Index: source/ps/Profiler2.h
===================================================================
--- source/ps/Profiler2.h
+++ source/ps/Profiler2.h
@@ -81,6 +81,7 @@
 #include "lib/timer.h"
 #include "ps/ThreadUtil.h"
 
+#include <atomic>
 #include <mutex>
 #include <string>
 #include <thread>
@@ -261,11 +262,13 @@
 		// outside the range Pos1 <= x < Pos0 are safe to use. (Any in that range might
 		// be half-written and corrupted.) (All ranges are modulo BUFFER_SIZE.)
 		// Outside of Write(), these will always be equal.
-		//
-		// TODO: does this attempt at synchronisation (plus use of COMPILER_FENCE etc)
-		// actually work in practice?
-		u32 m_BufferPos0;
-		u32 m_BufferPos1;
+		struct RingBufferSpan
+		{
+			// If 'begin >= end' the range does wrap around.
+			std::atomic<u32> begin{0};
+			std::atomic<u32> end{0};
+		};
+		RingBufferSpan m_ValidRange;
 	};
 
 public:
Index: source/ps/Profiler2.cpp
===================================================================
--- source/ps/Profiler2.cpp
+++ source/ps/Profiler2.cpp
@@ -312,7 +312,7 @@
 }
 
 CProfiler2::ThreadStorage::ThreadStorage(CProfiler2& profiler, const std::string& name) :
-m_Profiler(profiler), m_Name(name), m_BufferPos0(0), m_BufferPos1(0), m_LastTime(timer_Time()), m_HeldDepth(0)
+m_Profiler(profiler), m_Name(name), m_LastTime(timer_Time()), m_HeldDepth(0)
 {
 	m_Buffer = new u8[BUFFER_SIZE];
 	memset(m_Buffer, ITEM_NOP, BUFFER_SIZE);
@@ -330,33 +330,30 @@
 		WriteHold(type, item, itemSize);
 		return;
 	}
-	// See m_BufferPos0 etc for comments on synchronisation
+	// See RingBufferSpan etc for comments on synchronisation
 
 	u32 size = 1 + itemSize;
-	u32 start = m_BufferPos0;
+	u32 start = m_ValidRange.begin.load(std::memory_order_relaxed);
 	if (start + size > BUFFER_SIZE)
 	{
 		// The remainder of the buffer is too small - fill the rest
 		// with NOPs then start from offset 0, so we don't have to
 		// bother splitting the real item across the end of the buffer
 
-		m_BufferPos0 = size;
-		COMPILER_FENCE; // must write m_BufferPos0 before m_Buffer
+		m_ValidRange.begin.store(size, std::memory_order_release);
 
 		memset(m_Buffer + start, 0, BUFFER_SIZE - start);
 		start = 0;
 	}
 	else
 	{
-		m_BufferPos0 = start + size;
-		COMPILER_FENCE; // must write m_BufferPos0 before m_Buffer
+		m_ValidRange.begin.store(start + size, std::memory_order_release);
 	}
 
 	m_Buffer[start] = (u8)type;
 	memcpy(&m_Buffer[start + 1], item, itemSize);
 
-	COMPILER_FENCE; // must write m_BufferPos1 after m_Buffer
-	m_BufferPos1 = start + size;
+	m_ValidRange.end.store(start + size, std::memory_order_release);
 }
 
 void CProfiler2::ThreadStorage::WriteHold(EItem type, const void* item, u32 itemSize)
@@ -380,13 +377,11 @@
 
 	std::shared_ptr<u8> buffer(new u8[BUFFER_SIZE], ArrayDeleter());
 
-	u32 pos1 = m_BufferPos1;
-	COMPILER_FENCE; // must read m_BufferPos1 before m_Buffer
+	u32 pos1 = m_ValidRange.end.load(std::memory_order_acquire);
 
 	memcpy(buffer.get(), m_Buffer, BUFFER_SIZE);
 
-	COMPILER_FENCE; // must read m_BufferPos0 after m_Buffer
-	u32 pos0 = m_BufferPos0;
+	u32 pos0 = m_ValidRange.begin.load(std::memory_order_acquire);
 
 	// The range [pos1, pos0) modulo BUFFER_SIZE is invalid, so concatenate the rest of the buffer
 
@@ -701,22 +696,19 @@
 	else
 	{
 		u32 size = m_HoldBuffers[m_HeldDepth - 1].pos;
-		u32 start = m_BufferPos0;
+		u32 start = m_ValidRange.begin.load(std::memory_order_relaxed);
 		if (start + size > BUFFER_SIZE)
 		{
-			m_BufferPos0 = size;
-			COMPILER_FENCE;
+			m_ValidRange.begin.store(size, std::memory_order_release);
 			memset(m_Buffer + start, 0, BUFFER_SIZE - start);
 			start = 0;
 		}
 		else
 		{
-			m_BufferPos0 = start + size;
-			COMPILER_FENCE; // must write m_BufferPos0 before m_Buffer
+			m_ValidRange.begin.store(start + size, std::memory_order_release);
 		}
 		memcpy(&m_Buffer[start], m_HoldBuffers[m_HeldDepth - 1].buffer, size);
-		COMPILER_FENCE; // must write m_BufferPos1 after m_Buffer
-		m_BufferPos1 = start + size;
+		m_ValidRange.end.store(start + size, std::memory_order_release);
 	}
 	m_HeldDepth--;
 }