shutdown function (winsock.h)

The shutdown function disables sends or receives on a socket.

Syntax

Parameters

A descriptor identifying a socket.

A flag that describes what types of operation will no longer be allowed. Possible values for this flag are listed in the Winsock2.h header file.

Value	Meaning
SD_RECEIVE 0	Shutdown receive operations.
SD_SEND 1	Shutdown send operations.
SD_BOTH 2	Shutdown both send and receive operations.

Return value

If no error occurs, shutdown returns zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError.

Error code	Meaning
WSAECONNABORTED	The virtual circuit was terminated due to a time-out or other failure. The application should close the socket as it is no longer usable. This error applies only to a connection-oriented socket.
WSAECONNRESET	The virtual circuit was reset by the remote side executing a hard or abortive close. The application should close the socket as it is no longer usable. This error applies only to a connection-oriented socket.
WSAEINPROGRESS	A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.
WSAEINVAL	The how parameter is not valid, or is not consistent with the socket type. For example, SD_SEND is used with a UNI_RECV socket type.
WSAENETDOWN	The network subsystem has failed.
WSAENOTCONN	The socket is not connected. This error applies only to a connection-oriented socket.
WSAENOTSOCK
WSANOTINITIALISED	A successful WSAStartup call must occur before using this function.

Remarks

The shutdown function is used on all types of sockets to disable reception, transmission, or both.

If the how parameter is SD_RECEIVE, subsequent calls to the recv function on the socket will be disallowed. This has no effect on the lower protocol layers. For TCP sockets, if there is still data queued on the socket waiting to be received, or data arrives subsequently, the connection is reset, since the data cannot be delivered to the user. For UDP sockets, incoming datagrams are accepted and queued. In no case will an ICMP error packet be generated.

If the how parameter is SD_SEND, subsequent calls to the send function are disallowed. For TCP sockets, a FIN will be sent after all data is sent and acknowledged by the receiver.

Setting how to SD_BOTH disables both sends and receives as described above.

The shutdown function does not close the socket. Any resources attached to the socket will not be freed until closesocket is invoked.

To assure that all data is sent and received on a connected socket before it is closed, an application should use shutdown to close connection before calling closesocket. One method to wait for notification that the remote end has sent all its data and initiated a graceful disconnect uses the WSAEventSelect function as follows :

1. Call WSAEventSelect to register for FD_CLOSE notification.
2. Call shutdown with how=SD_SEND.
3. When FD_CLOSE received, call the recv or WSARecv until the function completes with success and indicates that zero bytes were received. If SOCKET_ERROR is returned, then the graceful disconnect is not possible.
4. Call closesocket.

Another method to wait for notification that the remote end has sent all its data and initiated a graceful disconnect uses overlapped receive calls follows :

1. Call shutdown with how=SD_SEND.
2. Call recv or WSARecv until the function completes with success and indicates zero bytes were received. If SOCKET_ERROR is returned, then the graceful disconnect is not possible.
3. Call closesocket.

Once the shutdown function is called to disable send, receive, or both, there is no method to re-enable send or receive for the existing socket connection.

An application should not rely on being able to reuse a socket after it has been shut down. In particular, a Windows Sockets provider is not required to support the use of connect on a socket that has been shut down.

If an application wants to reuse a socket, then the DisconnectEx function should be called with the dwFlags parameter set to TF_REUSE_SOCKET to close a connection on a socket and prepare the socket handle to be reused. When the DisconnectEx request completes, the socket handle can be passed to the AcceptEx or ConnectEx function.

If an application wants to reuse a socket, the TransmitFile or TransmitPackets functions can be called with the dwFlags parameter set with TF_DISCONNECT and TF_REUSE_SOCKET to disconnect after all the data has been queued for transmission and prepare the socket handle to be reused. When the TransmitFile request completes, the socket handle can be passed to the function call previously used to establish the connection, such as AcceptEx or ConnectEx. When the TransmitPackets function completes, the socket handle can be passed to the AcceptEx function.

Notes for ATM

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

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

Socket. Close Метод

Определение

Закрывает подключение Socket и освобождает все связанные ресурсы. Closes the Socket connection and releases all associated resources.

Перегрузки

Закрывает подключение Socket и освобождает все связанные ресурсы. Closes the Socket connection and releases all associated resources.

Закрывает подключение Socket и освобождает все связанные ресурсы с заданным временем ожидания, чтобы разрешить отправку данных в очереди. Closes the Socket connection and releases all associated resources with a specified timeout to allow queued data to be sent.

Close()

Закрывает подключение Socket и освобождает все связанные ресурсы. Closes the Socket connection and releases all associated resources.

Примеры

В следующем примере кода закрывается Socket . The following code example closes a Socket.

Комментарии

CloseМетод закрывает подключение к удаленному узлу и освобождает все управляемые и неуправляемые ресурсы, связанные с Socket . The Close method closes the remote host connection and releases all managed and unmanaged resources associated with the Socket. После закрытия Connected свойству присваивается значение false . Upon closing, the Connected property is set to false .

Для протоколов, ориентированных на соединение, рекомендуется вызывать Shutdown метод перед вызовом Close метода. For connection-oriented protocols, it is recommended that you call Shutdown before calling the Close method. Это гарантирует, что все данные отправляются и получаются на подключенном сокете до его закрытия. This ensures that all data is sent and received on the connected socket before it is closed.

Если необходимо вызвать Close без первого вызова Shutdown , можно убедиться, что данные, поставленные в очередь для исходящей передачи, будут отправлены, задав DontLinger Socket для параметра значение false и указав интервал времени ожидания, отличный от нуля. If you need to call Close without first calling Shutdown, you can ensure that data queued for outgoing transmission will be sent by setting the DontLingerSocket option to false and specifying a non-zero time-out interval. Close будет блокироваться до тех пор, пока эти данные не будут отправлены или пока не истечет указанное время ожидания. Close will then block until this data is sent or until the specified time-out expires. Если задано DontLinger значение false и задан нулевой интервал времени ожидания, Close освобождает соединение и автоматически удаляет исходящие данные из очереди. If you set DontLinger to false and specify a zero time-out interval, Close releases the connection and automatically discards outgoing queued data.

Чтобы присвоить DontLinger параметру сокета значение false , создайте LingerOption , задайте для свойства Enabled значение true , а для LingerTime Свойства — требуемый период времени ожидания. To set the DontLinger socket option to false , create a LingerOption, set the enabled property to true , and set the LingerTime property to the desired time out period. Используйте его LingerOption вместе с DontLinger параметром Socket для вызова SetSocketOption метода. Use this LingerOption along with the DontLinger socket option to call the SetSocketOption method.

Данный член генерирует сведения трассировки, если в приложении включена трассировка сети. This member outputs trace information when you enable network tracing in your application. Дополнительные сведения см. в разделе Сетевая трассировка в платформа .NET Framework. For more information, see Network Tracing in the .NET Framework.

См. также раздел

Применяется к

Close(Int32)

Закрывает подключение Socket и освобождает все связанные ресурсы с заданным временем ожидания, чтобы разрешить отправку данных в очереди. Closes the Socket connection and releases all associated resources with a specified timeout to allow queued data to be sent.

Параметры

Процесс ожидает указанное число секунд timeout , прежде чем отправить оставшиеся данные, а затем закрывает сокет. Wait up to timeout seconds to send any remaining data, then close the socket.

Примеры

В следующем примере кода показано, как закрыть Socket . The following code example demonstrates how to close a Socket.

Комментарии

CloseМетод закрывает подключение к удаленному узлу и освобождает все управляемые и неуправляемые ресурсы, связанные с Socket . The Close method closes the remote host connection and releases all managed and unmanaged resources associated with the Socket. После закрытия Connected свойству присваивается значение false . Upon closing, the Connected property is set to false .

Для протоколов, ориентированных на соединение, рекомендуется вызывать метод Shutdown перед вызовом метода Close . For connection-oriented protocols, it is recommended that you call Shutdown before calling Close. Это гарантирует, что все данные отправляются и получаются на подключенном сокете до его закрытия. This ensures that all data is sent and received on the connected socket before it is closed.

Если необходимо вызвать Close без первого вызова Shutdown , можно убедиться, что данные, поставленные в очередь для исходящей передачи, будут отправлены, задав DontLinger для параметра значение false и указав интервал времени ожидания, отличный от нуля. If you need to call Close without first calling Shutdown, you can ensure that data queued for outgoing transmission will be sent by setting the DontLinger option to false and specifying a non-zero time-out interval. Close будет блокироваться до тех пор, пока эти данные не будут отправлены или пока не истечет указанное время ожидания. Close will then block until this data is sent or until the specified time-out expires. Если задано DontLinger значение false и задан нулевой интервал времени ожидания, Close освобождает соединение и автоматически удаляет исходящие данные из очереди. If you set DontLinger to false and specify a zero time-out interval, Close releases the connection and automatically discards outgoing queued data.

Чтобы присвоить DontLinger параметру сокета значение false , создайте LingerOption , задайте для свойства Enabled значение true и задайте LingerTime для свойства требуемый период ожидания. To set the DontLinger socket option to false , create a LingerOption, set the enabled property to true , and set the LingerTime property to the desired time-out period. Используйте его LingerOption вместе с DontLinger параметром Socket для вызова SetSocketOption метода. Use this LingerOption along with the DontLinger socket option to call the SetSocketOption method.

Данный член генерирует сведения трассировки, если в приложении включена трассировка сети. This member outputs trace information when you enable network tracing in your application. Дополнительные сведения см. в разделе Сетевая трассировка в платформа .NET Framework. For more information, see Network Tracing in the .NET Framework.

closesocket function (winsock2.h)

The closesocket function closes an existing socket.

Syntax

Parameters

A descriptor identifying the socket to close.

Return value

If no error occurs, closesocket returns zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError.

Error code	Meaning
WSANOTINITIALISED	A successful WSAStartup call must occur before using this function.
WSAENETDOWN	The network subsystem has failed.
WSAENOTSOCK	The descriptor is not a socket.
WSAEINPROGRESS	A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.
WSAEINTR	The (blocking) Windows Socket 1.1 call was canceled through WSACancelBlockingCall.
WSAEWOULDBLOCK	The socket is marked as nonblocking, but the l_onoff member of the linger structure is set to nonzero and the l_linger member of the linger structure is set to a nonzero timeout value.

Remarks

The closesocket function closes a socket. Use it to release the socket descriptor passed in the s parameter. Note that the socket descriptor passed in the s parameter may immediately be reused by the system as soon as closesocket function is issued. As a result, it is not reliable to expect further references to the socket descriptor passed in the s parameter to fail with the error WSAENOTSOCK. A Winsock client must never issue closesocket on s concurrently with another Winsock function call.

Any pending overlapped send and receive operations ( WSASend/ WSASendTo/ WSARecv/ WSARecvFrom with an overlapped socket) issued by any thread in this process are also canceled. Any event, completion routine, or completion port action specified for these overlapped operations is performed. The pending overlapped operations fail with the error status WSA_OPERATION_ABORTED.

An application should not assume that any outstanding I/O operations on a socket will all be guaranteed to completed when closesocket returns. The closesocket function will initiate cancellation on the outstanding I/O operations, but that does not mean that an application will receive I/O completion for these I/O operations by the time the closesocket function returns. Thus, an application should not cleanup any resources (WSAOVERLAPPED structures, for example) referenced by the outstanding I/O requests until the I/O requests are indeed completed.

An application should always have a matching call to closesocket for each successful call to socket to return any socket resources to the system.

The linger structure maintains information about a specific socket that specifies how that socket should behave when data is queued to be sent and the closesocket function is called on the socket.

The l_onoff member of the linger structure determines whether a socket should remain open for a specified amount of time after a closesocket function call to enable queued data to be sent. This member can be modified in two ways:

Call the setsockopt function with the optname parameter set to SO_DONTLINGER. The optval parameter determines how the l_onoff member is modified.

Call the setsockopt function with the optname parameter set to SO_LINGER. The optval parameter specifies how both the l_onoff and l_linger members are modified.

The l_linger member of the linger structure determines the amount of time, in seconds, a socket should remain open. This member is only applicable if the l_onoff member of the linger structure is nonzero.

The default parameters for a socket are the l_onoff member of the linger structure is zero, indicating that the socket should not remain open. The default value for the l_linger member of the linger structure is zero, but this value is ignored when the l_onoff member is set to zero.

To enable a socket to remain open, an application should set the l_onoff member to a nonzero value and set the l_linger member to the desired timeout in seconds. To disable a socket from remaining open, an application only needs to set the l_onoff member of the linger structure to zero.

If an application calls the setsockopt function with the optname parameter set to SO_DONTLINGER to set the l_onoff member to a nonzero value, the value for the l_linger member is not specified. In this case, the timeout used is implementation dependent. If a previous timeout has been established for a socket (by previously calling the setsockopt function with the optname parameter set to SO_LINGER), this timeout value should be reinstated by the service provider.

The semantics of the closesocket function are affected by the socket options that set members of linger structure.

l_onoff l_linger Type of close Wait for close? zero Do not care Graceful close No nonzero zero Hard No nonzero nonzero Graceful if all data is sent within timeout value specified in the l_linger member.

Hard if all data could not be sent within timeout value specified in the l_linger member.

If the l_onoff member of the LINGER structure is zero on a stream socket, the closesocket call will return immediately and does not receive WSAEWOULDBLOCK whether the socket is blocking or nonblocking. However, any data queued for transmission will be sent, if possible, before the underlying socket is closed. This is also called a graceful disconnect or close. In this case, the Windows Sockets provider cannot release the socket and other resources for an arbitrary period, thus affecting applications that expect to use all available sockets. This is the default behavior for a socket.

If the l_onoff member of the linger structure is nonzero and l_linger member is zero, closesocket is not blocked even if queued data has not yet been sent or acknowledged. This is called a hard or abortive close, because the socket’s virtual circuit is reset immediately, and any unsent data is lost. On Windows, any recv call on the remote side of the circuit will fail with WSAECONNRESET.

If the l_onoff member of the linger structure is set to nonzero and l_linger member is set to a nonzero timeout on a blocking socket, the closesocket call blocks until the remaining data has been sent or until the timeout expires. This is called a graceful disconnect or close if all of the data is sent within timeout value specified in the l_linger member. If the timeout expires before all data has been sent, the Windows Sockets implementation terminates the connection before closesocket returns and this is called a hard or abortive close.

Setting the l_onoff member of the linger structure to nonzero and the l_linger member with a nonzero timeout interval on a nonblocking socket is not recommended. In this case, the call to closesocket will fail with an error of WSAEWOULDBLOCK if the close operation cannot be completed immediately. If closesocket fails with WSAEWOULDBLOCK the socket handle is still valid, and a disconnect is not initiated. The application must call closesocket again to close the socket.

If the l_onoff member of the linger structure is nonzero and the l_linger member is a nonzero timeout interval on a blocking socket, the result of the closesocket function can’t be used to determine whether all data has been sent to the peer. If the data is sent before the timeout specified in the l_linger member expires or if the connection was aborted, the closesocket function won’t return an error code (the return value from the closesocket function is zero).

The closesocket call will only block until all data has been delivered to the peer or the timeout expires. If the connection is reset because the timeout expires, then the socket will not go into TIME_WAIT state. If all data is sent within the timeout period, then the socket can go into TIME_WAIT state.

If the l_onoff member of the linger structure is nonzero and the l_linger member is a zero timeout interval on a blocking socket, then a call to closesocket will reset the connection. The socket will not go to the TIME_WAIT state.

The getsockopt function can be called with the optname parameter set to SO_LINGER to retrieve the current value of the linger structure associated with a socket.

Here is a summary of closesocket behavior:

• If the l_onoff member of the LINGER structure is zero (the default for a socket), closesocket returns immediately and the connection is gracefully closed in the background.
• If the l_onoff member of the linger structure is set to nonzero and the l_linger member is set to zero (no timeout) closesocket returns immediately and the connection is reset or terminated.
• If the l_onoff member of the linger structure is set to nonzero and the l_linger member is set to a nonzero timeout:– For a blocking socket, closesocket blocks until all data is sent or the timeout expires.

– For a nonblocking socket, closesocket returns immediately indicating failure.

For additional information please see Graceful Shutdown, Linger Options, and Socket Closure for more information.

Notes for IrDA Sockets

Keep the following in mind:

• The Af_irda.h header file must be explicitly included.
• The standard linger options are supported.
• Although IrDA does not provide a graceful close, IrDA will defer closing until receive queues are purged. Thus, an application can send data and immediately call the socket function, and be confident that the receiver will copy the data before receiving an FD_CLOSE message.

Notes for ATM

The following are important issues associated with connection teardown when using Asynchronous Transfer Mode (ATM) and Windows Sockets 2:

• Using the closesocket or shutdown functions with SD_SEND or SD_BOTH results in a RELEASE signal being sent out on the control channel. Due to ATM’s use of separate signal and data channels, it is possible that a RELEASE signal could reach the remote end before the last of the data reaches its destination, resulting in a loss of that data. One possible solutions is programming a sufficient delay between the last data sent and the closesocket or shutdown function calls for an ATM socket.
• Half close is not supported by ATM.
• Both abortive and graceful disconnects result in a RELEASE signal being sent out with the same cause field. In either case, received data at the remote end of the socket is still delivered to the application. See Graceful Shutdown, Linger Options, and Socket Closure for more information.

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

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