LPFN_RIORECEIVE callback function (mswsock.h)

The RIOReceive function receives network data on a connected registered I/O TCP socket or a bound registered I/O UDP socket for use with the Winsock registered I/O extensions.



BOOL LpfnRioreceive(
  RIO_RQ SocketQueue,
  PRIO_BUF pData,
  ULONG DataBufferCount,
  DWORD Flags,
  PVOID RequestContext



A descriptor that identifies a connected registered I/O TCP socket or a bound registered I/O UDP socket.


A description of the portion of the registered buffer in which to receive data.

This parameter may be NULL for a bound registered I/O UDP socket if the application does not need to receive the data payload in the UDP datagram.


A data buffer count parameter that indicates if data is to be received in the buffer pointed to by the pData parameter.

This parameter should be set to zero if the pData is NULL. Otherwise, this parameter should be set to 1.


A set of flags that modify the behavior of the RIOReceive function.

The Flags parameter can contain a combination of the following options defined in the Mswsockdef.h header file:

Previous requests added with RIO_MSG_DEFER flag will be committed.
When the RIO_MSG_COMMIT_ONLY flag is set, no other flags may be specified. When the RIO_MSG_COMMIT_ONLY flag is set, the pData and RequestContext parameters must be NULL and the DataBufferCount parameter must be zero.
This flag would normally be used occasionally after a number of requests were issued with the RIO_MSG_DEFER flag set. This eliminates the need when using the RIO_MSG_DEFER flag to make the last request without the RIO_MSG_DEFER flag, which causes the last request to complete much slower than other requests.
Unlike other calls to the RIOReceive function, when the RIO_MSG_COMMIT_ONLY flag is set calls to the RIOReceive function do not need to be serialized. For a single [RIO_RQ](/windows/win32/winsock/riorqueue), the RIOReceive function can be called with RIO_MSG_COMMIT_ONLY on one thread while calling the RIOReceive function on another thread.
The request should not trigger the [RIONotify](./nc-mswsock-lpfn_rionotify.md) function when request completion is inserted into its completion queue.
The request does not need to be executed immediately. This will insert the request into the request queue, but it may or may not trigger the execution of the request.
Data reception may be delayed until a receive request is made on the [RIO_RQ](/windows/win32/winsock/riorqueue) passed in the SocketQueue parameter without the RIO_MSG_DEFER flag set. To trigger execution for all receives in a request queue, call the RIOReceive or [RIOReceiveEx](./nc-mswsock-lpfn_rioreceiveex.md) function without the RIO_MSG_DEFER flag set.
The receive request is charged against the outstanding I/O capacity on the [RIO_RQ](/windows/win32/winsock/riorqueue) passed in the SocketQueue parameter regardless of whether RIO_MSG_DEFER is set.

The RIOReceive function will not complete until one of the following events occurs:
  • The buffer segment supplied by the caller in the pData parameter is completely full.
  • The connection has been closed.
  • The request has been canceled or an error occurred.

This flag is not supported on UDP sockets.


The request context to associate with this receive operation.

Return value

If no error occurs, the RIOReceive function returns TRUE. In this case, the receive operation is successfully initiated and the completion will have already been queued or the operation has been successfully initiated and the completion will be queued at a later time.

A value of FALSE indicates the function failed, the operation was not successfully initiated and no completion indication will be queued. A specific error code can be retrieved by calling the WSAGetLastError function.

Return code Description
The system detected an invalid pointer address in attempting to use a pointer argument in a call. This error is returned if a buffer identifier is deregistered or a buffer is freed for any of the RIO_BUF structures passed in parameters before the operation is queued or invoked.
An invalid parameter was passed to the function.
This error is returned if the SocketQueue parameter is not valid, the Flags parameter contains an value not valid for a receive operation, or the integrity of the completion queue has been compromised. This error can also be returned for other issues with parameters.
Sufficient memory could not be allocated. This error is returned if the I/O completion queue associated with the SocketQueue parameter is full or the I/O completion queue was created with zero receive entries.
The operation has been canceled while the receive operation was pending. This error is returned if the socket is closed locally or remotely, or the SIO_FLUSH command in WSAIoctl is executed on this socket.


An application can use the RIOReceive function to receive network data into any buffer completely contained within a single registered buffer. The Offset and Length members of the RIO_BUF structure pointed to by the pData parameter determine where the network data is received in the buffer.

Once the RIOReceive function is called, the buffer passed in the pData parameter including the RIO_BUFFERID in the BufferId member of RIO_BUF structure must remain valid for the duration of the receive operation.

In order to avoid race conditions, a buffer associated with a receive request should not be read or written before the request completes. This includes using the buffer as the source for a send request or the destination for another receive request. Portions of a registered buffer not associated with any receive request are not included in this restriction.

The Flags parameter can be used to influence the behavior of the RIOReceive function invocation beyond the options specified for the associated socket. The behavior of this function is determined by a combination of any socket options set on the socket associated with the SocketQueue parameter and the values specified in the Flags parameter.


The function pointer to the RIOReceive function must be obtained at run time by making a call to the WSAIoctl function with the SIO_GET_MULTIPLE_EXTENSION_FUNCTION_POINTER opcode specified. The input buffer passed to the WSAIoctl function must contain WSAID_MULTIPLE_RIO, a globally unique identifier (GUID) whose value identifies the Winsock registered I/O extension functions. On success, the output returned by the WSAIoctl function contains a pointer to the RIO_EXTENSION_FUNCTION_TABLE structure that contains pointers to the Winsock registered I/O extension functions. The SIO_GET_MULTIPLE_EXTENSION_FUNCTION_POINTER IOCTL is defined in the Ws2def.h header file. The WSAID_MULTIPLE_RIO GUID is defined in the Mswsock.h header file.


Windows Phone 8: This function is supported for Windows Phone Store apps on Windows Phone 8 and later.

Windows 8.1 and Windows Server 2012 R2: This function is supported for Windows Store apps on Windows 8.1, Windows Server 2012 R2, and later.


Header mswsock.h