Default execution context is now parallel (MT:1) #16136
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mverzilli
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Sep 6, 2025
Co-authored-by: Johannes Müller <[email protected]>
Sija
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straight-shoota
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This was referenced Oct 27, 2025
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Since the concurrent context doesn't exhibit any performance improvement over the parallel context (see #16135) and that we can resize a parallel context (see #15956), we can make the default execution context parallel and set the parallelism to 1 (aka MT:1) by default.
By default the parallelism would be disabled and the execution context remain concurrent only, which is backward compatible (nothing changes).
Resizing the context to enable parallelism will be at the discretion of the application: it can keep using the
CRYSTAL_WORKERSenvironment variable, and/or fallback to the number of CPUs or use a hardcoded value, and/or provide a command line argument, or anything else.