The anchor and the extents allow callable cell pool services to keep track of the cell pool.

This section gives an example of one way a program would use the callable cell pool services. This example has only one cell pool with one extent. In the example, you will see that the program has to reserve storage for the anchor and the extent and get their addresses.

For more information on how to use the services and an example that includes assembler instructions, see the section on callable cell pool services in z/OS MVS Programming: Assembler Services Guide.

Example of Using Callable Cell Pool Services with a Data Space

Assume that you have an application that requires up to 4,000 records that are each 512 bytes in length. You have decided that a data space is the best place to hold this data. Callable cell pool services can help you build a cell pool, each cell having a size of 512 bytes. The steps are as follows:

1. Create a data space (DSPSERV CREATE macro)

   Specify a size large enough to hold 2,048,000 bytes of data (4000 times 512) plus the data structures that callable cell pool services need.

2. Add the data space to an access list (ALESERV macro)

   The choice of DU-AL or PASN-AL depends on how you plan to share the data space.

3. Reserve storage for the anchor and obtain its address

   The anchor (of 64 bytes) can be in the address space or the data space. In this example, the anchor is in the data space.

4. Initialize the anchor (CSRPBLD service) for the cell pool

   Input to CSRPBLD includes the ALET of the data space, the address of the anchor, the name you assign to the pool, and the size of each cell (in this case, 512 bytes). Because the anchor is in the data space, the caller must be in AR mode.

5. Reserve storage for the extent and obtain the address of the extent

   The size of the extent is 128 bytes plus one byte for every eight cells. In this example, adding 128 to 500 (that is, 4000 divided by 8) equals 628 bytes. The system then rounds up to a doubleword making the extent 632 bytes.

6. Obtain the address of the beginning of the cell storage

   Add the size of the anchor (64 bytes) and the size of the extent (632) to get the location where the cell storage can start. You might want to make this starting address on a given boundary, such as a doubleword or page.

7. Add an extent for the cell pool and establish a connection between the extent and the cells (CSRPEXP service)

   Input to CSRPEXP includes the ALET for the data space, the address of the anchor, the address of the extent, the size of the extent (in this case, 632 bytes), and the starting address of the cell storage. Because the extent is in the data space, the caller must be in AR mode.

At this point, the cell pool structures are in place and users can begin to request cells. Figure 1 describes the areas you have defined in the data space.

Figure 1. Example of Using Callable Cell Pool Services for Data Spaces

A program that has addressability to the data space can then obtain a cell (or cells) through the CSRPGET service. Input to CSRPGET includes the ALET of the space and the address of the anchor. CSRPGET returns the address of the cell (or cells) it allocates.