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Raul, FYI, in next week's "Midrange Developer" newsletter, I publish a RTVUSRSPC (retrieve user space) CL command that has parameters similar to (identical to?) the RTVDTAARA command. -Bob -----Original Message----- From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Raul A Jager Sent: Friday, February 13, 2004 11:58 AM To: RPG programming on the AS400 / iSeries Subject: Re: User space My application needs to share the last event in a series. Anything that happens before is irrelevant, and in case two or more users finish at the "same time", any of them will do. That's why I don't need to synchronize. When I need to serialize, I use a data queue, if I need to lock, I can use a data ara or a file. In this case locking bothers, so the user space does the trick. The advice I received here saved me quite a bit of experimenting. __________________________________________________________________________ Rusling, John B. (Alliance) wrote: I'm thinking out loud here... ...for those of us who are repelled by the idea of delving into mi to lock a user space however we do utilize user spaces where beneficial, wouldn't we derive the same anti-lock capabilities using the ALCOBJ command..? (We don't want to scare people away from user spaces :-) searched IBM site, from programming api's -- <Snip> The Retrieve Pointer to User Space (QUSPTRUS) API retrieves a pointer to the contents of a user-domain user space. The data in that user space then can be directly manipulated by high-level language programs that support pointers, such as C or COBOL. The QUSPTRUS API will not return a pointer to a system-domain user space; you must use system APIs to access system-domain user spaces. If you attempt to retrieve the pointer to a system-domain user space, an error will be returned. The QUSPTRUS API even returns a pointer to an object that is subject to an exclusive (*EXCL) lock. If you create application programs using HLLs that can directly update user spaces using pointers (instead of using the Change User Space (QUSCHGUS) API), you should use your own synchronization data methods. You can use one of the following methods to avoid updates at the same time to the same location within a user space: CMPSW MI instruction CMPSWP MI instruction LOCK MI instruction LOCKSL MI instruction Allocate Object (ALCOBJ) command Use of the QUSPTRUS API does not update the object usage information (such as last changed date, last date used, and so on). You should use the Change User Space or the Retrieve User Space API to update the object usage information if needed. </Snip> John B. ---------------------------------------------------------------------- message: 1 date: Thu, 12 Feb 2004 13:08:38 -0500 from: "Steve Richter" <srichter@xxxxxxxxxxxxx> subject: RE: User space everything scott says in right on target. I would add that there is a way to syncronize access to a user space amoung multiple jobs. http://publib.boulder.ibm.com/iseries/v5r1/ic2924/tstudio/tech_ref/mi/LOCKSL .htm LOCKSL ( lock space location ) accepts a pointer to a space location and effectively locks it from use by other jobs that also use LOCKSL before accessing the space location. -Steve -----Original Message----- From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]On Behalf Of Scott Klement Sent: Thursday, February 12, 2004 12:29 PM To: RPG programming on the AS400 / iSeries Subject: Re: User space On Thu, 12 Feb 2004, Raul A Jager wrote: I need to share data between users. Can I use an "USER SPACE"? Sure. Will the system allow several users updating it? Yes, but IMHO, not gracefully. when will the upates be seen by others? As soon as they check for the updates. A user space is similar to a file, except for three things: a) It does not have any particular structure. b) Since there are no records, there's no record locks, etc. c) It's directly addressable with a pointer from an HLL program. (Technically, you can do that with any file, but you need to use MI tricks rather than normal HLL operations with non-userspaces) The big problem is making sure that two jobs don't conflict with one another. You have to be very careful about any situation that could lead to two processes writing data to it at the same time. I recommend having the jobs communicate with each other using data queues so that they can synchronize their operations -- preventing them from conflicting with one another. But, since they can send data to one another via the data queues, the question becomes, do you still need the user space? The only reason I can think of why you'd want to use a user space for something like this would be if the data that needs to be accessed is very large. With a user space they are sharing a common piece of information, but with data queues the info is copied from one to the other -- so for very large pieces of information, user spaces would be quicker. Hope that makes sense... _______________________________________________ This is the RPG programming on the AS400 / iSeries (RPG400-L) mailing list To post a message email: RPG400-L@xxxxxxxxxxxx To subscribe, unsubscribe, or change list options, visit: http://lists.midrange.com/mailman/listinfo/rpg400-l or email: RPG400-L-request@xxxxxxxxxxxx Before posting, please take a moment to review the archives at http://archive.midrange.com/rpg400-l. _______________________________________________ This is the RPG programming on the AS400 / iSeries (RPG400-L) mailing list To post a message email: RPG400-L@xxxxxxxxxxxx To subscribe, unsubscribe, or change list options, visit: http://lists.midrange.com/mailman/listinfo/rpg400-l or email: RPG400-L-request@xxxxxxxxxxxx Before posting, please take a moment to review the archives at http://archive.midrange.com/rpg400-l. _______________________________________________ This is the RPG programming on the AS400 / iSeries (RPG400-L) mailing list To post a message email: RPG400-L@xxxxxxxxxxxx To subscribe, unsubscribe, or change list options, visit: http://lists.midrange.com/mailman/listinfo/rpg400-l or email: RPG400-L-request@xxxxxxxxxxxx Before posting, please take a moment to review the archives at http://archive.midrange.com/rpg400-l.
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