Guardian Procedure Calls Reference Manual

count-n
input
INT:value
The use of this parameter depends on the presence or absence of the corresponding buffer-n
parameter:
• If buffer-n is present, then count-n specifies the number of words to be checkpointed.
• If buffer-n is absent, then count-n is the filenum of a file whose file synchronization
block is to be checkpointed.
NOTE: If the message is too large (that is, the total of the stack size and the counts of all
buffers and the size of all file synchronization blocks is too big), status.<0:7> is set to 3
and the parameter number is set to 26.
Returned Value
INT
A status word of this form:
No error.<0:7> = 0
No backup process or unable to communicate with backup process; then <8:15> = file-system error
number.
<0:7> = 1
Takeover from primary process; then <8:15> =<0:7> = 2
Primary process stopped.0
Primary process abnormally ended.1
Primarys process processor failed.2
Primary process called CHECKSWITCH.3
Invalid parameter; then <8:15> = number of parameter in error (leftmost position = 1).<0:7> = 3
Considerations
• Checkpointing the process' data stack
The CHECKPOINT procedure provides for checkpointing the process' data stack and any
combination of up to 13 separate data blocks and file synchronization blocks. A data block
can be from any location in the data area. (Data blocks are usually file buffers that are not
checkpointed as part of the stack, and they cannot be in an extended data area.)
• Maximum checkpoint size
The largest stack area or data item that can be checkpointed is 32,500 bytes. Additionally,
the sum total of the sizes of the stack area and each checkpoint item, plus an allowance of
20 bytes for each item, can not exceed 32,500 bytes. An item in this context means either a
data item (user-declared size) or a file synchronization block with varying sizes.
• Identification of the backup process
The system identifies the process to be affected by the CHECKPOINT operation from the
process' mom field in the process control block (PCB). For named process pairs, this field is
automatically set up during the creation of a backup process.
• Checkpointing a file's synchronization (sync) block
If a file's sync block is checkpointed, the call to CHECKPOINT contains an implicit call to the
GETSYNCINFO procedure for the file. Therefore, checkpointing of a file's sync block must
not be performed between an I/O completion and a call to the FILE_GETINFO_ (or FILEINFO)
CHECKPOINT Procedure (Superseded by CHECKPOINTX Procedure) 143