LINGER structure (winsock2.h)

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.

Syntax

typedef struct linger {
  u_short l_onoff;
  u_short l_linger;
} LINGER, *PLINGER, *LPLINGER;

Members

l_onoff

Type: u_short

Specifies 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 have one of the following values.

Value	Meaning
0	The socket will not remain open. This is the value set if the setsockopt function is called with the optname parameter set to SO_DONTLINGER and the optval parameter is zero. This value is also set if the setsockopt function is called with the optname parameter set to SO_LINGER and the linger structure passed in the optval parameter has the l_onoff member set to 0.
nonzero	The socket will remain open for a specified amount of time. This value is set if the setsockopt function is called with the optname parameter set to SO_DONTLINGER and the optval parameter is nonzero. This value is also set if the setsockopt function is called with the optname parameter set to SO_LINGER and the linger structure passed in the optval parameter has the l_onoff member set to a nonzero value.

l_linger

Type: u_short

The linger time in seconds. This member specifies how long to remain open after a closesocket function call to enable queued data to be sent. This member is only applicable if the l_onoff member of the linger structure is set to a nonzero value.

This value is set if the setsockopt function is called with the optname parameter set to SO_LINGER. The optval parameter passed to the setsockopt function must contain a linger structure that is copied to the internal linger structure maintained for the socket.

Remarks

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. Somewhat confusing is that 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.

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 time-out 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 time-out used is implementation dependent. If a previous time-out has been established for a socket (by enabling SO_LINGER), this time-out value should be reinstated by the service provider.

Note that enabling a nonzero timeout on a nonblocking socket is not recommended.

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.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Header	winsock2.h (include Winsock2.h)

See also

Graceful Shutdown, Linger Options, and Socket Closure

closesocket

getsockopt

setsockopt