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How do I avoid two (or more) threads that work on a table at the same time to not work on same row?


How do I avoid two (or more) threads that work on a table at the same time to not work on same row?

By : Yohanes Satria
Date : November 25 2020, 03:01 PM
I think the issue was by ths following , For a multithreaded solution, the standard engineering approach is to use a pool of workers and a pool of work.
This is just a conceptual sketch - you should adapt it to your circumstances:
code :


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How to make two threads work in same time

How to make two threads work in same time


By : Evan Reed
Date : March 29 2020, 07:55 AM
seems to work fine You want an implementation of producer-consumer problem bro... Frankly speaking, without having a lock on the Object's monitor, you dont have control over anything. You dont have control over how much time a thread executes (Timeslice provided to it). If the time slice is too long, you will feel that one thread executes after another because your processor is so fast, your first thread will get ample time to finish its work . If you want to know how threads work exactly, use wait() and notify() and synchronized methods to change it into a producer-consumer problem.
Jeanne is also right, you can put sleep() , there's a 90 percent chance that it might work. You could increase the number of elements being filled/printed. There's a 70% chance of you reading more than what you wrote(filled in the array) if you dont use syncronized/wait/notify.
Dividing work to more threads takes more time, why?

Dividing work to more threads takes more time, why?


By : user2777765
Date : March 29 2020, 07:55 AM
hop of those help? The most expensive operation your thread performs is calling rand(). The rand() is a naive, simplistic, and generally non-MT scalable function (since it guarantees for the same seed to produce the same sequence of random numbers). I think the lock inside the rand() is serializing all the threads.(*)
A simple trick to confirm whether it is the problem or not, is to start the program under debugger, then, several times: pause it, capture the stack trace of the threads, continue. Whatever appears most often in the stacktraces, very likely is the bottleneck.
Will Rayon avoid spawning threads for a small amount of work?

Will Rayon avoid spawning threads for a small amount of work?


By : Jason Morris
Date : March 29 2020, 07:55 AM
seems to work fine Weight API was deprecated in favor of split length control. By default Rayon will split at every item, effectively making all computation parallel, this behavior can be configured via with_min_len.
code :
extern crate rayon; // 1.0.3
use rayon::prelude::*;
use std::thread;

fn main() {
    println!("Main thread: {:?}", thread::current().id());
    let ids: Vec<_> = (0..4)
        .into_par_iter()
        .with_min_len(4)
        .map(|_| thread::current().id())
        .collect();
    println!("Iterations: {:?}", ids);
}
Main thread: ThreadId(0)
Iterations: [ThreadId(0), ThreadId(0), ThreadId(0), ThreadId(0)]
How to fix a problem with threads which are trying work at the same time?

How to fix a problem with threads which are trying work at the same time?


By : user2619719
Date : March 29 2020, 07:55 AM
help you fix your problem On Form1_Load event you are adding things to your fSelectedPrinter.Listbox. If you items you are adding are coming from a different thread, that will cause an error. Only UI thread can update objects on a form without using SynchornizationContext.
code :
   private readonly SynchronizationContext synchronizationContext;

   InitializeComponent();
   synchronizationContext = SynchronizationContext.Current;
   private async void btnListFiles1_Click(object sender, EventArgs e)
  {

     if (txtDirectory1.Text == "")
     {
       MessageBox.Show(InfoDialog.SELECT_DIRECTORY,PROGRAM_NAME);
        return;
     }

     if (!Directory.Exists(txtDirectory1.Text))
     {
       MessageBox.Show(InfoDialog.DIRECTORY_NOT_EXIST, PROGRAM_NAME);
        return;
     }

     try
     {
        string fileTypes = (txtFileTypes1.Text == "") ? "" : txtFileTypes1.Text;
        string[] files = Directory.GetFiles(txtDirectory1.Text.TrimEnd(),
                 (fileTypes == "") ? "*.*" : fileTypes,
                 (chkSub1.Checked) ? SearchOption.AllDirectories : SearchOption.TopDirectoryOnly);

        listBoxFiles.Items.Clear();         
        progressBar.Step = 1;
        progressBar.Value = 1;
        progressBar.Maximum = files.Length + 1;
        listBoxFiles.BeginUpdate();

        if (txtSearchPattern1.Text != "")
        {
           string searchPattern = txtSearchPattern1.Text.ToLower();

           await System.Threading.Tasks.Task.Run(() =>
           {
              foreach (string file in files)
              {
                 if (file.ToLower().Contains(searchPattern))
                 {
                    AddToListBox(file);
                 }
              }
           });

        }
        else
        {
           await System.Threading.Tasks.Task.Run(() =>
           { 
              foreach(string file in files)
              {
                 AddToListBox(file);
              }
           });
        }

        listBoxFiles.EndUpdate();
        progressBar.Value = 0;

  }


private void AddToListBox(string item)
  {
     synchronizationContext.Send(new SendOrPostCallback(o =>
     {
        listBoxFiles.Items.Add((string)o);
        progressBar.Value++;
     }), item);         
  }
How many threads (or work-item) can run at the same time?

How many threads (or work-item) can run at the same time?


By : Aye Pyae Aung
Date : March 29 2020, 07:55 AM
like below fixes the issue The OpenCL standard does not specify how the abstract execution model provided by OpenCL is mapped to the hardware. You can enqueue any number T of threads (work items), and provide a workgroup size (WG), with at least the following constraints (see OpenCL spec 5.7.3 and 5.8 for details):
WG must divide T WG must be at most DEVICE_MAX_WORK_GROUP_SIZE WG must be at most KERNEL_WORK_GROUP_SIZE returned by GetKernelWorkGroupInfo ; it may be smaller than the device max workgroup size if the kernel consumes a lot of resources.
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