Sending and Receiving Early Information
When issuing an APPCVM CONNECT, you can send data to your communications partner that the partner can use before it accepts your connection.
This early data is referred to as program initialization parameters, or PIP data. Regular application programs can set up PIP data in storage and then specify the data's address and length in the APPCVM CONNECT parameter list extension. PIP data is sent to a partner program through a PIP variable.
- The target program can use the information to initialize values.
- A source program could send an entire start-up program to a target.
- In a distributed environment, a central program can send identical loader information to all remote nodes.
Target programs know if PIP data is present on an incoming connection by looking at a field (IPPIPLEN) in the connection pending interrupt. The target program can obtain information in a PIP variable by specifying APPCVM RECEIVE PIP=YES before accepting the connection. Programs running on CMS and using CMS support for communication do not need to issue a receive to get a PIP variable. CMS receives the PIP variable and places its address in register 4.
Communications servers must set up a special area when forwarding PIP data for a requesting application. This area is called a VM communications server area. For more information on PIP data in z/VM®, see the z/VM: CP Programming Services.