/// <summary>
/// Closes the shared memory queue currently opened.
/// </summary>
public void Close()
{
if (mMemoryMappedViewAccessor != null)
{
if (mQueueHeader != null)
{
mMemoryMappedViewAccessor.SafeMemoryMappedViewHandle.ReleasePointer();
mQueueHeader = null;
}
mMemoryMappedViewAccessor.Dispose();
mMemoryMappedViewAccessor = null;
}
if (mMemoryMappedFile != null)
{
mMemoryMappedFile.Dispose();
mMemoryMappedFile = null;
}
mQueueHeader = null;
mFirstBlockInMemory = null;
mFirstBlockUnderRead = null;
mNumberOfBlocks = 0;
mBufferSize = 0;
mBlockSize = 0;
mInitialized = false;
}
/// <summary>
/// Creates a new shared memory queue (only supported on the full .NET framework).
/// </summary>
/// <param name="name">Name of the shared memory region to create the queue in.</param>
/// <param name="bufferSize">Size of a buffer in the shared memory queue (in bytes).</param>
/// <param name="numberOfBlocks">Number of blocks the queue should keep.</param>
/// <exception cref="NotSupportedException">This method is not supported on the current platform/framework.</exception>
/// <remarks>
/// This method creates a new queue in a shared memory region specified by the given name and the given size.
/// </remarks>
public void Create(string name, int bufferSize, int numberOfBlocks)
{
#if NETFRAMEWORK
if (name == null)
{
throw new ArgumentNullException(nameof(name));
}
if (bufferSize < 0)
{
throw new ArgumentOutOfRangeException(nameof(bufferSize), "The block size must be positive.");
}
if (numberOfBlocks < 0)
{
throw new ArgumentOutOfRangeException(nameof(numberOfBlocks), "The number of blocks must be positive.");
}
// close currently opened queue, if necessary
Close();
mNumberOfBlocks = numberOfBlocks;
mBufferSize = bufferSize;
// ensure that the block sizes are a multiple of the cache line size to avoid false sharing
mBlockSize = (sizeof(QueueBlock) + mBufferSize + CacheLineSize - 1) & ~(CacheLineSize - 1);
mQueueHeaderSize = (sizeof(QueueHeader) + CacheLineSize - 1) & ~(CacheLineSize - 1);
long dataSize = (long)mNumberOfBlocks * mBlockSize;
long totalBufferSize = mQueueHeaderSize + dataSize;
// create the shared memory region
string queueName = $"{name} - Shared Memory";
mMemoryMappedFile = MemoryMappedFile.CreateNew(
queueName,
totalBufferSize,
MemoryMappedFileAccess.ReadWrite,
MemoryMappedFileOptions.None,
sMemoryMappedFileSecurity,
HandleInheritability.None);
mMemoryMappedViewAccessor = mMemoryMappedFile.CreateViewAccessor();
// get pointer to the buffer
byte *ptr = null;
mMemoryMappedViewAccessor.SafeMemoryMappedViewHandle.AcquirePointer(ref ptr);
mQueueHeader = (QueueHeader *)ptr;
mFirstBlockInMemory = (QueueBlock *)((byte *)mQueueHeader + mQueueHeaderSize);
// init the queue
InitQueue();
// the queue is initialized now
mFirstBlockUnderRead = null;
mInitialized = true;
#else
throw new NotSupportedException("The Created() method is only supported on the full .NET framework.");
#endif
}
/// <summary>
/// Pushes a sequence of blocks onto the top of the 'used block stack'.
/// </summary>
/// <param name="firstBlock">First block to push onto the 'used block stack'.</param>
/// <param name="lastBlock">Last block to push onto the 'used block stack'.</param>
/// <param name="overflowCount">Number of lost single blocks or block sequences since the last successful transferred block.</param>
private void PushUsedBlocks(QueueBlock *firstBlock, QueueBlock *lastBlock, int overflowCount)
{
lastBlock->OverflowCount = overflowCount; // last block is the first block of the pushed sequence
int firstBlockIndex = (int)(((byte *)firstBlock - (byte *)mFirstBlockInMemory) / mBlockSize);
while (true)
{
int firstIndex = lastBlock->NextIndex = mQueueHeader->UsedStackHeaderIndex;
if (Interlocked.CompareExchange(ref mQueueHeader->UsedStackHeaderIndex, firstBlockIndex, firstIndex) == firstIndex)
{
break;
}
}
}
/// <summary>
/// Opens an existing queue in the shared memory region with the specified name.
/// </summary>
/// <param name="name">Name of the shared memory region to open.</param>
public void Open(string name)
{
// close currently opened queue, if necessary
Close();
try
{
// open the shared memory region the queue resides in
string queueName = $"{name} - Shared Memory";
mMemoryMappedFile = MemoryMappedFile.OpenExisting(queueName, MemoryMappedFileRights.ReadWrite);
mMemoryMappedViewAccessor = mMemoryMappedFile.CreateViewAccessor();
// get pointer to the buffer in shared memory
byte *ptr = null;
mMemoryMappedViewAccessor.SafeMemoryMappedViewHandle.AcquirePointer(ref ptr);
mQueueHeader = (QueueHeader *)ptr;
// check the queue's signature
// (for an explanation why 'ALVA' see InitQueue()
if (mQueueHeader->Signature[0] != 'A' ||
mQueueHeader->Signature[1] != 'L' ||
mQueueHeader->Signature[2] != 'V' ||
mQueueHeader->Signature[3] != 'A')
{
throw new InvalidDataException("Shared region does not start with the magic word 'ALVA'.");
}
// read administrative information from the queue's header
mNumberOfBlocks = mQueueHeader->NumberOfBlocks;
mBufferSize = mQueueHeader->BufferSize;
mBlockSize = mQueueHeader->BlockSize;
mQueueHeaderSize = (sizeof(QueueHeader) + CacheLineSize - 1) & ~(CacheLineSize - 1);
mFirstBlockInMemory = (QueueBlock *)((byte *)mQueueHeader + mQueueHeaderSize);
// the queue is initialized now!
mFirstBlockUnderRead = null;
mInitialized = true;
}
catch (Exception)
{
Close();
throw;
}
}
/// <summary>
/// Pushes a block onto the top of the 'used block stack'.
/// </summary>
/// <param name="block">Block to push onto the 'used block stack'.</param>
/// <param name="overflowCount">Number of lost single blocks or block sequences since the last successful transferred block.</param>
private void PushUsedBlock(QueueBlock *block, int overflowCount)
{
Debug.Assert(block->MagicNumber == QueueBlock.MagicNumberValue);
Debug.Assert(block->NextIndex == -1);
block->OverflowCount = overflowCount;
Debug.Assert(((byte *)block - (byte *)mFirstBlockInMemory) % mBlockSize == 0);
int blockIndex = (int)(((byte *)block - (byte *)mFirstBlockInMemory) / mBlockSize);
Debug.Assert(blockIndex < mNumberOfBlocks);
while (true)
{
int firstIndex = block->NextIndex = mQueueHeader->UsedStackHeaderIndex;
if (Interlocked.CompareExchange(ref mQueueHeader->UsedStackHeaderIndex, blockIndex, firstIndex) == firstIndex)
{
break;
}
}
}
/// <summary>
/// Begins reading a new block.
/// </summary>
/// <param name="validSize">Receives the number of valid bytes in the block.</param>
/// <param name="overflowCount">Receives the number of lost single blocks or block sequences since the last reading attempt.</param>
/// <param name="blocksFollowingInSequence">
/// Receives <c>true</c>, if there are more blocks in the queue that belong to the block;
/// otherwise false.
/// </param>
/// <returns>
/// Pointer to the data buffer within the retrieved block;
/// null if no block is available for reading.
/// </returns>
/// <exception cref="InvalidOperationException">The queue was not initialized using <see cref="Create"/> or <see cref="Open"/>.</exception>
public void *BeginReading(out int validSize, out int overflowCount, out bool blocksFollowingInSequence)
{
// abort, if the queue is not initialized
if (!mInitialized)
{
throw new InvalidOperationException("Queue is not initialized, call Create() or Open() to initialize it.");
}
if (mFirstBlockUnderRead != null)
{
// there are some blocks to read left from the last flush
// => take one of these blocks
// prepare stuff to return
validSize = mFirstBlockUnderRead->DataSize;
overflowCount = mFirstBlockUnderRead->OverflowCount;
var block = mFirstBlockUnderRead;
var buffer = (void *)((byte)block + sizeof(QueueBlock));
// proceed with the next block
if (mFirstBlockUnderRead->NextIndex >= 0)
{
Debug.Assert(mFirstBlockUnderRead->NextIndex < mNumberOfBlocks);
mFirstBlockUnderRead = (QueueBlock *)((byte *)mFirstBlockInMemory + (long)mFirstBlockUnderRead->NextIndex * mBlockSize);
Debug.Assert(mFirstBlockUnderRead->MagicNumber == QueueBlock.MagicNumberValue);
}
else
{
mFirstBlockUnderRead = null;
}
blocksFollowingInSequence = mFirstBlockUnderRead != null;
Debug.Assert(((long)buffer & 15) == 0);
block->NextIndex = -1;
return(buffer);
}
// there are no blocks to read left from the last flush
// => try to flush the queue, re-initialize the buffer and proceed...
while (true)
{
int blockIndex = mQueueHeader->UsedStackHeaderIndex;
if (blockIndex < 0)
{
// no block on the 'used block stack'
validSize = 0;
overflowCount = 0;
blocksFollowingInSequence = false;
return(null);
}
// flush the 'used block stack'
Debug.Assert(blockIndex < mNumberOfBlocks);
if (Interlocked.CompareExchange(ref mQueueHeader->UsedStackHeaderIndex, -1, blockIndex) != blockIndex)
{
continue;
}
// reverse the sequence of blocks to restore the original order
var block = (QueueBlock *)((byte *)mFirstBlockInMemory + (long)blockIndex * mBlockSize);
int currentBlockIndex = blockIndex;
int previousIndex = -1;
while (true)
{
Debug.Assert(block->MagicNumber == QueueBlock.MagicNumberValue);
Debug.Assert(block->NextIndex < 0 || block->NextIndex < mNumberOfBlocks);
int nextIndex = block->NextIndex;
block->NextIndex = previousIndex;
previousIndex = currentBlockIndex;
currentBlockIndex = nextIndex;
if (currentBlockIndex < 0)
{
break;
}
block = (QueueBlock *)((byte *)mFirstBlockInMemory + (long)currentBlockIndex * mBlockSize);
}
Debug.Assert(previousIndex < mNumberOfBlocks);
mFirstBlockUnderRead = (QueueBlock *)((byte *)mFirstBlockInMemory + (long)previousIndex * mBlockSize);
validSize = mFirstBlockUnderRead->DataSize;
overflowCount = mFirstBlockUnderRead->OverflowCount;
void *buffer = (byte *)mFirstBlockUnderRead + sizeof(QueueBlock);
// proceed with the next block
if (mFirstBlockUnderRead->NextIndex >= 0)
{
Debug.Assert(mFirstBlockUnderRead->NextIndex < mNumberOfBlocks);
mFirstBlockUnderRead = (QueueBlock *)((byte *)mFirstBlockInMemory + (long)mFirstBlockUnderRead->NextIndex * mBlockSize);
}
else
{
mFirstBlockUnderRead = null;
}
blocksFollowingInSequence = mFirstBlockUnderRead != null;
Debug.Assert(((long)buffer & 15) == 0);
block->NextIndex = -1;
return(buffer);
}
}
