Don't disable the MSBuild server for /mt builds when node reuse is off - #14248
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Pull request overview
This PR adjusts MSBuild Server routing so /mt builds can still run on the MSBuild Server even when node reuse is disabled (-nr:false), preserving the performance benefit of Server GC while honoring the “no reuse” intent by shutting the server down immediately after the build.
Changes:
- Decouples “can host build on server” from “can keep server resident,” allowing
/mt+-nr:falseto use the server but request post-build teardown. - Plumbs a new
shutdownServerAfterBuild/ShutdownAfterBuildflag from CLI parsing → client → IPC packet → server shutdown behavior. - Adds unit test coverage for the new packet field and an end-to-end test for
/mt+-nr:false.
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 |
|---|---|
| src/MSBuild/XMake.cs | Computes shutdownServerAfterBuild during the authoritative command-line parse and passes it to the server client path. |
| src/MSBuild/MSBuildClientApp.cs | Extends the server client execution entrypoints to pass the shutdown-after-build intent through. |
| src/Build/BackEnd/Client/MSBuildClient.cs | Stores and sends shutdown intent on ServerNodeBuildCommand. |
| src/Build/BackEnd/Node/ServerNodeBuildCommand.cs | Adds ShutdownAfterBuild field to the server build-command packet and serializes it. |
| src/Build/BackEnd/Node/OutOfProcServerNode.cs | Honors ShutdownAfterBuild by exiting after the build instead of returning to reuse mode. |
| src/MSBuild.UnitTests/MSBuildServer_Tests.cs | Adds E2E test that /mt -nr:false uses the server but does not leave it resident. |
| src/Build.UnitTests/BackEnd/ServerNodeBuildCommand_Tests.cs | Adds round-trip serialization test for the new packet field. |
| documentation/MSBuild-Server.md | Documents server lifetime behavior when node reuse is disabled, including the /mt exception. |
AR-May
marked this pull request as ready for review
July 2, 2026 10:13
JanProvaznik
approved these changes
Jul 2, 2026
OvesN
approved these changes
Jul 3, 2026
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Jul 8, 2026
Resolves conflicts with dotnet#14248 ("Don't disable the MSBuild server for /mt builds when node reuse is off"), which introduced the short-lived server (a /mt build with node reuse off uses the server for Server GC but tears it down after the build via ServerNodeBuildCommand.ShutdownAfterBuild). - CanRunServerBasedOnCommandLineSwitches: integrate dotnet#14248's shutdownServerAfterBuild and the new node-reuse gate (nodeReuseDisqualifies = !nodeReuse && !multiThreaded) with my serverDisabledReason/reasonCode outputs. The node-reuse-disabled reason now only fires for non-/mt builds (a /mt build uses a short-lived server instead). - MSBuildServerLifecycleEventArgs gains a ShortLived flag (serialized in the v27 record and node packets). XMake sets it for a spawned server that will shut down afterward, and logs a distinct "spawned (short-lived)" message. The flag is surfaced from OutOfProcServerNode.CurrentBuildShutsDownServerNode (additive; the public BuildCallback delegate is left unchanged to avoid an API break). - New MSBuildServerNodeSpawnedShortLived resource (+ xlf); docs updated. - Tests: round-trip covers ShortLived; new e2e ServerShortLivedForMultithreadedWhenNodeReuseOff. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Updated [Microsoft.Build.Utilities.Core](https://github.com/dotnet/msbuild) from 18.9.6 to 18.10.1. <details> <summary>Release notes</summary> _Sourced from [Microsoft.Build.Utilities.Core's releases](https://github.com/dotnet/msbuild/releases)._ ## 18.10.1 ## What's Changed * [vs16.11] Update dependencies from dotnet/arcade by @dotnet-maestro[bot] in dotnet/msbuild#13103 * [vs17.12] Update dependencies from dotnet/arcade by @dotnet-maestro[bot] in dotnet/msbuild#13796 * [vs17.8] Update dependencies from dotnet/arcade by @dotnet-maestro[bot] in dotnet/msbuild#13902 * [vs17.11] Update dependencies from dotnet/arcade by @dotnet-maestro[bot] in dotnet/msbuild#13903 * [vs17.12] Update dependencies from dotnet/arcade by @dotnet-maestro[bot] in dotnet/msbuild#13909 * [vs17.12] Update dependencies from dotnet/arcade by @dotnet-maestro[bot] in dotnet/msbuild#13986 * Add vs18.9 to merge-flow config; retire vs18.3 by @JanProvaznik in dotnet/msbuild#14214 * Bump labeler-cache-retention to use issue-labeler v2.1.0 by @jeffhandley in dotnet/msbuild#14171 * Bump main to 18.10.0 after vs18.9 snap by @JanProvaznik in dotnet/msbuild#14216 * Improve release skill: Phase 2 DARC rules, VMR backflow, deterministic baseline by @JanProvaznik in dotnet/msbuild#14220 * Determinize release: hardcode OptProf baseline + Phase 3.2 baseline resolver by @JanProvaznik in dotnet/msbuild#14222 * Serialize BuildRequestConfiguration.RequestedTargets to fix solution metaproject MSB4057 in parallel builds by @ViktorHofer in dotnet/msbuild#14223 * [main] Update dependencies from nuget/nuget.client by @dotnet-maestro[bot] in dotnet/msbuild#14203 * Core support for AbsolutePath/FileInfo/DirectoryInfo and ITaskItem<T> as task parameters by @baronfel in dotnet/msbuild#13971 * [main] Update dependencies from dotnet/roslyn by @dotnet-maestro[bot] in dotnet/msbuild#14206 * Fix existence cache kind poisoning by @AlesProkop in dotnet/msbuild#14249 * [main] Source code updates from dotnet/dotnet by @dotnet-maestro[bot] in dotnet/msbuild#14226 * Don't disable the MSBuild server for /mt builds when node reuse is off by @AR-May in dotnet/msbuild#14248 * Enhance expert reviewer guidelines with additional checks. by @AR-May in dotnet/msbuild#14255 * [main] Source code updates from dotnet/dotnet by @dotnet-maestro[bot] in dotnet/msbuild#14253 * [main] Update dependencies from dotnet/roslyn by @dotnet-maestro[bot] in dotnet/msbuild#14268 * [main] Update dependencies from nuget/nuget.client by @dotnet-maestro[bot] in dotnet/msbuild#14267 * Bump github/gh-aw-actions/setup from 0.81.6 to 0.82.2 by @dependabot[bot] in dotnet/msbuild#14266 * Avoid boxing the struct enumerator in PropertyDictionary<T>.GetEnumerator() by @nareshjo in dotnet/msbuild#14272 * Refresh copy marker when implementation output changes by @AlesProkop in dotnet/msbuild#14231 * Send task-host build process environment as delta by @OvesN in dotnet/msbuild#14126 * Add regression coverage for metadata newline preservation by @VolPlita in dotnet/msbuild#14261 * Fix EmbedInBinlog items with relative paths from child projects by @huulinhnguyen-dev in dotnet/msbuild#13990 * Stop requiring VersionPrefix updates in servicing - insert prerelease versions to VS by @ViktorHofer in dotnet/msbuild#14277 * Fix WriteLinesToFile rewriting unchanged file when custom encoding is used by @huulinhnguyen-dev in dotnet/msbuild#14146 * Enable trim/AOT analyzers for Microsoft.Build and clean up annotations by @JeremyKuhne in dotnet/msbuild#14064 * [automated] Merge branch 'vs18.9' => 'main' by @github-actions[bot] in dotnet/msbuild#14291 * Fix MicroBuild plugin feed URL to use allowed pkgs.dev.azure.com format by @AlesProkop in dotnet/msbuild#14295 * Pass ExcludeRestorePackageImports during restore to avoid redundant evaluations by @ViktorHofer with @Copilot in dotnet/msbuild#14274 * [vs18.7] Update dependencies from dotnet/arcade by @dotnet-maestro[bot] in dotnet/msbuild#13988 * Adopt Clever Test Selection (CTS) as parallel, non-blocking PR pipeline by @jankratochvilcz in dotnet/msbuild#14212 * Harden exceptions when connecting to server by @JanProvaznik in dotnet/msbuild#14292 * Update MicrosoftBuildVersion in analyzer template by @github-actions[bot] in dotnet/msbuild#13886 * Fix MSBuild Server client dropping build result under WaitAny race (#14172) by @JanProvaznik in dotnet/msbuild#14251 * Partially revert #13660: remove NuGet RestoreTask transient TaskHost workaround by @JanProvaznik in dotnet/msbuild#14297 * Disable daily AI credits guardrail for Expert Code Review workflow by @JanProvaznik with @Copilot in dotnet/msbuild#14314 * Localized file check-in by OneLocBuild Task: Build definition ID 9434: Build ID 14614733 by @dotnet-bot in dotnet/msbuild#14246 * Add opt-in partial (stop-after-pass) project evaluation by @ViktorHofer in dotnet/msbuild#14290 * Use partial evaluation for -getProperty/-getItem without a target by @ViktorHofer in dotnet/msbuild#14296 * [main] Source code updates from dotnet/dotnet by @dotnet-maestro[bot] in dotnet/msbuild#14324 * [main] Update dependencies from dotnet/roslyn by @dotnet-maestro[bot] in dotnet/msbuild#14333 * [main] Update dependencies from nuget/nuget.client by @dotnet-maestro[bot] in dotnet/msbuild#14330 * Bump github/gh-aw-actions/setup from 0.82.2 to 0.82.8 by @dependabot[bot] in dotnet/msbuild#14328 * Restrict partial evaluation to ProjectInstance by @ViktorHofer in dotnet/msbuild#14340 ... (truncated) Commits viewable in [compare view](dotnet/msbuild@v18.9.6...v18.10.1). </details> [](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores) Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting `@dependabot rebase`. [//]: # (dependabot-automerge-start) [//]: # (dependabot-automerge-end) --- <details> <summary>Dependabot commands and options</summary> <br /> You can trigger Dependabot actions by commenting on this PR: - `@dependabot rebase` will rebase this PR - `@dependabot recreate` will recreate this PR, overwriting any edits that have been made to it - `@dependabot show <dependency name> ignore conditions` will show all of the ignore conditions of the specified dependency - `@dependabot ignore this major version` will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this minor version` will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this dependency` will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself) </details> Signed-off-by: dependabot[bot] <support@github.com> Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
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Fixes #14157
Context
When node reuse is disabled (
-nr:false), MSBuild refused to use the server node. For a multithreaded ( /mt ) build that's a problem: the server is the only way to get Server GC, which /mt builds depend on for performance reasons.Changes Made
Decouple "may we use the server for this build?" from "may the server stay resident afterward?":
shutdownServerAfterBuildflag tears the server down immediately after the build completes, so it doesn't persist and each build gets a fresh process.Testing
Added a unit test.
Notes
Previous attempt: #14161. It tries to shut down the server after the build by issuing a shutdown command. However, previous implementation does not guarantee that the server will not accept another client's request in the meantime and subsequently fail to shut down. Another option would be to re-parse the command line and identify cases where a server shutdown is required, but I would prefer the initial parsing to remain the single source of truth and avoid re-parsing. Client and server are the same handshake-gated MSBuild version, so there's no cross-version serialization concern over the communication protocol.