Questions tagged [multithreading]
Multi-threading related questions including technique, structure, and safety issues.
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Testing multi-threaded race conditions
Reading the comments to this answer, specifically:
Just because you can't write a test doesn't mean it's not broken. Undefined behaviour which usually happens to work as expected (C and C++ are ...
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Does immutability entirely eliminate the need for locks in multi-processor programming?
Part 1
Clearly Immutability minimizes the need for locks in multi-processor programming, but does it eliminate that need, or are there instances where immutability alone is not enough? It seems to me ...
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What is a thread pool?
How would one implement a threadpool? I've been reading on wikipedia for "threadpool" but I still can't figure out what one should do to solve this question (possibly because I didn't quite understand ...
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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 ...
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What constitutes proper use of threads in programming?
I am tired of hearing people recommend that you should use only one thread per processor, while many programs use up to 100 per process!
take for example some common programs
vb.net ide uses about 25 ...
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Why does shared state degrade performance?
I've been working under the share-nothing principle of concurrent programming. Essentially, all my worker threads have immutable read-only copies of the same state which is never shared between them (...
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How are queues made thread-safe in Python
I admit this was asked to me in interview a long time ago, but I never bothered to check it.
The question was simple, how does Python make Queue thread-safe?
My answer was, because of Interpreter ...
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Multi-threading on a single core
Hypothetically, if you (I / someone) were to create a multi-threaded application, utilising the processing powers of multiple cores (for example, using TPL in C#). Would that program crash, if it were ...
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How does a single thread run on multiple cores?
I am trying to understand, at a high-level, how single threads run across multiple cores. Below is my best understanding. I do not believe it is correct though.
Based on my reading of Hyper-threading,...
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Are go-langs goroutine pools just green threads?
The commentator here offers the following criticism of green threads:
I was initially sold on the N:M model as a means of having event driven programming without the callback hell. You can write code ...
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How important is multithreading in the current software industry? [closed]
I have close to 3 years experience writing web applications in Java using MVC frameworks (like struts). I have never written multithreaded code till now though I have written code for major retail ...
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Why not Green Threads?
Whilst I know questions on this have been covered already (e.g. https://stackoverflow.com/questions/5713142/green-threads-vs-non-green-threads), I don't feel like I've got a satisfactory answer.
The ...
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Can someone explain in simple terms what is the disruptor pattern?
I would like if you could explain to me in a simple way how does the disruptor patter work. This concept has been elusive to me as of know.
Perhaps with your help I could comprehend it.
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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 ...
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Do compilers utilize multithreading for faster compile times?
If I remember my compilers course correctly, the typical compiler has the following simplified outline:
A lexical analyzer scans (or calls some scanning function on) the source code character-by-...
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Can multiple CPU's / cores access the same RAM simultaneously?
This is what I guess would happen:
If two cores tried to access the same address in RAM, one would have to wait for the other to access the RAM. The second time that each core would try to access ...
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Uses of persistent data structures in non-functional languages
Languages that are purely functional or near-purely functional benefit from persistent data structures because they are immutable and fit well with the stateless style of functional programming.
But ...
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Is It "Wrong"/Bad Design To Put A Thread/Background Worker In A Class?
I have a class that will read from Excel (C# and .Net 4) and in that class I have a background worker that will load the data from Excel while the UI can remain responsive. My question is as follows: ...
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Best practise is not to poll...but isn't polling happening internally anyway when a thread calls wait()?
Say we have some thread that wants to check when another thread is finished its task. I have read that we should call a wait() type function that will make this thread wait until it receives a ...
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Drawing thread interaction
I'd like to draw (pen and pencils) threads interaction in a UML(-like) notation. I don't insist on UML, anything that is obvious to the reader should do.
I started with sequence diagrams, but I don't ...
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Is it a performance hit to create threads that loop a lot to check for things?
This is a generic question that I've always wondered.
In general, is it intensive for a CPU to create threads that perform "while not true ..." loops or similar?
For example, suppose I do:
// ...
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Threads or ThreadPool? Fixed or Dynamic ThreadPool?
I have a java program which listens on a port for input. Based on Input, it calls a webservice and then returns a success/failure back to the client program.
I fork a thread for each client ...
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Mutex vs Semaphore: How to implement them _not_ in terms of the other?
Recently I had to implement a Semaphore using a Mutex and a Conditional Variable (this combination is also known as a Monitor) for an exercise at the university:
the Semaphore's decrement operation ...
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Concurrency pattern of logger in multithreaded application
The context:
We are working on a multi-threaded (Linux-C) application that follows a pipeline model.
Each module has a private thread and encapsulated objects which do processing of data; and each ...
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Should I use a boolean or a cancellation-token to stop this task?
I have a program that starts a task as follows:
token = this.tokenSource.Token;
var t = Task.Factory.StartNew(() =>
{
while(!token.IsCancellationRequested)
{
// do the work...
...
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2
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Pthread scheduling (System and Process)
I've read the operating system concepts 8th edition written by abraham silberschatz. However, I don't understand Pthread Scheduling.
Thread-library schedules user-level-threads on LWP(Lightweight ...
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Am I looking at multithreading the wrong way? (Java)
This is a re-post from my question in StackOverflow, so here goes:
For the past few weeks now I've been studying Concurrency(Multithreading) in Java. I find it difficult and rather different than ...
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Performance: Is There a Reason to Use Processes over Threads?
This is a general question but I work in the .NET world so I'd like to know if there any specific quirks about the .NET Framework / Core platforms that I should be concerned about here.
I think it's ...
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JUnit Testing in Multithread Application
This is a problem me and my team faces in almost all of the projects. Testing certain parts of the application with JUnit is not easy and you need to start early and to stick to it, but that's not the ...
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Is there a limit on the number of threads that can be spawned simultaneously?
Yesterday I came across this question: How can i call robocopy within a python script to bulk copy multiple folders?, and I though it might be a good exercise for multithreading.
I though of spawning ...
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are multithreading, multiprocessing, multitasking implemented at instruction set or OS?
On a computer with a single cpu core,
must a multithreading program be implemented based on an OS? Can it be implemented in the instruction set and run without an OS?
Can multiple programs run in ...
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What are the so-called "levels" of understanding multithreading?
I seem to remember reading somewhere some list of 4 "levels" of understanding multithreading. This may have been in a formal publication, or it may have been in an extremely informal context (even ...
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Implementation of Asynchronous function call in C
I took it upon myself recently to work towards making a general-purpose Translator to automatically translate js programs into C, but I got stuck when thinking of asynchronous behaviour. Using ANSI / ...
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Evaluating concurrent application design approaches on Linux
Working on relatively low-speed hardware, I need to grab a snapshot of a rapidly changing datastream and then post-process the snapshot data and save it to disk.
I need help with designing the ...
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Is there a formula to figure out the total execution time of sequential asynchronous processes?
I have a set of steps that need to run sequentially over a list of data. However each step only operates on a single piece of data at a time. Because of this, I can run the steps asynchronously.
For ...
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Internal Mutation of Persistent Data Structures
To clarify, when I mean use the terms persistent and immutable on a data structure, I mean that:
The state of the data structure remains unchanged for its lifetime. It always holds the same data, ...
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Threads - When to use barrier?
Using python syntax,
threading.Barrier(NUM_THREADS) establishes a control point and all participating threads block until all of the participating “parties” have reached that point. It lets threads ...
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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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What's the simplest way to deal with events in C in this situation?
I'm writing a text-based game, in C. I want the game to handle NPCs movement and actions in the background, while the user is making his moves. I'd also use time-based events to tell the user when ...
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Is the singleton pattern prone to thread safety problems?
Is the singleton pattern prone to thread safety problems? If so, what are the best methods to work around them?
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Sharing buffer between multiple threads
I had a job process that was executing a lot of IO to read and write temporary files.
Now I want to (need to) reduce the quantity of IO executions.
So I want to create a sort of circular buffer ...
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How is it possible to have limitless availability of threads while only having a finite number of physical processing units?
So I'm having trouble understanding the relationship between threads (software) and processor cores (hardware).
Basically my understanding of a processor core is a unit that deals with commands and ...
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WCF service - best way to accept requests from a client and do background work?
For a project at work, I was tasked to create a WCF service that will receive email messages from client and queue them on a database, while at the same time the service will check the DB every 30 ...
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Is it possible to perform mutual exclusion of threads without OS support?
I suppose you could adapt distributed mutual exclusion algorithms (Ricart/Agrawala, etc), but aside from these more exotic approaches, are you required to use primitives provided by the OS in order to ...
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Good strategy to implement a listener processing tasks provided by the database
Let's assume this conceptual scenario:
The database is constantly populated with "a ton" of tasks named PleaseSendAnEmail.
A scheduler/listener in background is aimed to handle those tasks.
Of ...
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Push instead of pull on a list that might change due to a command in addition to events? [closed]
I need to show a refreshable/searchable list of items and update/add-to it whenever an event is published. How do I make sure no events are lost while refreshing/searching is happening?
Some sort of ...
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Trade off between concurrency and stagnation in a Dining Philosophers problem analogue?
I am currently facing a problem in the application I am developing that I think is the same as, or an analogue of, the Dining Philosophers Problem.
In my application I have a list of N resources. I ...
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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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I/O bound or CPU-bound
I have a telephony application, there is a windows service(third party product) running on a remote server. The application runs against the server. To connect the server, we have the code.
public ...
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Multiprocessing vs multithreading
During my last job interview which was about half year ago, the technical guy asked me, whether the better option is to use e.g. 100 processes to do some work, or only one process but with 100 threads....
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