C++11
I am trying to learn concurrent programming in C++11. I tried to write code for a classic producer consumer concurrency problem. Would you please review and make any comments about it?
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Python Port Scanner 2.1
I made lots of changes to the script presented in my previous question. I was tempted to edit that one with the new code, but it would invalidate @200_success's helpful answer. It was also ...
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Do not share same socket between two threads at the same time
I have a code in which I am dealing with sockets and I need to make sure that I don't share same socket between two threads. In my below code, I have a background thread which runs every 60 seconds ...
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Multi Threaded High Performance txt file parsing
EDIT
A port of Björn's answer to C++ with further improvements at bottom achieving up to 2.4GB/s on the reference machine.
Text file parsing and processing continues to be a common task. Often it's ...
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Shady Characters
As part of my familiarization with the features of Java 8, and inspired by this question, I thought I would take the 'Shady Character' problem to 'the next level'.
The basic problem is that you have ...
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Poke-a-Dot (Provider)
I need to create variable-length strings of dots/periods/full-stops to add to some text content, in a way that is similar to a formatted table-of-contents:
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Generic Java task-scheduler
I wrote this generic task scheduler for executing tasks in fixed-delay intervals. Can you find anything wrong with it, or issues that may arise from using it for sending something like queued mails in ...
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Concurrent LRU cache using sychronizedMap() or ReadWriteLock
Trying to implement a simple, thread-safe LRU cache that's meant for "read mostly" use.
Collections.sychronizedMap()
Clean, simple, not much else to say.
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Lock-free multi-producer / multi-consumer queue in C++
I've been working on a lockless multi-producer, multi-consumer queue in an effort to learn as much as I can about concurrency, without the use of mutual exclusion. The queue uses a bounded ring buffer ...
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Sorting Algorithm Visualizer
Over the course of the past month I've worked on a little visualizer to show how different algorithms are sorted. I'm pretty happy with how it turned out but would be interested in any feedback ...
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A portable parallel loop construct in C89
(There is a next iteration available.)
I was practicing writing some portable C89 code and came up with this parallel for loop construct. Basically, if you have a ...
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Solving a race condition
In my application, I have a message dispatcher. Each message gets relayed to a dispatcher thread.
In some scenarios, I can get two responses from the third party in the same millisecond:
An "I ...
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URLEncoder implementation
I'm looking for feedback on my URLEncoder implementation, which is a drop-in replacement for Apache Tomcat's URLEncoder. It was ...
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General Batched Job Runner
This question is inspired by:
Generic Task Scheduler
where the problem is to run tasks on a scheduled basis, in parallel, and have individual timeouts for each job.
For example, consider this use-...
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Thread-safe retirement account class
Are these classes properly guarded for thread safety? Do you see any issues with any of the classes?
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Canonical Implementation for a Concurrent Subclass of NSOperation in Swift 2
I would like to develop a kind of template or canonical implementation for a concurrent subclass of NSOperation in Swift.
See here for my previous request which is implemented in Objective-C.
In that ...
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Single Producer Single Consumer lockless ring buffer implementation
I am writing a simple ring buffer for my own education. Below is a crack at a strategy described in http://www.cse.cuhk.edu.hk/~pclee/www/pubs/ancs09poster.pdf : Producer and Consumer keep local ...
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Hybrid Lock Implementation
I have an algorithm that is painfully slow if I use 'pure' mutexes. That's because most of the critical sections are short and far shorter than the work to sleep a thread. However, it is also slower ...
user59064
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Parallel for loop in Java 8
This is my first attempt to provide some syntactic sugar for doing mutually independent loop iterations in parallel. Thanks to Java 8 lambdas, I can write the parallel loops in pretty elegant fashion ...
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Concurrent for loop in C++
(See the next iteration.)
I have this easy to use facility that maps input elements to output elements concurrently by the means of a thread pool:
concurrent.h:
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Class to manage updates coming in from another thread
Managing updates from other threads into Swing is a hard problem. In MVC design, if you don't want to have the Presenter be responsible for Thread safety, you can end up with deadlock issues, and also ...
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Debounce and throttle tasks using Swift Concurrency
There are many debouncer and throttle implementations created using Grand Central Dispatch, and even one built into Combine. I ...
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Golang HTTPS certificate expiry checking CLI tool
I am a beginner at using Golang, I would like advice about the following program. It is a CLI tool that can check the expiration dates of HTTPS certificates concurrently. I have only used the standard ...
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C++20 Single Queue Thread Pool
This is a follow up to my previous post. I've made a number of improvements to the thread pool and corrected some bugs as well.
The most up to date version of the code is available on my Github.
I ...
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Copying into two different folders on a machine simultaneously
I am trying to copy files from machineB and machineC into machineA as I am running my shell ...
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C++11 Blocking Queue learning exercise
As part of my own C++11 learning exercise I have implemented this Blocking Queue using the new C++11 thread API. One of the aspects I would like to improve is efficiency i.e. in the ...
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Parallel Task Queue that runs in sequence
I'm in need of a solution that runs constantly incoming requests in a per-resource sequence, but parallel in general.
The use-case:
Many clients connect to a server and start issuing work. The work ...
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Reader-writers problem using semaphores in Java
I have written my own solution to the Reader-Writers problems using semaphores based on the psuedocode from Wikipedia. I would like to gauge the correctness and quality of the code.
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Optimizing code using semaphore to control Netty channel pool
I am using Netty to exchange messages between a client and server. For this, I am maintaining a channel pool on client side. Please help me in optimizing this code.
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Concurrent for loop in C++ - follow-up
I have incorporated all the cool points made by ChrisWue in the initial iteration of this post.
Now, I am not reinventing the wheel for my concurrent queue, but use internally ...
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Concurrent fire and forget async task queue
I had to do a lot of IO stuff on my server running Node JS where I did not really care about the result of the operations. The list of incoming tasks could be huge, so I had to limit the number of ...
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Managing socket pool per datacenter
I have a list of sockets per datacenter (in general, I have around three datacenter and each datacenter having 20 sockets, so in total I have around 60 sockets). Now I have 20 business threads which ...
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Blocking call to an async function
While migrating to structured concurrency it may be sometimes convenient to temporarily make a blocking call to an async function - e.g.:
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Ensuring no race conditions in my concurrent/parallel ForEachAsync method
Hopefully the final chapter of my ForEachAsync code review. The original question was the starting point and the second question contained modifications suggested ...
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Send data on a socket from multiple threads
I have around 60 sockets, 20 business threads and 1 pinger timer thread and I want to make sure each of those thread works on different socket every time so I don't want to share same socket between ...
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C++20 Multi-queue Thread Pool with Work Stealing
This is a follow up to my previous post which also follows up on my first post regarding my thread pool implementation. I have since made some further changes and attempted to improve performance with ...
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Many-readers-one-writer with semaphores and multithreading
I've been looking for a solution to the may readers one writer in Java.
I was intrigued by this question posted here and I read the Wikipedia entry about it.
So far, I've reached a fine solution, or ...
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Parallel for loop in Java 8 - follow-up
The previous and initial iteration at Parallel for loop in Java 8.
Changes are as follows:
ParallelLoopBody removed; ...
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Optimizing code using semaphore to control Netty channel pool - Part 2
Please have a look at my original question:
Optimizing code using semaphore to control Netty channel pool
I have made some changes as pointed out by @rolfl
The new code is as follows. Is this better?...
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Implementation of a latch
As an exercise to learn more about multi-threading and atomic operations work in C++, I decided to implement a latch class in C++11 loosely based off of std::latch ...
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Golang HTTPS certificate expiry checking CLI tool (UPDATED)
I previously submitted this CLI tool to this site for review and have made changes based on comments by the reviewer. I have refactored the code, fixed a bug (the tool will no longer output ...
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Threadsafe filtering queue
I have implemented a thread safe filtering queue. The queue allows any objects, of the specified type to be added. A thread interested to take an object must specify which object it is interested in ...
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Concurrent blocking stack
I just want to train before interview. I googled concurrency interview questions and one of the question was write concurrent ready stack.
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