Socket SO LINGER

Internal

• Java Networking
• Tomcat Configuration

Overview

The purpose of SO_LINGER is very specific and only a tiny minority of socket applications actually need it. The effect of an setsockopt(..., SO_LINGER,...) depends on what the values in the linger structure (the third parameter passed to setsockopt()) are:

Case 1: linger->l_onoff is zero. This is the default. On close(), the underlying stack attempts to gracefully shutdown the connection after ensuring all unsent data is sent. In the case of connection-oriented protocols such as TCP, the stack also ensures that sent data is acknowledged by the peer. The stack will perform the above-mentioned graceful shutdown in the background (after the call to close() returns), regardless of whether the socket is blocking or non-blocking.

Case 2: linger->l_onoff is non-zero and linger->l_linger is zero. A close() returns immediately. The underlying stack discards any unsent data, and, in the case of connection-oriented protocols such as TCP, sends a RST (reset) to the peer (this is termed a hard or abortive close). All subsequent attempts by the peer's application to read()/recv() data will result in an ECONNRESET.

Case 3: linger->l_onoff is non-zero and linger->l_linger is non-zero. A close() will either block (if a blocking socket) or fail with EWOULDBLOCK (if non-blocking) until a graceful shutdown completes or the time specified in linger->l_linger elapses (time-out). Upon time-out the stack behaves as in case 2 above.