fix: Suppress SIGSEGV errors on startup

[erichare]

This pull request introduces improvements to error handling in the server code and adds new unit tests for worker count logic in the CLI. The main changes are grouped into error handling enhancements and test coverage expansion.

Error handling enhancements:

• Added an override for the error method in the server class (src/backend/base/langflow/server.py) to filter out "SIGSEGV" messages. These messages, common on macOS due to multiprocessing issues, are now logged at the debug level instead of error to reduce noise in error logs.

Test coverage expansion:

• Imported platform and get_number_of_workers in the CLI test module to support new tests for worker count logic (src/backend/tests/unit/test_cli.py).
• Added a unit test for get_number_of_workers to verify that it correctly uses CPU count on Linux and respects explicit worker values (src/backend/tests/unit/test_cli.py).

Summary by CodeRabbit

• Bug Fixes

  • Enhanced error logging to better handle system-level messages.

• New Features

  • Added worker count calculation optimized for available system resources.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

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Walkthrough

Two changes across two files: A Logger.error method override in the server module filters SIGSEGV-related messages to debug level instead of error. A new unit test in test_cli.py validates the get_number_of_workers function behavior under mocked system conditions.

Changes

Cohort / File(s)	Change Summary
Logging filter enhancement src/backend/base/langflow/server.py	Adds error() method override to Logger class that intercepts SIGSEGV messages and logs them at debug level; other error messages delegate to base class.
Worker count test src/backend/tests/unit/test_cli.py	Adds test imports (get_number_of_workers, platform module) and introduces test_get_number_of_workers() to validate default worker calculation (cpu_count × 2 + 1) and explicit value handling.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

• Verify the SIGSEGV filtering does not inadvertently suppress legitimate application errors or warnings
• Confirm the worker calculation formula aligns with intended concurrency behavior across different platform types
• Ensure test mocking of platform.system and cpu_count produces representative coverage

Pre-merge checks and finishing touches

Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error, 2 warnings)

Check name	Status	Explanation	Resolution
Test Coverage For New Implementations	❌ Error	PR adds Logger.error override in server.py for SIGSEGV filtering but includes no unit tests for this functionality, creating a test coverage gap for a core code change.	Add unit tests in src/backend/tests/unit/test_server.py to verify Logger.error correctly logs SIGSEGV at debug level and other errors at error level.
Docstring Coverage	⚠️ Warning	Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.
Test Quality And Coverage	⚠️ Warning	Logger.error override lacks unit tests; test_get_number_of_workers covers only Linux with single cpu_count; unused platform import remains.	Add comprehensive unit tests for Logger.error override and expand test_get_number_of_workers to cover Windows, macOS, edge cases, and remove unused platform import.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'fix: Suppress SIGSEGV errors on startup' directly matches the main change in the changeset: an override of the Logger.error method to filter and suppress SIGSEGV-related messages.
Excessive Mock Usage Warning	✅ Passed	Test demonstrates appropriate mock usage with only two necessary external system dependencies mocked, validating worker count calculation logic without unnecessary complexity.

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[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.54%. Comparing base (613f682) to head (2f3fe8c).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/backend/base/langflow/server.py	25.00%	3 Missing ⚠️

❌ Your patch status has failed because the patch coverage (25.00%) is below the target coverage (40.00%). You can increase the patch coverage or adjust the target coverage.
❌ Your project status has failed because the head coverage (39.99%) is below the target coverage (60.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10849      +/-   ##
==========================================
- Coverage   32.55%   32.54%   -0.02%     
==========================================
  Files        1370     1370              
  Lines       63514    63517       +3     
  Branches     9391     9391              
==========================================
- Hits        20678    20671       -7     
- Misses      41797    41806       +9     
- Partials     1039     1040       +1     

Flag	Coverage Δ
backend	51.53% <25.00%> (-0.05%)	⬇️
lfx	39.99% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/backend/base/langflow/server.py	62.22% <25.00%> (-3.64%)	⬇️

... and 4 files with indirect coverage changes

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

src/backend/tests/unit/test_cli.py (1)

151-161: Consider expanding test coverage for edge cases.

The test correctly validates default and explicit worker count behavior. However, the implementation in langflow.__main__.get_number_of_workers (lines 126-130) also handles workers == -1 as a trigger for default behavior, which is not currently tested.

Consider adding a test case for the -1 value:

def test_get_number_of_workers():
    """Test that get_number_of_workers uses cpu_count on Linux."""
    with patch("langflow.__main__.platform.system", return_value="Linux"), \
         patch("langflow.__main__.cpu_count", return_value=4):
            # Test default behavior (None)
            workers = get_number_of_workers(None)
            assert workers == (4 * 2) + 1  # 9 workers

            # Test -1 triggers default behavior
            workers = get_number_of_workers(-1)
            assert workers == (4 * 2) + 1  # 9 workers

            # Test explicit value is respected
            workers = get_number_of_workers(2)
            assert workers == 2

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📥 Commits

Reviewing files that changed from the base of the PR and between 692d659 and 304e1a0.

📒 Files selected for processing (2)

• src/backend/base/langflow/server.py (1 hunks)
• src/backend/tests/unit/test_cli.py (2 hunks)

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src/backend/**/*.py

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src/backend/**/*.py: Use FastAPI async patterns with await for async operations in component execution methods
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• src/backend/base/langflow/server.py
• src/backend/tests/unit/test_cli.py

src/backend/tests/**/*.py

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Files:

• src/backend/tests/unit/test_cli.py

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src/backend/tests/unit/test_cli.py (1)

src/backend/base/langflow/__main__.py (1)

• get_number_of_workers (127-131)

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src/backend/tests/unit/test_cli.py

[error] 1-1: Ruff lint error: F401 'platform' imported but unused. Command: 'uv run --only-dev ruff check --output-format=github .'

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src/backend/tests/unit/test_cli.py

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🔇 Additional comments (1)

src/backend/base/langflow/server.py (1)

53-61: LGTM! Error filtering implementation is sound.

The override correctly filters SIGSEGV messages to debug level, reducing log noise while preserving other error messages. The string matching approach using str(msg) is defensive and the method signature properly delegates *args, **kwargs.

One minor consideration: this will suppress all SIGSEGV messages, which could potentially mask legitimate segmentation faults. However, the comment indicates these are "typically handled by worker restart" on macOS, suggesting this is an intentional trade-off for cleaner logs.

[carlosrcoelho]

LGTM