Protect varTable and assemblyTable with typeTablesLock for thread safety (#525) - #526
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The var translation tables (varTableFwd/varTableBwd) and assemblyTableFwd have the same check-then-create race as the type tables fixed in #522. Under ParallelCompilation, concurrent quotation translation or assembly resolution can hit the unguarded Dictionary with duplicate Add calls (ArgumentException) or produce duplicate target objects. Wrap convVarToSrc, convVarToTgt, and convProvidedAssembly in the existing typeTablesLock. The lock is already re-entrant (Monitor), so the recursive calls to convTypeToTgt/convTypeToSrc inside these functions are safe. Fixes #525
Three new tests exercise the translation tables under parallel access: 1. Concurrent ConvertSourceExprToTarget on shared Vars - exercises convVarToTgt/convVarToSrc under contention (8 threads, shared Var instances, barrier-synchronized start). 2. Concurrent ConvertSourceTypeToTarget - exercises convType/convTypeRef with various type kinds (generics, arrays, primitives) from 8 threads. 3. Concurrent type translation through ProvidedAssembly - exercises convProvidedAssembly by translating 16 types sharing one ProvidedAssembly from 8 threads simultaneously. Without the locks from #522 and this PR, these tests would fail with ArgumentException (duplicate Dictionary key) or state corruption.
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Hmm, the new version of ProvidedTypes.fs seems to be slow in a real environment. (At least it works, unlike the old version, so that's good.) Could the locking also be making it slow? I tested #522 alone, and it felt ok. Do we have any (parallel) perf tests to have any rough estimates of figures? |
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Problem
varTableFwd/varTableBwd and assemblyTableFwd in ProvidedTypesContext have the same unguarded check-then-create race condition that typeTableFwd/typeTableBwd had before #522.
Under ParallelCompilation=true (default in recent .NET SDKs):
Fix
Wrap convVarToSrc, convVarToTgt, and convProvidedAssembly in the existing typeTablesLock (introduced in #522). The lock is already re-entrant (Monitor), so the recursive calls to convTypeToTgt/convTypeToSrc inside these functions are safe.
The lock comment is updated to reflect the broader scope.
Validation
Fixes #525