diff --git a/docs/release-notes/.FSharp.Compiler.Service/9.0.200.md b/docs/release-notes/.FSharp.Compiler.Service/9.0.200.md
index 7c7f9652b19..a6ea239c57d 100644
--- a/docs/release-notes/.FSharp.Compiler.Service/9.0.200.md
+++ b/docs/release-notes/.FSharp.Compiler.Service/9.0.200.md
@@ -15,6 +15,7 @@
* Fix locals allocating for the special `copyOfStruct` defensive copy ([PR #18025](https://github.com/dotnet/fsharp/pull/18025))
* Fix lowering of computed array expressions when the expression consists of a simple mapping from a `uint64` or `unativeint` array. [PR #18081](https://github.com/dotnet/fsharp/pull/18081)
* Add missing nullable-metadata for C# consumers of records,exceptions and DU subtypes generated from F# code. [PR #18079](https://github.com/dotnet/fsharp/pull/18079)
+* Fix a race condition in file book keeping in the compiler service ([#18008](https://github.com/dotnet/fsharp/pull/18008))
### Added
diff --git a/src/Compiler/Utilities/range.fs b/src/Compiler/Utilities/range.fs
index 6d0002a97ba..09633136dbe 100755
--- a/src/Compiler/Utilities/range.fs
+++ b/src/Compiler/Utilities/range.fs
@@ -196,38 +196,43 @@ type FileIndexTable() =
match fileToIndexTable.TryGetValue filePath with
| true, idx -> idx
| _ ->
-
- // Try again looking for a normalized entry.
- let normalizedFilePath =
- if normalize then
- FileSystem.NormalizePathShim filePath
- else
- filePath
-
- match fileToIndexTable.TryGetValue normalizedFilePath with
- | true, idx ->
- // Record the non-normalized entry if necessary
- if filePath <> normalizedFilePath then
- lock fileToIndexTable (fun () -> fileToIndexTable[filePath] <- idx)
-
- // Return the index
- idx
-
- | _ ->
- lock fileToIndexTable (fun () ->
- // Get the new index
- let idx = indexToFileTable.Count
-
- // Record the normalized entry
- indexToFileTable.Add normalizedFilePath
- fileToIndexTable[normalizedFilePath] <- idx
-
- // Record the non-normalized entry if necessary
- if filePath <> normalizedFilePath then
- fileToIndexTable[filePath] <- idx
-
- // Return the index
- idx)
+ // If a write operation can happen, we have to lock the whole read-check-write to avoid race conditions
+ lock fileToIndexTable
+ <| fun () ->
+ match fileToIndexTable.TryGetValue filePath with
+ | true, idx -> idx
+ | _ ->
+
+ // Try again looking for a normalized entry.
+ let normalizedFilePath =
+ if normalize then
+ FileSystem.NormalizePathShim filePath
+ else
+ filePath
+
+ match fileToIndexTable.TryGetValue normalizedFilePath with
+ | true, idx ->
+ // Record the non-normalized entry if necessary
+ if filePath <> normalizedFilePath then
+ fileToIndexTable[filePath] <- idx
+
+ // Return the index
+ idx
+
+ | _ ->
+ // Get the new index
+ let idx = indexToFileTable.Count
+
+ // Record the normalized entry
+ indexToFileTable.Add normalizedFilePath
+ fileToIndexTable[normalizedFilePath] <- idx
+
+ // Record the non-normalized entry if necessary
+ if filePath <> normalizedFilePath then
+ fileToIndexTable[filePath] <- idx
+
+ // Return the index
+ idx
member t.IndexToFile n =
if n < 0 then
diff --git a/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj b/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
index 4338fbd807b..e8f044ed2f4 100644
--- a/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
+++ b/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
@@ -317,6 +317,7 @@
+
diff --git a/tests/FSharp.Compiler.ComponentTests/Miscellaneous/FileIndex.fs b/tests/FSharp.Compiler.ComponentTests/Miscellaneous/FileIndex.fs
new file mode 100644
index 00000000000..0d5caabb982
--- /dev/null
+++ b/tests/FSharp.Compiler.ComponentTests/Miscellaneous/FileIndex.fs
@@ -0,0 +1,21 @@
+module Miscellaneous.FileIndex
+
+open FSharp.Compiler.Text
+open System.Threading.Tasks
+open Xunit
+
+// This is a regression test for a bug that existed in FileIndex.fileIndexOfFile
+[]
+let NoRaceCondition() =
+ let parallelOptions = ParallelOptions()
+ let mutable count = 10000
+ while count > 0 do
+ let file = $"test{count}.fs"
+ let files = Array.create 2 file
+ let indices = Array.create 2 -1
+ let getFileIndex i = indices[i] <- FileIndex.fileIndexOfFile files[i]
+ Parallel.For(0, files.Length, parallelOptions, getFileIndex) |> ignore
+ if indices[0] <> indices[1] then
+ Assert.Fail $"Found different indices: {indices[0]} and {indices[1]}"
+ count <- count - 1
+
\ No newline at end of file
diff --git a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_net9.0.bsl b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_net9.0.bsl
index c527d99ccf5..03328728f4c 100644
--- a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_net9.0.bsl
+++ b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_net9.0.bsl
@@ -59,7 +59,7 @@
[IL]: Error [StackUnexpected]: : FSharp.Compiler.AbstractIL.IL::parseILVersion(string)][offset 0x0000000B][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : FSharp.Compiler.AbstractIL.IL::parseILVersion(string)][offset 0x00000021][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : .$FSharp.Compiler.DiagnosticsLogger::.cctor()][offset 0x000000CD][found Char] Unexpected type on the stack.
-[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@543::System.Collections.Generic.IEqualityComparer.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
+[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@548::System.Collections.Generic.IEqualityComparer.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
[IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000037][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000043][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : .$Internal.Utilities.XmlAdapters::.cctor()][offset 0x0000000A][found Char] Unexpected type on the stack.
diff --git a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_netstandard2.0.bsl b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_netstandard2.0.bsl
index 7d4eff968ac..a863787a54e 100644
--- a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_netstandard2.0.bsl
+++ b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Debug_netstandard2.0.bsl
@@ -84,7 +84,7 @@
[IL]: Error [StackUnexpected]: : Internal.Utilities.FSharpEnvironment+probePathForDotnetHost@321::Invoke([FSharp.Core]Microsoft.FSharp.Core.Unit)][offset 0x00000028][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : FSharp.Compiler.CodeAnalysis.SimulatedMSBuildReferenceResolver+Pipe #6 input at line 68@68::FSharp.Compiler.CodeAnalysis.ILegacyReferenceResolver.Resolve([FSharp.Compiler.Service]FSharp.Compiler.CodeAnalysis.LegacyResolutionEnvironment, [S.P.CoreLib]System.Tuple`2[], string, [FSharp.Core]Microsoft.FSharp.Collections.FSharpList`1, string, string, [FSharp.Core]Microsoft.FSharp.Collections.FSharpList`1, string, [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2, [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2>>)][offset 0x0000034D][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : .$FSharp.Compiler.DiagnosticsLogger::.cctor()][offset 0x000000CD][found Char] Unexpected type on the stack.
-[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@543::System.Collections.Generic.IEqualityComparer.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
+[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@548::System.Collections.Generic.IEqualityComparer.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
[IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000037][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000043][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : .$Internal.Utilities.XmlAdapters::.cctor()][offset 0x0000000A][found Char] Unexpected type on the stack.
diff --git a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_net9.0.bsl b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_net9.0.bsl
index a930478a45e..d1f7525cef2 100644
--- a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_net9.0.bsl
+++ b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_net9.0.bsl
@@ -85,7 +85,7 @@
[IL]: Error [StackUnexpected]: : FSharp.Compiler.AbstractIL.IL::parseILVersion(string)][offset 0x0000000B][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : FSharp.Compiler.AbstractIL.IL::parseILVersion(string)][offset 0x00000021][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : .$FSharp.Compiler.DiagnosticsLogger::.cctor()][offset 0x000000B6][found Char] Unexpected type on the stack.
-[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@543::System.Collections.Generic.IEqualityComparer.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
+[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@548::System.Collections.Generic.IEqualityComparer.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
[IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000035][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000041][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : .$Internal.Utilities.XmlAdapters::.cctor()][offset 0x0000000A][found Char] Unexpected type on the stack.
diff --git a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_netstandard2.0.bsl b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_netstandard2.0.bsl
index b97ede137b1..9de22b5cd79 100644
--- a/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_netstandard2.0.bsl
+++ b/tests/ILVerify/ilverify_FSharp.Compiler.Service_Release_netstandard2.0.bsl
@@ -111,7 +111,7 @@
[IL]: Error [StackUnexpected]: : Internal.Utilities.FSharpEnvironment::probePathForDotnetHost@320([FSharp.Core]Microsoft.FSharp.Core.Unit)][offset 0x0000002A][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : FSharp.Compiler.CodeAnalysis.SimulatedMSBuildReferenceResolver+SimulatedMSBuildResolver@68::FSharp.Compiler.CodeAnalysis.ILegacyReferenceResolver.Resolve([FSharp.Compiler.Service]FSharp.Compiler.CodeAnalysis.LegacyResolutionEnvironment, [S.P.CoreLib]System.Tuple`2[], string, [FSharp.Core]Microsoft.FSharp.Collections.FSharpList`1, string, string, [FSharp.Core]Microsoft.FSharp.Collections.FSharpList`1, string, [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2, [FSharp.Core]Microsoft.FSharp.Core.FSharpFunc`2>>)][offset 0x000002F5][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : .$FSharp.Compiler.DiagnosticsLogger::.cctor()][offset 0x000000B6][found Char] Unexpected type on the stack.
-[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@543::System.Collections.Generic.IEqualityComparer.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
+[IL]: Error [CallVirtOnValueType]: : FSharp.Compiler.Text.RangeModule+comparer@548::System.Collections.Generic.IEqualityComparer.GetHashCode([FSharp.Compiler.Service]FSharp.Compiler.Text.Range)][offset 0x00000002] Callvirt on a value type method.
[IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000035][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : Internal.Utilities.PathMapModule::applyDir([FSharp.Compiler.Service]Internal.Utilities.PathMap, string)][offset 0x00000041][found Char] Unexpected type on the stack.
[IL]: Error [StackUnexpected]: : .$Internal.Utilities.XmlAdapters::.cctor()][offset 0x0000000A][found Char] Unexpected type on the stack.