Transferring data between programs using channels

Channels are a method of transferring data between programs, in amounts that far exceed the 32 KB limit that applies to COMMAREAs.

Channels: quick start
A brief introduction to channels and containers.
Using channels: some typical scenarios
Channels and containers provide a powerful way to pass data between programs. These scenarios show some examples of how channels can be used.
Benefits of channels
Using the channel and container model in CICS programs to exchange data has several advantages over using communication areas (COMMAREAs) .
Creating a channel
You can create a channel by naming it on one of a number of API commands. If the channel does not exist in the current program scope, CICS creates it.
The current channel
A program's current channel is the channel - if there is one - with which it was invoked. These examples show how the current channel and its containers are passed between programs.
The scope of a channel
The scope of a channel is the code from which it can be accessed. These examples show the scope of each channel in the diagram.
Discovering which containers were passed to a program
When a program is invoked, it can determine the names of the channel, and any containers that were passed to it.
Discovering which containers were returned from a link
Following a LINK command, a program can discover the names of the containers returned by the program that was linked to.
Deleting channels and containers and freeing their storage
Containers can be large objects, so it is important to manage the storage of these objects correctly to avoid causing your CICS regions to become short of storage. CICS automatically deletes containers and channels when they can no longer be used by the applications that had access to them. Applications can also issue commands to delete individual containers or complete channels.
Designing a channel: Best practices
Containers are used to pass information between programs. These containers are grouped together in sets called channels. It is advisable to design your channels to follow a set of best practices.
Constructing and using a channel: an example
In this example, a client program constructs a channel, passes it to a server program, and retrieves the server's output. The server program retrieves data from the channel's containers, and returns output to the client.
CICS read-only containers
CICS can create channels and containers for its own use, and pass them to user programs. In some cases CICS marks these containers as read-only, so that the user program cannot modify data that CICS needs on return from the user program.
Using channels from JCICS
CICS provides JCICS classes that CICS Java™ programs can use to pass and receive channels
Channels and BTS activities
The PUT, GET, MOVE, and DELETE CONTAINER commands used to build and interact with a channel are similar to those used in CICS business transaction services (BTS) applications.
Dynamic routing with channels
EXEC CICS LINK and EXEC CICS START commands, which pass channels, can be dynamically routed.
Data conversion
Application programs that use channels and containers frequently need to convert data from one code page to another.
Migrating from COMMAREAs to channels
CICS application programs that use traditional communications areas (COMMAREAs) to exchange data can continue to work as before. If you want to migrate to channels, here are examples of how to migrate several types of existing application to use channels and containers rather than COMMAREAs.

Parent topic: Designing applications