Fix backend factory fallback before simulator initialization by sylvesterkaczmarek · Pull Request #7121 · isaac-sim/IsaacLab

sylvesterkaczmarek · 2026-08-15T23:33:39Z

Description

FactoryBase._get_backend() can be called before a SimulationContext has been created, but it previously dereferenced SimulationContext.instance().physics_manager unconditionally. SimulationContext.instance() returns None before initialization, so backend resolution could fail before any fallback was applied.

Following maintainer confirmation, the pre-context fallback is now newton. Initialized backend resolution remains unchanged for Newton, PhysX, and OV PhysX contexts.

A separate follow-up should update SimulationCfg(physics=None) to default to Newton as well; that broader configuration-default change is intentionally outside this PR.

Validation

Adds unit coverage for backend resolution with SimulationContext._instance unset and verifies the newton fallback.

Type of change

Bug fix

greptile-apps · 2026-08-15T23:35:55Z

Greptile Summary

The PR fixes backend detection before simulator initialization by returning the documented PhysX compatibility fallback when no SimulationContext exists.

Preserves existing backend detection when a simulation context is active.
Adds focused unit coverage for the uninitialized singleton state.
Documents the fix in the changelog.

Confidence Score: 5/5

The PR appears safe to merge with no actionable defects identified.

The null guard makes the implementation match its documented pre-initialization contract, and backend selection remains dynamically resolved after a simulation context exists.

Important Files Changed

Filename	Overview
source/isaaclab/isaaclab/utils/backend_utils.py	Adds the missing null-context guard while leaving initialized backend-name mapping unchanged.
source/isaaclab/test/utils/test_backend_fallback.py	Adds focused unit coverage that safely restores the patched singleton state through pytest's monkeypatch fixture.
source/isaaclab/changelog.d/sylvesterkaczmarek-fix-backend-fallback.rst	Accurately describes the corrected pre-initialization fallback behavior.

_{Reviews (1): Last reviewed commit: "docs: note backend fallback fix" | Re-trigger Greptile}

isaaclab-review-bot

Isaac Lab Review Bot

The change adds the missing None guard so backend resolution returns the documented physx fallback before SimulationContext initialization. The focused regression test and changelog fragment align with that behavior.

Design and architecture: Backend selection remains contained within FactoryBase._get_backend(). Existing initialized-context routing for newton, ovphysx, and physx is unchanged, and the fallback continues through the established registry and module-resolution paths.
API: The method retains its str return contract and changes no public symbols or exports. Pre-initialization behavior now matches the existing docstring rather than raising while dereferencing a nonexistent context.
Implementation: The early return directly prevents access to physics_manager when SimulationContext.instance() is None. The regression test covers that boundary, though its setup uses the private SimulationContext._instance attribute as a small non-blocking maintenance tradeoff.

No blocking issues. No inline issue met the actionable-evidence threshold; the assessment above records the review feedback.

Automated review; human maintainers own approval decisions.

Signed-off-by: Sylvester Kaczmarek <16242628+sylvesterkaczmarek@users.noreply.github.com>

sylvesterkaczmarek · 2026-08-21T21:02:47Z

Updated per the team confirmation: the pre-context backend fallback is now newton, with the regression test and changelog updated accordingly. I’ve kept the SimulationCfg(physics=None) default change separate as the requested follow-up.

ooctipus · 2026-08-22T10:32:44Z

Hi @sylvesterkaczmarek thanks for the pr, we have a test file called source/isaaclab/test/utils/test_backend_utils.py, can you put your test there

sylvesterkaczmarek · 2026-08-22T10:35:27Z

Hi @sylvesterkaczmarek thanks for the pr, we have a test file called source/isaaclab/test/utils/test_backend_utils.py, can you put your test there

Sure. Thanks for your guidance.

sylvesterkaczmarek · 2026-08-22T10:41:43Z

Done. The fallback test is now in test_backend_utils.py, and the standalone test file has been removed.

…7299) ## Summary Backports the following merged changes to `release/3.0.0` as separate provenance-preserving cherry-picks: - #7292 — scope Newton global imports with clone plans - #7285 — stabilize the sensor/PhysX video recording test - #7269 — streamline Newton contact and raycast sensor startup - #7119 — normalize non-finite depth display values safely - #7295 — avoid repeated Newton model and articulation startup work Each source squash commit was cherry-picked with `-x` and applied without conflicts. ## Validation - Stable patch IDs match all five source squash commits exactly. - File-by-file manifests match each source squash commit. - `git diff --check upstream/release/3.0.0..HEAD` - `uv run --frozen python tools/changelog/cli.py check backport-7285-7292-base` - `SKIP=check-changelog-fragments uv run --frozen isaaclab -f` - Cloner/Newton focused tests: 98 passed - Scene global-ownership tests: 2 passed - Simulator clone-plan tests: 4 passed - Video recording regression test: 1 passed - Newton BVH lifecycle tests: 2 passed - Newton contact-selector tests: 7 passed - Newton raycast BVH test: 4 passed - Non-finite depth display tests: 4 passed - #7295 physics lifecycle, cloner, manager, and coupling tests: 248 passed - #7295 Newton joint-wrench sensor tests: 11 passed - #7295 PhysX joint-wrench sensor tests: 16 passed PR #7121 remains open and is intentionally excluded; it will be backported from its final merge commit after merging. --------- Signed-off-by: Sylvester Kaczmarek <16242628+sylvesterkaczmarek@users.noreply.github.com> Co-authored-by: matthewtrepte <mtrepte@nvidia.com> Co-authored-by: camevor <camevor@nvidia.com> Co-authored-by: Sylvester Kaczmarek <16242628+sylvesterkaczmarek@users.noreply.github.com> Co-authored-by: Antoine RICHARD <antoiner@nvidia.com>

…im#7121) # Description `FactoryBase._get_backend()` can be called before a `SimulationContext` has been created, but it previously dereferenced `SimulationContext.instance().physics_manager` unconditionally. `SimulationContext.instance()` returns `None` before initialization, so backend resolution could fail before any fallback was applied. Following maintainer confirmation, the pre-context fallback is now `newton`. Initialized backend resolution remains unchanged for Newton, PhysX, and OV PhysX contexts. A separate follow-up should update `SimulationCfg(physics=None)` to default to Newton as well; that broader configuration-default change is intentionally outside this PR. ## Validation Adds unit coverage for backend resolution with `SimulationContext._instance` unset and verifies the `newton` fallback. ## Type of change - Bug fix --------- Signed-off-by: Sylvester Kaczmarek <16242628+sylvesterkaczmarek@users.noreply.github.com> Co-authored-by: ooctipus <zhengyuz@nvidia.com> (cherry picked from commit 9f65e3d)

…#7303 (#7313) # Description Backports six merged PRs to `release/3.0.0` as separate provenance-preserving cherry-picks: | Source PR | Source commit | Backport commit | Scope | | --- | --- | --- | --- | | #7272 | `0081477fea2` | `c9fc1997476` | Fix scene-wide gravity distributions for PhysX and OvPhysX. | | #7121 | `9f65e3d4fd2` | `cce8acd84e1` | Fix backend-factory fallback before simulator initialization. | | #7183 | `3fcc9c6b824` | `99d58d3d3c4` | Streamline the getting-started documentation. | | #7306 | `6aad90be0ae` | `9a786cc028a` | Optimize Newton test runtime. | | #7305 | `1c9ba908cf1` | `a2dc8ce948e` | Disable Warp autodiff in the test suite. | | #7303 | `393fc37d2b0` | `249a5cb97d8` | Remove post-Hydra preset resolution. | #7272 forwards the validated `uniform`, `log_uniform`, or `gaussian` distribution through both scene-wide backend paths. Newton behavior is unchanged. #7121 makes factory resolution fall back to Newton when no `SimulationContext` exists while retaining the visualizer contract of reporting no active backend before context creation. #7183 is documentation-only. #7306 and #7305 change test infrastructure only; they do not change runtime behavior. #7303 makes `resolve_task_config` and `parse_env_cfg` the task-composition boundary. Runtime consumers now require concrete physics, renderer, and camera configurations and no longer attempt late preset fallback after Hydra composition. The branch was synchronized with the current `release/3.0.0` tip containing #7301 before #7303 was applied. All six source cherry-picks applied without conflicts. A file-by-file existence, mode, and blob audit confirmed that every #7303 path matches its merged source commit exactly. ## Validation ### #7272 - Regression verification against the unpatched `release/3.0.0` tip — both PhysX and OvPhysX cases failed as expected. - `uv run --extra test --frozen python -m pytest -q source/isaaclab/test/envs/test_gravity_randomization.py source/isaaclab/test/envs/test_mdp_event_selectors.py` — 7 passed. - `uv run --extra test --extra ovphysx --frozen python -m pytest -q source/isaaclab_ov/test/physics/test_ovphysx_gravity.py` — 1 passed. ### #7121 - Regression verification before the #7121 cherry-pick reproduced the original `NoneType.physics_manager` failure. - `uv run --extra test --frozen python -m pytest -q source/isaaclab/test/utils/test_backend_utils.py source/isaaclab/test/visualizers/test_visualizer.py` — 18 passed. ### #7183 - `uv run --frozen --extra test python -m pytest --noconftest -q tools/test/test_environ_docs.py` — 26 passed. ### #7306 - All 9 affected paths match the merged source PR exactly. - The full simulator-backed Newton suite is left to backport CI because this local worktree does not include the full Isaac Sim runtime. ### #7305 - Loaded the root `conftest.py` successfully with Warp unavailable. - Loaded it with Warp installed and confirmed `wp.config.enable_backward is False`. ### #7303 - Hydra and Shadow Hand camera suites — 129 passed. - Benchmark capture and RL entrypoint suites — 31 passed. - Experimental frontend and custom-coupling suites — 74 passed, 1 skipped. - Ruff and Ruff-format passed for every changed Python path. - Source/backport audit — 54 paths checked, 0 mismatches. - The Isaac Sim-backed integration case is left to CI because this local worktree is kitless. ### Repository gates - `git diff --check upstream/release/3.0.0...HEAD` — passed. --------- Signed-off-by: Sylvester Kaczmarek <16242628+sylvesterkaczmarek@users.noreply.github.com> Co-authored-by: Antoine RICHARD <antoiner@nvidia.com> Co-authored-by: Sylvester Kaczmarek <16242628+sylvesterkaczmarek@users.noreply.github.com> Co-authored-by: Mustafa H <34825877+StafaH@users.noreply.github.com>

sylvesterkaczmarek requested a review from a team August 15, 2026 23:33

sylvesterkaczmarek requested review from AntoineRichard, StafaH, fatimaanes, kellyguo11, ooctipus and pbarejko as code owners August 15, 2026 23:33

github-actions Bot added bug Something isn't working isaac-lab Related to Isaac Lab team labels Aug 15, 2026

isaaclab-review-bot Bot reviewed Aug 15, 2026

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sylvesterkaczmarek force-pushed the fix/backend-fallback-without-sim-context branch from 1de1346 to 63ece49 Compare August 16, 2026 10:08

Fix backend factory fallback before simulator initialization

e39376f

Signed-off-by: Sylvester Kaczmarek <16242628+sylvesterkaczmarek@users.noreply.github.com>

sylvesterkaczmarek force-pushed the fix/backend-fallback-without-sim-context branch from 63ece49 to e39376f Compare August 16, 2026 10:29

AntoineRichard reviewed Aug 20, 2026

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Comment thread source/isaaclab/isaaclab/utils/backend_utils.py Outdated

sylvesterkaczmarek added 3 commits August 21, 2026 21:57

Use Newton as pre-context backend fallback

84ca92b

Update backend fallback regression for Newton

48ab329

Document Newton pre-context backend fallback

9a5d310

ooctipus approved these changes Aug 22, 2026

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sylvesterkaczmarek and others added 4 commits August 22, 2026 11:39

test: move backend fallback coverage into backend utils tests

7871d6e

test: remove standalone backend fallback test file

a5abd95

style: separate backend utility tests

0fbeb51

Merge branch 'develop' into fix/backend-fallback-without-sim-context

4466a45

ooctipus enabled auto-merge (squash) August 22, 2026 10:42

ooctipus mentioned this pull request Aug 22, 2026

[Backport release/3.0.0] Newton startup, cloner, and rendering fixes #7299

Merged

Remove stale pre-context visualizer assertion

cd112ef

fix: preserve visualizer backend contract before context

c6854ba

auto-merge was automatically disabled August 22, 2026 14:49
Head branch was pushed to by a user without write access

sylvesterkaczmarek and others added 2 commits August 22, 2026 15:49

test: retain pre-context visualizer coverage

1d9764b

Merge branch 'develop' into fix/backend-fallback-without-sim-context

fc80c03

ooctipus merged commit 9f65e3d into isaac-sim:develop Aug 23, 2026
47 of 48 checks passed

ooctipus mentioned this pull request Aug 24, 2026

[Backport release/3.0.0] Bundle #7272, #7121, #7183, #7306, #7305, and #7303 #7313

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Fix backend factory fallback before simulator initialization - #7121

Fix backend factory fallback before simulator initialization#7121
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Confidence Score: 5/5

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sylvesterkaczmarek commented Aug 15, 2026 •

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