added support for dynamic LLM tags (#245)

* added FLLMTag which can be used to register memory tags outside of core
* changed `UE_MEMSCOPE` -> `ZEN_MEMSCOPE` for consistency
* instrumented some subsystems with dynamic tags

1 files changed, 77 insertions, 0 deletions

diff --git a/src/zencore/memory/llm.cpp b/src/zencore/memory/llm.cpp
new file mode 100644
index 000000000..fe4853d49
--- /dev/null
+++ b/src/zencore/memory/llm.cpp
@@ -0,0 +1,77 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#include <zencore/memory/llm.h>
+
+#include <zencore/string.h>
+#include <zencore/thread.h>
+
+#include <atomic>
+
+namespace zen {
+
+static std::atomic<int32_t> CustomTagCounter = 257;	 // NOTE: hard-coded TRACE_TAG = 257
+
+static const int32_t TagNamesBaseIndex	 = 256;
+static const int32_t TrackedTagNameCount = 256;
+static const char*	 TagNames[TrackedTagNameCount];
+static uint32_t		 TagNameHashes[TrackedTagNameCount];
+
+static RwLock TableLock;
+
+FLLMTag::FLLMTag(const char* TagName)
+{
+	// NOTE: should add verification to prevent multiple definitions of same name?
+
+	AssignAndAnnounceNewTag(TagName);
+}
+
+FLLMTag::FLLMTag(const char* TagName, const FLLMTag& ParentTag)
+{
+	// NOTE: should add verification to prevent multiple definitions of same name?
+
+	m_ParentTag = ParentTag.GetTag();
+
+	AssignAndAnnounceNewTag(TagName);
+}
+
+void
+FLLMTag::AssignAndAnnounceNewTag(const char* TagName)
+{
+	const uint32_t TagNameHash = HashStringDjb2(TagName);
+
+	{
+		RwLock::ExclusiveLockScope _(TableLock);
+
+		const int32_t CurrentMaxTagIndex = CustomTagCounter - TagNamesBaseIndex;
+
+		for (int TagIndex = 0; TagIndex <= CurrentMaxTagIndex; ++TagIndex)
+		{
+			if (TagNameHashes[TagIndex] == TagNameHash)
+			{
+				m_Tag = TagIndex + TagNamesBaseIndex;
+				// could verify the string matches here to catch hash collisions
+
+				// return early, no need to announce the tag as it is already known
+				return;
+			}
+		}
+
+		m_Tag = ++CustomTagCounter;
+
+		const int TagIndex = m_Tag - TagNamesBaseIndex;
+
+		if (TagIndex < TrackedTagNameCount)
+		{
+			TagNameHashes[TagIndex] = TagNameHash;
+			TagNames[TagIndex]		= TagName;
+		}
+		else
+		{
+			// should really let user know there's an overflow
+		}
+	}
+
+	MemoryTrace_AnnounceCustomTag(m_Tag, m_ParentTag, TagName);
+}
+
+}  // namespace zen