IBM AS/400 manual Record Locking

Record Locking

Record Locking

When a record is read by a program, it is read in one of two mod update. If a program reads a record for update, a lock is placed Another program cannot read the same record for update until the firs releases that lock. If a program reads a record for input, no lock record. A record that is locked by one program can be read for inp program.

In RPG IV programs, you use an	update		file	to read		records for					up
read from a file with a type other than update					can	be		read		for
default, any record that is read from an update					file		will	be		read
update files, you can specify	that	a	record be		read		for		input		by
input operations CHAIN, READ, READE, READP, or READPE and					specifying				an
operation code extender (N) in	the	operation		code	field		following			the
name.

When a record is locked by an RPG IV program, that lock remains until following occurs:

¹ the record is updated.

¹ the record is deleted.

¹ another record is read from the file (either for inquiry or upda

¹ a SETLL or SETGT operation is performed against the file

¹ an UNLOCK operation is performed against the file.

¹an output operation defined by an output specification with no fie included is performed against the file.

Note: An output operation that adds a record to a file does not r record lock being released.

If your program reads a record for update and that record is lock program in your job or through another job, your read operation will w record is unlocked (except in the case of shared files, see “Sharing Path” on page 277). If the wait time exceeds that specified on the parameter of the file, an exception occurs. If your program does no

exception (RNX1218)			then	the	default error	handler is		given	control		whe
lock timeout	occurs,		an RNQ1218 inquiry message will				be	issued. One			of
options listed		for	this message is to retry the				operation		on	which	th
occurred.	This	will	cause	the	operation on	which	the	timeout		occurred

issued, allowing the program to continue as if the record lock timeout occurred. Note that if the file has an INFSR specified in which an

performed		on the	file	before		the default error handler is given cont
results	can	occur	if	the	input	operation that is retried is a seque
since	the	file cursor		may	have	been modified.

Note: Subprocedures do not get inquiry message, and so this situation s handled by using an error indicator on the read operation and c status 1218 following the read.

If no changes are required to a locked record, you can release it state, without modifying the file cursor, by using the UNLOCK operation essing output operations defined by output specifications with no fiel

276 ILE RPG for AS/400 Programmer's Guide