Description

Consolidates the common "lazy-initialized cached bool" pattern into a single shared NullableBool : sbyte enum, replacing local volatile int/volatile sbyte tri-state fields and the private Tristate enum in TextInfo.

Changes

• New: src/libraries/Common/src/System/NullableBool.cs — internal enum NullableBool : sbyte { Undefined = 0, False = -1, True = 1 }. sbyte backing fits in one byte (same as bool) and is valid for volatile. Unlike bool?, it is safe to use from multiple threads (a Nullable<T> is a two-field struct that can tear under concurrent access).

• Removed: private nested NullableBool enum from SafeFileHandle.Unix.cs (fields already typed NullableBool, now reference Common).

• Replaced Tristate in TextInfo: The local Tristate : byte { NotInitialized=0, False=1, True=2 } driving _isAsciiCasingSameAsInvariant and _needsTurkishCasing is replaced with NullableBool.

• Replaced volatile int tri-state fields (-1 = unset, 0 = false, 1 = true) in:

  • ConsoleUtils.cs — s_emitAnsiColorCodes
  • AuthenticationHelper.NtAuth.cs — s_usePortInSpn
  • SslStream.Protocol.cs — s_disableTlsResume and s_enableServerAiaDownloads
  • NameResolutionPal.Windows.cs — s_getAddrInfoExSupported (also removes the now-unnecessary Interlocked.CompareExchange; initialization is idempotent, consistent with all other patterns)

• Replaced volatile sbyte tri-state fields (same encoding: 0 = unset, 1 = true, -1 = false) in:

  • Environment.cs — s_privilegedProcess
  • Interop.MemfdCreate.cs — s_memfdSupported (also removes Interlocked.CompareExchange; MemfdSupportedImpl() is idempotent — read-only kernel version check and syscall)

• Replaced volatile int field with non-standard encoding (remapped to NullableBool equivalents) in:

  • ProcessManager.Linux.cs — _procMatchesPidNamespace (was 0 = unset, 1 = match, 2 = no match; remapped to NullableBool.Undefined, NullableBool.True, NullableBool.False)

• Project file updates: Added NullableBool.cs to System.Private.CoreLib.Shared.projitems, System.Console.csproj, Microsoft.Extensions.Logging.Console.csproj, System.Net.Http.csproj, System.Net.NameResolution.csproj, System.Net.Security.csproj, System.IO.MemoryMappedFiles.csproj (unix/browser/wasi group), System.Diagnostics.Process.csproj (linux group), and System.Net.NameResolution.Pal.Tests.csproj (Windows group — the test project directly compiles NameResolutionPal.Windows.cs and also needs the type).

Before / After

// Before
private static volatile int s_usePortInSpn = -1;
int usePortInSpn = s_usePortInSpn;
if (usePortInSpn != -1)
    return usePortInSpn != 0;
s_usePortInSpn = value ? 1 : 0;

// After
private static volatile NullableBool s_usePortInSpn;
NullableBool usePortInSpn = s_usePortInSpn;
if (usePortInSpn != NullableBool.Undefined)
    return usePortInSpn == NullableBool.True;
s_usePortInSpn = value ? NullableBool.True : NullableBool.False;

Testing

All affected libraries build successfully (System.Private.CoreLib, System.Console, System.Net.Http, System.Net.NameResolution, System.Net.Security, System.IO.MemoryMappedFiles, System.Diagnostics.Process). Windows CI build break (CS0246 in System.Net.NameResolution.Pal.Tests) resolved by adding NullableBool.cs to the test project's Windows ItemGroup.

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