Generating a Unique Identifier

July 26, 2002 Timothy Prickett Morgan

Hey, Ted:

I just read your article, “Using Timestamps as Unique Keys,” in the July 17 issue of Midrange Guru, OS/400 Edition.

There might be a better way of creating a unique ID, one that doesn’t require retries. It’s the GENUUID API and/or MI built-in.

Universal Unique Identifier (UUID) is supposed be a totally unique ID, even across all the machines in the entire world. I’m assuming that in reality this is 100 percent true, but I wouldn’t worry about it.

Here’s some code that I’ve had stashed away:

H option(*NoSrcStmt) DftActGrp(*No)                       
                                                               
D UUIDTemplate    ds                                          
D   BytesProv                   10u 0 Inz(%Size(UUIDTemplate))
D   BytesAvail                  10u 0                         
D                                8a   Inz(*Allx'00')        
D   UUID                        16a                           
                                                              
D GenUuid         pr                  ExtProc('_GENUUID')     
D  Template                       *   Value                   
                                                               
C                   callp     GenUuid( %Addr(UUIDTemplate))   
C                   eval      *inlr = *on                     
C                   return

After the CALLP, UUID should contain a unique value.

For more technical information about UUIDs, read the Internet Engineering Task Force (IETF) memo, “UUIDs and GUIDs“

— Mark

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