gtpm1m3y | TPF V4R1 Migration Guide: 3.1 to 4.1 |
Block checking mode is a debugging tool that flags certain coding errors,
such as writing beyond the end of a block, passing blocks chained to other
blocks, and using storage that has already been released.
When block checking mode is turned on:
- ECBs run in single block mode. Single block mode dispenses a single
block in each frame. The block is located in the last block slot
available in the frame. Therefore, if a program overwrites the block,
there is an increased chance of receiving a page fault for going beyond the
end of the frame. This is not foolproof, however. If the
subsequent frame is valid in the ECB's address space, a page fault will
not occur. Furthermore, L0 (127-byte) blocks are located in the same
size block slot as used for L1 (384-byte) blocks, and overwriting these blocks
will not result in a page fault until the end of the logical block is
reached. Single block mode is automatically suspended for an individual
ECB if the available storage for the ECB falls below 10 pages.
- Release block processing will disconnect a frame from an ECB if the block
being released is the only block in the frame. Subsequent references to
the block will result in a page fault because the address is no longer valid
in the address space of the ECB.
- ECB exit processing interrogates each frame it disconnects from the ECB to
look for lost blocks. If a block is flagged as in use, then
the TPF 4.1 system issues a CTL-749 system error to indicate that a
missing block was found.
You can turn on and turn off block checking mode by using the ZSTRC
command without re-IPLing the TPF 4.1 system.
- Note:
- You should use block checking mode with caution in a production system,
because block checking mode degrades CPU performance and depletes working
storage.
- Issue the ZSTRC ALTER BLKCHK command by entering ZSTRC ALTER
BLKCHK.
- Issue the ZSTRC ALTER NOBLKCHK command by entering ZSTRC ALTER
NOBLKCHK.