Runtime Settings

Scala Native comes with some ability to change the runtime characteristics.

Garbage Collector (GC) Settings

Scala Native supports the Boehm-Demers-Weiser Garbage Collector. The environment variables defined in Boehm are planned to be shared by all the Garbage Collectors supported in Scala Native so they are consistent. The variables supported are listed below for each GC.

All Garbage Collectors

The following environment variables will be used for all GCs. They can go from 1 MB to the system memory maximum or up to about 512 GB. The size is in bytes, kilobytes(k or K), megabytes(m or M), or gigabytes(g or G). Examples: 1024k, 1M, or 1G etc.

  • GC_INITIAL_HEAP_SIZE changes the minimum heap size.

  • GC_MAXIMUM_HEAP_SIZE changes the maximum heap size.

The plan is to add more GC settings in the future using the Boehm setting names where applicable.

Boehm GC

The Boehm GC uses the two variables shown above. The following is available for Boehm and Commix.


The following document shows all the variables available for Boehm: README.

None GC

The None GC uses the two variables shown above.

Immix GC

The Immix GC uses the two variables shown above as well as the following variable.

  • GC_STATS_FILE (set to the file name)

Commix GC

In addition to the variables described above for Immix, Commix has the following variable shared with Boehm.

  • GC_NPROCS (default is processor count - 1 up to 8 maximum)

Commix also adds a few more variables which do not match the Boehm settings yet.

  • GC_TIME_RATIO (default is .05)

  • GC_FREE_RATIO (default is .5)

Note: GC_STATS_FILE shared with Immix is only honored if the compiler defines -DGC_ENABLE_STATS for Commix.


If you are developing in the Scala Native sandbox, the following are examples showing some error conditions using Immix, the default GC. Adjust the path to your executable as needed:

$ export GC_INITIAL_HEAP_SIZE=64k; export GC_MAXIMUM_HEAP_SIZE=512k; sandbox/.2.13/target/scala-2.13/sandbox
GC_MAXIMUM_HEAP_SIZE too small to initialize heap.
Minimum required: 1m

$ export GC_INITIAL_HEAP_SIZE=2m; export GC_MAXIMUM_HEAP_SIZE=1m; sandbox/.2.13/target/scala-2.13/sandbox

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