A program's current channel is the channel (if any) with which it was invoked. The program can create other channels. However, the current channel, for a particular invocation of a particular program, does not change. It is analogous to a parameter list.
The following figure illustrates the origin of a program's current channel. It shows five interactive programs. Program A is a top-level program started by, for example, a terminal end-user. It isn't started by a program and doesn't have a current channel.
B, C, D, and E are second-, third-, fourth-, and fifth-level programs, respectively.
Program B's current channel is X, passed by the CHANNEL option on the EXEC CICS LINK command issued by program A. Program B modifies channel X by adding one container and deleting another.
Program C's current channel is also X, passed by the CHANNEL option on the EXEC CICS LINK command issued by program B.
Program D has no current channel, because C doesn't pass it one.
Program E's current channel is Y, passed by the CHANNEL option on the EXEC CICS LINK command issued by D.
The following table lists the name of the current channel (if any) of each of the five programs shown in the previous figure.
Prog. | Current CH | Issues commands | Comments |
---|---|---|---|
A | None |
|
Program A creates channel X and passes it to program
B.
Note that, by the time control is returned to program A by program B, the X channel has been modified--it doesn't contain the same set of containers as when it was created by program A. (Container TWO has been deleted and container THREE added by program B.) |
B | X |
|
Program B modifies channel X (its current channel)
by adding and deleting containers, and passes the modified channel to program
C.
Program B doesn't need to specify the CHANNEL option on the PUT CONTAINER and DELETE CONTAINER commands; its current channel is implied. |
C | X |
|
Program C links to program D, but does not pass it a channel. |
D | None |
|
Program D creates a new channel, Y, which it passes to program E. |
E | Y |
|
Program E performs some processing on the data it's been passed and returns. |
Figure 48 shows four interactive programs. A1 is a top-level program started by, for example, a terminal end-user. It isn't started by a program and doesn't have a current channel. B1, B2, and B3 are all second-level programs.
B1's current channel is X, passed by the CHANNEL option on the EXEC CICS LINK command issued by A1.
B2 has no current channel, because B1 doesn't pass it one.
B3's current channel is Y, passed by the CHANNEL option on the EXEC CICS XCTL command issued by B2.
When B3 returns, channel Y and its containers are deleted by CICS.
The following table lists the name of the current channel (if any) of each of the four programs shown in Figure 48.
Program | Current channel | Issues command |
---|---|---|
A1 | None |
|
B1 | X |
|
B2 | None |
|
B3 | Y |
|
Besides EXEC CICS LINK and XCTL, two other commands can be used to invoke a program and pass it a channel:
The program that implements the next transaction is passed the channel, which becomes its current channel.