User spaces (was: Text on report)

[pcunnane@xxxxxxxxxxxxxx (Paul Cunnane)]

     Jim,
     
     A user space is a system object of type *USRSPC.  It is essentially 
     just an area of storage, with arbitrary user-defined contents.  You 
     can use APIs to create, retrieve, change and delete a user space.
     
     By far the easiest way to work with the data in a user space is to use 
     the QUSPTRUS API, to retrieve a pointer to the space.  If you then 
     base a variable on the returned pointer, you can access the data in 
     the space through the variable.  The only real drawback to this 
     approach is that locking is not implemented, so it is possible for two 
     users to change the same space at the same time.
     
     Why use a user space instead of (say) a data area?  For me, there are 
     a couple of reasons:  First, the access through the QUSPTRUS interface 
     makes reading/writing the space trivial.  Second, the space will be 
     dynamically resized by the system as required.  Third, user spaces are 
     *way* faster.  And finally, because there is no CHGUSRSPC command, it 
     is harder for someone to accidentally trash the contents of the space.
     
     In a previous life, I wrote a dynamic trigger handler.  This one 
     trigger program was added to all relevant files.  Each file had a 
     corresponding user space, containing the names of the programs that 
     should be called by the generic trigger.  The user space contained a 
     number of fields at the start -- offset to *BEFORE *UPDATE program 
     list; number of *BEFORE *UPDATE programs, offset to *AFTER *UPDATE 
     program list, number of *AFTER *UPDATE programs... (you get the idea) 
     followed by the lists of programs.  The programs to both maintain and 
     read these user spaces were very straightforward, and extremely fast.
     
     -- 
     Paul


______________________________ Reply Separator _________________________________
Subject: Re: Text on report
Author:  Jim Langston <jlangston@conexfreight.com> at INTERNET
Date:    21-06-00 9:53 am


Hmm... what exactly is a "user space"?  I've heard mention of these, 
but always thought they were the same thing as a User Data Structure 
(UDS).  Are they one in the same?
     
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