HP 3000 Manuals HP 3000 Manuals
CKLOCK
A call to CKLOCK dynamically locks a KSAM file.
CALL "CKLOCK" USING filetable, status, lockcond
When access is shared, you must lock the file before calling CKWRITE,
CKREWRITE, or CKDELETE. This insures that another user cannot attempt to
modify the file at the same time, and it guarantees that the most recent
data is available to each user who accesses the file.
In order to call CKLOCK, the file must have been opened with a call to
CKOPENSHR, not CKOPEN.
PARAMETERS
filetable an 8-word record containing the number and name of the
file, its input-output type, access mode, and a code
indicating whether the previous operation was successful
and if so, what it was. (Refer to Filetable Parameter
discussion earlier in this section.)
status one-word (two 8-bit characters) set to a pair of values
upon completion of the call to CKLOCK. It indicates
whether or not the file was successfully locked and if
not, why not. The status word ="00" if the call was
successful. It ="30" if the file was locked by another
process; it = "9n," where n is a file system error code,
if the call failed for some other reason. (Refer to the
Status Parameter discussion earlier in this section.)
lockcond one-word computational item whose value determines the
action taken if the file is locked by another user when
CKLOCK is executed. The value is either zero (0) or one
(1).
0 locking is conditional; if the file is
already locked, control is returned to
your program immediately with the
status word set to "30".
1 locking is unconditional; if the file
cannot be locked immediately because
another use has locked it, your program
suspends until the file can be locked.
USING CKLOCK
In order to call CKLOCK, the file must be opened with dynamic access
enabled. This can be done only with the CKOPENSHR procedure. CKOPEN
will not open the file for shared access with dynamic locking.
When users are sharing a file, it is essential to lock the file before
modifying it. An error is returned if any user attempts to write,
rewrite, or delete records without first locking the file. It is also
important to avoid situations where one user locks the file and forgets
to unlock it. If the file is already locked when you call CKLOCK with
lockcond set to zero, the call will fail with "30" returned to status,
and your process will continue. If, however, lockcond is set to 1, your
process suspends until the other user unlocks the file or logs off.
EXAMPLES
The following example opens file KSAMFILE for shared access with dynamic
locking allowed. It then locks the file unconditionally. If another
user has locked the file, the process suspends until the file is unlocked
and then continues by locking your file. The status value is checked as
soon as control returns to your process to insure that the file has been
locked before continuing.
DATA DIVISION.
77 LOCKCOND PICTURE S9(4) COMP VALUE 1.
77 RESULT PICTURE 9(4) VALUE 0.
01 STATUSKEY.
02 STATUS-KEY1 PICTURE X VALUE " ".
02 STATUS-KEY2 PICTURE X VALUE " ".
01 FILETABLE.
02 FILENUMBER PICTURE S9(4) COMP VALUE 0.
02 FILENAME PICTURE X(8) VALUE "KSAMFILE".
02 I-O-TYPE PICTURE S9(4) COMP VALUE 0.
02 A-MODE PICTURE S9(4) COMP VALUE 0.
02 PREV-OP PICTURE S9(4) COMP VALUE 0.
PROCEDURE DIVISION.
START.
CALL "CKOPENSHR" USING FILETABLE, STATUSKEY.
IF STATUS-KEY1 = "0" THEN GO TO LOCK-FILE.
IF STATUS-KEY1 = "9" THEN
CALL "CKERROR" USING STATUSKEY, RESULT
DISPLAY "ERROR NO. ",RESULT.
LOCK-FILE.
CALL "CKLOCK" USING FILETABLE, STATUSKEY, LOCKCOND.
IF STATUSKEY="0"
THEN DISPLAY "CKLOCK IS OK"
ELSE IF STATUSKEY = "30"
THEN DISPLAY"FILE LOCKED BY ANOTHER PROCESS"
ELSE IF STATUS-KEY1="9"
THEN CALL "CKERROR" USING STATUSKEY, RESULT
DISPLAY "ERROR NO.", RESULT.