IO Completion ports

async intro

what is it?

public override IAsyncResult BeginRead(
	byte[] array,
	int offset,
	int numBytes,
	AsyncCallback userCallback,
	Object stateObject
)
						

public IAsyncResult BeginAccept(
	Socket acceptSocket,
	int receiveSize,
	AsyncCallback callback,
	Object state
)
						

async .NET API

Asynchronous .NET API for operations like

• BeginXXX / EndXXX
• SocketAsyncEventArgs

uses I/O Completion Ports

what is it?

I/O completion port

• a threading model for IO on multicore machines
• an object created for a given process
• is extremely fast
• a handle can be bound to a port. A handle can be:
• file
• socket
• named pipe

I/O completion port flow

• create a port
• anytime, bind an object handle to the port. There's no unbinding
• once, overlapped asynchronous operation is issued...
• query completion port for its status...
• finally you'll be given the result
• use it massively, for each handle you want to work with in async way

functions working with completion ports

• file & directory
• ReadFile
• ReadDirectoryChangesW
• Sockets
• WSASend
• WSARecv

API - create & bind

HANDLE WINAPI CreateIoCompletionPort(
  _In_      HANDLE FileHandle,
  _In_opt_  HANDLE ExistingCompletionPort,
  _In_      ULONG_PTR CompletionKey,
  _In_      DWORD NumberOfConcurrentThreads
);
						

[DllImport("kernel32.dll", SetLastError = true)]
public static extern IntPtr CreateIoCompletionPort(
	IntPtr fileHandle, 
	IntPtr existingCompletionPort, 
	IntPtr completionKey, 
	uint numberOfConcurrentThreads
);
						

API - get status

BOOL WINAPI GetQueuedCompletionStatus(
  _In_   HANDLE CompletionPort,
  _Out_  LPDWORD lpNumberOfBytes,
  _Out_  PULONG_PTR lpCompletionKey,
  _Out_  LPOVERLAPPED *lpOverlapped,
  _In_   DWORD dwMilliseconds
);
						

[DllImport("kernel32.dll", SetLastError = true)]
public static extern bool GetQueuedCompletionStatus(
	IntPtr CompletionPort, 
	out uint numberOfTransferredBytes, 
	out IntPtr completionKey, 
	out NativeOverlapped* overlapped, 
	uint milisecondsTimeout
);
						

API - get status ex (1)

BOOL WINAPI GetQueuedCompletionStatusEx(
  _In_   HANDLE CompletionPort,
  _Out_  LPOVERLAPPED_ENTRY lpCompletionPortEntries,
  _In_   ULONG ulCount,
  _Out_  PULONG ulNumEntriesRemoved,
  _In_   DWORD dwMilliseconds,
  _In_   BOOL fAlertable
);

typedef struct _OVERLAPPED_ENTRY {
  ULONG_PTR    lpCompletionKey;
  LPOVERLAPPED lpOverlapped;
  ULONG_PTR    Internal;
  DWORD        dwNumberOfBytesTransferred;
} OVERLAPPED_ENTRY, *LPOVERLAPPED_ENTRY;
						

API - get status ex (2)

[DllImport("kernel32.dll")]
public static extern bool GetQueuedCompletionStatusEx(
	IntPtr completionPort, 
	OverlappedEntry* entries, 
	uint count, 
	out uint entriesRemoved, 
	uint milisecondsTimeout, 
	bool alertable
);
public struct OverlappedEntry
{
    public IntPtr CompletionKey;
    public NativeOverlapped* Overlapped;
    public UIntPtr Internal;
    public uint NumberOfTransferredBytes;
}
						

API - post status

BOOL WINAPI PostQueuedCompletionStatus(
  _In_      HANDLE CompletionPort,
  _In_      DWORD dwNumberOfBytesTransferred,
  _In_      ULONG_PTR dwCompletionKey,
  _In_opt_  LPOVERLAPPED lpOverlapped
);
						

[DllImport("kernel32.dll")]
public static extern bool PostQueuedCompletionStatus(
	IntPtr completionPort,
	uint numberOfBytes,
	IntPtr completionKey,
	NativeOverlapped* overlapped
);