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Reduce binary size in agile reference context cache #1468

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Jan 25, 2024
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Reduce binary size in agile reference context cache #1468

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16 changes: 11 additions & 5 deletions src/WinRT.Runtime/ObjectReference.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -609,9 +609,9 @@ internal sealed class ObjectReferenceWithContext<
private readonly IntPtr _contextCallbackPtr;
private readonly IntPtr _contextToken;

private volatile ConcurrentDictionary<IntPtr, ObjectReference<T>> __cachedContext;
private ConcurrentDictionary<IntPtr, ObjectReference<T>> CachedContext => __cachedContext ?? Make_CachedContext();
private ConcurrentDictionary<IntPtr, ObjectReference<T>> Make_CachedContext()
private volatile ConcurrentDictionary<IntPtr, IObjectReference> __cachedContext;
private ConcurrentDictionary<IntPtr, IObjectReference> CachedContext => __cachedContext ?? Make_CachedContext();
private ConcurrentDictionary<IntPtr, IObjectReference> Make_CachedContext()
{
global::System.Threading.Interlocked.CompareExchange(ref __cachedContext, new(), null);
return __cachedContext;
Expand Down Expand Up @@ -702,9 +702,15 @@ private ObjectReference<T> GetCurrentContext()
return null;
}

return CachedContext.GetOrAdd(currentContext, CreateForCurrentContext);
// We use a non-generic map of just <IntPtr, IObjectReference> values, to avoid all generic instantiations
// of ConcurrentDictionary<,> and transitively dependent types for every vtable type T, since it's not
// something we actually need. Because the cache is private and we're the only ones using it, we can
// just store the per-context agile references as IObjectReference values, and then cast them on return.
IObjectReference objectReference = CachedContext.GetOrAdd(currentContext, CreateForCurrentContext);

ObjectReference<T> CreateForCurrentContext(IntPtr _)
return Unsafe.As<ObjectReference<T>>(objectReference);

IObjectReference CreateForCurrentContext(IntPtr _)
{
var agileReference = AgileReference;
// We may fail to switch context and thereby not get an agile reference.
Expand Down