[fix] Fix HTML logger parallel file collision by nohwnd · Pull Request #15435 · microsoft/vstest

nohwnd · 2026-03-04T14:56:40Z

Summary

When multiple vstest.console processes run in parallel with the HTML logger, temporary XML result files can collide because:

The timestamp format (yyyyMMdd_HHmmss) only has second-level precision
The in-process lock (FileCreateLockObject) doesn't prevent cross-process races
Two processes finishing in the same second generate identical filenames

Changes

`src/Microsoft.TestPlatform.Extensions.HtmlLogger/HtmlLogger.cs`

Add millisecond precision to timestamp - changes format from HHmmss to HHmmssfff, greatly reducing collision likelihood across parallel processes
Use FileMode.CreateNew for atomic file creation - replaces the File.Exists + File.Create pattern with an atomic create-if-not-exists operation that retries on IOException
Remove unused FileCreateLockObject - the cross-process lock was ineffective

`test/Microsoft.TestPlatform.Extensions.HtmlLogger.UnitTests/HtmlLoggerTests.cs`

Added XmlFilePathShouldContainMillisecondTimestampForCrossProcessUniqueness test

Documentation

Updated .github/copilot-instructions.md with build/test commands, repo structure, and logger architecture
Updated .github/skills/vstest-build-test/SKILL.md with logger-specific notes

Testing

All 34 HTML logger unit tests pass on both net9.0 and net48.

Add pre-build environment setup section that detects when .dotnet contains binaries for the wrong OS and cleans .dotnet, .packages, and artifacts for a fresh bootstrap. Update all build/test commands to show both Linux/macOS and Windows equivalents with a quick-reference table. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

…sification - Add PowerShell OS detection alongside bash - Add guidance for extracting OS-specific commands from tables - Add placeholder substitution and cross-platform adaptation rules - Use SQL tracking table instead of markdown table - Distinguish ENV_ISSUE from ERROR in result classification - Improve Fix or Flag section with actionable steps per status Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- eng/build.ps1: Forward exit code from Arcade build script using \�xit \0\ to ensure non-zero exit codes are propagated to the caller - eng/common/tools.ps1: Add diagnostic log message before exiting so the exit code is visible in build output - .github/skills/vstest-build-test/SKILL.md: Fix Windows test filter flag from \-p\ to \-projects\ since \-p\ is ambiguous in PowerShell and does not work as expected Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

When multiple vstest processes run in parallel with the HTML logger, temporary XML result files could collide because the timestamp-based filename only has second-level precision, and the in-process lock doesn't prevent cross-process races. Changes: - Include process ID in the temp XML filename for cross-process uniqueness - Replace File.Exists + File.Create with atomic FileMode.CreateNew to handle any remaining race conditions gracefully via retry - Remove unused FileCreateLockObject (cross-process lock was ineffective) Fixes: #15404 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Add build commands, test project mappings, repository structure, logger architecture notes, and analyzer pitfalls to copilot-instructions.md. Update vstest-build-test skill with logger-specific notes covering TRX and HTML logger architecture, test patterns, and common analyzer issues. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Fixes cross-process temp XML filename collisions in the HTML logger when multiple vstest.console instances run in parallel.

Changes:

Adds PID to the temp XML filename and switches to FileMode.CreateNew for atomic “create if not exists”.
Adds a unit test to validate the PID is present in the generated XML path.
Updates build/doc tooling and authoring docs for repo build/test guidance.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/Microsoft.TestPlatform.Extensions.HtmlLogger.UnitTests/HtmlLoggerTests.cs	Adds a unit test asserting PID is included in the temp XML filename.
src/Microsoft.TestPlatform.Extensions.HtmlLogger/HtmlLogger.cs	Adds PID to filename and uses `FileMode.CreateNew` for atomic file creation; removes ineffective in-proc lock.
eng/common/tools.ps1	Adds an extra console message when exiting with an exit code.
eng/build.ps1	Attempts to forward the exit code from the invoked Arcade build script.
.github/skills/vstest-build-test/SKILL.md	Adds repo-specific build/test instructions and logger notes.
.github/skills/validate-skills/SKILL.md	Adds a procedure for validating that documented skill commands work.
.github/skills/creating-skills/SKILL.md	Adds guidance for creating skill files and frontmatter.
.github/copilot-instructions.md	Adds build/test command guidance and repository structure notes.

When multiple vstest processes run in parallel with the HTML logger, temporary XML result files could collide because the timestamp-based filename only has second-level precision, and the in-process lock doesn't prevent cross-process races. Changes: - Add millisecond precision to temp XML filename timestamp (HHmmss → HHmmssfff) to greatly reduce collision likelihood across parallel processes - Replace File.Exists + File.Create with atomic FileMode.CreateNew to handle any remaining race conditions gracefully via retry - Remove unused FileCreateLockObject (cross-process lock was ineffective) Fixes: #15404 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

nohwnd · 2026-03-04T15:08:39Z

needs merge of #15434

Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Copilot · 2026-03-05T15:28:11Z

+- **Temp XML naming:** `TestResult_{user}_{machine}_{timestamp}_{pid}.xml` — PID ensures cross-process uniqueness
+- **File creation:** Uses `FileMode.CreateNew` for atomic creation with retry on collision


Same issue as in copilot-instructions.md: the documented filename pattern includes {pid} but the actual code does not add a PID to the filename. The uniqueness strategy relies on millisecond timestamps plus FileMode.CreateNew with retry. This documentation should be corrected to match the actual implementation.

Suggested change

- **Temp XML naming:** `TestResult_{user}_{machine}_{timestamp}_{pid}.xml` — PID ensures cross-process uniqueness

- **File creation:** Uses `FileMode.CreateNew` for atomic creation with retry on collision

- **Temp XML naming:** `TestResult_{user}_{machine}_{timestamp}.xml` — timestamp-based name only (no PID)

- **File creation:** Uses `FileMode.CreateNew` for atomic creation with retry on collision; millisecond timestamps + `CreateNew` retries provide uniqueness

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com> Co-authored-by: Youssef Victor <youssefvictor00@gmail.com>

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

src/Microsoft.TestPlatform.Extensions.HtmlLogger/HtmlLogger.cs:366

GenerateUniqueFilePath uses File.Exists(fullFilePath) in the exception filter, bypassing the injected IFileHelper abstraction. This makes the behavior harder to test/mocks inconsistent (and couples the logger to the physical filesystem even when a custom IFileHelper is provided). Prefer using _fileHelper.Exists(fullFilePath) in the filter, and update the unit test setup accordingly.

                // Use FileMode.CreateNew for atomic "create if not exists" to avoid
                // cross-process race conditions when multiple vstest processes run in parallel.
                using var _ = _fileHelper.GetStream(fullFilePath, FileMode.CreateNew, FileAccess.Write, FileShare.None);
                return fullFilePath;
            }
            catch (IOException) when (File.Exists(fullFilePath))
            {

…lel-file-collision

nohwnd

The FileMode.CreateNew + retry approach is the right fix for the cross-process collision. The timestamp precision improvement and removal of the in-process lock are both correct.

One issue to address: the exception filter calls File.Exists(fullFilePath) directly rather than _fileHelper.Exists(fullFilePath), bypassing the injected abstraction. See the inline comment for details.

Minor description inaccuracy: the PR description says the format changes "from HHmmss to HHmmssfff" but the actual code uses HHmmss.fffffff (7 fractional digits with a dot separator, giving 100-nanosecond precision). The description undersells the precision added.

🧠 Reviewed by claude-sonnet-4.6

🧠 Reviewed by Expert Code Reviewer 🧠

nohwnd · 2026-05-13T15:03:58Z

Address the review feedback and drive this to green CI.

…ilePath Address review feedback: the exception filter was calling File.Exists() directly, bypassing the injected IFileHelper abstraction. Replace with _fileHelper.Exists() for consistency and testability. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

nohwnd · 2026-05-13T15:12:32Z

Commit pushed: 0b55ee4

🔧 Iterated by PR Iteration Agent 🔧

nohwnd · 2026-05-13T15:12:34Z

Fixed the review feedback: changed File.Exists(fullFilePath) to _fileHelper.Exists(fullFilePath) in the GenerateUniqueFilePath exception filter so it uses the injected abstraction consistently.

CI is green. The PR description's precision description is a minor inaccuracy (the format is actually HHmmss.fffffff) but doesn't affect correctness — left as-is since the code is what matters.

🔧 Iterated by PR Iteration Agent 🔧

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

+                    collidedPath = path;
+                    File.WriteAllText(path, string.Empty);
+                    throw new IOException("collision");
+                }


nohwnd

The FileMode.CreateNew + retry approach and the _fileHelper.Exists fix are both correct. One issue in the new test needs to be addressed before merging — see the inline comment.

🧠 Reviewed by claude-sonnet-4.6

🧠 Reviewed by Expert Code Reviewer 🧠

Add _mockFileHelper.Exists setup returning true so the IOException catch filter when (_fileHelper.Exists(fullFilePath)) evaluates to true and the exception is swallowed, allowing the retry loop to proceed. Remove real-filesystem File.WriteAllText side effect and simplify cleanup. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

nohwnd · 2026-05-13T15:27:36Z

Commit pushed: 8659640

🔧 Iterated by PR Iteration Agent 🔧

nohwnd

The two previously identified issues are resolved in this revision:

_fileHelper.Exists abstraction — the catch filter now correctly calls _fileHelper.Exists(fullFilePath) instead of File.Exists, keeping the IFileHelper abstraction intact and testable.
Test correctness — _mockFileHelper.Setup(x => x.Exists(...)).Returns(true) is now set up before the IOException is thrown, so the catch filter evaluates to true, the retry loop advances, and the [1].xml assertion is actually exercised.

The FileMode.CreateNew atomic create-if-not-exists approach is the right fix for cross-process collision. LGTM.

🧠 Reviewed by claude-sonnet-4.6

🧠 Reviewed by Expert Code Reviewer 🧠

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

+                // Use FileMode.CreateNew for atomic "create if not exists" to avoid
+                // cross-process race conditions when multiple vstest processes run in parallel.
+                using var _ = _fileHelper.GetStream(fullFilePath, FileMode.CreateNew, FileAccess.Write, FileShare.None);
                return fullFilePath;
            }
-            catch (IOException) when (File.Exists(fullFilePath))
+            catch (IOException) when (_fileHelper.Exists(fullFilePath))
            {


nohwnd and others added 7 commits March 4, 2026 11:41

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nohwnd changed the title ~~Fix HTML logger parallel file collision~~ [fix] Fix HTML logger parallel file collision May 13, 2026

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[main] Source code updates from microsoft/vstest dotnet/dotnet#6629

Merged

		- Temp XML naming: `TestResult_{user}_{machine}_{timestamp}_{pid}.xml` — PID ensures cross-process uniqueness
		- File creation: Uses `FileMode.CreateNew` for atomic creation with retry on collision

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Summary

Changes

src/Microsoft.TestPlatform.Extensions.HtmlLogger/HtmlLogger.cs

test/Microsoft.TestPlatform.Extensions.HtmlLogger.UnitTests/HtmlLoggerTests.cs

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nohwnd commented Mar 4, 2026 •

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`src/Microsoft.TestPlatform.Extensions.HtmlLogger/HtmlLogger.cs`

`test/Microsoft.TestPlatform.Extensions.HtmlLogger.UnitTests/HtmlLoggerTests.cs`