CLOSE call

The CLOSE call performs the following functions:

The CLOSE call shuts down a socket and frees all resources allocated to it. If the socket refers to an open TCP connection, the connection is closed.
The CLOSE call is also issued by a concurrent server after it gives a socket to a child server program. After issuing the GIVESOCKET and receiving notification that the client child has successfully issued a TAKESOCKET, the concurrent server issues the close command to complete the passing of ownership. In high-performance, transaction-based systems the timeout associated with the CLOSE call can cause performance problems. In such systems you should consider the use of a SHUTDOWN call before you issue the CLOSE call. See SHUTDOWN call for more information.
Note:
1. If a stream socket is closed while input or output data is queued, the TCP connection is reset and data transmission might be incomplete. The SETSOCKET call can be used to set a linger condition, in which TCP⁄IP continues to attempt to complete data transmission for a specified period of time after the CLOSE call is issued. See SO-LINGER in the description of SETSOCKOPT call.
2. A concurrent server differs from an iterative server. An iterative server provides services for one client at a time; a concurrent server receives connection requests from multiple clients and creates child servers that actually serve the clients. When a child server is created, the concurrent server obtains a new socket, passes the new socket to the child server, and then dissociates itself from the connection. The CICS® listener is an example of a concurrent server.
3. After an unsuccessful socket call, a close should be issued and a new socket should be opened. An attempt to use the same socket with another call results in a nonzero return code.

The following requirements apply to this call:

Requirement	Description
Authorization:	Supervisor state or problem state, any PSW key
Dispatchable unit mode:	Task
Cross memory mode:	PASN = HASN
Amode:	31-bit or 24-bit
ASC mode:	Primary address space control (ASC) mode
Interrupt status:	Enabled for interrupts
Locks:	Unlocked
Control parameters:	All parameters must be addressable by the caller and in the primary address space

Figure 1 shows an example of CLOSE call instructions.

Figure 1. CLOSE call instruction example

    WORKING-STORAGE SECTION.
        01  SOC-FUNCTION    PIC X(16)  VALUE IS 'CLOSE'.
        01  S               PIC 9(4) BINARY.
        01  ERRNO           PIC 9(8) BINARY.
        01  RETCODE         PIC S9(8) BINARY.
    
    
    PROCEDURE DIVISION.
         CALL 'EZASOKET' USING SOC-FUNCTION S ERRNO RETCODE.

For equivalent PL/I and assembler language declarations, see Converting parameter descriptions.