1 files changed, 454 insertions, 0 deletions
diff --git a/src/zenhorde/hordecomputebuffer.cpp b/src/zenhorde/hordecomputebuffer.cpp
new file mode 100644
index 000000000..0d032b5d5
--- /dev/null
+++ b/src/zenhorde/hordecomputebuffer.cpp
@@ -0,0 +1,454 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#include "hordecomputebuffer.h"
+
+#include <algorithm>
+#include <cassert>
+#include <chrono>
+#include <condition_variable>
+#include <cstring>
+
+namespace zen::horde {
+
+// Simplified ring buffer implementation for in-process use only.
+// Uses a single contiguous buffer with write/read cursors and
+// mutex+condvar for synchronization. This is simpler than the UE version
+// which uses lock-free atomics and shared memory, but sufficient for our
+// use case where we're the initiator side of the compute protocol.
+
+struct ComputeBuffer::Detail : TRefCounted<Detail>
+{
+	std::vector<uint8_t> Data;
+	size_t				 NumChunks	 = 0;
+	size_t				 ChunkLength = 0;
+
+	// Current write state
+	size_t WriteChunkIdx = 0;
+	size_t WriteOffset	 = 0;
+	bool   WriteComplete = false;
+
+	// Current read state
+	size_t ReadChunkIdx = 0;
+	size_t ReadOffset	= 0;
+	bool   Detached		= false;
+
+	// Per-chunk written length
+	std::vector<size_t> ChunkWrittenLength;
+	std::vector<bool>	ChunkFinished;	// Writer moved to next chunk
+
+	std::mutex				Mutex;
+	std::condition_variable ReadCV;	  ///< Signaled when new data is written or stream completes
+	std::condition_variable WriteCV;  ///< Signaled when reader advances past a chunk, freeing space
+
+	bool HasWriter = false;
+	bool HasReader = false;
+
+	uint8_t*	   ChunkPtr(size_t ChunkIdx) { return Data.data() + ChunkIdx * ChunkLength; }
+	const uint8_t* ChunkPtr(size_t ChunkIdx) const { return Data.data() + ChunkIdx * ChunkLength; }
+};
+
+// ComputeBuffer
+
+ComputeBuffer::ComputeBuffer()
+{
+}
+ComputeBuffer::~ComputeBuffer()
+{
+}
+
+bool
+ComputeBuffer::CreateNew(const Params& InParams)
+{
+	auto* NewDetail		   = new Detail();
+	NewDetail->NumChunks   = InParams.NumChunks;
+	NewDetail->ChunkLength = InParams.ChunkLength;
+	NewDetail->Data.resize(InParams.NumChunks * InParams.ChunkLength, 0);
+	NewDetail->ChunkWrittenLength.resize(InParams.NumChunks, 0);
+	NewDetail->ChunkFinished.resize(InParams.NumChunks, false);
+
+	m_Detail = NewDetail;
+	return true;
+}
+
+void
+ComputeBuffer::Close()
+{
+	m_Detail = nullptr;
+}
+
+bool
+ComputeBuffer::IsValid() const
+{
+	return static_cast<bool>(m_Detail);
+}
+
+ComputeBufferReader
+ComputeBuffer::CreateReader()
+{
+	assert(m_Detail);
+	m_Detail->HasReader = true;
+	return ComputeBufferReader(m_Detail);
+}
+
+ComputeBufferWriter
+ComputeBuffer::CreateWriter()
+{
+	assert(m_Detail);
+	m_Detail->HasWriter = true;
+	return ComputeBufferWriter(m_Detail);
+}
+
+// ComputeBufferReader
+
+ComputeBufferReader::ComputeBufferReader()
+{
+}
+ComputeBufferReader::~ComputeBufferReader()
+{
+}
+
+ComputeBufferReader::ComputeBufferReader(const ComputeBufferReader& Other)	   = default;
+ComputeBufferReader::ComputeBufferReader(ComputeBufferReader&& Other) noexcept = default;
+ComputeBufferReader& ComputeBufferReader::operator=(const ComputeBufferReader& Other) = default;
+ComputeBufferReader& ComputeBufferReader::operator=(ComputeBufferReader&& Other) noexcept = default;
+
+ComputeBufferReader::ComputeBufferReader(Ref<ComputeBuffer::Detail> InDetail) : m_Detail(std::move(InDetail))
+{
+}
+
+void
+ComputeBufferReader::Close()
+{
+	m_Detail = nullptr;
+}
+
+void
+ComputeBufferReader::Detach()
+{
+	if (m_Detail)
+	{
+		std::lock_guard<std::mutex> Lock(m_Detail->Mutex);
+		m_Detail->Detached = true;
+		m_Detail->ReadCV.notify_all();
+	}
+}
+
+bool
+ComputeBufferReader::IsValid() const
+{
+	return static_cast<bool>(m_Detail);
+}
+
+bool
+ComputeBufferReader::IsComplete() const
+{
+	if (!m_Detail)
+	{
+		return true;
+	}
+	std::lock_guard<std::mutex> Lock(m_Detail->Mutex);
+	if (m_Detail->Detached)
+	{
+		return true;
+	}
+	return m_Detail->WriteComplete && m_Detail->ReadChunkIdx == m_Detail->WriteChunkIdx &&
+		   m_Detail->ReadOffset >= m_Detail->ChunkWrittenLength[m_Detail->ReadChunkIdx];
+}
+
+void
+ComputeBufferReader::AdvanceReadPosition(size_t Size)
+{
+	if (!m_Detail)
+	{
+		return;
+	}
+
+	std::lock_guard<std::mutex> Lock(m_Detail->Mutex);
+
+	m_Detail->ReadOffset += Size;
+
+	// Check if we need to move to next chunk
+	const size_t ReadChunk = m_Detail->ReadChunkIdx;
+	if (m_Detail->ChunkFinished[ReadChunk] && m_Detail->ReadOffset >= m_Detail->ChunkWrittenLength[ReadChunk])
+	{
+		const size_t NextChunk = (ReadChunk + 1) % m_Detail->NumChunks;
+		m_Detail->ReadChunkIdx = NextChunk;
+		m_Detail->ReadOffset   = 0;
+		m_Detail->WriteCV.notify_all();
+	}
+
+	m_Detail->ReadCV.notify_all();
+}
+
+size_t
+ComputeBufferReader::GetMaxReadSize() const
+{
+	if (!m_Detail)
+	{
+		return 0;
+	}
+	std::lock_guard<std::mutex> Lock(m_Detail->Mutex);
+	const size_t				ReadChunk = m_Detail->ReadChunkIdx;
+	return m_Detail->ChunkWrittenLength[ReadChunk] - m_Detail->ReadOffset;
+}
+
+const uint8_t*
+ComputeBufferReader::WaitToRead(size_t MinSize, int TimeoutMs, bool* OutTimedOut)
+{
+	if (!m_Detail)
+	{
+		return nullptr;
+	}
+
+	std::unique_lock<std::mutex> Lock(m_Detail->Mutex);
+
+	auto Predicate = [&]() -> bool {
+		if (m_Detail->Detached)
+		{
+			return true;
+		}
+
+		const size_t ReadChunk = m_Detail->ReadChunkIdx;
+		const size_t Available = m_Detail->ChunkWrittenLength[ReadChunk] - m_Detail->ReadOffset;
+
+		if (Available >= MinSize)
+		{
+			return true;
+		}
+
+		// If chunk is finished and we've read everything, try to move to next
+		if (m_Detail->ChunkFinished[ReadChunk] && m_Detail->ReadOffset >= m_Detail->ChunkWrittenLength[ReadChunk])
+		{
+			if (m_Detail->WriteComplete)
+			{
+				return true;  // End of stream
+			}
+			// Move to next chunk
+			const size_t NextChunk = (ReadChunk + 1) % m_Detail->NumChunks;
+			m_Detail->ReadChunkIdx = NextChunk;
+			m_Detail->ReadOffset   = 0;
+			m_Detail->WriteCV.notify_all();
+			return false;  // Re-check with new chunk
+		}
+
+		if (m_Detail->WriteComplete)
+		{
+			return true;  // End of stream
+		}
+
+		return false;
+	};
+
+	if (TimeoutMs < 0)
+	{
+		m_Detail->ReadCV.wait(Lock, Predicate);
+	}
+	else
+	{
+		if (!m_Detail->ReadCV.wait_for(Lock, std::chrono::milliseconds(TimeoutMs), Predicate))
+		{
+			if (OutTimedOut)
+			{
+				*OutTimedOut = true;
+			}
+			return nullptr;
+		}
+	}
+
+	if (m_Detail->Detached)
+	{
+		return nullptr;
+	}
+
+	const size_t ReadChunk = m_Detail->ReadChunkIdx;
+	const size_t Available = m_Detail->ChunkWrittenLength[ReadChunk] - m_Detail->ReadOffset;
+
+	if (Available < MinSize)
+	{
+		return nullptr;	 // End of stream
+	}
+
+	return m_Detail->ChunkPtr(ReadChunk) + m_Detail->ReadOffset;
+}
+
+size_t
+ComputeBufferReader::Read(void* Buffer, size_t MaxSize, int TimeoutMs, bool* OutTimedOut)
+{
+	const uint8_t* Data = WaitToRead(1, TimeoutMs, OutTimedOut);
+	if (!Data)
+	{
+		return 0;
+	}
+
+	const size_t Available = GetMaxReadSize();
+	const size_t ToCopy	   = std::min(Available, MaxSize);
+	memcpy(Buffer, Data, ToCopy);
+	AdvanceReadPosition(ToCopy);
+	return ToCopy;
+}
+
+// ComputeBufferWriter
+
+ComputeBufferWriter::ComputeBufferWriter()									   = default;
+ComputeBufferWriter::ComputeBufferWriter(const ComputeBufferWriter& Other)	   = default;
+ComputeBufferWriter::ComputeBufferWriter(ComputeBufferWriter&& Other) noexcept = default;
+ComputeBufferWriter::~ComputeBufferWriter()									   = default;
+ComputeBufferWriter& ComputeBufferWriter::operator=(const ComputeBufferWriter& Other) = default;
+ComputeBufferWriter& ComputeBufferWriter::operator=(ComputeBufferWriter&& Other) noexcept = default;
+
+ComputeBufferWriter::ComputeBufferWriter(Ref<ComputeBuffer::Detail> InDetail) : m_Detail(std::move(InDetail))
+{
+}
+
+void
+ComputeBufferWriter::Close()
+{
+	if (m_Detail)
+	{
+		{
+			std::lock_guard<std::mutex> Lock(m_Detail->Mutex);
+			if (!m_Detail->WriteComplete)
+			{
+				m_Detail->WriteComplete = true;
+				m_Detail->ReadCV.notify_all();
+			}
+		}
+		m_Detail = nullptr;
+	}
+}
+
+bool
+ComputeBufferWriter::IsValid() const
+{
+	return static_cast<bool>(m_Detail);
+}
+
+void
+ComputeBufferWriter::MarkComplete()
+{
+	if (m_Detail)
+	{
+		std::lock_guard<std::mutex> Lock(m_Detail->Mutex);
+		m_Detail->WriteComplete = true;
+		m_Detail->ReadCV.notify_all();
+	}
+}
+
+void
+ComputeBufferWriter::AdvanceWritePosition(size_t Size)
+{
+	if (!m_Detail || Size == 0)
+	{
+		return;
+	}
+
+	std::lock_guard<std::mutex> Lock(m_Detail->Mutex);
+	const size_t				WriteChunk = m_Detail->WriteChunkIdx;
+	m_Detail->ChunkWrittenLength[WriteChunk] += Size;
+	m_Detail->WriteOffset += Size;
+	m_Detail->ReadCV.notify_all();
+}
+
+size_t
+ComputeBufferWriter::GetMaxWriteSize() const
+{
+	if (!m_Detail)
+	{
+		return 0;
+	}
+	std::lock_guard<std::mutex> Lock(m_Detail->Mutex);
+	const size_t				WriteChunk = m_Detail->WriteChunkIdx;
+	return m_Detail->ChunkLength - m_Detail->ChunkWrittenLength[WriteChunk];
+}
+
+size_t
+ComputeBufferWriter::GetChunkMaxLength() const
+{
+	if (!m_Detail)
+	{
+		return 0;
+	}
+	return m_Detail->ChunkLength;
+}
+
+size_t
+ComputeBufferWriter::Write(const void* Buffer, size_t MaxSize, int TimeoutMs)
+{
+	uint8_t* Dest = WaitToWrite(1, TimeoutMs);
+	if (!Dest)
+	{
+		return 0;
+	}
+
+	const size_t Available = GetMaxWriteSize();
+	const size_t ToCopy	   = std::min(Available, MaxSize);
+	memcpy(Dest, Buffer, ToCopy);
+	AdvanceWritePosition(ToCopy);
+	return ToCopy;
+}
+
+uint8_t*
+ComputeBufferWriter::WaitToWrite(size_t MinSize, int TimeoutMs)
+{
+	if (!m_Detail)
+	{
+		return nullptr;
+	}
+
+	std::unique_lock<std::mutex> Lock(m_Detail->Mutex);
+
+	if (m_Detail->WriteComplete)
+	{
+		return nullptr;
+	}
+
+	const size_t WriteChunk = m_Detail->WriteChunkIdx;
+	const size_t Available	= m_Detail->ChunkLength - m_Detail->ChunkWrittenLength[WriteChunk];
+
+	// If current chunk has enough space, return pointer
+	if (Available >= MinSize)
+	{
+		return m_Detail->ChunkPtr(WriteChunk) + m_Detail->ChunkWrittenLength[WriteChunk];
+	}
+
+	// Current chunk is full - mark it as finished and move to next.
+	// The writer cannot advance until the reader has fully consumed the next chunk,
+	// preventing the writer from overwriting data the reader hasn't processed yet.
+	m_Detail->ChunkFinished[WriteChunk] = true;
+	m_Detail->ReadCV.notify_all();
+
+	const size_t NextChunk = (WriteChunk + 1) % m_Detail->NumChunks;
+
+	// Wait until reader has consumed the next chunk
+	auto Predicate = [&]() -> bool {
+		// Check if read has moved past this chunk
+		return m_Detail->ReadChunkIdx != NextChunk || m_Detail->Detached;
+	};
+
+	if (TimeoutMs < 0)
+	{
+		m_Detail->WriteCV.wait(Lock, Predicate);
+	}
+	else
+	{
+		if (!m_Detail->WriteCV.wait_for(Lock, std::chrono::milliseconds(TimeoutMs), Predicate))
+		{
+			return nullptr;
+		}
+	}
+
+	if (m_Detail->Detached)
+	{
+		return nullptr;
+	}
+
+	// Reset next chunk
+	m_Detail->ChunkWrittenLength[NextChunk] = 0;
+	m_Detail->ChunkFinished[NextChunk]		= false;
+	m_Detail->WriteChunkIdx					= NextChunk;
+	m_Detail->WriteOffset					= 0;
+
+	return m_Detail->ChunkPtr(NextChunk);
+}
+
+}  // namespace zen::horde