How to change num threads in startup jl on windows julia

When working with Julia on Windows, you may need to change the number of threads in the startup to optimize performance. In this article, we will explore three different ways to achieve this.

Option 1: Editing the startup.jl file

The first option is to manually edit the startup.jl file. This file is located in the .julia/config folder. Open the file in a text editor and add the following line:

ENV["JULIA_NUM_THREADS"] = "4"

Replace “4” with the desired number of threads. Save the file and restart Julia for the changes to take effect.

Option 2: Setting the JULIA_NUM_THREADS environment variable

An alternative approach is to set the JULIA_NUM_THREADS environment variable. Open the command prompt and enter the following command:

set JULIA_NUM_THREADS=4

Replace “4” with the desired number of threads. Restart Julia for the changes to be applied.

Option 3: Using the Threads.@threads macro

If you want to change the number of threads dynamically within your Julia code, you can use the Threads.@threads macro. This macro allows you to specify the number of threads for a specific block of code. Here’s an example:

using Threads

@threads 4 for i in 1:10
    # Code to be executed in parallel
    println("Thread ", Threads.threadid(), " executing iteration ", i)
end

In this example, the code block will be executed in parallel using 4 threads. Adjust the number of threads as needed.

After exploring these three options, it is clear that the best approach depends on your specific requirements. If you want to change the number of threads globally for all Julia sessions, editing the startup.jl file or setting the JULIA_NUM_THREADS environment variable are good options. On the other hand, if you need to change the number of threads dynamically within your code, using the Threads.@threads macro is the way to go.

Choose the option that suits your needs and optimize the performance of your Julia code on Windows.