Instruction file imported from dotnet/msbuild (
.github/instructions/backend-execution.instructions.md). Copyright stays with the author.
BackEnd & Execution Engine Instructions
MSBuild's multi-process execution engine: BuildManager, node communication, scheduler, result caching, and task execution.
Concurrency & Thread Safety (Critical)
- All shared mutable state must be synchronized — tasks run across in-proc and out-of-proc nodes concurrently.
BuildManager.csis the most complex file —BeginBuild/EndBuild/ResetCachessequences must remain correct.- Test in both in-proc and out-of-proc scenarios — they differ in state isolation, type loading, and serialization.
- Lock ordering must be consistent to prevent deadlocks. Document acquisition order when introducing new locks.
Node Communication & IPC
- Never change the IPC packet format without versioning — old nodes must communicate with new ones during rolling updates.
- IPC message ordering matters — race conditions cause intermittent, hard-to-reproduce failures.
- Task host node (
NodeProviderOutOfProcTaskHost.cs) has additional isolation constraints for type loading.
Scheduler Correctness
- Changes can cause deadlocks, starvation, or incorrect parallelism.
- Yield/unyield semantics must be preserved — tasks that yield allow their node to process other requests.
Result Caching
- Results are cached by
(project path, global properties, targets)— changes to cache key computation break incremental builds. - Cache coherence between nodes is critical — stale results cause incorrect builds.
- See Results Cache and Cache Flow.
SDK Resolution
SdkResolverService.csresolves SDK references during evaluation — changes affect every SDK-style project.- SDK resolution must not have side effects that persist across evaluations.
BuildManager Lifecycle
BeginBuild→ submissions →EndBuildis the required sequence. Handle reentrant calls and out-of-order events gracefully.ResetCachesmust not lose in-flight results.