@@ -110,6 +110,7 @@ - Core: Ability to enumerate and modify video and audio channels
  - Debugger: Make attaching a backend idempotent
  - VFS: Optimize expanding in-memory files
  - VFS: Add VFileFIFO for operating on circle buffers
+ - Core: Move rewind diffing to its own thread
 
 0.5.2: (2016-12-31)
 Bugfixes:

@@ -11,6 +11,9 @@
 CXX_GUARD_START
 
 #include <mgba-util/vector.h>
+#ifndef DISABLE_THREADING
+#include <mgba-util/threading.h>
+#endif
 
 DECLARE_VECTOR(mCoreRewindPatches, struct PatchFast);
 
@@ -22,9 +25,16 @@ size_t size;
 	int stateFlags;
 	struct VFile* previousState;
 	struct VFile* currentState;
+
+#ifndef DISABLE_THREADING
+	bool onThread;
+	Thread thread;
+	Condition cond;
+	Mutex mutex;
+#endif
 };
 
-void mCoreRewindContextInit(struct mCoreRewindContext*, size_t entries);
+void mCoreRewindContextInit(struct mCoreRewindContext*, size_t entries, bool onThread);
 void mCoreRewindContextDeinit(struct mCoreRewindContext*);
 
 struct mCore;

@@ -12,7 +12,13 @@ #include <mgba-util/vfs.h>
 
 DEFINE_VECTOR(mCoreRewindPatches, struct PatchFast);
 
-void mCoreRewindContextInit(struct mCoreRewindContext* context, size_t entries) {
+void _rewindDiff(struct mCoreRewindContext* context);
+
+#ifndef DISABLE_THREADING
+THREAD_ENTRY _rewindThread(void* context);
+#endif
+
+void mCoreRewindContextInit(struct mCoreRewindContext* context, size_t entries, bool onThread) {
 	mCoreRewindPatchesInit(&context->patchMemory, entries);
 	size_t e;
 	for (e = 0; e < entries; ++e) {
@@ -22,9 +28,30 @@ context->previousState = VFileMemChunk(0, 0);
 	context->currentState = VFileMemChunk(0, 0);
 	context->size = 0;
 	context->stateFlags = SAVESTATE_SAVEDATA;
+#ifndef DISABLE_THREADING
+	context->onThread = onThread;
+	if (onThread) {
+		MutexInit(&context->mutex);
+		ConditionInit(&context->cond);
+		ThreadCreate(&context->thread, _rewindThread, context);
+	}
+#else
+	UNUSED(onThread);
+#endif
 }
 
 void mCoreRewindContextDeinit(struct mCoreRewindContext* context) {
+#ifndef DISABLE_THREADING
+	if (context->onThread) {
+		MutexLock(&context->mutex);
+		context->onThread = false;
+		MutexUnlock(&context->mutex);
+		ConditionWake(&context->cond);
+		ThreadJoin(context->thread);
+		MutexDeinit(&context->mutex);
+		ConditionDeinit(&context->cond);
+	}
+#endif
 	context->previousState->close(context->previousState);
 	context->currentState->close(context->currentState);
 	size_t s;
@@ -35,7 +62,26 @@ mCoreRewindPatchesDeinit(&context->patchMemory);
 }
 
 void mCoreRewindAppend(struct mCoreRewindContext* context, struct mCore* core) {
+#ifndef DISABLE_THREADING
+	if (context->onThread) {
+		MutexLock(&context->mutex);
+	}
+#endif
 	struct VFile* nextState = context->previousState;
+	mCoreSaveStateNamed(core, nextState, context->stateFlags);
+	context->previousState = context->currentState;
+	context->currentState = nextState;
+#ifndef DISABLE_THREADING
+	if (context->onThread) {
+		ConditionWake(&context->cond);
+		MutexUnlock(&context->mutex);
+		return;
+	}
+#endif
+	_rewindDiff(context);
+}
+
+void _rewindDiff(struct mCoreRewindContext* context) {
 	++context->current;
 	if (context->size < mCoreRewindPatchesSize(&context->patchMemory)) {
 		++context->size;
@@ -43,27 +89,34 @@ }
 	if (context->current >= mCoreRewindPatchesSize(&context->patchMemory)) {
 		context->current = 0;
 	}
-	mCoreSaveStateNamed(core, nextState, context->stateFlags);
 	struct PatchFast* patch = mCoreRewindPatchesGetPointer(&context->patchMemory, context->current);
-	size_t size2 = nextState->size(nextState);
-	size_t size = context->currentState->size(context->currentState);
+	size_t size2 = context->currentState->size(context->currentState);
+	size_t size = context->previousState->size(context->previousState);
 	if (size2 > size) {
-		context->currentState->truncate(context->currentState, size2);
+		context->previousState->truncate(context->previousState, size2);
 		size = size2;
 	} else if (size > size2) {
-		nextState->truncate(nextState, size);
+		context->currentState->truncate(context->currentState, size);
 	}
-	void* current = context->currentState->map(context->currentState, size, MAP_READ);
-	void* next = nextState->map(nextState, size, MAP_READ);
+	void* current = context->previousState->map(context->previousState, size, MAP_READ);
+	void* next = context->currentState->map(context->currentState, size, MAP_READ);
 	diffPatchFast(patch, current, next, size);
-	context->currentState->unmap(context->currentState, current, size);
-	nextState->unmap(next, nextState, size);
-	context->previousState = context->currentState;
-	context->currentState = nextState;
+	context->previousState->unmap(context->previousState, current, size);
+	context->currentState->unmap(context->currentState, next, size);
 }
 
 bool mCoreRewindRestore(struct mCoreRewindContext* context, struct mCore* core) {
+#ifndef DISABLE_THREADING
+	if (context->onThread) {
+		MutexLock(&context->mutex);
+	}
+#endif
 	if (!context->size) {
+#ifndef DISABLE_THREADING
+		if (context->onThread) {
+			MutexUnlock(&context->mutex);
+		}
+#endif
 		return false;
 	}
 	--context->size;
@@ -88,5 +141,29 @@ if (context->current == 0) {
 		context->current = mCoreRewindPatchesSize(&context->patchMemory);
 	} 
 	--context->current;
+#ifndef DISABLE_THREADING
+	if (context->onThread) {
+		MutexUnlock(&context->mutex);
+	}
+#endif
 	return true;
 }
+
+#ifndef DISABLE_THREADING
+THREAD_ENTRY _rewindThread(void* context) {
+	struct mCoreRewindContext* rewindContext = context;
+	ThreadSetName("Rewind Diff Thread");
+	MutexLock(&rewindContext->mutex);
+	struct VFile* state = rewindContext->currentState;
+	while (rewindContext->onThread) {
+		if (rewindContext->currentState != state) {
+			_rewindDiff(rewindContext);
+			state = rewindContext->currentState;
+		}
+		ConditionWait(&rewindContext->cond, &rewindContext->mutex);
+	}
+	MutexUnlock(&rewindContext->mutex);
+	return 0;
+}
+#endif
+

@@ -168,7 +168,7 @@ mLogFilterLoad(threadContext->logger.d.filter, &core->config);
 	}
 
 	if (core->opts.rewindEnable && core->opts.rewindBufferCapacity > 0) {
-		 mCoreRewindContextInit(&threadContext->rewind, core->opts.rewindBufferCapacity);
+		 mCoreRewindContextInit(&threadContext->rewind, core->opts.rewindBufferCapacity, true);
 		 threadContext->rewind.stateFlags = core->opts.rewindSave ? SAVESTATE_SAVEDATA : 0;
 	}
 

@@ -741,8 +741,8 @@ m_threadContext.core->opts.rewindEnable = enable;
 		m_threadContext.core->opts.rewindBufferCapacity = capacity;
 		m_threadContext.core->opts.rewindSave = rewindSave;
 		if (enable && capacity > 0) {
-			mCoreRewindContextInit(&m_threadContext.rewind, capacity);
-			 m_threadContext.rewind.stateFlags = rewindSave ? SAVESTATE_SAVEDATA : 0;
+			mCoreRewindContextInit(&m_threadContext.rewind, capacity, true);
+			m_threadContext.rewind.stateFlags = rewindSave ? SAVESTATE_SAVEDATA : 0;
 		}
 	}
 }