From a2267936a2f08f0c3bca6ebb2907fdac5a6b7abe Mon Sep 17 00:00:00 2001
From: John Hodge <tpg@mutabah.net>
Date: Sun, 7 Aug 2011 11:44:24 +0800
Subject: [PATCH] Kernel - Fixed concurrency in the RingBuffer type

---
 Kernel/adt.c         | 37 +++++++++++++++++++++++++++++--------
 Kernel/include/adt.h |  1 +
 2 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/Kernel/adt.c b/Kernel/adt.c
index 77c8d995..1a001c99 100644
--- a/Kernel/adt.c
+++ b/Kernel/adt.c
@@ -21,45 +21,66 @@ tRingBuffer *RingBuffer_Create(size_t Space)
 
 size_t RingBuffer_Read(void *Dest, tRingBuffer *Buffer, size_t Length)
 {
-	if(Length > Buffer->Length)	Length = Buffer->Length;
+	size_t	tmpLen;
+
+	tmpLen = Buffer->Length;	// Changed in Write, so cache it for our read
+
+	if(Length > tmpLen)	Length = tmpLen;
 	
 	if( Buffer->Start + Length > Buffer->Space )
 	{
 		 int	endData = Buffer->Space - Buffer->Start;
 		memcpy(Dest, &Buffer->Data[Buffer->Start], endData);
-		memcpy((Uint8*)Dest + endData, &Buffer->Data, Length - endData);
+		memcpy((Uint8*)Dest + endData, Buffer->Data, Length - endData);
 	}
 	else
 	{
 		memcpy(Dest, &Buffer->Data[Buffer->Start], Length);
 	}
+
+	// Lock then modify
+	SHORTLOCK( &Buffer->Lock );
 	Buffer->Start += Length;
 	if( Buffer->Start > Buffer->Space )
 		Buffer->Start -= Buffer->Space;
 	Buffer->Length -= Length;
+	SHORTREL( &Buffer->Lock );
+
 	return Length;
 }
 
 size_t RingBuffer_Write(tRingBuffer *Buffer, const void *Source, size_t Length)
 {
-	size_t	bufEnd = Buffer->Start + Buffer->Length;
-	size_t	endSpace = Buffer->Space - bufEnd;
+	size_t	bufEnd, endSpace;
+	size_t	tmpLen, tmpStart;
+	
+	// Cache Start and Length because _Read can change these
+	SHORTLOCK( &Buffer->Lock );
+	tmpStart = Buffer->Start;
+	tmpLen = Buffer->Length;
+	SHORTREL( &Buffer->Lock );
+
+	bufEnd = (Buffer->Start + Buffer->Length) % Buffer->Space;
+	endSpace = Buffer->Space - bufEnd;
 	
 	// Force to bounds
-	if(Length > Buffer->Space - Buffer->Length)
-		Length = Buffer->Space - Buffer->Length;
+	if(Length > Buffer->Space - tmpLen)	Length = Buffer->Space - tmpLen;
 	
 	if(endSpace < Length)
 	{
 		memcpy( &Buffer->Data[bufEnd], Source, endSpace );
 		memcpy( Buffer->Data, (Uint8*)Source + endSpace, Length - endSpace );
-		Buffer->Length = Length - endSpace;
 	}
 	else
 	{
 		memcpy( &Buffer->Data[bufEnd], Source, Length );
-		Buffer->Length += Length;
 	}
+
+	// Lock then modify
+	SHORTLOCK( &Buffer->Lock );
+	Buffer->Length += Length;
+	SHORTREL( &Buffer->Lock );
 	
 	return Length;
 }
+
diff --git a/Kernel/include/adt.h b/Kernel/include/adt.h
index 91a8ae5f..67e12665 100644
--- a/Kernel/include/adt.h
+++ b/Kernel/include/adt.h
@@ -14,6 +14,7 @@ typedef struct sRingBuffer
 	size_t	Start;	//!< Start of data in ring buffer
 	size_t	Length;	//!< Number of data bytes in buffer
 	size_t	Space;	//!< Allocated space in buffer
+	tShortSpinlock	Lock;	//!< Lock to prevent collisions
 	char	Data[];	//!< Buffer
 }	tRingBuffer;
 
-- 
2.20.1