[raknet] Add SingleProducerConsumer

* Implements SingleProducerConsumer ctor
* Implements `SingleProducerConsumer::ReadLock()`
* Implements `SingleProducerConsumer::ReadUnlock()`

raknet/SingleProducerConsumer.h

@@ -0,0 +1,105 @@
+// TODO: Implement SingleProducerConsumer.h
+
+#ifndef __SINGLE_PRODUCER_CONSUMER_H
+#define __SINGLE_PRODUCER_CONSUMER_H
+
+#include <assert.h>
+
+static const int MINIMUM_LIST_SIZE=8;
+
+#include "Export.h"
+
+/// The namespace DataStructures was only added to avoid compiler errors for commonly named data structures
+/// As these data structures are stand-alone, you can use them outside of RakNet for your own projects if you wish.
+namespace DataStructures
+{
+	/// \brief A single producer consumer implementation without critical sections.
+	template <class SingleProducerConsumerType>
+	class RAK_DLL_EXPORT SingleProducerConsumer
+	{
+	public:
+		/// Constructor
+		SingleProducerConsumer();
+
+		/// ReadLock must be immediately followed by ReadUnlock. These two functions must be called in the same thread.
+		/// \retval 0 No data is availble to read
+		/// \retval Non-zero The data previously written to, in another thread, by WriteLock followed by WriteUnlock.
+		SingleProducerConsumerType* ReadLock(void);
+
+		/// Signals that we are done reading the the data from the least recent call of ReadLock.
+		/// At this point that pointer is no longer valid, and should no longer be read.
+		void ReadUnlock(void);
+
+	private:
+		struct DataPlusPtr
+		{
+			SingleProducerConsumerType object;
+
+			// Ready to read is so we can use an equality boolean comparison, in case the writePointer var is trashed while context switching.
+			volatile bool readyToRead;
+			volatile DataPlusPtr *next;
+		};
+		volatile DataPlusPtr *readAheadPointer;
+		volatile DataPlusPtr *writeAheadPointer;
+		volatile DataPlusPtr *readPointer;
+		volatile DataPlusPtr *writePointer;
+		unsigned readCount, writeCount;
+	};
+
+	template <class SingleProducerConsumerType>
+		SingleProducerConsumer<SingleProducerConsumerType>::SingleProducerConsumer()
+	{
+		// Preallocate
+		readPointer = new DataPlusPtr;
+		writePointer=readPointer;
+		readPointer->next = new DataPlusPtr;
+		int listSize;
+#ifdef _DEBUG
+		assert(MINIMUM_LIST_SIZE>=3);
+#endif
+		for (listSize=2; listSize < MINIMUM_LIST_SIZE; listSize++)
+		{
+			readPointer=readPointer->next;
+			readPointer->next = new DataPlusPtr;
+		}
+		readPointer->next->next=writePointer; // last to next = start
+		readPointer=writePointer;
+		readAheadPointer=readPointer;
+		writeAheadPointer=writePointer;
+		readCount=writeCount=0;
+	}
+
+	template <class SingleProducerConsumerType>
+		SingleProducerConsumerType* SingleProducerConsumer<SingleProducerConsumerType>::ReadLock( void )
+	{
+		if (readAheadPointer==writePointer ||
+			readAheadPointer->readyToRead==false)
+		{
+			return 0;
+		}
+
+		volatile DataPlusPtr *last;
+		last=readAheadPointer;
+		readAheadPointer=readAheadPointer->next;
+		return (SingleProducerConsumerType*)last;
+	}
+
+	template <class SingleProducerConsumerType>
+		void SingleProducerConsumer<SingleProducerConsumerType>::ReadUnlock( void )
+	{
+#ifdef _DEBUG
+		assert(readAheadPointer!=readPointer); // If hits, then called ReadUnlock before ReadLock
+		assert(readPointer!=writePointer); // If hits, then called ReadUnlock when Read returns 0
+#endif
+		readCount++;
+
+		// Allow writes to this memory block
+		readPointer->readyToRead=false;
+		readPointer=readPointer->next;
+	}
+
+
+
+}
+
+#endif