In the UNIX operating system, a new process is dispatched with the fork() system call after the server has established the connection; the new process automatically inherits the socket attached to the client. In MVS™, an independent task is started using the attach() supervisor call instruction. A server can perform an attach() call for a subtask after each connection is established in a way similar to the UNIX operating system, or it can request an attach() several times when it begins execution and pass clients to tasks that exist. In either case, the server must manually give the new socket to the subtask. Because each task has its own socket table, it is not sufficient to pass only the socket number to the subtask. Socket Number 4 for Task A is not the same as socket Number 4 for Task B.

When takesocket() acquires the socket, it assigns a new socket number for the subtask to use, but the new socket number represents the same line of communication as the parent socket. The transferred socket can be referred to as socket Number 4 by the parent task, and as socket Number 3 by the subtask. However, both sockets represent the same connection to the TCPIP address space.

After the socket has successfully been transferred, the TCPIP address space posts an exception condition on the parent socket. The parent uses the select() call to test for this condition. After the notification, the parent task must issue close() call on its socket to deallocate the socket.

Multitasking C socket sample program contains examples of a server, a subtask, and a client. Three examples are written in C, and one example is written in System/370 assembler language.