Integrated: 8374153: Add a MAX_COMPILE_THREADS gradle property to limit number of threads

[Kevin Rushforth]

On Fri, 19 Dec 2025 18:29:43 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

> This PR adds a new `MAX_COMPILE_THREADS` gradle property to to limit the number of build-time parallel compilation threads to the smaller of this property and the number of avialable processors.
> 
> Our gradle build spawns up to `NUM_COMPILE_THREADS` compilation tasks in parallel when building native libraries. By default, `NUM_COMPILE_THREADS` is set to the value returned by `Runtime.getRuntime().availableProcessors()`. That value can be overridden on the command line by setting the `NUM_COMPILE_THREADS` gradle property. We need a way to clamp `NUM_COMPILE_THREADS` at some maximum value without the caller having to compute it.
> 
> The change in `build.gradle` is simple:
> 
> * Define a new `MAX_COMPILE_THREADS` gradle property, which will default to 0 (meaning unlimited) for compatibility with current behavior.
> 
> * Set the default value of `NUM_COMPILE_THREADS` as follows:
> 
> 
>     NUM_COMPILE_THREADS = MAX_COMPILE_THREADS > 0
>                         ? Math.min(MAX_COMPILE_THREADS, availableProcessors)
>                         : availableProcessors(
> 
> 
> This will allow a test scripts that runs on a number of different platforms to clamp to a maximum value without having to use jshell or similar to implement `Math.min(MAX_COMPILE_THREADS, Runtime.getRuntime().availableProcessors())` in the script.
> 
> We have a practical need for this in our headful test systems, several of which report a higher number of processors than they can effectively support. Without clamping, the build will either run slower (due to too much swapping) or fail altogether when building WebKit.

This pull request has now been integrated.

Changeset: 1e6c94b3
Author:    Kevin Rushforth <kcr at openjdk.org>
URL:       https://git.openjdk.org/jfx/commit/1e6c94b3c46db66df5856183859e05a683d1249a
Stats:     23 lines in 2 files changed: 20 ins; 0 del; 3 mod

8374153: Add a MAX_COMPILE_THREADS gradle property to limit number of threads

Reviewed-by: arapte, hmeda

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PR: https://git.openjdk.org/jfx/pull/2014