Open the asset server connection before the scene needs it

[camevor]

Description

Every remote asset lookup is one round trip on a kept-alive connection, but the first one also pays DNS resolution and the TCP and TLS handshakes. Instead, open the connection on a background thread once the extensions are loaded, so the handshake overlaps with the rest of startup. A run whose configured asset root is local opens no connection at all.

Type of change

• (Startup performance enhancement)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have added a changelog fragment under source/<pkg>/changelog.d/ for every touched package (do not edit CHANGELOG.rst or bump extension.toml — CI handles that)
• I have added my name to the CONTRIBUTORS.md or my name already exists there

[isaaclab-review-bot]

Isaac Lab Review Bot

The asset-server prewarm is appropriately isolated in a private assets helper and covered for remote, repeated, and local-root behavior. One startup-order issue should be fixed: importing the assets module before the post-extension path sanitization can permanently cache dependencies from a conflicting Kit path.

• Design and architecture: The lifecycle split is sound: AppLauncher triggers the work after extensions load, while the assets module owns remote-root detection and the deferred omni.client operation. However, the trigger must occur after AppLauncher restores the intended Python import precedence.
• API: No public API compatibility issue is introduced. The helper remains private, existing asset-root symbols are unchanged, and the user-visible startup behavior has an appropriately phrased changelog fragment.
• Implementation: The one-shot guard, background daemon thread, local-path filtering, and deferred error handling match the intended prewarm behavior. Move the import and call below _deprioritize_prebundle_paths(); otherwise assets.py and its module-level dependencies, including filelock, may be resolved and cached from conflicting pip_prebundle paths before sanitization can take effect.

Minor fixes needed. Posted 1 actionable finding inline.

Automated review; human maintainers own approval decisions.

[isaaclab-review-bot]

🟡 Warning · Implementation — Prewarm import precedes path sanitization

This imports isaaclab.utils.assets (which imports filelock at module scope) before the _deprioritize_prebundle_paths() pass a few lines below, whose comment states the second pass exists because Kit and its extensions may have just inserted conflicting pip_prebundle directories onto sys.path. Modules resolved and cached here cannot be corrected afterwards. Move the prewarm import and call below _deprioritize_prebundle_paths(); the startup overlap benefit is unchanged.

[greptile-apps]

Greptile Summary

The PR starts a best-effort background request to a configured remote asset root after Isaac Sim extensions load, allowing connection setup to overlap the remaining startup work. It skips local roots, suppresses prewarm failures, and adds coverage for remote and local configurations.

• Adds asset-server prewarming to AppLauncher.
• Uses a single daemon thread to issue the initial remote omni.client.stat.
• Adds tests for one-time remote prewarming and local-root exclusion.
• Adds the required changelog fragment.

Confidence Score: 5/5

The PR appears safe to merge, with no concrete changed-code failure identified.

The prewarm is limited to remote roots, runs after extension loading, contains failures without changing normal lookup behavior, and is covered for its principal remote and local cases.

Important Files Changed

Filename	Overview
source/isaaclab/isaaclab/app/app_launcher.py	Starts asset-server prewarming after extensions load and before scene construction.
source/isaaclab/isaaclab/utils/assets.py	Adds a guarded, best-effort daemon thread that contacts only remote configured asset roots.
source/isaaclab/test/utils/test_assets.py	Covers one-time remote prewarming and verifies that POSIX and Windows local roots are ignored.
source/isaaclab/changelog.d/asset-server-prewarm.rst	Documents the startup-performance enhancement and local-root behavior.

Sequence Diagram

sequenceDiagram
    participant L as AppLauncher
    participant P as Prewarm thread
    participant C as omni.client
    participant S as Scene construction
    L->>L: Load Isaac Sim extensions
    L->>P: Start daemon thread for remote root
    par Connection prewarm
        P->>C: stat(asset root)
    and Remaining startup
        L-->>S: Return initialized application
        S->>C: Perform first asset lookup
    end

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[ooctipus]

HI @camevor
do you know how much improvement this pr gives?
In my end it seems only improve 50-100ms