anthropics/nix-eval-jobs

anthropics/nix-eval-jobs

Description: Parallel nix evaluator with a streamable json output [maintainers @Mic92, @adisbladis]

License: GPL-3.0

Stars: 8

Forks: 4

Open issues: 0

Created: 2026-01-26T14:26:13Z

Pushed: 2026-01-14T11:59:31Z

Default branch: main

Fork: yes

Parent repository: NixOS/nix-eval-jobs

Archived: no

README:

nix-eval-jobs

This project evaluates nix attribute sets in parallel with streamable json output. This is useful for time and memory intensive evaluations such as NixOS machines, i.e. in a CI context. The evaluation is done with a controllable number of threads that are restarted when their memory consumption exceeds a certain threshold.

To facilitate integration, nix-eval-jobs creates garbage collection roots for each evaluated derivation (drv file, not the build) within the provided attribute. This prevents race conditions between the nix garbage collection service and user-started nix builds processes.

Why using nix-eval-jobs?

• Faster evaluation by using threads
• Memory used for evaluation is reclaimed after nix-eval-jobs finish, so that

the build can use it.

• Evaluation of jobs can fail individually

Example

In the following example we evaluate the hydraJobs attribute of the patchelf flake:

$ nix-eval-jobs --gc-roots-dir gcroot --flake 'github:NixOS/patchelf#hydraJobs'
{"attr":"coverage","attrPath":["coverage"],"drvPath":"/nix/store/fmbqzaq8mim1423879lhn9whs6imx5w4-patchelf-coverage-0.18.0.drv","inputDrvs":{"/nix/store/23632hx2c98lbbjld279dx0w08lxn6kp-hook.drv":["out"],"/nix/store/6z1jfnqqgyqr221zgbpm30v91yfj3r45-bash-5.1-p16.drv":["out"],"/nix/store/ap9g09fxbicj836zm88d56dn3ff4clxl-stdenv-linux.drv":["out"],"/nix/store/c0gg7lj101xhd8v2b3cjl5dwwkpxfc0q-patchelf-tarball-0.18.0.drv":["out"],"/nix/store/vslywm6kbazi37q1vbq8y7bi884yc6yx-lcov-1.16.drv":["out"],"/nix/store/y964yq4vz1gsn7azd44vyg65gnr4gpvi-hook.drv":["out"]},"name":"patchelf-coverage-0.18.0","outputs":{"out":"/nix/store/gfni9sbhhwhxxfqziq1fs3n82bvw962l-patchelf-coverage-0.18.0"},"system":"x86_64-linux"}
{"attr":"patchelf-win32","attrPath":["patchelf-win32"],"drvPath":"/nix/store/s38l0fg5ja6j8qpws7slw2ws0c6v0qcf-patchelf-i686-w64-mingw32-0.18.0.drv","inputDrvs":{"/nix/store/6z1jfnqqgyqr221zgbpm30v91yfj3r45-bash-5.1-p16.drv":["out"],"/nix/store/b2p151ilwqpd47fbmzz50a5cmj12ixbf-hook.drv":["out"],"/nix/store/fbnhh18m4jh6cwa92am2sv3aqzjnzpdd-stdenv-linux.drv":["out"]},"name":"patchelf-i686-w64-mingw32-0.18.0","outputs":{"out":"/nix/store/w8r4h1xk71fryb99df8aszp83kfhw3bc-patchelf-i686-w64-mingw32-0.18.0"},"system":"x86_64-linux"}
{"attr":"patchelf-win64","attrPath":["patchelf-win64"],"drvPath":"/nix/store/wxpym6d3dxr1w9syhinp7f058gwxfmd3-patchelf-x86_64-w64-mingw32-0.18.0.drv","inputDrvs":{"/nix/store/6z1jfnqqgyqr221zgbpm30v91yfj3r45-bash-5.1-p16.drv":["out"],"/nix/store/71lv5lsr1y59bv1b91jc9gg0n85kf1sq-stdenv-linux.drv":["out"],"/nix/store/b2p151ilwqpd47fbmzz50a5cmj12ixbf-hook.drv":["out"]},"name":"patchelf-x86_64-w64-mingw32-0.18.0","outputs":{"out":"/nix/store/fkq5428l2xsb84yj0cc6q1lkvsrga7sv-patchelf-x86_64-w64-mingw32-0.18.0"},"system":"x86_64-linux"}
{"attr":"release","attrPath":["release"],"drvPath":"/nix/store/3xpwg8f623dpkh6cblv2fzcq5n99xl0j-patchelf-0.18.0.drv","inputDrvs":{"/nix/store/6z1jfnqqgyqr221zgbpm30v91yfj3r45-bash-5.1-p16.drv":["out"],"/nix/store/9rmihrl9ys0sap6827xyns0y73vqafjx-patchelf-0.18.0.drv":["out"],"/nix/store/am2zqx3pyc1i14f888jna785h0f841sg-patchelf-0.18.0.drv":["out"],"/nix/store/c0gg7lj101xhd8v2b3cjl5dwwkpxfc0q-patchelf-tarball-0.18.0.drv":["out"],"/nix/store/csjiccxbwpfv55m8kqs2xwrkkha14dnq-patchelf-0.18.0.drv":["out"],"/nix/store/jsrnpxdx5vmpnakd9bkb3sk3lgh0k8hm-patchelf-0.18.0.drv":["out"],"/nix/store/k8a51ax83554c67g98xf3y751vjgjs7m-patchelf-0.18.0.drv":["out"],"/nix/store/wq3ncl207isqqkqmsa5ql4fg19jbrhxg-stdenv-linux.drv":["out"]},"name":"patchelf-0.18.0","outputs":{"out":"/nix/store/d0mzprvv3vhasj23r1a6qn8qip0srbc4-patchelf-0.18.0"},"system":"x86_64-linux"}
{"attr":"tarball","attrPath":["tarball"],"drvPath":"/nix/store/c0gg7lj101xhd8v2b3cjl5dwwkpxfc0q-patchelf-tarball-0.18.0.drv","inputDrvs":{"/nix/store/6z1jfnqqgyqr221zgbpm30v91yfj3r45-bash-5.1-p16.drv":["out"],"/nix/store/9d754glmsvpjm5kxvgsjslvgv356kbmn-libtool-2.4.7.drv":["out"],"/nix/store/ap9g09fxbicj836zm88d56dn3ff4clxl-stdenv-linux.drv":["out"],"/nix/store/f1ksgsyplvb0sli4pls6k6vsfvmv519d-autoconf-2.71.drv":["out"],"/nix/store/jf58lcnch1bmpbi2188c59w5zr1cqrx2-automake-1.16.5.drv":["out"]},"name":"patchelf-tarball-0.18.0","outputs":{"out":"/nix/store/72pz5awc7gpwdqxrdsy8j0bvg2n7z78q-patchelf-tarball-0.18.0"},"system":"x86_64-linux"}

The output here is newline-seperated json according to https://jsonlines.org.

The code is derived from hydra's eval-jobs executable.

Further options

USAGE: nix-eval-jobs [options] expr

--apply Apply provided Nix function to each derivation. The result of this function will be serialized as a JSON value and stored inside `"extraValue"` key of the json line output.
--arg Pass the value *expr* as the argument *name* to Nix functions.
--arg-from-file Pass the contents of file *path* as the argument *name* to Nix functions.
--arg-from-stdin Pass the contents of stdin as the argument *name* to Nix functions.
--argstr Pass the string *string* as the argument *name* to Nix functions.
--check-cache-status Check if the derivations are present locally or in any configured substituters (i.e. binary cache). The information will be exposed in the `cacheStatus` field of the JSON output.
--constituents whether to evaluate constituents for Hydra's aggregate feature
--debug Set the logging verbosity level to 'debug'.
--eval-store
The [URL of the Nix store](@docroot@/store/types/index.md#store-url-format)
to use for evaluation, i.e. to store derivations (`.drv` files) and inputs referenced by them.

--expr treat the argument as a Nix expression
--flake build a flake
--force-recurse force recursion (don't respect recurseIntoAttrs)
--gc-roots-dir garbage collector roots directory
--help show usage information
--impure allow impure expressions
--include
Add *path* to search path entries used to resolve [lookup paths](@docroot@/language/constructs/lookup-path.md)

This option may be given multiple times.

Paths added through `-I` take precedence over the [`nix-path` configuration setting](@docroot@/command-ref/conf-file.md#conf-nix-path) and the [`NIX_PATH`…