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Questions tagged [multithreading]

For questions regarding multi-threading, the ability of a computer or a program to perform work concurrently or asynchronously by utilizing multiple concurrent streams of execution (generally referred to as threads).

Multi-threading is a common model to implement SM in multi-cored machines, where threads share memory through shared variables. In this model in parallel programming a processor can create multiple threads that will be executed in parallel. Each thread has its own stack, variables and ID, considered private state. For every thread there is a unique heap shared by all, then considered shared memory.

In order to allow a volume of work to be most effectively and safely divided into multiple concurrent streams of execution, a number of critical areas need to be addressed.

  • Scheduling: ensure worker tasks are able to progress independently and effectively (e.g. deadlock/livelock avoidance)
  • Publication: ensure data altered in one thread is only visible to others as expected
  • Synchronization: ensure critical regions are protected from multiple concurrent updates causing data loss/corruption.

The underlying tenet of concurrent processing is Amdahl's law (graph). This law governs the diminishing amount of throughput that can be achieved by greater numbers of concurrent processors/cores. Therefore the overall aim of multi-threading is to minimize the amount of serial execution (exclusive locking) within any concurrent system.

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139166 questions
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Use cases for RxJava schedulers

In RxJava there are 5 different schedulers to choose from: immediate(): Creates and returns a Scheduler that executes work immediately on the current thread. trampoline(): Creates and returns a Scheduler that queues work on the current thread to…
bcorso
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What's the difference between Thread start() and Runnable run()

Say we have these two Runnables: class R1 implements Runnable { public void run() { … } … } class R2 implements Runnable { public void run() { … } … } Then what's the difference between this: public static void main() { R1 r1 =…
Ori Popowski
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Handling exceptions from Java ExecutorService tasks

I'm trying to use Java's ThreadPoolExecutor class to run a large number of heavy weight tasks with a fixed number of threads. Each of the tasks has many places during which it may fail due to exceptions. I've subclassed ThreadPoolExecutor and I've…
Tom
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C# Events and Thread Safety

I frequently hear/read the following advice: Always make a copy of an event before you check it for null and fire it. This will eliminate a potential problem with threading where the event becomes null at the location right between where you check…
Daniel Earwicker
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Creating Threads in python

I have a script and I want one function to run at the same time as the other. The example code I have looked at: import threading def MyThread (threading.thread): # doing something........ def MyThread2 (threading.thread): # doing…
chrisg
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ExecutorService, how to wait for all tasks to finish

What is the simplest way to to wait for all tasks of ExecutorService to finish? My task is primarily computational, so I just want to run a large number of jobs - one on each core. Right now my setup looks like this: ExecutorService es =…
george smiley
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Task continuation on UI thread

Is there a 'standard' way to specify that a task continuation should run on the thread from which the initial task was created? Currently I have the code below - it is working but keeping track of the dispatcher and creating a second Action seems…
Greg Sansom
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How to test methods that call System.exit()?

I've got a few methods that should call System.exit() on certain inputs. Unfortunately, testing these cases causes JUnit to terminate! Putting the method calls in a new Thread doesn't seem to help, since System.exit() terminates the JVM, not just…
Chris Conway
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Can't pickle when using multiprocessing Pool.map()

I'm trying to use multiprocessing's Pool.map() function to divide out work simultaneously. When I use the following code, it works fine: import multiprocessing def f(x): return x*x def go(): pool = multiprocessing.Pool(processes=4) …
ventolin
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Redis is single-threaded, then how does it do concurrent I/O?

Trying to grasp some basics of Redis I came across an interesting blog post . The author states: Redis is single-threaded with epoll/kqueue and scale indefinitely in terms of I/O concurrency. I surely misunderstand the whole threading thing,…
Przemysław Pietrzkiewicz
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The calling thread must be STA, because many UI components require this

I am using http://www.codeproject.com/KB/IP/Facebook_API.aspx I am trying to call the XAML which is created using WPF. But it gives me an error: The calling thread must be STA, because many UI components require this. I don't know what to do. I am…
C..
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Java synchronized method lock on object, or method?

If I have 2 synchronized methods in the same class, but each accessing different variables, can 2 threads access those 2 methods at the same time? Does the lock occur on the object, or does it get as specific as the variables inside the synchronized…
wuntee
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Cross-thread operation not valid: Control 'textBox1' accessed from a thread other than the thread it was created on

I want to send temperature value from a microcontroller using UART to C# interface and Display temperature on Label.Content. Here is my microcontroller code: while(1) { key_scan(); // get value of temp if (Usart_Data_Ready()) { …
Fatima Zohra
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What is the Haskell response to Node.js?

I believe the Erlang community is not envious of Node.js as it does non-blocking I/O natively and has ways to scale deployments easily to more than one processor (something not even built-in in Node.js). More details at…
gawi
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9 answers

What is the difference between a thread and a fiber?

What is the difference between a thread and a fiber? I've heard of fibers from ruby and I've read heard they're available in other languages, could somebody explain to me in simple terms what is the difference between a thread and a fiber.
tatsuhirosatou
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